Quantum switching system, control method and program

Abstract

A quantum switching system that improves the efficiency of a quantum network, a control method thereof, and a program are provided. [Solution] A quantum switching system 1 that distributes two photons in a quantum entangled state to a photon emission section 100 and a photon input section 200, and includes: a plurality of input ports, a plurality of output ports, a photon transport path 10 that connects the plurality of input ports and the plurality of output ports; a switching element arrangement section 20 that is arranged across two adjacent paths of the photon transport paths 10 and has a plurality of two-input, two-output switching elements that switch the photon travel path; and a control section 30 that controls the switching elements to pair photons input to each of the plurality of input ports into any two pairs and output them to two adjacent pairs of output ports.

Description

[Technical Field]

[0001] The present invention relates to a quantum switching system, a control method, and a program. [Background technology]

[0002] In order to scale up quantum computers, network technology that can share quantum entanglement between arbitrary quantum nodes is important. To transmit entangled photons between quantum nodes, switching circuits that transfer and distribute photons are essential.

[0003] In conventional classical networks, as shown in Reference 1, switching circuits have been developed that combine a planar structure with arbitrary input / output support while keeping the number of switches to the theoretical minimum. This makes it possible to reduce losses due to wiring crossings and implementation costs. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] RA Spanke and VE Benes, “N-stage planar optical permutation network,” Applied Optics, Vol. 26, No. 7, pp. 1205-1212, Apr. 1, 1987. Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the transmission of photons in a quantum network, it is not always necessary to support all input / output combinations. For example, in a circuit that outputs photon pairs to adjacent ports, the number of switches in a switching circuit such as that shown in Reference 1 becomes excessive, resulting in problems such as increased implementation area and cost, as well as increased photon loss.

[0006] The present invention has been made in view of the above circumstances, and has as its object to improve the efficiency of quantum networks. [Means for solving the problem]

[0007] A quantum switching system according to one aspect of the present invention, comprising: a plurality of input ports; a plurality of output ports; photon transport paths connecting the plurality of input ports and the plurality of output ports; a plurality of two-input, two-output switching elements arranged across two adjacent paths of the photon transport paths and switching the photon travel paths; and a control unit that controls the switching elements to pair photons input to each of the plurality of input ports into any two pairs and output them to two adjacent pairs of output ports. [Effects of the Invention]

[0008] According to the present invention, it is possible to improve the efficiency of quantum networks. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a quantum switching system according to the present disclosure. [Figure 2] FIG. 2 is a diagram for explaining an example of a switching element arrangement section in the present disclosure. [Figure 3] FIG. 2 is a diagram for explaining control of a switching element in the present disclosure. [Figure 4] FIG. 3 is a diagram for explaining a control algorithm for a switching element in the first embodiment. [Figure 5] FIG. 4 is a flowchart illustrating a control process of a switching element in the first embodiment. [Figure 6] 4 is a flowchart showing a control method for setting the switching element SWlj in the first embodiment. FIG. [Figure 7]FIG. 10 is a diagram for explaining the arrangement of switching elements in the second embodiment. [Figure 8] FIG. 10 is a diagram for explaining a control algorithm for a switching element in the second embodiment. [Figure 9] FIG. 10 is a flowchart illustrating a control process of a switching element in the second embodiment. [Figure 10] FIG. 10 is a diagram for explaining the arrangement of switching elements in a third embodiment. [Figure 11] FIG. 10 is a diagram for explaining a control algorithm for a switching element in the third embodiment. [Figure 12] FIG. 11 is a flowchart illustrating a control process of a switching element in a third embodiment. [Figure 13] FIG. 10 is a diagram for explaining a quantum switching system according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention will be described below with reference to the drawings, but the scope of the present invention is not limited to the embodiment described here, and various modifications can be made without departing from the spirit of the present invention. In addition, when a plurality of upper and lower limit values ​​are described for a specific parameter, a suitable numerical range can be obtained by combining any of these upper and lower limit values. <Quantum Switching System Overview> 1 is a diagram showing the configuration of a quantum switching system 1 according to the present disclosure. The quantum switching system 1 includes N input ports E(n), N output ports Y(n), a switching element arrangement unit 20, and a control unit 30. The input ports E(n), the output ports Y(n), and the switching element arrangement unit 20 are connected by a photon transport path 10.

