Quantum router, quantum information relay method, quantum network system, and quantum computer

Abstract

A quantum router 1 for relaying quantum information within a quantum network comprises: a Bell measurement unit 11 for performing Bell measurements on two quantum states; a first entangled photon receiving unit 14 for receiving a first photon having a first quantum state from the quantum network; a second entangled photon receiving unit 15 for receiving a second photon having a second quantum state from the quantum network; a first quantum memory 12 connected between the Bell measurement unit 11 and the first entangled photon receiving unit 14; a second quantum memory 13 connected between the Bell measurement unit 11 and the second entangled photon receiving unit 15; and a control unit 16. The first quantum memory 12 includes a first quantum bit array AR1 composed of a plurality of rows and a plurality of columns. The second quantum memory 13 includes a second quantum bit array AR2 composed of a plurality of rows and a plurality of columns. The first entangled photon receiving unit 14 distributes the first quantum state to each row of the first quantum bit array AR1. The second entangled photon receiving unit 15 distributes the second quantum state to each row of the second quantum bit array AR2. The first quantum memory 12 transfers the first quantum state toward the Bell measurement unit 11 within the first quantum bit array AR1. The second quantum memory 13 transfers the second quantum state toward the Bell measurement unit 11 within the second quantum bit array AR2. Upon receiving a first quantum entanglement generation success signal relating to the first quantum state and a second quantum entanglement generation success signal relating to the second quantum state, the control unit 16 controls the Bell measurement unit 11, the first quantum memory 12, and the second quantum memory 13 so as to execute a Bell measurement on the first quantum state and the second quantum state.

Description

Quantum router, quantum information relay method, quantum network system and quantum computer

[0001] The present invention relates to a quantum router, a quantum information relay method, a quantum network system and a quantum computer.

[0002] As a quantum router for realizing a quantum network, an architecture including a quantum memory and an optical switch has been proposed (see, for example, Non-Patent Document 1).

[0003] Yuan Lee, Eric Bersin, Axel Dahlberg, Stephanie Wehner & Dirk Englund, “A quantum router architecture for high-fidelity entanglement flows in quantum networks”, npj Quantum Information volume 8, Article number: 75 (2022)

[0004] Generally, in quantum relay between remote nodes, it takes time to transmit quantum information propagating through an optical fiber, and there are losses associated with optical fiber propagation, quantum wavelength conversion, and emission / absorption of quantum information, so the success rate of quantum entanglement generation is not high. Under such circumstances, the quantum router described in Non-Patent Document 1 has to wait for the execution of Bell measurement until it receives a quantum entanglement generation success signal from the transmitting node and the receiving node. As a result, such a quantum router has the problem that the quantum entanglement generation rate between remote nodes is low, and therefore the throughput of quantum information relay is low.

[0005] The technology according to the present disclosure has been made in view of such circumstances, and an object thereof is to realize a quantum router with a high quantum entanglement generation rate that enables high-throughput quantum information relay between remote nodes.

[0006] To solve the above problems, a quantum router according to one aspect of the present invention is a quantum router that relays quantum information within a quantum network. This quantum router includes a Bell measurement unit that performs Bell measurements on two quantum states, a first entangled photon receiver that receives a first photon having a first quantum state from the quantum network, a second entangled photon receiver that receives a second photon having a second quantum state from the quantum network, a first quantum memory connected between the Bell measurement unit and the first entangled photon receiver, a second quantum memory connected between the Bell measurement unit and the second entangled photon receiver, and a control unit. The first quantum memory includes a first qubit array composed of a plurality of rows and a plurality of columns. The second quantum memory includes a second qubit array composed of a plurality of rows and a plurality of columns. The first entangled photon receiver distributes the first quantum state to each row of the first qubit array. The second entangled photon receiver distributes the second quantum state to each row of the second qubit array. The first quantum memory transfers the first quantum state to the Bell measurement unit within the first qubit array. The second quantum memory transfers the second quantum state to the Bell measurement unit within the second qubit array. When the control unit receives the first quantum entanglement generation success signal for the first quantum state and the second quantum entanglement generation success signal for the second quantum state, it controls the Bell measurement unit, the first quantum memory, and the second quantum memory to perform Bell measurements on the first and second quantum states.

[0007] Another aspect of the present invention is a quantum router that relays quantum information within a quantum network. This quantum router comprises a Bell measurement unit that performs Bell measurements on two quantum states; a first entangled photon generation unit that generates and transmits a first photon having a first quantum state to the quantum network; a second entangled photon generation unit that generates and transmits a second photon having a second quantum state to the quantum network; a first quantum memory connected between the Bell measurement unit and the first entangled photon receiver; a second quantum memory connected between the Bell measurement unit and the second entangled photon receiver; and a control unit. The first quantum memory includes a first qubit array composed of a plurality of rows and a plurality of columns. The second quantum memory includes a second qubit array composed of a plurality of rows and a plurality of columns. The first entangled photon generation unit distributes the quantum states entangled with the first quantum state to each row of the first qubit array. The second entangled photon receiver distributes the quantum state entangled with the second quantum state to each row of the second qubit array. The first quantum memory transfers the quantum state entangled with the first quantum state to the Bell measurement unit within the first qubit array. The second quantum memory transfers the quantum state entangled with the first quantum state to the Bell measurement unit within the second qubit array. When the control unit receives the first quantum entanglement generation success signal for the first quantum state and the second quantum entanglement generation success signal for the second quantum state, it controls the Bell measurement unit, the first quantum memory, and the second quantum memory to perform Bell measurements on the quantum state entangled with the first quantum state and the quantum state entangled with the second quantum state.

[0008] A further aspect of the present invention is a quantum information relay method. This method relays quantum information within a quantum network using a quantum router comprising a Bell measurement unit, a first quantum memory, and a second quantum memory. The first quantum memory includes a first qubit array consisting of multiple rows and multiple columns. The second quantum memory includes a second qubit array consisting of multiple rows and multiple columns. This method includes the steps of: receiving a first photon having a first quantum state from a quantum network; receiving a second photon having a second quantum state from a quantum network; distributing the first quantum state to each row of a first qubit array; distributing the second quantum state to each row of a second qubit array; transferring the first quantum state distributed to each row of the first qubit array to a Bell measurement unit within the first qubit array; transferring the second quantum state distributed to each row of the second qubit array to a Bell measurement unit within the second qubit array; and, upon receiving a first entanglement generation success signal for the first quantum state and a second entanglement generation success signal for the second quantum state, having the Bell measurement unit perform a Bell measurement on the first and second quantum states.

[0009] Another aspect of the present invention is also a quantum information relay method. This method is a quantum information relay method that relays quantum information within a quantum network using a quantum router comprising a Bell measurement unit, a first quantum memory, and a second quantum memory. The first quantum memory includes a first qubit array composed of a plurality of rows and a plurality of columns. The second quantum memory includes a second qubit array composed of a plurality of rows and a plurality of columns. The steps are: to generate a first photon having a first quantum state and transmit the first photon to the quantum network; to generate a second photon having a second quantum state and transmit the second photon to the quantum network; to distribute the quantum state entangled with the first quantum state to each row of the first qubit array; to distribute the quantum state entangled with the second quantum state to each row of the second qubit array; and to return the quantum state entangled with the first quantum state distributed to each row of the first qubit array to the first qubit The process includes the steps of: transferring within the qubit array to the Bell measurement unit; transferring the quantum states entangled with the second quantum state, which have been allocated to each row of the second qubit array, to the Bell measurement unit within the second qubit array; and, upon receiving a first quantum entanglement generation success signal for the first quantum state and a second quantum entanglement generation success signal for the second quantum state, having the Bell measurement unit perform a Bell measurement on the quantum state entangled with the first quantum state and the quantum state entangled with the second quantum state.

[0010] A further aspect of the present invention is a quantum network system. This quantum network system is a quantum network system in which a plurality of nodes and a plurality of the aforementioned quantum routers are connected. This quantum network system attempts to generate quantum entanglement between adjacent quantum routers by exchanging photons between adjacent quantum routers. If this quantum network system succeeds in generating quantum entanglement, it stores the quantum entanglement in the bell measurement unit of each quantum router and repeats the process of generating quantum entanglement until it is possible to connect the nodes that are to be connected. After adjacent quantum routers are connected by quantum entanglement, this quantum network system performs a bell measurement on the entangled pairs stored in the bell measurement units of the quantum routers.

[0011] A further aspect of the present invention is a quantum computer. This quantum computer performs quantum computations by sharing quantum entanglement with an external quantum computer. This quantum computer comprises a Bell measurement unit, a computation unit connected to the Bell measurement unit and performing quantum computations, a quantum memory connected to the Bell measurement unit from the other side of the computation unit and storing the quantum state of photons received from the external quantum computer, and a control unit. The computation unit includes a first qubit array consisting of a plurality of rows and a plurality of columns. The quantum memory includes a second qubit array consisting of a plurality of rows and a plurality of columns. When the control unit receives a quantum entanglement success signal from the computation unit and a quantum entanglement success signal from the external quantum computer, it controls the Bell measurement unit, the computation unit, and the quantum memory to perform Bell measurements on the quantum state of photons received from the external quantum computer and the quantum state of the computation unit.

[0012] Furthermore, any combination of the above components, as well as conversions of the expression of the present invention between devices, methods, systems, recording media, computer programs, etc., are also valid embodiments of the present invention.

[0013] According to the present invention, it is possible to provide a quantum router with a high quantum entanglement generation rate that enables high-throughput quantum information relay between remote nodes.

[0014] This is a diagram illustrating the principle of quantum relay based on quantum teleportation. This is a diagram illustrating the principle of another example of quantum relay based on quantum teleportation. This is a diagram illustrating the principle of another example of quantum relay based on quantum teleportation. This is a functional block diagram of a quantum router according to the first embodiment. This is a schematic diagram showing how the first entangled photon receiver distributes the first quantum state to each row of the first qubit array. This is a schematic diagram showing how the first quantum memory transfers the first quantum states distributed to each row of the first qubit array to the Bell measurement unit for each row. This is a schematic diagram showing how, as a result of receiving both the first and second successful quantum entanglement generation signals, a Bell measurement is performed on adjacent first and second quantum states. This is a schematic diagram showing how a Bell measurement is performed when the first and second quantum states are not adjacent. This is a functional block diagram of another quantum router according to the first embodiment. This is a schematic diagram showing how the first entangled photon generation unit distributes the first quantum state to each row of the first qubit array. This is a schematic diagram showing how the first quantum memory transfers the first quantum states distributed to each row of the first qubit array to the Bell measurement unit for each row. This is a schematic diagram showing how, as a result of receiving both the first and second quantum entanglement generation success signals, a Bell measurement is performed on adjacent first and second quantum states. This is a schematic diagram showing how a Bell measurement is performed when the first and second quantum states are not adjacent. This is a functional block diagram of yet another quantum router according to the first embodiment. This is a functional block diagram of a quantum router equipped with a multiplexer / demultiplexer and a wavelength converter. This is a functional block diagram of a quantum router further equipped with a multiplexer / demultiplexer and a wavelength converter. This is a diagram showing two CNOT gates for transferring the first and second quantum states to the Bell measurement unit. This is a diagram showing an example of a circuit for performing a Bell measurement. This is a functional block diagram of a quantum router according to the first embodiment, which is equipped with a cooling system. This is a flowchart showing the processing procedure of a quantum information relay method according to the second embodiment and a quantum information relay program according to the third embodiment.This is a flowchart showing the processing procedures of another quantum information relay method according to the second embodiment and another quantum information relay program according to the third embodiment. This is a schematic diagram of a quantum network system according to the fourth embodiment. This is a functional block diagram of a quantum computer according to the fifth embodiment. This is a diagram showing the first quantum memory and Bell measurement unit of the quantum router of Modification 17 extracted. This is a diagram showing the first quantum memory and Bell measurement unit of the quantum router of Modification 17 extracted. This is a diagram showing the first quantum memory and Bell measurement unit of the quantum router of Modification 17 extracted. This is a diagram showing the first quantum memory and Bell measurement unit of the quantum router of Modification 17 extracted. This is a diagram showing the first quantum memory and Bell measurement unit of the quantum router of Modification 17 extracted. This is a diagram showing the first quantum memory and Bell measurement unit of the quantum router of Modification 18 extracted. This is a diagram showing the quantum memory and Bell measurement unit of the quantum router of Modification 18 extracted. This is a diagram showing the quantum memory and Bell measurement unit of the quantum router of Modification 18 extracted. This is a diagram showing the quantum memory and Bell measurement unit of the quantum router in modified example 18. This is a diagram showing the quantum memory and Bell measurement unit of the quantum router in modified example 18. This is a diagram showing the quantum memory and Bell measurement unit of the quantum router in modified example 18.

[0015] The present invention will be described below with reference to the drawings, based on preferred embodiments. In embodiments and modifications, the same or equivalent components, steps, and members will be denoted by the same reference numerals, and redundant explanations will be omitted as appropriate. In addition, the dimensions of members in each drawing will be enlarged or reduced as appropriate to facilitate understanding. Furthermore, some members that are not important for explaining the embodiments will be omitted from each drawing. In addition, terms including ordinal numbers such as "first," "second," etc., are used to describe various components, but these terms are used only to distinguish one component from others, and the components are not limited by these terms.

[0016] Before describing specific embodiments, let's explain some basic concepts. A quantum network is a network that connects quantum information processing nodes (hereinafter sometimes simply called "quantum nodes" or "nodes"), such as quantum computers and quantum memories, with transmission lines such as optical fibers.

[0017] Let's consider the communication of quantum information within a quantum network. For example, if we have two nodes in a quantum network, one is the transmitting node and the other is the receiving node, then quantum information needs to be transferred from the transmitting node to the receiving node. In this case, the transmitting node and the receiving node (i.e., the distant nodes) need to be in a quantum entangled state.