[0011] The quantum switching system 1 includes a system for distributing entangled photons among multiple quantum nodes. As shown in Fig. 1, in the quantum switching system 1, a photon transport path 10 may be connected to a photon emitting unit 100 and / or a photon input unit 200 via an input port and / or an output port. This allows the quantum switching system 1 to distribute photons emitted by the photon emitting unit 100 to the photon input unit 200.

[0012] The photon emitter 100 may be, for example, an entangled photon-pair source (EPPS), a single photon source, a quantum memory, a quantum processor, a quantum dot device, etc. The photon input unit 200 may be a Bell State Analyzer (BSA), a photon detector, a quantum memory, a quantum processor, or other switching / routing device, etc.

[0013] For example, a photon emitter 100 may be connected to one side of the input port E(n), and a switching element arrangement unit 20 may be connected to the other side. In the example shown in FIG. 1, one input port E(n) is connected to one photon emitter 100. However, this is not limited to the example shown in FIG. 1, and one input port E(n) may be connected to multiple photon emitters 100. Photons emitted by the photon emitter 100 are input to the switching element arrangement unit 20 of the quantum switching system 1 via the input port E(n).

[0014] Furthermore, the output port Y(n) may be connected to, for example, a photon input unit 200 on one side and a switching element arrangement unit 20 on the other side. In the example shown in Fig. 1, two output ports Y(n) are connected to one photon input unit 200. However, this is not limited to the example shown in Fig. 1, and one output port Y(n) may be connected to each of a plurality of photon input units 200.

[0015] Photons output from the switching element arrangement unit 20 are input to the photon input unit 200 via the output port Y(n). In the present disclosure, an example will be described in which a single photon is input to the output port Y(n). However, this is not limiting, and for example, photons in a multi-photon state may be input. In this case, the photon emitter 100 may input one single photon of two photons in a quantum entangled state held by the photon emitter 100 to the input port E(n). This allows the quantum switching system 1 to distribute the two photons in a quantum entangled state to the photon emitter 100 and the photon input unit 200.

[0016] As shown in Fig. 2, the switching element arrangement section 20 has a plurality of photon transport paths 10 connecting input ports E(n) and output ports Y(n). For example, the switching element arrangement section 20 has a plurality of photon transport paths each connecting one input port and one output port. As an example, the switching element arrangement section 20 has N two-input, two-output (2x2) switching elements SW lj The switching element SW lj are provided across two adjacent paths of the photon transport path 10, and switch the travel path of the photon. For example, the switching element arrangement unit 20 has 2×2 switching elements SW so that photons input to any two input ports can be output to any pair of adjacent two output ports. lj are arranged on the photon transport path 10.

[0017] The switching element arrangement section 20 includes a plurality of photon transport paths 10 and a plurality of switching elements SW lj A photon input from the input port E(n) is switched to any one of the switching elements SW lj , and is transferred to the output port Y(n). lj can dynamically switch the photon path using either a BAR (straight) setting or a CROSS (cross) setting.

[0018] The switching element arrangement section 20 is composed of a plurality of layers, and a plurality of switching elements SW are arranged in each layer. lj In this specification, the "layer" refers to a group of switching elements SW arranged at the same depth position along the direction from the input port E(n) side to the output port Y(n) side. lj In the present disclosure, photons travel in one direction between layers and do not perform loop recycling, but are not limited thereto.

[0019] For example, as the layer number increases or decreases, photons sequentially travel toward the output port Y(n) side and are finally output to two adjacent pairs of output ports Y(n). The switching element arrangement section 20 illustrated in FIG. 2 is composed of layer 1 to layer 5. In layer 1, two switching elements SW are arranged. 1j In layer 2, four switching elements SW are arranged. 2j After that, as the layer number increases, two switching elements are added one by one. The switching element SW lj is uniquely identified as follows.

[0020] SW lj : The j-th switching element from the top in layer l (l and j are arbitrary integers) Here, l is the layer index, indicating the position in the depth direction of the network. In this specification, the number of layers in the depth direction is L, and l takes a value of 0 ≦ l < L. j indicates the order of the switches within the layer (arrangement from left to right or from top to bottom). For example, as illustrated in FIG. 2, the first switch in layer 1 is SW 11 , the second switch in layer 1 is SW 12 , and the fourth switch in layer 2 is SW 24 are represented. Each switching element SW lj is arranged across two adjacent photon transport paths 10.

[0021] The switching element SW ljDepending on the setting of either straight (BAR) or cross (CROSS), the photon is either passed through the same photon transport path 10 as the photon transport path 10 from which the photon was input (straight (BAR)), or crossed to another photon transport path 10 (cross (CROSS)). In this way, the quantum switching system 1 gradually changes the arrangement of photons for each layer, and ultimately outputs the desired pair of photons to two adjacent output ports Y(n). In this specification, photon pairing refers to the selection of two photons from photons input to each of multiple input ports E(n).

[0022] Furthermore, in the quantum switching system 1 according to the present disclosure, the control unit 30 controls the switching element SW lj This allows for dynamic changes to the pair configuration, making it possible to support adjacent outputs in response to the new pair even if the pair configuration is changed while the network is in use.

[0023] The control unit 30 controls the switching elements SW1, SW2, and SW3 of the switching element arrangement unit 20. lj This allows the control of the switching circuit formed in the switching element arrangement section 20. The control section 30 pairs photons input to each of the multiple input ports E(n) of the switching element arrangement section 20 into any two pairs. Then, the switching elements SW lj By controlling the setting of the output port Y(n), the paired two photons are output to two adjacent output ports Y(n). This allows any two photons input from different photon emitters 100 to be distributed to the same photon input unit 200.

[0024] The control unit 30 determines the travel paths of any two photons input to each of the multiple input ports based on predetermined adjacent output conditions for output to two adjacent output ports, and controls the switching between straight travel and crossing for each of the multiple switching elements based on the determined travel paths. The predetermined adjacent output conditions will be described in each embodiment below.

[0025] The control unit 30 may be a control device including one or more processors and a storage device. The control unit 30 may be configured to execute the disclosed processes by having the one or more processors execute a program stored in the storage device. The program may be recorded on a non-transitory computer-readable recording medium.

[0026] In the present disclosure, a case where the photon input unit 200 is a BSA will be described as an example. A BSA is a device that measures whether photons input to two connected output ports are in a Bell state. By measuring the state of two photons, the two photons, which were originally in an entangled state, can be put into a new entangled state. In the present disclosure, a plurality of photon input units 200 form a group, and this group is connected to the quantum switching system 1. For example, a plurality of photon input units 200 may form a BSA pool, which is a collection of a plurality of BSAs, and be connected to the quantum switching system 1.

[0027] Furthermore, two adjacent pairs of output ports Y(n) among the multiple output ports Y(n) may be connected to the same BSA. In the present disclosure, the control unit 30 can output any pair of photons input from the photon emitter 100 to two adjacent pairs of output ports Y(n). Therefore, any pair of photons can be input to any of the same BSAs forming the BSA group. Therefore, a small number of BSAs can be shared without assigning a dedicated BSA to each photon pair. This can save resources and improve efficiency.

[0028] <Switching circuit design> Next, we will explain the design of the switching circuit formed in the switching element arrangement section 20. The inventors have designed the switching circuit in the present disclosure based on at least one of the following design goals.

[0029] One of the design goals is to output any two photons from two adjacent output ports Y(n). Photons X(0), X(1), …, X(N−1) are input from N input ports E(n) to the switching circuit formed in the switching element arrangement unit 20 (at this time, the numbers 0…N−1 assigned to each photon may be referred to as the indices of the photons). And the N output ports Y(n) are connected to N / 2 photon input units 200.

[0030] Here, the pairs of photons paired by the control unit 30 are defined as (X(i), X(j)) (where 0 ≤ i < j < N). In the present disclosure, for the input photons X(0), X(1), …, X(N−1), the purpose is to pair them without omission and duplication. Here, consider the pairing of any two photons. At this time, the set of pairing targets is represented by a pair list PL(N / 2) = {(X(i), X(j)} that satisfies the condition that each photon appears only once in the pairing. For example, each photon X(i) appears only in one of the pairs in PL(N / 2), and the same photon is not included across multiple pairs. One of the design goals of the switching circuit in the present disclosure is that for such a pair list PL(N / 2), each photon pair (X(i), X(j)) is output from two adjacent output ports Y(n).

[0031] The quantum switching system 1 in the present disclosure can appropriately lead to measurement for any photon pairing requirement by appropriately controlling the switch settings of the switching element SW lj For example, the quantum switching system 1 has a reconfigurable non-blocking structure, and stable communication performance is maintained even when the number and combination of photons change.