[0018] However, due to transmission losses in optical fibers, the distance over which a single photon can be directly transmitted is at most about 100 km, and in the real-world environment of existing optical fibers, it is even shorter, only a few tens of kilometers. Therefore, quantum repeaters are necessary to realize the communication of quantum information between remote nodes. A quantum repeater that has increased input / output paths, the number of qubits that can be stored and manipulated internally to two or more, and enables information routing control within the repeater will be referred to below as a "quantum router." This specification focuses on such quantum routers. The functions of a quantum router may include not only the relay of quantum information between quantum computers at different locations or between qubits within a quantum computer, but also quantum information routing and hub functions.

[0019] A quantum router is, in essence, a quantum computer equipped with, for example, quantum memory. As will be described later, quantum relay is based on quantum teleportation. To realize this, a quantum router is equipped with functions such as quantum entanglement generation and Bell measurement.

[0020] In conventional classical optical communication networks (hereinafter referred to as "classical networks"), amplifiers are installed as repeaters in the transmission path. This amplifies the attenuated received signal and retransmits the signal to the next repeater (or receiving node), thereby compensating for the attenuation of the optical signal. However, in the case of quantum networks, it is known that, in principle, it is not possible to copy an arbitrary quantum state to another quantum state to create the same quantum state (the quantum non-replica theorem). Therefore, the principle of information relay in classical networks does not apply to quantum networks.

[0021] Therefore, quantum networks achieve quantum relay through quantum teleportation via quantum entanglement generation and quantum entanglement swapping, as described below.

[0022] [Principle of quantum relay based on quantum teleportation] The principle of quantum relay based on quantum teleportation according to the embodiment of this disclosure will be explained below with reference to Figures 1 to 3.

[0023] Figure 1 is a schematic diagram of a quantum network consisting of node A, quantum router B, and node C. Node A comprises an entangled photon receiver RA and a quantum memory MA. Node C comprises an entangled photon receiver RC and a quantum memory RM. Quantum router B comprises a bell measurement unit BM and quantum memories MB1, MB2, and entangled photon receivers RB1 and RB2 on either side thereof.

[0024] Node A and quantum router B are connected by an optical fiber. A tangled photon generation light source a is located on this optical fiber.

[0025] Node C and quantum router B are connected by an optical fiber. A tangled photon generation light source c is located on this optical fiber.

[0026] The entangled photon generation light source a generates a pair of two photons that are in a quantum entanglement relationship (hereinafter referred to as "entangled photons") (hereinafter referred to as "entangled photon pair"). This will be called the first entangled photon pair 1.

[0027] One of the first entangled photon pair 1 generated by the entangled photon generation light source a is transmitted toward node A. The entangled photon receiver RA of node A receives this one of the first entangled photon pair 1. The quantum state of the one of the first entangled photon pair 1 received by the entangled photon receiver RA is stored in the quantum memory MA.

[0028] The other half of the first entangled photon pair 1, generated by the entangled photon generation light source a, is transmitted to the quantum router B. The quantum state of this other half of the first entangled photon pair 1 is defined as the first quantum state. The entangled photon receiver RB1 of the quantum router B receives this other half of the first entangled photon pair 1. The quantum state of the other half of the first entangled photon pair 1 (the first quantum state) received by the entangled photon receiver RB1 is stored in the quantum memory MB1.

[0029] The entangled photon pair generation light source c generates a second entangled photon pair 2.

[0030] One of the second entangled photon pair 2 generated by the entangled photon generation light source c is transmitted toward node C. The entangled photon receiver RC at node C receives this one of the second entangled photon pair 2. The quantum state of the one of the second entangled photon pair 2 received by the entangled photon receiver RC is stored in the quantum memory MC.

[0031] The other half of the second entangled photon pair 2, generated by the entangled photon generation light source c, is transmitted to the quantum router B. The quantum state of this other half of the second entangled photon pair 2 is defined as the second quantum state. The entangled photon receiver RB2 of the quantum router B receives this other half of the second entangled photon pair 2. The quantum state of the other half of the second entangled photon pair 2 (the second quantum state) received by the entangled photon receiver RB2 is stored in the quantum memory MB2.

[0032] At this point, there is no entanglement between the quantum state stored in node A's quantum memory MA (the first quantum state) and the quantum state stored in node C's quantum memory MC (the second quantum state).

[0033] Node A's entangled photon receiver RA transmits a signal (hereinafter also called the "quantum entanglement generation success signal") to quantum router B indicating that it has successfully received an entangled photon (i.e., one of the first entangled photon pair 1) transmitted from entangled photon generation light source a. This quantum entanglement generation success signal is a classical high-intensity signal also called a herald signal, and is transmitted between node A and quantum router B using a classical communication channel (the same applies between node C and router B).

[0034] The entangled photon receiver RC of node C transmits a signal (herald signal) to quantum router B indicating that it has successfully received an entangled photon (i.e., one of the second pair of entangled photons) transmitted from the entangled photon generation light source c.

[0035] When quantum router B receives both the herald signal from node A and the herald signal from node C, it performs a measurement called a Bell measurement on the two quantum states stored in quantum memories MB1 and MB2 (i.e., the first quantum state and the second quantum state). A Bell measurement is a method for determining what kind of quantum entanglement state the two quantum states in question are in. This extends the quantum entanglement between "node A-quantum router B" and "node C-quantum router B" to the quantum entanglement between "node A-node C". This conversion of the quantum entanglement between node A and quantum router B, and between node C and quantum router B, into quantum entanglement directly connecting node A and node C is called "quantum entanglement swapping".

[0036] When the "entanglement state" information obtained by Bell measurement is transmitted from quantum router B to nodes A and C, the "entanglement state" information is shared between the quantum memories of nodes A and C. As a result, nodes A and C become quantum entangled. Consequently, various operations that assume the quantum entanglement state is shared become possible between the quantum memories of nodes A and C.

[0037] FIG. 2 is a schematic diagram of a quantum network different from that in FIG. 1, which is configured of a node A', a quantum router B' and a node C'. The node A' comprises an entangled photon generator GA' and a quantum memory MA'. The node C' comprises an entangled photon generator GC' and a quantum memory MC'. The quantum router B' comprises a Bell measurement unit BM', a quantum memory MB'1, a quantum memory MB'2, an entangled photon generator GB'1 and an entangled photon generator GB'2 on both sides of the Bell measurement unit BM'.

[0038] The node A' and the quantum router B' are connected by an optical fiber. A quantum entanglement generation success signal generator a' is arranged on the optical fiber.

[0039] The node C' and the quantum router B' are connected by an optical fiber. A quantum entanglement generation success signal generator c' is arranged on the optical fiber.

[0040] The entangled photon generator GB'1 of the quantum router B' generates a first entangled photon 1'. The first entangled photon 1' has a first entangled state.

[0041] The first entangled photon 1' generated by the entangled photon generator GB'1 is transmitted toward the node A'.

[0042] On the other hand, a quantum state entangled with the quantum state of the first entangled photon 1' generated by the entangled photon generator GB'1 is stored in the quantum memory MB'1 of the quantum router B'.

[0043] The entangled photon generator GB'2 of the quantum router B' generates a second entangled photon 2'. The second entangled photon 2' has a second entangled state.

[0044] The second entangled photon 2' generated by the entangled photon generator GB'1 is transmitted toward the node C'.

[0045] On the other hand, a quantum state entangled with the quantum state of the second entangled photon 2' generated by the entangled photon generator GB'2 is stored in the quantum memory MB'2 of the quantum router B'.

[0046] A photon X generated by the entangled photon generator GA' of the node A' is transmitted toward the node B'.

[0047] The quantum state entangled with the quantum state of photon X generated by the entangled photon generation unit GA' is stored in the quantum memory MA' of node A'.

[0048] Photon Y generated by the entangled photon generation unit GC' of node C' is transmitted toward node B'.

[0049] The quantum state entangled with the quantum state of photon Y generated by the entangled photon generation unit GC' is stored in the quantum memory MC' of node C'.

[0050] At this point, the quantum state stored in the quantum memory MA' of node A' and the quantum state stored in the quantum memory MC' of node C' are not yet in an entangled state.

[0051] When the quantum entanglement generation success signal generator a' disposed between node A' and quantum router B' receives the first entangled photon 1' transmitted from the entangled photon generation unit GB'1 of quantum router B', or the entangled photon X' transmitted from the entangled photon generation unit GA' of node A', it may transmit a signal notifying that reception has succeeded (a herald signal) toward quantum router B' and node A'.

[0052] When the quantum entanglement generation success signal generator c' disposed between node C' and quantum router B' receives the second entangled photon 2' transmitted from the entangled photon generation unit GB'2 of quantum router B', or the entangled photon X'' transmitted from the entangled photon generation unit GC' of node C', it may transmit a signal notifying that reception has succeeded (a herald signal) toward quantum router B' and node C'.

[0053] When quantum router B' receives both the herald signal from quantum entanglement success signal generator a' and the herald signal from quantum entanglement success signal generator c', it performs a Bell measurement on the two quantum states stored in quantum memory MB'1 and quantum memory MB'2 (i.e., the quantum state entangled with the quantum state of the first entangled photon 1' and the quantum state entangled with the quantum state of the second entangled photon 2'). As a result, the quantum entanglement between node A' and quantum router B', and the quantum entanglement between node C' and quantum router B', are converted into quantum entanglement directly connecting node A' and node C', thereby realizing quantum entanglement swapping.

[0054] Therefore, nodes A' and C' become quantum entangled. As a result, various operations become possible between the quantum memories of nodes A' and C', assuming that the quantum entanglement state is shared.

[0055] Figure 3 is a schematic diagram of a quantum network different from those in Figures 1 and 2, consisting of node A'', quantum router B'', and node C''. Node A'' comprises an entangled photon receiver RA'', an entangled photon generator GA'', and a quantum memory MA''. Node C'' comprises an entangled photon receiver RC'', an entangled photon generator GC'', and a quantum memory MC''. Quantum router B'' comprises a bell measurement unit BM'', and on both sides thereof, quantum memories MB''1, an entangled photon generator GB''1, an entangled photon receiver RB''1, a quantum memory MB''2, an entangled photon generator GB''2, and an entangled photon receiver RB''2.

[0056] Node A'' and quantum router B'' are connected by optical fiber.

[0057] Node C'' and quantum router B'' are connected by optical fiber.

[0058] The entangled photon generation unit GB''1 of the quantum router B'' generates a first entangled photon 1''. The first entangled photon 1'' has a first entangled state in which it is entangled with itself.

[0059] The first entangled photon 1'' generated by the entangled photon generation unit GB''1 is transmitted toward node A''. The entangled photon receiver RA'' of node A'' receives this first entangled photon 1''. The quantum state (first quantum state) of the first entangled photon 1'' received by the entangled photon receiver RA'' is stored in the quantum memory MA''.

[0060] The quantum state of the first entangled photon 1'' generated in the entangled photon generation unit GB''1 is stored in the quantum memory MB''1 of the quantum router B''.

[0061] The entangled photon generation unit GB''2 of the quantum router B'' generates a second entangled photon 2''. The second entangled photon 2'' has a second entangled state, entangled with itself.

[0062] The second entangled photon 2'' generated by the entangled photon generation unit GB''2 is transmitted toward node C''. The entangled photon receiver RC'' of node C'' receives this second entangled photon 2''. The quantum state (second quantum state) of the second entangled photon 2'' received by the entangled photon receiver RC'' is stored in the quantum memory MC''.

[0063] The quantum state of the second entangled photon 2'' generated in the entangled photon generation unit GB''2 is stored in the quantum memory MB''2 of the quantum router B''.

[0064] At this point, there are no entangled states between the quantum state stored in the quantum memory MA of node A'' and the quantum state stored in the quantum memory MC of node C''.

[0065] The entangled photon receiver RA'' of node A'' transmits a signal (herald signal) to quantum router B'' indicating that it has successfully received the first entangled photon 1'' transmitted from the entangled photon generator GB''1 of quantum router B''.

[0066] The entangled photon receiver RC'' of node C'' transmits a signal (herald signal) to quantum router B'' indicating that it has successfully received the second entangled photon 2'' transmitted from the entangled photon generator GB''2 of quantum router B''.

[0067] When quantum router B'' receives both the herald signal from entangled photon receiver RA'' and the herald signal from entangled photon receiver RC'', it performs a Bell measurement on the two quantum states stored in quantum memory MB''1 and quantum memory MB''2 (i.e., the quantum state entangled with the quantum state of the first entangled photon 1'' and the quantum state entangled with the quantum state of the second entangled photon 2''). As a result, the quantum entanglement between node A'' and quantum router B'', and the quantum entanglement between node C'' and quantum router B'' are converted into quantum entanglement directly connecting node A'' and node C'', thereby realizing quantum entanglement swapping.

[0068] Therefore, nodes A'' and C'' become quantum entangled. As a result, various operations become possible between the quantum memories of nodes A'' and C'', assuming that the quantum entanglement state is shared.

[0069] The entangled photon generator GA''1 of node A'' generates a third entangled photon 3''. The third entangled photon 3'' has a third entangled state in which it is entangled with itself.

[0070] The third entangled photon 3'' may be received by the entangled photon receiver RB''1 of quantum router B'', or by the entangled photon receiver of another node or quantum router. When the entangled photon receiver RB''1 receives the third entangled photon 3'', it may send a signal (herald signal) to node A'' indicating that it has successfully received the third entangled photon 3'' transmitted from the entangled photon generator GA'' of node A''.

[0071] The entangled photon generator GC''1 of node C'' generates a fourth entangled photon 4''. The fourth entangled photon 4'' has a fourth entangled state with itself.