[0032] Here, "non-blocking" means that a specific switching element SW in the quantum switching system 1 ljThe term "reconfigurable" means that the photon transport path 10 can output any pair of photons to a predetermined output port Y(n) without blocking other photon pairing requests. lj This means that by dynamically reconfiguring the operating state (straight or crossing), it is possible to flexibly respond to any pairing request.

[0033] The second goal is to design a scalable circuit. For example, by designing a scalable circuit, the circuit can be easily expanded as the number of photons increases. Also, in a scalable circuit, the switching element SW lj It is also possible to employ a configuration in which additional routing is possible for some photon pairs by adding a layer l from the input port E(n) to the output port Y(n) or a layer near the end of the layer l.

[0034] The third goal is to have a planar circuit structure in which the photon transport pathways 10 do not cross each other. The planar structure eliminates the need for crossing optical paths or vertical connections, making it highly compatible with photonic integrated circuits and advantageous in terms of ease of manufacturing and optical loss. In addition, because the overall layout can be designed as a hierarchical structure, the circuit has good scalability and can easily accommodate a large number of photons.

[0035] In the examples of the present disclosure, the switching circuit is designed based on the above design goals, and the above design goals can be achieved by the architecture and algorithms described below.

[0036] In the quantum switching system 1, as illustrated in FIG. 2, the photons Xn input from the input port E(n) are arranged in a predetermined order (in the example shown in FIG. 2, they are arranged from top to bottom in the form of X0, ..., X11), and one BSAj is connected to every two adjacent input ports E(n), which is also arranged in a predetermined order (in the example shown in FIG. 2, they are arranged from top to bottom in the form of BSA0, ..., BSA5).

[0037] At this time, the switching element SW lj By controlling the settings, it can be said that quantum entanglement measurements are possible for all photon pairs (X(i), X(j)). With the configuration shown in Figure 2, it is possible to guide all photon pairs belonging to any pair list PL(N / 2) to adjacent outputs. In this way, the condition for guiding any photon pair to adjacent outputs is called the adjacent output condition.

[0038] <Optimal number of switches> The quantum switching system 1 according to the present disclosure accepts N input photons and outputs them as N / 2 photon pairs to adjacent output ports Y(n). Below, we consider the minimum number of switch points required by the quantum switching system 1 under this premise.

[0039] It is known that in a conventional classical N-input N-output switching circuit having a planar structure, at least {N(N-1)} / 2 switches are required to enable all connections from any input port to any output port. In contrast, the quantum switching system 1 in the present disclosure is required to pair all input photons without omission and to derive each pair to an adjacent output port. Therefore, compared to a conventional switching circuit that aims for all connections, the number of switching elements SW lj This reduces the manufacturing and design costs, reduces optical loss in the switching elements, and improves operational reliability.

[0040] Necessary switching element SW lj As a case where the number is maximum, consider the case where the pairing list of photon pairs (X(i),X(j)) consists of the following maximum distance pairs.

[0041] (X(0),X(N-1)),(X(1),X(N-2)),(X(2),X(N-3)),… In this case, to output the first pair (X(0),X(N-1)) as adjacent pairs, one photon must cross all N-2 photons between photon X0 and photon XN-1. Next, to output the pair (X(1),X(N-2)) as adjacent pairs, one photon must cross N-4 photons. Similarly, with each pair, the number of photons that must cross decreases by 2.

[0042] The total number of switching points required for this switching operation is expressed as the minimum number of switching elements, S, by the following formula: S=(N-2)+(N-4)+(N-6)+…+2 This sequence is an arithmetic sequence, and the sum is: S={N(N-2)} / 4 This becomes:

[0043] Therefore, a minimum number of {N(N-2)} / 4 switch points is required in a switching network such as quantum switching system 1. This is less than half the number of switching elements required in a conventional switching circuit intended for full connection. Quantum switching system 1 in the present disclosure achieves the minimum number of switching elements through the architecture and algorithm described below.

[0044] First Embodiment (Triangular Design) Hereinafter, an embodiment for achieving the above design goal and the minimum number of switching elements will be described. As shown in FIG. 2, in one embodiment of the present disclosure, the switching elements SW lj are arranged based on a triangular design.