[0072] The fourth entangled photon 4'' may be received by the entangled photon receiver RB''2 of the quantum router B'', or by the entangled photon receiver of another node or quantum router. If the entangled photon receiver RB''2 receives the fourth entangled photon 4'', it may send a signal (herald signal) to node C'' indicating that it has successfully received the fourth entangled photon 4'' transmitted from the entangled photon generator GC'' of node C''.

[0073] In this quantum network, nodes A'', C'', and quantum router B'' each include both an entangled photon generator and an entangled photon receiver. Therefore, it is not necessary to install an entangled photon generation light source or a quantum entanglement success signal generator on the optical fiber between the nodes and the quantum router.

[0074] As explained above, in quantum relay using quantum memory, quantum entanglement is first generated between adjacent nodes, and then the quantum entanglement between adjacent nodes is extended to non-adjacent nodes through quantum entanglement swapping, which applies the principle of quantum teleportation. Since the quantum entanglement state can be spatially extended through quantum entanglement swapping in this way, it can be used as a quantum router.

[0075] The three configurations described above were the simplest examples of point-to-point quantum information communication between node A and node C, relayed using a single quantum router. To further expand the network, for example, the following can be done: First, quantum routers equipped with quantum memory and Bell measurement units as described above are connected by optical fibers to form a network. In this network, an attempt is made to generate quantum entanglement between adjacent quantum routers by exchanging photons between them. If quantum entanglement is successfully generated, the entanglement is stored in the quantum memory of each quantum router. This quantum entanglement generation is repeated until the nodes to be connected can be connected. After adjacent quantum routers are connected by quantum entanglement, a Bell measurement is performed on one half of the entangled quantum pairs stored in the quantum routers. As a result, the quantum entanglement that connected adjacent quantum routers is converted into quantum entanglement that directly connects the transmitting node and the receiving node through the entire network.

[0076] In a network consisting of nodes A-B, B-C, and C-D, to generate quantum entanglement between node A and node D, the following procedure can be followed: (1) First, generate quantum entanglement between node A-B and node B-C. (2) If quantum entanglement is successfully generated between node A-B and node B-C, perform a Bell measurement at the intermediate node B and connect node A-C. (3) Next, generate quantum entanglement between node C and node D. (4) If entanglement is successfully generated between node C and node D, perform a Bell measurement at the intermediate node C and connect node A-D. In this way, by performing Bell measurements sequentially as entanglement is successfully generated, quantum entanglement can be generated between end-to-end nodes A and D.

[0077] Alternatively, after all adjacent nodes are entangled by quantum entanglement, a Bell measurement may be performed on each of the entangled quantum pairs stored in the Bell measurement unit of each node.

[0078] [First Embodiment] The first embodiment of the present disclosure is a quantum router.

[0079] (Quantum Router 1) Figure 4 is a functional block diagram of the quantum router 1 according to the first embodiment. The quantum router 1 corresponds to quantum router B used in the quantum network of Figure 1. The quantum router 1 relays quantum information within the quantum network. The quantum router 1 comprises a bell measurement unit 11, a first quantum memory 12, a second quantum memory 13, a first entangled photon receiving unit 14, a second entangled photon receiving unit 15, and a control unit 16.

[0080] The quantum router 1 is connected to the optical fiber F1 of the quantum network via the first entangled photon receiver 14.

[0081] The quantum router 1 is connected to the optical fiber F2 of the quantum network via the second entangled photon receiver 15.

[0082] The first quantum memory 12 is connected to the Bell measurement unit 11 from the left side. Therefore, the first quantum memory 12 is connected between the Bell measurement unit 11 and the first entangled photon receiving unit 14.

[0083] The second quantum memory 13 is connected to the Bell measurement unit 11 from the right side, that is, from the side opposite to the first quantum memory 12. Therefore, the second quantum memory 13 is connected between the Bell measurement unit 11 and the second entangled photon receiving unit 15.

[0084] The first quantum memory 12 includes a first qubit array AR1 of qubits 120 arranged in m1 rows × n1 columns (where m1 and n1 are integers greater than or equal to 2). That is, the first quantum memory 12 includes a first qubit array AR1 of qubits 120 arranged in multiple rows and multiple columns.

[0085] The second quantum memory 13 includes a second qubit array AR2 of qubits 130 arranged in m2 rows × n2 columns (where m2 and n2 are integers greater than or equal to 2). That is, the second quantum memory 13 includes a second qubit array AR2 of qubits 130 arranged in multiple rows and multiple columns.

[0086] The above describes the configuration of quantum router 1. Next, the operation of quantum router 1 will be explained with reference to Figures 4 to 8.

[0087] As shown in Figure 4, the first entangled photon receiver 14 of the quantum router 1 receives the first photon PH1 that has propagated from left to right through the optical fiber F1, which is the communication channel of the quantum network. Similarly, the second entangled photon receiver 15 receives the second photon PH2 that has propagated from right to left through the optical fiber F2, which is the communication channel of the quantum network. Hereafter, the first photon PH1 is assumed to have a first quantum state QS1, and the second photon PH2 is assumed to have a second quantum state QS2.

[0088] The first entangled photon receiver 14 distributes the quantum state QS1 of the first photon PH1 received from the quantum network to each row of the first qubit array AR1. This process is schematically shown in Figure 5 (the right half of the quantum router 1 is omitted in Figure 5).

[0089] In the example shown in Figure 5, m1 first photons PH11, PH12, PH13, ..., PH1m1 arrive at the first entangled photon receiver 14 in this order. The first entangled photon receiver 14 first distributes the quantum state QS11 of the first photon PH11 to the first row of the first qubit array AR1, then distributes the quantum state QS12 of the first photon PH12 to the second row of the first qubit array AR1, then distributes the quantum state QS13 of the first photon PH13 to the third row of the first qubit array AR1, and so on, repeating this process until finally distributing the quantum state QS1m1 of the first photon PH1m1 to the m1th row of the first qubit array AR1. In this way, the first entangled photon receiver 14 distributes the quantum state QS1 of the first photon PH1 received from the quantum network to each row of the first qubit array AR1.

[0090] Although not shown in the diagram, the second entangled photon receiver 15 similarly distributes the quantum state QS2 of the second photon PH2 received from the quantum network to each row of the second qubit array AR2.

[0091] Next, the first quantum memory 12 transfers the first quantum states QS1, which have been allocated to each row of the first qubit array AR1, to the Bell measurement unit 11 for each row. Figure 6 shows what happens at this point (the right half of the quantum router 1 is omitted in Figure 6).

[0092] In the example shown in Figure 6, in the first step, the first photons PH11 to PH1m1 all arrive at the first entangled photon receiver 14 at the same time (within the time range of a single operation step). Therefore, in the first step, all quantum states QS11 to QS1m1 are stored in the same column of the first quantum memory 12, and thereafter they are transferred simultaneously from left to right.

[0093] Next, in the second step, the second first photon PH11' to PH1m1', which arrives with a time delay equal to the operation step, is stored in the column next to the quantum states QS11 to QS1m1 of the first photon that arrived in the first step.

[0094] Similarly, in the third step, the third first photon PH11'' to PH1m1'', which arrived with a time delay equal to the operation step, is stored in the column next to the quantum states QS11' to QS1m1' of the first photon that arrived in the second step.

[0095] By repeating this process infinitely, it is possible to constantly fill the memory array with quantum states (although it is not immediately clear whether these quantum states are usable for quantum relay).

[0096] Although not shown in the diagram, the second quantum memory 13 similarly transfers the quantum state QS2 of the second photon PH2, which has been allocated to each row of the second qubit array AR2, to the Bell measurement unit 11 for each row.

[0097] When the first quantum state QS1 is transferred to the Bell measurement unit 11 and reaches a column adjacent to the Bell measurement unit 11, and when the second quantum state QS2 is transferred to the Bell measurement unit 11 and reaches a column adjacent to the Bell measurement unit 11, the control unit 16 determines whether it has received a first quantum entanglement success signal for the first quantum state QS1 and a second quantum entanglement success signal for the second quantum state QS2. If the control unit 16 determines that it has received both the first and second quantum entanglement success signals, it controls the Bell measurement unit 11 to perform a Bell measurement on the first quantum state QS1 and the second quantum state QS2. As a result, the Bell measurement unit 11 performs a Bell measurement on the first quantum state QS1 and the second quantum state QS2. This is shown in Figure 7.

[0098] In the example shown in Figure 7, the first quantum state QS1i has reached the second row, n1st column of the first qubit array AR1, and the second quantum state QS2i has reached the second row, first column of the second qubit array AR2. When the control unit 16 determines that it has received both the first and second quantum entanglement success signals, the Bell measurement unit 11 performs a Bell measurement on the first quantum state QS1i and the second quantum state QS2i.

[0099] On the other hand, if the control unit 16 determines that it has not received the first or second successful quantum entanglement generation signal, it initializes the state without having the bell measurement unit 11 perform a bell measurement.

[0100] Next, we will describe the operation when both the first and second quantum entanglement success signals are received, but the corresponding first quantum state QS1 and second quantum state QS2 are not adjacent. The control unit 16 identifies which row of the first qubit array AR1 contains the quantum state in which the first quantum entanglement was successfully generated, and which row of the second qubit array AR2 contains the quantum state in which the second quantum entanglement was successfully generated. Then, when a quantum state that has successfully generated a first quantum entanglement exists in any row of the first qubit array AR1, and a quantum state that has successfully generated a second quantum entanglement exists in any row of the second qubit array AR2, the control unit 16 moves the first quantum state QS1i and the second quantum state QS2i vertically (transfers them in the column direction) using the bell measurement unit 11 so that the row containing the quantum state that has successfully generated a first quantum entanglement and the row containing the quantum state that has successfully generated a second quantum entanglement are adjacent to each other. Figure 8 shows what happens at this time.

[0101] In the example shown in Figure 8, the first quantum state QS1i has reached the n1th column of the second row of the first qubit array AR1, and the second quantum state QS2i has reached the (m2-1)th column of the second qubit array AR2. That is, both the first quantum state QS1i and the second quantum state QS2i have reached columns adjacent to the Bell measurement unit 11, but they are not adjacent to each other. At this time, the control unit 16 controls the Bell measurement unit 11, the first quantum memory 12, and the second quantum memory 13 as follows: (1) Receive both the first and second quantum entanglement generation success signals. Once success signals are received from both communication channels, the first quantum state QS1i and the second quantum state QS2i are moved to the Bell measurement unit 11. (2) If the generation of the first or second quantum entanglement has failed, initialize them. (3) The first quantum state QS1i or the second quantum state QS2i is moved vertically (transferred in the column direction) by the Bell measurement unit 11. This makes the first quantum state QS1i and the second quantum state QS2i adjacent to each other, and then the Bell measurement unit 11 performs a Bell measurement on the first quantum state QS1i and the second quantum state QS2i.

[0102] In the example shown in Figure 8, initially, the first quantum state QS1i is moved to the second row of the Bell measurement unit 11, and the second quantum state QS2i is moved to the (m2-1)th row of the Bell measurement unit 11. At this time, the two states are not adjacent to each other. At this time, the control unit 16 moves the second quantum state QS2i vertically to the second row within the Bell measurement unit 11.

[0103] The transfer algorithm for bringing the first quantum state QS1i and the second quantum state QS2i adjacent (hereinafter also referred to as "vertical transfer in the Bell measurement unit") can be any suitable algorithm. For example, it could be an algorithm that "finds combinations of successful bits that can be brought adjacent with the minimum movement in the left and right columns, and transfers them to the adjacent bits so that they are close together. While performing a Bell measurement when successful bits are adjacent in the left and right columns, the above operation is repeated as many times as possible during the waiting time for the horizontal transfer."

[0104] The above describes the operation of the quantum router 1. Next, the effects of this embodiment will be explained.

[0105] The quantum router of this embodiment first receives a first photon and a second photon propagating along an optical fiber. Then, the quantum states of the received first and second photons are distributed to multiple rows of a qubit array constituting a quantum memory. As a result, the quantum states of the first and second photons propagating along the optical fiber are transferred in parallel within the quantum router. The quantum states distributed to each row are then swapped and transferred one row at a time towards the central Bell measurement unit. In other words, the quantum memory of the quantum router of this embodiment functions as a FIFO (First In First Out) memory. When the first and second quantum states, which have been swapped and transferred from the left and right sides of the qubit array, reach just before the Bell measurement unit, it is determined whether both the first and second quantum entanglement success signals exist. If both successfully entangled quantum states exist, a Bell measurement is promptly performed. In this embodiment of the quantum router, while the quantum entanglement success signal travels back and forth across the transmission path, the quantum state propagates in parallel within the quantum memory, and since the quantum memory functions as a FIFO memory, processing can continue without stopping. This significantly reduces the waiting time caused by the transmission delay of the quantum entanglement success signal, and thus greatly reduces the decrease in throughput.

[0106] Excluding the vertical transfer time in the bell measurement section and the time required for bell measurement (several hundred nanoseconds to 1 microsecond), the transmission delay time of the successful entanglement generation signal / (transfer time of the qubit array + waiting time) can be estimated as the number of columns in the qubit array. Therefore, if there are a sufficient number of columns, the waiting time can be reduced accordingly.

[0107] The number of rows and columns that maximize entanglement generation efficiency actually depends on the lifetime of the qubits and the fidelity of the operation. Therefore, the optimal values ​​for these can be determined, for example, through simulation.

[0108] In contrast, conventional quantum routers (such as those disclosed in Non-Patent Literature 1) cannot continuously process the quantum states of propagating photons within the memory, nor can they function as FIFO memory, because their quantum memory is not composed of a qubit array. As a result, processing must wait until both the first and second successful quantum entanglement generation signals arrive, and no processing can be done during this waiting period. In other words, in conventional quantum routers, the entire time it takes for the successful quantum entanglement generation signals to travel back and forth across the transmission path is idle, resulting in low throughput.

[0109] As described above, this embodiment provides a quantum router with a high quantum entanglement generation rate that enables high-throughput quantum information relay between remote nodes.

[0110] (Quantum Router 2) Figure 9 is a functional block diagram of the quantum router 2 according to the first embodiment. The quantum router 2 corresponds to quantum router B' used in the quantum network of Figure 2. The quantum router 2 comprises a bell measurement unit 11, a first quantum memory 12, a second quantum memory 13, a first entangled photon generation unit 17, a second entangled photon generation unit 18, and a control unit 16.

[0111] The quantum router 2 is connected to the optical fiber F1 of the quantum network via the first entangled photon generation unit 17.

[0112] The quantum router 2 is connected to the optical fiber F2 of the quantum network via the second entangled photon generation unit 18.

[0113] The first quantum memory 12 is connected to the Bell measurement unit 11 from the left side. Therefore, the first quantum memory 12 is connected between the Bell measurement unit 11 and the first entangled photon generation unit 17.

[0114] The second quantum memory 13 is connected to the Bell measurement unit 11 from the right side, that is, from the side opposite to the first quantum memory 12. Therefore, the second quantum memory 13 is connected between the Bell measurement unit 11 and the second entangled photon generation unit 18.

[0115] The first quantum memory 12 includes a first qubit array AR1 of qubits 120 arranged in m1 rows × n1 columns (where m1 and n1 are integers greater than or equal to 2). That is, the first quantum memory 12 includes a first qubit array AR1 of qubits 120 arranged in multiple rows and multiple columns.

[0116] The second quantum memory 13 includes a second qubit array AR2 of qubits 130 arranged in m2 rows × n2 columns (where m2 and n2 are integers greater than or equal to 2). That is, the second quantum memory 13 includes a second qubit array AR2 of qubits 130 arranged in multiple rows and multiple columns.

[0117] The above describes the configuration of quantum router 2. Next, the operation of quantum router 2 will be explained with reference to Figures 9 to 13.

[0118] As shown in Figure 9, the first entangled photon generation unit 17 of the quantum router 1 generates a first photon PH1 and transmits this first photon PH1 so that it propagates from right to left through the optical fiber F1, which is the communication channel of the quantum network. Similarly, the second entangled photon generation unit 18 generates a second photon PH2 and transmits this second photon PH2 so that it propagates from right to left through the optical fiber F2, which is the communication channel of the quantum network. Hereinafter, the first photon PH1 is assumed to have a first quantum state QS1. The second photon PH2 is assumed to have a second quantum state QS2. Furthermore, the quantum state entangled with the first quantum state QS1 is assumed to be quantum state QS'1. Similarly, the quantum state entangled with the second quantum state QS2 is assumed to be quantum state QS'2.

[0119] The first entangled photon generation unit 17 distributes the quantum state QS'1, which is entangled with the quantum state QS1 of the first photon PH1 transmitted to the quantum network, to each row of the first qubit array AR1. This process is schematically shown in Figure 10 (the right half of the quantum router 2 is omitted in Figure 10).

[0120] In the example shown in Figure 10, m1 first photons PH11, PH12, PH13, ..., PH1m1 are transmitted to the quantum network in this order. Correspondingly, the first entangled photon generator 17 distributes the quantum state QS'11, which is entangled with quantum state QS11, to the first row of the first qubit array AR1, then distributes the quantum state QS'12, which is entangled with quantum state QS12, to the second row of the first qubit array AR1, then distributes the quantum state QS'13, which is entangled with quantum state QS13, to the third row of the first qubit array AR1, and so on, repeating this operation until finally the quantum state QS'13m1, which is entangled with quantum state QS1m1, is distributed to the m1 row of the first qubit array AR1. In this way, the first entangled photon generation unit 17 distributes the quantum state QS'1, which is entangled with the quantum state QS1 of the first photon PH1 transmitted to the quantum network, to each row of the first qubit array AR1.

[0121] Although not shown in the diagram, the second entangled photon generation unit 18 similarly distributes the quantum state QS'2, which is entangled with the quantum state QS2 of the second photon PH2 transmitted to the quantum network, to each row of the second qubit array AR2.

[0122] Next, the first quantum memory 12 transfers the quantum state QS'1, which is entangled with the first quantum state QS1 distributed to each row of the first qubit array AR1, to the Bell measurement unit 11 for each row. Figure 11 shows what happens at this time (the right half of the quantum router 1 is omitted in Figure 11).

[0123] In the example shown in Figure 11, in the first step, the first photons PH11 to PH1m1 generated by the first entangled photon generation unit 17 all arrive at the first quantum memory 12 at the same time (within the time range of a single operation step). Therefore, in the first step, all quantum states QS11 to QS1m1 are stored in the same column in the first quantum memory 12, and thereafter they are transferred simultaneously from left to right at the same time.

[0124] Next, in the second step, the second first photon PH11' to PH1m1', which arrives with a time delay equal to the operation step, is stored in the column next to the quantum states QS11 to QS1m1 of the first photon that arrived in the first step.

[0125] Similarly, in the third step, the third first photon PH11'' to PH1m1'', which arrived with a time delay equal to the operation step, is stored in the column next to the quantum states QS11' to QS1m1' of the first photon that arrived in the second step.

[0126] By repeating this process infinitely, it is possible to constantly fill the memory array with quantum states (although it is not immediately clear whether these quantum states are usable for quantum relay).

[0127] Although not shown in the diagram, the second quantum memory 13 similarly transfers the quantum state QS'2, which is entangled with the second quantum state QS2 distributed to each row of the second qubit array AR2, to the Bell measurement unit 11 for each row.

[0128] When the quantum state QS'1 entangled with the first quantum state QS1 is transferred to the Bell measurement unit 11 and reaches a row adjacent to the Bell measurement unit 11, and when the quantum state QS'2 entangled with the second quantum state QS2 is transferred to the Bell measurement unit 11 and reaches a row adjacent to the Bell measurement unit 11, the control unit 16 determines whether it has received a first quantum entanglement success signal for the quantum state QS'1 entangled with the first quantum state QS1 and a second quantum entanglement success signal for the quantum state QS'2 entangled with the second quantum state QS2. If the control unit 16 determines that it has received both the first and second quantum entanglement success signals, it controls the Bell measurement unit 11 to perform a Bell measurement on the quantum state QS'1 entangled with the first quantum state QS1 and the quantum state QS'2 entangled with the second quantum state QS2. As a result, the Bell measurement unit 11 performs Bell measurements on the quantum state QS'1 entangled with the first quantum state QS1 and the quantum state QS'2 entangled with the second quantum state QS2. Figure 12 shows what happens at this time.

[0129] In the example shown in Figure 12, the quantum state QS'1i entangled with the first quantum state QS1i reaches the second row, n1st column of the first qubit array AR1, and the quantum state QS'2i entangled with the second quantum state QS2i reaches the second row, first column of the second qubit array AR2. When the control unit 16 determines that it has received both the first quantum entanglement generation success signal and the second quantum entanglement generation success signal, the Bell measurement unit 11 performs a Bell measurement on the quantum state QS'1i entangled with the first quantum state QS1i and the quantum state QS'2i entangled with the second quantum state QS2i.

[0130] On the other hand, if the control unit 16 determines that it has not received the first or second successful quantum entanglement generation signal, it initializes the state without having the bell measurement unit 11 perform a bell measurement.

[0131] Next, we will explain the operation when both the first and second quantum entanglement success signals are received, but the corresponding quantum state QS'1 entangled with the first quantum state QS1 and the quantum state QS'2 entangled with the second quantum state QS2 are not adjacent. The control unit 16 identifies which row of the first qubit array AR1 contains the quantum state in which the first quantum entanglement was successfully generated, and which row of the second qubit array AR2 contains the quantum state in which the second quantum entanglement was successfully generated. Then, when a quantum state that has successfully generated a first quantum entanglement exists in any row of the first qubit array AR1, and a quantum state that has successfully generated a second quantum entanglement exists in any row of the second qubit array AR2, the control unit 16 transfers either the quantum state QS'1 entangled with the first quantum state QS1 or the quantum state QS'2 entangled with the second quantum state QS2, such that the row containing the quantum state that has successfully generated a first quantum entanglement is adjacent to the row containing the quantum state that has successfully generated a second quantum entanglement. Figure 13 shows what happens at this time.

[0132] In the example shown in Figure 13, the quantum state QS'1i entangled with the first quantum state QS1i reaches the n1th column of the second row of the first qubit array AR1, and the quantum state QS'2i entangled with the second quantum state QS2i reaches the (m2-1)th column of the second qubit array AR2. That is, both the quantum state QS'1i entangled with the first quantum state QS1i and the quantum state QS'2i entangled with the second quantum state QS2i reach columns adjacent to the Bell measurement unit 11, but they are not adjacent to each other. At this time, the control unit 16 controls the Bell measurement unit 11, the first quantum memory 12, and the second quantum memory 13 as follows. (1) Receive both the first quantum entanglement generation success signal and the second quantum entanglement generation success signal. Once success signals are received from both communication channels, the first quantum state QS'1i and the second quantum state QS'2i are moved to the Bell measurement unit 11. (2) If the generation of the first or second quantum entanglement has failed, they are initialized. (3) The first quantum state QS'1i or the second quantum state QS'2i is moved vertically (transferred in the column direction) in the Bell measurement unit 11. This makes the first quantum state QS'1i and the second quantum state QS'2i adjacent to each other, and then the Bell measurement unit 11 performs a Bell measurement on the first quantum state QS'1i and the second quantum state QS'2i.

[0133] In the example shown in Figure 13, initially, the first quantum state QS'1i is moved to the second row of the Bell measurement unit 11, and the second quantum state QS'2i is moved to the (m2-1)th row of the Bell measurement unit 11. At this time, the two states are not adjacent to each other. At this point, the control unit 16 moves the second quantum state QS'2i vertically to the second row within the Bell measurement unit 11.

[0134] The algorithm for transferring the quantum state QS'1i entangled with the first quantum state QS1i and the quantum state QS'2i entangled with the second quantum state QS2i to adjacent states (hereinafter also referred to as "vertical transfer in the Bell measurement unit") can be any suitable algorithm. For example, it could be an algorithm that "finds combinations of successful bits that can be brought adjacent with the minimum movement in the left and right columns, and transfers them to the adjacent bits so that they are closer together. While performing a Bell measurement when successful bits are adjacent in the left and right columns, the above operation is repeated as many times as possible during the waiting time for horizontal transfers."

[0135] (Quantum Router 3) Figure 14 is a functional block diagram of the quantum router 3 according to the first embodiment. The quantum router 3 corresponds to quantum router B'' used in the quantum network of Figure 3. The quantum router 3 comprises a Bell measurement unit 11, a first quantum memory 12, a second quantum memory 13, a first entangled photon receiving unit 14, a second entangled photon receiving unit 15, a control unit 16, a first entangled photon generation unit 17, and a second entangled photon generation unit 18. In other words, the quantum router 3 comprises the configuration of the quantum router 2 of Figure 9 plus the first entangled photon receiving unit 14 and the second entangled photon receiving unit 15. The other configurations of the quantum router 3 are the same as those of the quantum router 2.

[0136] The quantum router 3 can perform the same operations as the quantum router 2 described above. However, since the quantum router 3 is further equipped with a first entangled photon receiver 14 and a second entangled photon receiver 15, it can receive a third photon PH3 and a fourth photon PH4 from the quantum network. Therefore, the quantum router 3 can also perform the same operations as the quantum router 1 in Figure 4.

[0137] (Various variations) Next, various variations of quantum routers 1 to 3 are shown.

[0138] (Modification 1) The number of rows in the first qubit array and the number of rows in the second qubit array may be different. That is, m1 ≠ m2.

[0139] (Modification 2) Similarly, the number of columns in the first qubit array and the number of columns in the second qubit array may be different. That is, n1 ≠ n2.

[0140] (Modification 3) Alternatively, the number of rows in the first qubit array may be equal to the number of rows in the second qubit array, and the number of columns in the first qubit array may be equal to the number of columns in the second qubit array. That is, m1 = m2 and n1 = n2.

[0141] If the number of rows in the first qubit array is equal to the number of rows in the second qubit array, and the number of columns in the first qubit array is equal to the number of columns in the second qubit array, then the first and second quantum states are distributed to the same number of rows and reach the Bell measurement unit 11 by following the same number of columns. In this case, compared to the case where the number of rows in the first qubit array is different to the number of rows in the second qubit array, or the number of columns in the first qubit array is different to the number of columns in the second qubit array, Bell measurements can be performed on the first and second quantum states at the appropriate timing without requiring any special processing.

[0142] (Modification 4) The number of rows and columns of the first qubit array and the number of rows and columns of the second qubit array may be different. That is, m1 ≠ n1 and m2 ≠ n2. In other words, the first qubit array and the second qubit array do not have to be square matrices.

[0143] (Modification 5) The number of rows and columns of the first qubit array and the number of rows and columns of the second qubit array may be equal. That is, m1 = n1 and m2 = n2. In other words, the first qubit array and the second qubit array may be square matrices.

[0144] (Modification 6) Figure 15 is a functional block diagram of quantum router 1', which is a modified version of quantum router 1 of Figure 4. In addition to the configuration of quantum router 1, quantum router 1' includes a first multiplexer / demultiplexer 20, a second multiplexer / demultiplexer 21, a first wavelength converter 22, and a second wavelength converter 23.