[0045] The triangular architecture includes a plurality of layer structures arranged along the input / output direction of photons, as illustrated in FIG. lj The switching elements SW included in each layer increase in number from the layer closest to the input port E(n) side to the output port Y(n) side. lj The number of increase In the example shown in FIG. 2, the layer of switching elements provided on each path at the first input port side is layer 5, and the layer levels decrease toward the output port. lj are arranged near one end (the output port layer side) of the multiple photon transport paths 10, thereby forming a triangular layer structure as a whole. The number of layers l in the triangular architecture is 0≦l≦(N / 2)−1, and 2l switch points are arranged in layer l. Therefore, the total number of switches is the minimum value of {N(N−2)} / 4.

[0046] FIG. 4 shows the switching element SW lj 5 is a diagram for explaining a control algorithm of the switching element SW1 in the first embodiment. lj 5 is a flowchart illustrating the control process of Fig. 5. The flowchart shown in Fig. 5 shows an example of a process flow for realizing the control algorithm shown in Fig. 4. In the triangular architecture, the control unit 30 performs photon routing based on the algorithm shown in Fig. 4.

[0047] In the first embodiment, the predetermined adjacent output condition for routing includes, for example, moving a paired photon of a photon at the bottom of a photon string to a position adjacent to the bottom photon, moving photons higher than the paired photon straight ahead, and moving a photon between the paired photon and the bottom photon one position higher by crossing, and repeating the above process for the bottom photon for which pairing has not been completed. Below, the routing process of the quantum switching system 1 in the first embodiment performed by the control unit 30 will be described using a specific example of the predetermined adjacent output condition.

[0048] The control unit 30 first receives an input photon sequence and a pairing request as input (S1). The input photon sequence is given as an indexed list (X(0), X(1), ... X(N-1)), with an initial value of N. The pairing request is provided as a pair set PL(N / 2) = {(X(i), X(j))} in which each photon appears once.

[0049] Next, the control unit 30 inputs the current photon number (the number of unpaired photons) into n, and evaluates the condition n>2 for the current photon number n (S2). If this condition is met, the control unit 30 repeats the following processes of S3 to S7. If the condition is not met (n≦2), it determines that all pairing processes have been completed, and proceeds to the end process.

[0050] Next, the control unit 30 defines the switch layer l to be processed based on the current number of photons n using the following formula (S3).

[0051] l=(n / 2)-1 This layer l has a switching element SW corresponding to the next photon pair to be processed. lj The layer on which the group is placed.

[0052] Next, the control unit 30 identifies X(j) which is a pair with the photon X(N-1) (X(11) in the example shown in FIG. 2) at the bottom of the photon train (S4). The photon X(N-1) at the bottom of the photon train is ljSince it is not connected to either, the position cannot be changed. Therefore, the control unit 30 first identifies the pair partner X(j) of X(N - 1) and performs switch settings for adjacent output of this pair.

[0053] Next, the control unit 30 performs setting of the switching element SW arranged in layer l lj (S5). Here, the index j indicates the order of the switches (arrangement from top to bottom) within layer l. FIG. 6 is a flowchart showing the control method for setting the switching element SW lj in the first embodiment. While referring to FIG. 6, the control method for setting the switching element SW lj in the first embodiment will be described.

[0054] The control unit 30 first initializes the switch index j to 0 (S11). This is for evaluating and setting in order from the top (upper) of the most input - side (left - end) of the switch group in the layer l.

[0055] Next, the control unit 30 makes a conditional determination j < i for the index of the switching element SW lj and the index of the photon X(j) which is a pair with the photon XN - 1 (herein referred to as i) (S12). When the currently evaluated switch index j is smaller than the index of the photon X(j), the control unit 30 sets the switch SW lj to straight - through (S13) and proceeds to S16. When the currently evaluated switch index j is greater than or equal to the index of the photon X(j), it proceeds to the conditional determination of S14.

[0056] In S14, for the index of the switching element SW lj and the index of the photon X(j) (herein referred to as i), the control unit 30 makes a conditional determination j ≤ n - 3. When j is greater than or equal to i and less than or equal to n - 3, the control unit 30 sets the switching element SW lj to cross - through (S15) and proceeds to step S16.

[0057] Next, the control unit 30 updates the index. The control unit 30 increments j by 1 (S16), and repeats the processing of S12 to S17 until j < n - 2 (S17).

[0058] When j becomes n - 2 or more, the control unit 30 determines that all switch settings in the layer have been completed, and ends the processing.

[0059] By this switch setting process, while maintaining the order of the photon sequence, the photon X(j) to be routed reaches a predetermined position below (the (n - 2)-th output port Y) by a continuous crossing operation in layer l. As a result, a switch configuration is realized in which the photon X(j) and the lowest-order photon X(N - 1) are led to adjacent output ports.

[0060] Returning to FIG. 5, the description of the control process of the switching element SW in the first embodiment will be continued. In S6, the control unit 30 updates the photon list. The control unit 30 updates the photon sequence as follows based on the switch setting. lj The control unit 30 moves the photon X(j) to the (n - 2)-th position, and sequentially moves the subsequent photons up to the upper index one by one. Next, the control unit 30 decreases the number of photons to be processed by two (n ← n - 2) (S7). Then, the control unit 30 repeats the processing from S2 for the updated photon sequence. The processing is continued until the condition N > 2 is no longer satisfied.

[0061] (X(0),…,X(j - 1),X(j + 1),…X(N - 2),X(j),X(N - 1)) When the number of photons n becomes 2 or less, the remaining two photons are arranged adjacent to each other, and all pairs reach the adjacent output port Y(n). At this time, the order of the photon sequence and the set state of each switching element SW

[0062] are taken as the final output. lj

[0063] ​This routing algorithm realizes a configuration in which all photon pairs are output adjacently in a reconfigurable non-blocking triangular architecture.

[0064] In this algorithm, for each switch layer, the photon sequence corresponding to that layer is scanned once, and the switching element SW lj Therefore, in this embodiment, for the number of photons N, the process of determining the state (straight or crossing) of N is performed. 2 Since the routing process can be completed in this calculation time, it can operate within a practical processing time even when the number of photons increases. Therefore, it has high scalability and can be implemented in large-scale networks.

[0065] Furthermore, because the switch layout structure is regularly expanded in a stepped or triangular pattern, layout design is simplified and integrated implementation in a planar structure is easy. In particular, when applied to photonic integrated circuit technology, it has high consistency in mask design, wiring constraints, and photolithography control. Therefore, the quantum switching system 1 in this embodiment can provide a structure that is excellent in both theoretical computational efficiency and ease of implementation.

[0066] Second Embodiment (Chevron Design) In the second and subsequent embodiments, the description of the matters common to the first embodiment will be omitted, and only the differences will be described. In particular, similar effects due to similar configurations will not be mentioned in each embodiment.

[0067] The switching element SW of the quantum switching system 1 according to the second embodiment of the present disclosure ljare arranged to form a Chevron architecture (Chevron Design) as shown in FIG. 7. In this specification, the photon transport path 10 to which the photon X(n) is input is defined as a path 10(n). The value of the index n of the photon and the index n of the path 10 are the same. Therefore, the photon transport paths 10 are made up of N paths with indexes 0 to N-1. Switching elements SW are provided between the N-1 adjacent photon transport paths 10 sandwiched between them. lj can be placed.

[0068] In this embodiment, the switching element SW lj The group as a whole forms a V-shape with a central axis (for example, X5, X6) as the reference. In this specification, "forming a V-shape with a central axis as the reference" refers to the group of multiple switching elements SW lj is a structure in which the elements are arranged symmetrically from both the ascending and descending sides of the path 10(n) (n = 0 to N-1) toward the central path 10(N / 2).

[0069] Switching element SW lj are distributed symmetrically on the low-index and high-index sides of the path 10(n) in each layer. In even-numbered layers, the central path 10(n) is used as the axis of symmetry, while in odd-numbered layers, the paths are arranged to avoid the central path 10(n). As a result, the switch configuration of each layer as a whole is formed into a V-shape that symmetrically spreads out from the central path of the multiple photon transport paths 10.

[0070] With such an arrangement of switching elements, photons traveling from the input port E(n) to the output port Y(n) take a routing path that converges toward the central output port Y(n).

[0071] Specifically, the switching elements SW lj will be placed.

[0072] When the layer l is an even number, the switching element SW ljIn the even-numbered layer 1, switching elements are arranged in the following two index regions, which are divided into two halves by the path 10(N / 2) at the center. In the front region, which is the side with the smaller value of the index N of the path 10, switching elements SW lj are arranged continuously in the range of j=(N / 2)-l-1, (N / 2)-l, ..., (N / 2)-2. In the rear region where the value of N is large, the switching elements SW lj are arranged consecutively in the range of j=N / 2, (N / 2)+1, ... (N / 2)+l-1. In this way, a configuration in which the indexes are symmetrical with respect to the path 10(N / 2) is formed, and the switching elements SW lj The groups together form a V shape.