[0145] The first multiplexer / demultiplexer 20 is positioned between the optical fiber F1 of the quantum network and the first entangled photon receiving unit 14. The second multiplexer / demultiplexer 21 is positioned between the optical fiber F2 of the quantum network and the second entangled photon receiving unit 15. A multiplexer / demultiplexer is also called a Mux / Demux device and is a device that multiplexes multiple optical fibers into one optical fiber, and conversely separates one fiber into multiple optical fibers.

[0146] In the example shown in Figure 15, the first multiplexer / demultiplexer 20 performs multiplexing and demultiplexing of light between a single optical fiber F1 and a first quantum memory 12 composed of a first qubit array AR1. This enables signal multiplexing and demultiplexing between the optical fiber F1 and the first entangled photon receiver 14. The second multiplexer / demultiplexer 21 then performs multiplexing and demultiplexing of light between a single optical fiber F2 and a second quantum memory 13 composed of a second qubit array AR2. This enables signal multiplexing and demultiplexing between the optical fiber F1 and the second entangled photon receiver 15.

[0147] Furthermore, if, for example, each row of the qubit array between routers is connected by individual optical fibers or electrical wiring, a multiplexer / demultiplexer may not be necessary.

[0148] The first wavelength conversion device 22 is positioned between the optical fiber F1 of the quantum network and the first entangled photon receiving unit 14. The second wavelength conversion device 23 is positioned between the optical fiber F2 of the quantum network and the second entangled photon receiving unit 15.

[0149] The first wavelength conversion device 22 performs wavelength conversion between communication photons propagating within the quantum network and quantum states propagating within the first qubit array AR1 of the first quantum memory 12. The second wavelength conversion device 23 performs wavelength conversion between communication photons propagating within the quantum network and quantum states propagating within the second qubit array AR2 of the second quantum memory 13. As a result, communication can be performed even when the wavelengths of the communication photons propagating within the quantum network and the quantum states propagating within the first qubit array AR1 and the second qubit array AR2 are different.

[0150] For example, if all communication between routers is performed on the same wavelength, a wavelength converter is not necessary.

[0151] (Modification 7) Figure 16 is a functional block diagram of quantum router 2', which is a modified version of quantum router 2 of Figure 9. In addition to the configuration of quantum router 2, quantum router 2' includes a first multiplexer / demultiplexer 20, a second multiplexer / demultiplexer 21, a first wavelength converter 22, and a second wavelength converter 23.

[0152] The first multiplexer / demultiplexer 20 is positioned between the optical fiber F1 of the quantum network and the first entangled photon generation unit 17. The second multiplexer / demultiplexer 21 is positioned between the optical fiber F2 of the quantum network and the second entangled photon generation unit 18.

[0153] The first wavelength conversion device 22 is positioned between the optical fiber F1 of the quantum network and the first entangled photon generation unit 17. The second wavelength conversion device 23 is positioned between the optical fiber F2 of the quantum network and the second entangled photon generation unit 18.

[0154] The operation and function of the first multiplexer / demultiplexer 20, the second multiplexer / demultiplexer 21, the first wavelength converter 22, and the second wavelength converter 23 in Figure 16 are the same as those in Figure 15, so a detailed explanation is omitted.

[0155] (Modification 8) There are no particular limitations on the first and second successful quantum entanglement generation signals, and any suitable ones may be used. For example, the first and second successful quantum entanglement generation signals may be classical signals transmitted through a classical channel. In particular, the first and second successful quantum entanglement generation signals may be herald signals or herald photons.

[0156] (Modification 9) There are no particular limitations on the means for transferring the first quantum state and the second quantum state to the Bell measurement unit, and any suitable means may be used. As an example, the transfer of the first quantum state and the second quantum state to the Bell measurement unit may be performed using two CNOT gates. Figure 17 shows two CNOT gates for transferring the first quantum state and the second quantum state to the Bell measurement unit.

[0157] (Modification 10) In particular, the transfer of the first quantum state and the second quantum state to the Bell measurement unit may be performed using a SWAP gate or an iSWAP gate.

[0158] (Modification 11) There are no particular limitations on the means of bell measurement, and any suitable means may be used. For example, bell measurement may be performed using a CNOT gate and an Adamard gate. Figure 18 shows a CNOT gate and an Adamard gate for performing bell measurement.

[0159] (Modification 12) There are no particular limitations on the qubits constituting the first qubit array and the qubits constituting the second qubit array, and any suitable ones may be used. For example, the qubits constituting the first qubit array and the qubits constituting the second qubit array may be superconducting qubits. Alternatively, the qubits may be semiconductors (e.g., silicon), optical qubits, ion traps, cold atoms, etc.

[0160] (Modification 13) There are no particular limitations on the quantum states that propagate within the first and second qubit arrays, and any suitable ones may be used. For example, the quantum states that propagate within the first and second qubit arrays may be quantum states of superconducting qubits.

[0161] (Modification 14) When the qubits constituting the first qubit array and the qubits constituting the second qubit array are made up of superconducting qubits, the quantum router may further include a cooling system. Figure 19 is a functional block diagram of the quantum router 4 equipped with a cooling system 30. The configuration of the quantum router 4 other than the cooling system 30 is the same as the configuration of the quantum router 1 in Figure 4.

[0162] (Modification 15) The cooling system 30 is not particularly limited, and any suitable one may be used. For example, the cooling system 30 may be a system equipped with a refrigerator such as a dilution refrigerator.

[0163] (Modification 16) In the embodiments described above, a two-dimensional (array) arrangement of superconducting qubits was shown as an example, but it goes without saying that the invention is not limited to this, and multi-dimensional (array) arrangements (three-dimensional arrangements, etc.) are also applicable.

[0164] [Second Embodiment] A second embodiment of the present disclosure is a quantum information relay method.

[0165] (Quantum Information Relay Method 1) Figure 20 is a flowchart showing the processing procedure of the quantum information relay method according to the second embodiment. This method is a quantum information relay method that relays quantum information within a quantum network using a quantum router equipped with a Bell measurement unit, a first quantum memory, and a second quantum memory.

[0166] The first quantum memory includes a first qubit array consisting of multiple rows and multiple columns. The second quantum memory includes a second qubit array consisting of multiple rows and multiple columns.

[0167] The method includes: step S1 receiving a first photon having a first quantum state from a quantum network; step S2 receiving a second photon having a second quantum state from a quantum network; step S3 distributing the first quantum state to each row of a first qubit array; step S4 distributing the second quantum state to each row of a second qubit array; step S5 transferring the first quantum state distributed to each row of the first qubit array to a Bell measurement unit within the first qubit array; step S6 transferring the second quantum state distributed to each row of the second qubit array to a Bell measurement unit within the second qubit array; and step S7 having the Bell measurement unit perform a Bell measurement on the first and second quantum states upon receiving a first entanglement generation success signal for the first quantum state and a second entanglement generation success signal for the second quantum state.

[0168] The procedure from step S1 to step S3 to step S5 and the procedure from step S2 to step S4 to step S6 may be executed simultaneously.

[0169] (Quantum Information Relay Method 2) Figure 21 is a flowchart showing the processing procedure of a quantum information relay method, which is different from that of Figure 20, according to a second embodiment. This method is also a quantum information relay method that relays quantum information within a quantum network using a quantum router equipped with a Bell measurement unit, a first quantum memory, and a second quantum memory.

[0170] The first quantum memory includes a first qubit array consisting of multiple rows and multiple columns. The second quantum memory includes a second qubit array consisting of multiple rows and multiple columns.

[0171] This method comprises the steps of: generating a first photon having a first quantum state and transmitting the first photon to a quantum network (S11); generating a second photon having a second quantum state and transmitting the second photon to a quantum network (S12); distributing the quantum state entangled with the first quantum state to each row of a first qubit array (S13); distributing the quantum state entangled with the second quantum state to each row of a second qubit array (S14); and distributing the quantum state entangled with the first quantum state distributed to each row of the first qubit array to the first The process includes: step S15 transferring the quantum states within the quantum bit array to the Bell measurement unit; step S16 transferring the quantum states entangled with the second quantum state, which have been allocated to each row of the second quantum bit array, to the Bell measurement unit within the second quantum bit array; and step S17, upon receiving a first quantum entanglement generation success signal for the first quantum state and a second quantum entanglement generation success signal for the second quantum state, the Bell measurement unit performing a Bell measurement on the quantum state entangled with the first quantum state and the quantum state entangled with the second quantum state.

[0172] The procedure from step S11 to step S13 to step S15 and the procedure from step S12 to step S14 to step S16 may be executed simultaneously.

[0173] According to this embodiment, high-throughput quantum information relay between remote nodes can be achieved by using a quantum router with a high quantum entanglement generation rate.

[0174] [Third Embodiment] A third embodiment of the present disclosure is a quantum information relay program.

[0175] (Quantum Information Relay Program 1) Figure 20 is a flowchart showing the processing procedure of a quantum information relay program according to the third embodiment. This program is a quantum information relay program that relays quantum information within a quantum network using a quantum router equipped with a Bell measurement unit, a first quantum memory, and a second quantum memory.

[0176] The first quantum memory includes a first qubit array consisting of multiple rows and multiple columns. The second quantum memory includes a second qubit array consisting of multiple rows and multiple columns.

[0177] This program causes a computer to execute a method that includes: step S1 receiving a first photon having a first quantum state from a quantum network; step S2 receiving a second photon having a second quantum state from the quantum network; step S3 distributing the first quantum state to each row of a first qubit array; step S4 distributing the second quantum state to each row of a second qubit array; step S5 transferring the first quantum state distributed to each row of the first qubit array to the Bell measurement unit within the first qubit array; step S6 transferring the second quantum state distributed to each row of the second qubit array to the Bell measurement unit within the second qubit array; and step S7 having the Bell measurement unit perform a Bell measurement on the first and second quantum states upon receiving a first entanglement generation success signal for the first quantum state and a second entanglement generation success signal for the second quantum state.

[0178] The procedure from step S1 to step S3 to step S5 and the procedure from step S2 to step S4 to step S6 may be executed simultaneously.

[0179] (Quantum Information Relay Program 2) Figure 21 is a flowchart showing the processing procedure of a quantum information relay program, different from that shown in Figure 20, according to a third embodiment. This program is also a quantum information relay program that relays quantum information within a quantum network using a quantum router equipped with a Bell measurement unit, a first quantum memory, and a second quantum memory.

[0180] The first quantum memory includes a first qubit array consisting of multiple rows and multiple columns. The second quantum memory includes a second qubit array consisting of multiple rows and multiple columns.

[0181] This program includes the steps of: generating a first photon having a first quantum state and transmitting the first photon to a quantum network in step S11; generating a second photon having a second quantum state and transmitting the second photon to a quantum network in step S12; distributing the quantum state entangled with the first quantum state to each row of the first qubit array in step S13; distributing the quantum state entangled with the second quantum state to each row of the second qubit array in step S14; and processing the quantum state entangled with the first quantum state distributed to each row of the first qubit array into the first qubit. The computer is instructed to perform a method that includes the steps of: transferring within the array to the Bell measurement unit in step S15; transferring the quantum states entangled with the second quantum states, which have been allocated to each row of the second qubit array, to the Bell measurement unit within the second qubit array in step S16; and, upon receiving a first quantum entanglement generation success signal for the first quantum state and a second quantum entanglement generation success signal for the second quantum state, causing the Bell measurement unit to perform a Bell measurement on the quantum states entangled with the first quantum state and the quantum states entangled with the second quantum state in step S17.

[0182] The procedure from step S11 to step S13 to step S15 and the procedure from step S12 to step S14 to step S16 may be executed simultaneously.

[0183] According to this embodiment, a program that enables high-throughput quantum information relay between remote nodes can be implemented in software using a quantum router with a high quantum entanglement generation rate.

[0184] [Fourth Embodiment] The fourth embodiment of the present disclosure is a quantum network system. Figure 22 is a schematic diagram of the quantum network system NW1 according to the fourth embodiment. The quantum network system NW1 is configured in a topology connecting node 41, quantum router 51, quantum router 52, quantum router 53, quantum router 54, and node 42. Nodes 41 and 42 are quantum information processing nodes such as quantum computers and quantum memory. Quantum routers 51, 52, 53, and 54 are quantum routers according to the first embodiment.

[0185] In the quantum network system NW1, the system attempts to generate quantum entanglement between adjacent quantum routers by exchanging photons between them. If quantum entanglement is successfully generated, it is stored in the Bell measurement section of each quantum router, and this process is repeated until quantum entanglement is successfully generated between the desired nodes. After adjacent quantum routers are connected by quantum entanglement, a Bell measurement is performed on the entangled pairs stored in the Bell measurement sections of these quantum routers.

[0186] According to this embodiment, a large-scale quantum network system can be constructed using a quantum router with a high quantum entanglement generation rate that enables high-throughput quantum information relay between remote nodes.

[0187] [Fifth Embodiment] The fifth embodiment of the present disclosure is a quantum computer. Figure 23 is a functional block diagram of a quantum computer 100 according to the fifth embodiment. The quantum computer 100 performs quantum computation by sharing quantum entanglement with an external quantum computer. The quantum computer 100 includes a Bell measurement unit 101, a calculation unit 102 connected to the Bell measurement unit 101 to perform quantum computation, a quantum memory 103 connected to the Bell measurement unit 101 from the other side of the calculation unit 102 to store the quantum state of photons received from an external quantum computer, and a control unit 104.

[0188] The quantum computer 100 may implement error correction codes such as surface codes or LDPC codes (Low Density Parity Check Codes).

[0189] The calculation unit 102 includes a first qubit array consisting of multiple rows and multiple columns. The quantum memory 103 includes a second qubit array consisting of multiple rows and multiple columns. When the control unit 104 receives a quantum entanglement success signal from the calculation unit 102 and a quantum entanglement success signal from an external quantum computer, it controls the Bell measurement unit 101, the calculation unit 102, and the quantum memory 103 to perform Bell measurements on the quantum state of the photon received from the external quantum computer and the quantum state of the calculation unit 102.

[0190] Quantum computers consume a large amount of generated quantum entanglement during computation. Therefore, it is necessary to store the quantum entanglement between two nodes so that it can be immediately used for computation, and to move it to the appropriate row so that it can be passed to the necessary computation unit 102 qubits. In the quantum computer of this embodiment, by making the number of columns of the qubit array constituting the quantum memory 103 sufficiently large, the quantum entanglement memory or buffer function required by the quantum computer can be realized.

[0191] [Further Modifications of the Quantum Router] (Modification 17) A further modification 17 of the quantum router described above will be explained below. The quantum router 1 of Modification 17 has the same configuration as the quantum router 1 in Figure 4. That is, the quantum router 1 of Modification 17 comprises a bell measuring unit 11, a first quantum memory 12, a second quantum memory 13, a first entangled photon receiving unit 14, a second entangled photon receiving unit 15, and a control unit 16.

[0192] In the modified example 17, the control unit 16 of the quantum router 1 identifies which rows and columns of the first qubit array AR1 contain a quantum state in which the first quantum entanglement was successfully generated, and which rows and columns of the second qubit array AR2 contain a quantum state in which the second quantum entanglement was successfully generated. The control unit 16 then transfers the first quantum state or a quantum state entangled with the first quantum state, or the second quantum state or a quantum state entangled with the second quantum state, so that all qubits in the Bell measurement unit 11 on the first quantum memory 12 side become a quantum state in which the first quantum entanglement was successfully generated, and all qubits in the Bell measurement unit 11 on the second quantum memory 13 side become a quantum state in which the second quantum entanglement was successfully generated.

[0193] The operation of the first quantum memory 12 and the Bell measurement unit 11 of the modified quantum router 17 will be explained below with reference to Figures 24 to 29. Figures 24 to 29 show the first quantum memory 12 and the Bell measurement unit 11 of the modified quantum router 17. Hereafter, the qubit in the mth row and nth column of the first bit array AR1 of the first quantum memory 12 will be represented as (m, n). In Figures 24 to 29, quantum states that have successfully generated quantum entanglement are represented by white circles, and qubits that have not been generated are represented by black circles.

[0194] Hereafter, with respect to time t, we assume t1 < t2 < t3 < t4 < t5 < t6.

[0195] Figure 24 shows the quantum state of the first quantum memory 12 at t=t1. Here, only qubits (1, n1-2) and qubit (3, n1-2) have successfully generated quantum entanglement (indicated by white circles). Subsequently, each qubit of the first quantum memory 12 is transferred in the row direction toward the bell measurement unit 11 (i.e., from left to right in the figure).

[0196] Figure 25 shows the quantum state of the first quantum memory 12 at t=t2. Here, only qubits (3, n1-2), qubit (m1, n1-2), qubit (1, n1-1), and qubit (3, n1-1) have successfully generated quantum entanglement.

[0197] Figure 26 shows the quantum state of the first quantum memory 12 at t=t3. Here, only qubits (2, n1-2), (3, n1-1), (m1, n1-1), (1, n1), and (3, n1) have successfully generated quantum entanglement. The qubits (1, n1) and (3, n1) that have reached the n1th column are transferred to the Bell measurement unit 11.

[0198] Figure 27 shows the quantum state of the first quantum memory 12 at t=t4. Here, only qubits (2, n1-1), qubit (3, n1), and qubit (m1, n1) have successfully generated quantum entanglement. In addition, the qubits in the first and third rows of the Bell measurement unit 11 have successfully generated quantum entanglement. The qubit (m1, n1) that reaches the n1th column is transferred to the Bell measurement unit 11.

[0199] Here, if the qubit (3, n1) were transferred directly to the Bell measurement unit 11, it would collide with the qubit in the third row of the Bell measurement unit 11. Therefore, the control unit 16 moves the qubit in the third row of the Bell measurement unit 11 vertically (transfers it in the column direction) to a row that has not successfully generated quantum entanglement, for example, the (m1-1) row. As a result, the third row of the Bell measurement unit 11 is in a state where quantum entanglement has not been successfully generated. Consequently, the qubit (3, n1) can be transferred to the Bell measurement unit 11 while avoiding a collision.

[0200] Figure 28 shows the quantum state of the first quantum memory 12 at t=t5. Here, only qubits (2, n1) and (3, n1) have successfully generated quantum entanglement. Also, the qubits in the first row, the (m1-1)th row, and the m1th row of the Bell measurement unit 11 have successfully generated quantum entanglement. The qubits (2, n1) and (3, n1) that have reached the n1th column are transferred to the Bell measurement unit 11.

[0201] Figure 29 shows the quantum state of the first quantum memory 12 at t=t6. Here, all rows of qubits in the Bell measurement unit 11 have successfully generated quantum entanglement.

[0202] The operation of the second quantum memory 13 and Bell measurement unit 11 of the quantum router 1 in modified example 17 is the same as the operation of the first quantum memory 12 and Bell measurement unit 11. That is, by horizontally reversing Figures 24 to 29, replacing the first quantum memory 12 with the second quantum memory 13, and replacing the first memory array AR1 with the second memory array AR2, the operation of the second quantum memory 13 and Bell measurement unit 11 can be understood.

[0203] Thus, according to this modified version, all rows of qubits in the Bell measurement unit 11 can be brought into a state where quantum entanglement generation has been successfully achieved. This further improves the throughput of quantum information relay, such as quantum state distillation, which requires the simultaneous consumption of multiple qubits.

[0204] In the above embodiment, the vertical movement (transfer in the column direction) of the entangled qubits was performed by the Bell measurement unit 11. However, the invention is not limited to this, and the vertical movement (transfer in the column direction) of the entangled qubits may also be performed by the first qubit array AR1 of the first quantum memory 12 or the second qubit array AR2 of the second quantum memory 13.

[0205] [Further Modifications of the Quantum Computer] (Modification 18) A further modification 18 of the quantum computer described above will be explained below. The quantum computer of Modification 18 has the same configuration as the quantum computer 100 in Figure 23. That is, the quantum computer 100 of Modification 18 comprises a Bell measurement unit 101, a calculation unit 102 connected to the Bell measurement unit 101 to perform quantum calculations, a quantum memory 103 connected to the Bell measurement unit 101 from the other side of the calculation unit 102 to store the quantum state of photons received from an external quantum computer, and a control unit 104.

[0206] In the modified example 18, the control unit 104 of the quantum computer 100 identifies which row and column of the first qubit array AR1 contains a quantum state in which quantum entanglement has been successfully generated, and transfers the quantum state on the quantum memory 103 side or the quantum state entangled with the quantum state on the quantum memory 103 side so that all qubits of the Bell measurement unit 101 on the quantum memory 103 side become quantum states in which quantum entanglement has been successfully generated.

[0207] The operation of the quantum memory 103 of the quantum computer 100 of Modification 18 will be explained below with reference to Figures 30 to 35. Figures 30 to 35 show the quantum memory 103 and Bell measurement unit 101 of the quantum computer 101 of Modification 18. Hereafter, the qubit in the mth row and nth column of the first bit array AR1 of the quantum memory 103 will be represented as (m, n). In Figures 30 to 35, quantum states that have successfully generated quantum entanglement are represented by white circles, and qubits that have not been generated are represented by black circles.

[0208] Hereafter, with respect to time t, we assume t1 < t2 < t3 < t4 < t5 < t6.

[0209] Figure 30 shows the quantum state of the quantum memory 103 at t=t1. Here, only qubits (1, n1-2) and qubits (3, n1-2) have successfully generated quantum entanglement (indicated by white circles). Subsequently, each qubit of the quantum memory 103 is transferred in the row direction toward the bell measurement unit 101 (i.e., from left to right in the figure).

[0210] Figure 31 shows the quantum state of the quantum memory 103 at t=t2. Here, only qubits (3, n1-2), qubit (m1, n1-2), qubit (1, n1-1), and qubit (3, n1-1) have successfully generated quantum entanglement.

[0211] Figure 32 shows the quantum state of the quantum memory 103 at t=t3. Here, only qubits (2, n1-2), qubit (3, n1-1), qubit (m1, n1-1), qubit (1, n1), and qubit (3, n1) have successfully generated quantum entanglement. The qubits (1, n1) and (3, n1) that have reached the n1th column are transferred to the Bell measurement unit 101.

[0212] Figure 33 shows the quantum state of the quantum memory 103 at t=t4. Here, only qubits (2, n1-1), (3, n1), and (m1, n1) have successfully generated quantum entanglement. In addition, the qubits in the first and third rows of the Bell measurement unit 101 have successfully generated quantum entanglement. The qubit (m1, n1) that reaches the n1th column is transferred to the Bell measurement unit 101.

[0213] Here, if the qubit (3, n1) were transferred directly to the Bell measurement unit 101, it would collide with the qubit in the third row of the Bell measurement unit 101. Therefore, the control unit 104 moves the qubit in the third row of the Bell measurement unit 101 vertically (transfers it in the column direction) to a row that has not successfully generated quantum entanglement, for example, the (m1-1) row. As a result, the third row of the Bell measurement unit 101 becomes a state where quantum entanglement has not been successfully generated. Consequently, the qubit (3, n1) can be transferred to the Bell measurement unit 101 while avoiding a collision.

[0214] Figure 34 shows the quantum state of the quantum memory 103 at t=t5. Here, only qubit (2, n1) and qubit (3, n1) have successfully generated quantum entanglement. Also, the qubits in the first row, the (m1-1)th row, and the m1th row of the Bell measurement unit 101 have successfully generated quantum entanglement. The qubits (2, n1) and qubit (3, n1) that have reached the n1th column are transferred to the Bell measurement unit 101.

[0215] Figure 35 shows the quantum state of the quantum memory 103 at t=t6. Here, all rows of qubits in the Bell measurement unit 101 have successfully generated quantum entanglement.

[0216] Thus, according to this modification, the qubits on the quantum memory side of the Bell measurement unit 101 can be put into a state where quantum entanglement generation has been successfully achieved. As a result, Bell measurements can be performed in parallel on all bits, which further speeds up quantum computations by quantum computers that require such operations.

[0217] In the above embodiment, the vertical movement (transfer in the column direction) of the entangled qubits was performed by the Bell measurement unit 101. However, the embodiment is not limited to this, and the vertical movement (transfer in the column direction) of the entangled qubits may also be performed by the first qubit array AR1 of the quantum memory 103 or the second qubit array AR2 of the calculation unit 102.

[0218] [Verification] The inventors conducted simulations to verify the usefulness of the technology of this disclosure. Assuming quantum information relay with a transmission distance of 20 km, and when the quantum memory of the quantum router of this embodiment was configured with an array of 100 to 300 qubits, the throughput was 1 MHz. In contrast, when quantum information relay was simulated under the same conditions without the quantum router of this embodiment, the throughput was 6 kHz. Therefore, the quantum router of this embodiment showed an improvement in throughput of approximately 160 times. Thus, this simulation showed that the technology of this disclosure contributes significantly to improving the throughput of quantum information relay.

[0219] [Each Embodiment of the Disclosure] The embodiments of the Disclosure described above are summarized below. One embodiment of a quantum router is a quantum router that relays quantum information within a quantum network and comprises: a Bell measurement unit that performs Bell measurements on two quantum states; a first entangled photon receiver that receives a first photon having a first quantum state from the quantum network; a second entangled photon receiver that receives a second photon having a second quantum state from the quantum network; a first quantum memory connected between the Bell measurement unit and the first entangled photon receiver; a second quantum memory connected between the Bell measurement unit and the second entangled photon receiver; and a control unit. The first quantum memory includes a first qubit array composed of a plurality of rows and a plurality of columns. The second quantum memory includes a second qubit array composed of a plurality of rows and a plurality of columns. The first entangled photon receiver distributes the first quantum state to each row of the first qubit array. The second entangled photon receiver distributes the second quantum state to each row of the second qubit array. The first quantum memory transfers the first quantum state to the Bell measurement unit within the first qubit array. The second quantum memory transfers the second quantum state to the Bell measurement unit within the second qubit array. When the control unit receives the first quantum entanglement generation success signal for the first quantum state and the second quantum entanglement generation success signal for the second quantum state, it controls the Bell measurement unit, the first quantum memory, and the second quantum memory to perform Bell measurements on the first and second quantum states.

[0220] According to this embodiment, it is possible to provide a quantum router with a high quantum entanglement generation rate that enables high-throughput quantum information relay between remote nodes.

[0221] One embodiment of a quantum router is a quantum router that relays quantum information within a quantum network, and comprises: a Bell measurement unit that performs Bell measurements on two quantum states; a first entangled photon generation unit that generates and transmits a first photon having a first quantum state to the quantum network; a second entangled photon generation unit that generates and transmits a second photon having a second quantum state to the quantum network; a first quantum memory connected between the Bell measurement unit and the first entangled photon receiver; a second quantum memory connected between the Bell measurement unit and the second entangled photon receiver; and a control unit. The first quantum memory includes a first qubit array composed of a plurality of rows and a plurality of columns. The second quantum memory includes a second qubit array composed of a plurality of rows and a plurality of columns. The first entangled photon generation unit distributes the quantum states entangled with the first quantum state to each row of the first qubit array. The second entangled photon receiver distributes the quantum state entangled with the second quantum state to each row of the second qubit array. The first quantum memory transfers the quantum state entangled with the first quantum state to the Bell measurement unit within the first qubit array. The second quantum memory transfers the quantum state entangled with the second quantum state to the Bell measurement unit within the second qubit array. When the control unit receives the first quantum entanglement generation success signal for the first quantum state and the second quantum entanglement generation success signal for the second quantum state, it controls the Bell measurement unit, the first quantum memory, and the second quantum memory to perform Bell measurements on the quantum state entangled with the first quantum state and the quantum state entangled with the second quantum state.

[0222] According to this embodiment, it is possible to provide a quantum router with a high quantum entanglement generation rate that enables high-throughput quantum information relay between remote nodes.

[0223] In one embodiment of a quantum router, the number of rows in the first qubit array is equal to the number of rows in the second qubit array, and the number of columns in the first qubit array is equal to the number of columns in the second qubit array.

[0224] According to this embodiment, Bell measurements can be performed on the first and second quantum states at more precise timings.

[0225] In one embodiment of a quantum router, the first quantum memory transfers the first quantum states, which are assigned to each row of the first qubit array, to the Bell measurement unit for each row, and the second quantum memory transfers the second quantum states, which are assigned to each row of the second qubit array, to the Bell measurement unit for each row.

[0226] According to this embodiment, the first and second quantum states received from the quantum network, or the quantum states entangled with the first and second quantum states transmitted to the quantum network, are spatially distributed to each row of the qubit array, and then transferred sequentially by traversing each column of the qubit array, thereby enabling FIFO-like operation. This improves relay throughput.

[0227] In one embodiment of a quantum router, the control unit identifies which row of the first qubit array contains a quantum state that has successfully generated a first quantum entanglement, and which row of the second qubit array contains a quantum state that has successfully generated a second quantum entanglement. When a quantum state that has successfully generated a first quantum entanglement exists in any row of the first qubit array, and a quantum state that has successfully generated a second quantum entanglement exists in any row of the second qubit array, the control unit transfers the first quantum state or a quantum state entangled with the first quantum state, or the second quantum state or a quantum state entangled with the second quantum state, such that the row containing the quantum state that has successfully generated a first quantum entanglement is adjacent to the row containing the quantum state that has successfully generated a second quantum entanglement.

[0228] According to this embodiment, when a first quantum entanglement generation success signal and a second quantum state for which quantum entanglement generation has been successfully achieved exist, the Bell measurement can be performed with a higher probability.

[0229] One embodiment of a quantum router further comprises a quantum network and a signal combiner / demultiplexer that combines and demultiplexes signals between a first entangled photon receiver and a second entangled photon receiver.

[0230] According to this embodiment, signal combination and decomposition can be performed between the optical fiber connected to the quantum network and the entangled photon receiver.

[0231] One embodiment of the quantum router further comprises a quantum network and a signal multiplexer / demultiplexer that performs signal multiplexing and demultiplexing between a first entangled photon generation unit and a second entangled photon generation unit.

[0232] According to this embodiment, signal combination and decomposition can be performed between the optical fiber connected to the quantum network and the entangled photon generation unit.

[0233] One embodiment of a quantum router further comprises a wavelength conversion device that performs wavelength conversion between communication photons propagating within a quantum network and quantum states propagating within a first qubit array and a second qubit array.

[0234] According to this embodiment, communication can be performed even when the wavelengths of the communication photons propagating within the quantum network and the quantum states propagating within the first qubit array AR1 and the second qubit array AR2 are different.

[0235] In one embodiment of a quantum router, the first and second successful quantum entanglement generation signals are classical signals (e.g., herald signals) transmitted through a classical channel.

[0236] According to this embodiment, the success of generating quantum entanglement can be communicated using a classical signal (e.g., a Herald signal).

[0237] In one embodiment of a quantum router, the qubits constituting the first qubit array and the qubits constituting the second qubit array are superconducting qubits.

[0238] According to this embodiment, the qubit array of the quantum memory can be constructed using superconducting qubits.

[0239] In one embodiment of the quantum router, the transfer of the first quantum state and the second quantum state to the Bell measurement unit is performed using a SWAP gate or an iSWAP gate.

[0240] According to this embodiment, quantum states can be transferred within the quantum router using a SWAP gate or an iSWAP gate.

[0241] In one embodiment of a quantum router, Bell measurements are performed using a CNOT gate and a Hadamard gate.

[0242] According to this embodiment, a Bell measurement can be performed within the quantum router using a CNOT gate and a Hadamard gate.

[0243] In one embodiment of a quantum router, the quantum states propagating within the first and second qubit arrays are the quantum states of microwave photons.

[0244] According to this embodiment, the quantum state of photons transferred within the quantum router can be constructed using the quantum state of microwave photons.

[0245] In one embodiment of the quantum router, a cooling system for generating and maintaining superconducting qubits is further provided.

[0246] According to this embodiment, a quantum router using superconducting qubits can be implemented.

[0247] One embodiment of a quantum router includes both an entangled photon receiving unit that receives entangled photons from a quantum network and an entangled photon generating unit that generates entangled photons and transmits them to the quantum network.

[0248] According to this embodiment, both the functions of quantum router 1 and quantum router 2 described above can be realized.

[0249] In one embodiment of a quantum router, the control unit identifies which rows and columns of the first qubit array contain a quantum state that has successfully generated a first quantum entanglement, and which rows and columns of the second qubit array contain a quantum state that has successfully generated a second quantum entanglement. The control unit then transfers the first quantum state or a quantum state entangled with the first quantum state, or the second quantum state or a quantum state entangled with the second quantum state, such that all qubits in the Bell measurement unit on the first quantum memory side become a quantum state that has successfully generated a first quantum entanglement, and all qubits in the Bell measurement unit on the second quantum memory side become a quantum state that has successfully generated a second quantum entanglement.

[0250] According to this embodiment, quantum information relay, which requires the simultaneous consumption of multiple qubits, such as quantum state distillation, can be made to have even higher throughput.

[0251] In one embodiment of a quantum router, the control unit transfers quantum states in the column direction in the Bell measurement unit.

[0252] This embodiment allows for increased flexibility in configuration.

[0253] In one embodiment of a quantum router, the control unit transfers quantum states in the column direction in a first qubit array and a second qubit array.

[0254] This embodiment allows for increased flexibility in configuration.

[0255] One embodiment of a quantum information relay method is a quantum information relay method that relays quantum information within a quantum network using a quantum router comprising a Bell measurement unit, a first quantum memory, and a second quantum memory. The first quantum memory includes a first qubit array composed of multiple rows and multiple columns. The second quantum memory includes a second qubit array composed of multiple rows and multiple columns. This method includes the steps of: receiving a first photon having a first quantum state from a quantum network; receiving a second photon having a second quantum state from a quantum network; distributing the first quantum state to each row of a first qubit array; distributing the second quantum state to each row of a second qubit array; transferring the first quantum state distributed to each row of the first qubit array to a Bell measurement unit within the first qubit array; transferring the second quantum state distributed to each row of the second qubit array to a Bell measurement unit within the second qubit array; and, upon receiving a first entanglement generation success signal for the first quantum state and a second entanglement generation success signal for the second quantum state, having the Bell measurement unit perform a Bell measurement on the first and second quantum states.

[0256] According to this embodiment, high-throughput quantum information relay between remote nodes can be achieved using a quantum router with a high quantum entanglement generation rate.

[0257] One embodiment of a quantum information relay method is a quantum information relay method that relays quantum information within a quantum network using a quantum router comprising a Bell measurement unit, a first quantum memory, and a second quantum memory. The first quantum memory includes a first qubit array composed of multiple rows and multiple columns. The second quantum memory includes a second qubit array composed of multiple rows and multiple columns. This method includes the steps of generating a first photon having a first quantum state and transmitting the first photon to the quantum network; generating a second photon having a second quantum state and transmitting the second photon to the quantum network; distributing the quantum state entangled with the first quantum state to each row of the first qubit array; distributing the quantum state entangled with the second quantum state to each row of the second qubit array; and distributing the quantum state entangled with the first quantum state distributed to each row of the first qubit array to the first The process includes the steps of: transferring a quantum bit array to a Bell measurement unit; transferring the quantum states entangled with the second quantum state, which have been allocated to each row of the second quantum bit array, to the Bell measurement unit within the second quantum bit array; and, upon receiving a first quantum entanglement success signal for the first quantum state and a second quantum entanglement success signal for the second quantum state, having the Bell measurement unit perform a Bell measurement on the quantum state entangled with the first quantum state and the quantum state entangled with the second quantum state.

[0258] According to this embodiment, high-throughput quantum information relay between remote nodes can be achieved using a quantum router with a high quantum entanglement generation rate.

[0259] One embodiment of a quantum network system is a quantum network system comprising multiple nodes and a group of quantum routers formed by connecting multiple quantum routers as described above. This quantum network system attempts to generate quantum entanglement between adjacent quantum routers by exchanging photons between them. If quantum entanglement is successfully generated, the entanglement is stored in the Bell measurement unit of each quantum router, and the process of generating quantum entanglement is repeated until it is possible to connect the nodes that are to be connected. After adjacent quantum routers are connected by quantum entanglement, a Bell measurement is performed on the entangled pairs stored in the Bell measurement units of the quantum routers.

[0260] According to this embodiment, a network system capable of high-throughput quantum information relay between remote nodes can be realized using a quantum router with a high quantum entanglement generation rate.

[0261] One embodiment of a quantum computer is a quantum computer that performs quantum computation by sharing quantum entanglement with an external quantum computer, and comprises a Bell measurement unit, a computation unit connected to the Bell measurement unit and performing quantum computation, a quantum memory connected to the Bell measurement unit from the other side of the computation unit and storing quantum states received from the external quantum computer, and a control unit. The computation unit includes a first qubit array consisting of a plurality of rows and a plurality of columns. The quantum memory includes a second qubit array consisting of a plurality of rows and a plurality of columns. When the control unit receives a quantum entanglement success signal from the computation unit and a quantum entanglement success signal from the external quantum computer, it controls the Bell measurement unit, the computation unit, and the quantum memory to perform Bell measurements on the quantum states received from the external quantum computer and the quantum states of the computation unit.

[0262] According to this embodiment, a quantum computer capable of reliably storing the entangled quantum states necessary for quantum computation can be realized.

[0263] In one embodiment of a quantum computer, the control unit identifies which rows and columns of the first qubit array contain quantum states that have successfully generated quantum entanglement, and transfers the quantum state on the quantum memory side, or the quantum state entangled with the quantum state on the quantum memory side, so that all qubits in the Bell measurement unit on the quantum memory side become quantum states that have successfully generated quantum entanglement.

[0264] In one embodiment of a quantum computer, the control unit transfers quantum states in the column direction in the Bell measurement unit.

[0265] This embodiment allows for increased flexibility in configuration.

[0266] In one embodiment of a quantum computer, the control unit transfers quantum states in the column direction in a first qubit array and a second qubit array.

[0267] This embodiment allows for increased flexibility in configuration.

[0268] The present invention has been described above based on embodiments. The embodiments are illustrative, and it will be understood by those skilled in the art that various modifications are possible in combinations of their components and processing processes, and that such modifications also fall within the scope of the present invention.

[0269] For example, the quantum router of the embodiment included two entangled photon receivers, a first entangled photon receiver and a second entangled photon receiver, to realize quantum relay between two nodes. However, it is not limited to this, and the quantum router of the present disclosure may include three or more entangled photon receivers.

[0270] The quantum router of the embodiment comprises two entangled photon generators, a first entangled photon generator and a second entangled photon generator, to realize quantum relay between two nodes. However, it is not limited to this, and the quantum router of this disclosure may comprise three or more entangled photon generators.

[0271] These modifications make it possible to provide a quantum router that enables quantum relay between three or more nodes.

[0272] For example, in the quantum router of the embodiment, the qubits constituting the first qubit array and the qubits constituting the second qubit array were superconducting qubits. However, the invention is not limited to this, and the qubits constituting the first qubit array and the qubits constituting the second qubit array may be any suitable qubit, such as cold atomic qubits.

[0273] This modified version allows for greater flexibility in configuration.

[0274] For example, the quantum network system in the embodiment connected the quantum nodes at both ends in a cascade using multiple quantum routers. However, it is not limited to this, and the quantum network system may have any suitable topology, such as a star configuration or a mesh configuration.

[0275] This modified version allows for increased flexibility in constructing quantum network systems.

[0276] Any combination of the embodiments and modifications described above is also useful as an embodiment of this disclosure. The new embodiments resulting from such combinations possess the combined effects of both the combined embodiments and the modifications.

[0277] In understanding the technical concept abstracted from the embodiments, that technical concept should not be interpreted restrictively to the content of the embodiments. The embodiments and modifications described above are merely examples, and many design changes, such as changes, additions, and deletions of components, are possible. In the embodiments, the content in which such design changes are possible is emphasized with the notation "embodiment." However, design changes are also permitted in content without such notation.

[0278] The technology disclosed herein is applicable to a wide range of fields, including long-distance quantum relay networks, short-distance distributed quantum computers, connections between qubits in refrigerators, and cloud quantum computing.

[0279] a... Entangled photon generation light source, c... Entangled photon generation light source, a'... Quantum entanglement generation success signal generator, c'... Quantum entanglement generation success signal generator, A... Node, A'... Node, A''... Node, B... Quantum router, B'... Quantum router, B''... Quantum router, C... Node, C'... Node, C''... Node, BM... Bell measurement unit, BM'... Bell measurement unit, BM''... Bell measurement unit, MA... Quantum memory, MA'... Quantum memory, MA''... Quantum memory, MB1... Quantum memory, MB1'... Quantum memory, MB1''... Quantum memory, MB2... Quantum memory, MB2'... Quantum memory, MB2''... Quantum memory, MC... Quantum memory, MC'... Quantum memory, MC''...Quantum memory, RA...Entangled photon receiver, RA'...Entangled photon receiver, RA''...Entangled photon receiver, RB1...Entangled photon receiver, RB1'...Entangled photon receiver, RB1''...Entangled photon receiver, RB2...Entangled photon receiver, RB2'...Entangled photon receiver, RB2''...Entangled photon receiver, RC...Entangled photon receiver, RC'...Entangled photon receiver, RC''...Entangled photon receiver, GA...Entangled photon generator, GA'...Entangled photon generator, GA''...Entangled photon generator, GB1...Entangled photon generator, GB1'...Entangled photon generation unit, GB1''...Entangled photon generation unit, GB2...Entangled photon generation unit, GB2'...Entangled photon generation unit, GB2''...Entangled photon generation unit, GC...Entangled photon generation unit, GC'...Entangled photon generation unit, GC''...Entangled photon generation unit, 1...Quantum router, 2...Quantum router, 3...Quantum router, 4...Quantum router, 11...Bell measurement unit, 12...First quantum memory, 13...Second quantum memory, 14...First entangled photon receiving unit, 15...Second entangled photon receiving unit, 16...Control unit, 17...First entangled photon generation unit, 18...Second entangled photon generation unit, 20...First multiplexer / demultiplexer, 21... Second wave combining / demultiplexing device, 22... First wavelength conversion device,23...Second wavelength converter, 30...Cooling system, 41...Node, 42...Node, 51...Quantum router, 52...Quantum router, 53...Quantum router, 54...Quantum router, 100...Quantum computer, 101...Bell measurement unit, 102...Calculation unit, 103...Quantum memory, 104...Control unit, 120...Quantum bit, 130...Quantum bit, AR1...First quantum bit array, AR2...Second quantum bit array, F1...Optical fiber, F2...Optical fiber, NW1...Quantum network system, PH1...First photon, PH2...Second photon, PH11...First photon, PH12...First photon, PH13...First photon, PH1m1...First photon, PH1i...First photon PH2i...Second photon, QS1...First quantum state, QS2...Second quantum state, QS11...First quantum state, QS12...First quantum state, QS13...First quantum state, QS1m1...First quantum state, QS1i...First quantum state, QS2i...Second quantum state, S1...Step of receiving a first photon having the first quantum state from the quantum network, S2...Step of receiving a second photon having the first quantum state from the quantum network, S3...Step of distributing the first quantum state to each row of the first qubit array, S4...Step of distributing the second quantum state to each row of the first qubit array, S5...Step of transferring the first quantum state distributed to each row of the first qubit array towards the bell measurement unit within the first qubit array, S6... A step of transferring the second quantum states, which have been allocated to each row of the second qubit array, to the Bell measurement unit within the second qubit array; S7... A step of receiving a first entanglement generation success signal for the first quantum state and a second entanglement generation success signal for the second quantum state, in which the Bell measurement unit performs a Bell measurement on the first and second quantum states.S11... A step of generating a first photon having a first quantum state and transmitting the first photon to the quantum network. S12... A step of generating a second photon having a second quantum state and transmitting the second photon to the quantum network. S13... A step of distributing the quantum state entangled with the first quantum state to each row of the first qubit array. S14... A step of distributing the quantum state entangled with the second quantum state to each row of the second qubit array. S15... A step of transferring the quantum state entangled with the first quantum state distributed to each row of the first qubit array towards the Bell measurement unit within the first qubit array. S16... A step of transferring the quantum state entangled with the second quantum state distributed to each row of the second qubit array towards the Bell measurement unit within the second qubit array. S17... Upon receiving a first quantum entanglement success signal relating to the first quantum state and a second quantum entanglement success signal relating to the second quantum state, the Bell measurement unit performs Bell measurements on the quantum state entangled with the first quantum state and the quantum state entangled with the second quantum state.

Claims

1. A quantum router for relaying quantum information within a quantum network, comprising: a Bell measurement unit that performs Bell measurements on two quantum states; a first entangled photon receiver that receives a first photon having a first quantum state from the quantum network; a second entangled photon receiver that receives a second photon having a second quantum state from the quantum network; a first quantum memory connected between the Bell measurement unit and the first entangled photon receiver; a second quantum memory connected between the Bell measurement unit and the second entangled photon receiver; and a control unit, wherein the first quantum memory includes a first qubit array composed of a plurality of rows and a plurality of columns; the second quantum memory includes a second qubit array composed of a plurality of rows and a plurality of columns; and the first entangled photon receiver distributes the first quantum state to each row of the first qubit array. A quantum router characterized in that the second entangled photon receiver distributes the second quantum state to each row of the second qubit array; the first quantum memory transfers the first quantum state within the first qubit array toward the Bell measurement unit; the second quantum memory transfers the second quantum state within the second qubit array toward the Bell measurement unit; and the control unit, upon receiving a first quantum entanglement generation success signal for the first quantum state and a second quantum entanglement generation success signal for the second quantum state, controls the Bell measurement unit, the first quantum memory, and the second quantum memory to perform Bell measurements on the first and second quantum states.

2. A quantum router for relaying quantum information within a quantum network, comprising: a Bell measurement unit that performs Bell measurements on two quantum states; a first entangled photon generation unit that generates and transmits a first photon having a first quantum state to the quantum network; a second entangled photon generation unit that generates and transmits a second photon having a second quantum state to the quantum network; a first quantum memory connected between the Bell measurement unit and the first entangled photon receiving unit; a second quantum memory connected between the Bell measurement unit and the second entangled photon receiving unit; and a control unit, wherein the first quantum memory includes a first qubit array composed of a plurality of rows and a plurality of columns; the second quantum memory includes a second qubit array composed of a plurality of rows and a plurality of columns; and the first entangled photon generation unit distributes the quantum states entangled with the first quantum state to each row of the first qubit array. A quantum router characterized in that the second entangled photon receiver distributes the quantum state entangled with the second quantum state to each row of the second qubit array; the first quantum memory transfers the quantum state entangled with the first quantum state to the Bell measurement unit within the first qubit array; the second quantum memory transfers the quantum state entangled with the second quantum state to the Bell measurement unit within the second qubit array; and the control unit, upon receiving a first quantum entanglement generation success signal for the first quantum state and a second quantum entanglement generation success signal for the second quantum state, controls the Bell measurement unit, the first quantum memory, and the second quantum memory to perform Bell measurements on the quantum state entangled with the first quantum state and the quantum state entangled with the second quantum state.

3. The quantum router according to claim 1 or 2, characterized in that the number of rows of the first qubit array is equal to the number of rows of the second qubit array, and the number of columns of the first qubit array is equal to the number of columns of the second qubit array.

4. The quantum router according to claim 1 or 2, characterized in that the first quantum memory transfers the first quantum state or a quantum state entangled with the first quantum state, which is distributed to each row of the first qubit array, to the Bell measurement unit for each row, and the second quantum memory transfers the second quantum state or a quantum state entangled with the second quantum state, which is distributed to each row of the second qubit array, to the Bell measurement unit for each row.

5. The quantum router according to claim 1 or 2, characterized in that the control unit identifies which row of the first qubit array contains a quantum state in which the first quantum entanglement was successfully generated, and which row of the second qubit array contains a quantum state in which the second quantum entanglement was successfully generated, and when a quantum state in which the first quantum entanglement was successfully generated exists in any row of the first qubit array and a quantum state in which the second quantum entanglement was successfully generated exists in any row of the second qubit array, the control unit transfers the first quantum state or a quantum state entangled with the first quantum state, or the second quantum state or a quantum state entangled with the second quantum state, such that the row containing the quantum state in which the first quantum entanglement was successfully generated and the row containing the quantum state in which the second quantum entanglement was successfully generated are adjacent to each other.

6. The quantum router according to claim 1, further comprising a signal multiplexer / demultiplexer that performs signal multiplexing and demultiplexing between the quantum network and the first entangled photon receiving unit and the second entangled photon receiving unit.

7. The quantum router according to claim 2, further comprising a signal multiplexer / demultiplexer that performs signal multiplexing and demultiplexing between the quantum network and the first and second entangled photon generation units.

8. The quantum router according to claim 1 or 2, further comprising a wavelength conversion device that performs wavelength conversion between communication photons propagating within the quantum network and quantum states propagating within the first qubit array and the second qubit array.

9. The quantum router according to claim 1 or 2, characterized in that the first quantum entanglement success signal and the second quantum entanglement success signal are classical signals transmitted through a classical communication channel.

10. The quantum router according to claim 1 or 2, characterized in that the qubits constituting the first qubit array and the qubits constituting the second qubit array are superconducting qubits.

11. The quantum router according to claim 10, characterized in that the transfer of the first quantum state and the second quantum state to the Bell measurement unit is performed using a SWAP gate or an iSWAP gate.

12. The quantum router according to claim 10, characterized in that the quantum states propagating within the first qubit array and the second qubit array are quantum states of microwave photons.

13. The quantum router according to claim 1 or 2, further comprising a cooling system for generating and maintaining superconducting qubits.

14. The quantum router according to claim 2, further comprising: a first entangled photon receiving unit that receives a first photon having a first quantum state from the quantum network; and a second entangled photon receiving unit that receives a second photon having a second quantum state from the quantum network.

15. A quantum information relay method for relaying quantum information within a quantum network using a quantum router comprising a Bell measurement unit, a first quantum memory, and a second quantum memory, wherein the first quantum memory includes a first qubit array composed of a plurality of rows and a plurality of columns, the second quantum memory includes a second qubit array composed of a plurality of rows and a plurality of columns, the method comprising: receiving a first photon having a first quantum state from the quantum network; receiving a second photon having a second quantum state from the quantum network; distributing the first quantum state to each row of the first qubit array; distributing the second quantum state to each row of the second qubit array; transferring the first quantum state distributed to each row of the first qubit array towards the Bell measurement unit within the first qubit array; and transferring the second quantum state distributed to each row of the second qubit array towards the Bell measurement unit within the second qubit array. A quantum information relay method characterized by comprising the step of receiving a first quantum entanglement generation success signal for the first quantum state and a second quantum entanglement generation success signal for the second quantum state, and then having the Bell measurement unit perform a Bell measurement on the first quantum state and the second quantum state.

16. A quantum information relay method for relaying quantum information within a quantum network using a quantum router comprising a Bell measurement unit, a first quantum memory, and a second quantum memory, wherein the first quantum memory includes a first qubit array composed of a plurality of rows and a plurality of columns, the second quantum memory includes a second qubit array composed of a plurality of rows and a plurality of columns, the method comprising: generating a first photon having a first quantum state and transmitting the first photon to the quantum network; generating a second photon having a second quantum state and transmitting the second photon to the quantum network; distributing the quantum state entangled with the first quantum state to each row of the first qubit array; distributing the quantum state entangled with the second quantum state to each row of the second qubit array; and transferring the quantum state entangled with the first quantum state distributed to each row of the first qubit array toward the Bell measurement unit within the first qubit array. A quantum information relay method comprising: the step of transferring the quantum states entangled with the second quantum state, which are distributed to each row of the second qubit array, to the Bell measurement unit within the second qubit array; and the step of, upon receiving a first quantum entanglement generation success signal for the first quantum state and a second quantum entanglement generation success signal for the second quantum state, having the Bell measurement unit perform a Bell measurement on the quantum state entangled with the first quantum state and the quantum state entangled with the second quantum state.

17. A quantum network system comprising multiple nodes and multiple quantum routers as described in claim 1 or 2, wherein the system attempts to generate quantum entanglement between adjacent quantum routers by exchanging photons between them, and if successful in generating quantum entanglement, stores the entanglement in the bell measurement unit of each of the quantum routers, and repeats the process until successful in generating quantum entanglement between the nodes to be connected, and after adjacent quantum routers are connected by quantum entanglement, performs a bell measurement on the entangled pairs stored in the bell measurement units of the quantum routers.

18. A quantum computer that performs quantum computation by sharing quantum entanglement with an external quantum computer, comprising: a Bell measurement unit; a calculation unit connected to the Bell measurement unit and performing quantum computation; a quantum memory connected to the Bell measurement unit from the other side of the calculation unit and storing the quantum state of photons received from the external quantum computer; and a control unit, wherein the calculation unit includes a first qubit array consisting of a plurality of rows and a plurality of columns; the quantum memory includes a second qubit array consisting of a plurality of rows and a plurality of columns; and the control unit controls the Bell measurement unit, the calculation unit and the quantum memory to perform Bell measurements on the quantum state of photons received from the external quantum computer and the quantum state of the calculation unit upon receiving a quantum entanglement success signal from the calculation unit and a quantum entanglement success signal from the external quantum computer.

19. The quantum router according to claim 1 or 2, characterized in that the control unit identifies which rows and columns of the first qubit array contain the quantum state in which the first quantum entanglement was successfully generated, and which rows and columns of the second qubit array contain the quantum state in which the second quantum entanglement was successfully generated, and transfers the first quantum state or the quantum state entangled with the first quantum state or the second quantum state or the quantum state entangled with the second quantum state such that all qubits in the Bell measurement unit on the first quantum memory side become the quantum state in which the first quantum entanglement was successfully generated, and all qubits in the Bell measurement unit on the second quantum memory side become the quantum state in which the second quantum entanglement was successfully generated.

20. The quantum router according to claim 19, characterized in that the control unit transfers quantum states in the column direction in the bell measurement unit.

21. The quantum router according to claim 19, characterized in that the control unit transfers quantum states in the column direction in the first qubit array and the second qubit array.

22. The quantum computer according to claim 18, characterized in that the control unit identifies which rows and columns of the first qubit array contain quantum states in which quantum entanglement has been successfully generated, and transfers the quantum state on the quantum memory side or the quantum state entangled with the quantum state on the quantum memory side so that all qubits of the Bell measurement unit on the quantum memory side become quantum states in which quantum entanglement has been successfully generated.

23. The quantum computer according to claim 22, characterized in that the control unit transfers quantum states in the column direction in the Bell measurement unit.

24. The quantum computer according to claim 22, characterized in that the control unit transfers quantum states in the column direction in the first qubit array and the second qubit array.

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