[0073] The chevron architecture is composed of (N / 2)-1 layers for a number of photon inputs, N. In the example shown in Figure 7, it is composed of 5 layers (Layer 5) for a number of 11 photon inputs. Each layer k has 2k (0≦k<(N / 2)-1) switching elements SW. Therefore, the total number of switches is the minimum value of {N(N-2)} / 4.

[0074] Like the triangular architecture described above, the chevron architecture is constructed on a plane and has a reconfigurable non-blocking structure that can accommodate any photon pair. Furthermore, the V-shaped configuration ensures that the density of the switching elements SW is uniformly distributed rather than concentrated near the center. This reduces interference in the photon transport path 10. The symmetrical layout also makes it easy to balance the wiring. Furthermore, the structure of each layer is patterned, making it easy to design as an integrated circuit.

[0075] FIG. 8 shows the switching element SW lj 9 is a diagram for explaining a control algorithm of the switching element SW2 in the second embodiment. lj9 is a flowchart illustrating the control process of Fig. 9. The flowchart shown in Fig. 9 shows an example of a processing flow for realizing the control algorithm shown in Fig. 8. In the chevron architecture, the control unit 30 performs photon routing based on the algorithm shown in Fig. 8.

[0076] In the second embodiment, the predetermined adjacent output condition for routing includes: if the highest and lowest photons in a photon train are a pair, crossing all switching elements and moving the paired photons to two adjacent pairs of output ports in the middle; if the highest and lowest photons in a photon train are not a pair, extracting the paired photons and moving the two photons of the paired photons as a virtual pair to two adjacent output ports that are not a pair; moving the highest photon to the output port adjacent to the higher of the two output ports and moving the lowest photon to the output port adjacent to the lower of the two output ports. Below, the routing process of the quantum switching system 1 according to the second embodiment, performed by the control unit 30, will be described using a specific example of the predetermined adjacent output condition.

[0077] Steps S21 to S23 are the same as those in the first embodiment, and therefore will be omitted. In step S24, the control unit 30 acquires and removes the photons at both ends (the top and bottom). The control unit 30 acquires the top photon (top: X(0)) and the bottom photon (bot: X(N-1)), and temporarily removes photons X(1) to X(N-2) from the list PL.

[0078] Next, the control unit 30 determines whether the end photons top and bot acquired in step S24 are a pair (S25). If they are a pair, the process proceeds to step S26, and if they are not a pair, the process proceeds to step S29.

[0079] If top and bot are a pair, the control unit 30 determines a central insertion position i (S26). Here, the central insertion position i refers to the starting position for rearranging a photon pair temporarily removed from the pair list PL during the routing process in an adjacent positional relationship. For example, the central insertion position i is the first index among the positions (i and i+1) where the target pair is reinserted into the photon train. Therefore, i takes a value corresponding to the photon index 0 to n-1. The central insertion position i is determined based on the position of n / 2. For example, if n / 2 is even, i is set to left+n / 2, and if n / 2 is odd, i is set to left+(n / 2)-1. Here, left is a reference offset indicating the position in the original train from which the photon train to be processed starts. The initial value of left is 0. By defining it in this way, the paired photons merge at symmetrical positions toward the center, and can be input to the paired output port Y(n).

[0080] Next, the control unit 30 controls all the switching elements SW lj The setting is changed to intersect (S27).

[0081] Next, the control unit 30 performs a recursive call on the remaining pair list PL after removing the photon pair (top and bot) that was the processing target (S28). The recursive call in step S28 applies the same routing process as in step S21 and after to a reduced version of the photon train, and after returning from the recursion, the process continues to step S29, where the corresponding pair of photons is placed at the central insertion position. This sequentially rewinds the process, and all pairings are completed.

[0082] In step S30, the pair of photons (top and bot) that were the subject of processing are inserted into positions corresponding to the determined central insertion positions i and i+1 among the processed photon indices 0 to N-1 (S28).

[0083] If top and bot are not paired, the control unit 30 identifies top', which is the pair of top, and bot', which is the pair of bot. These pairs are deleted from the pair list PL and replaced with the virtual pair (top', bot') (S10). The control unit 30 generates a new virtual pair list PL'.

[0084] After that, based on the virtual pair list PL', the control unit 30 recursively applies the same routing process as steps S21 and subsequent steps to the remaining photon sequence (S31).

[0085] Next, the control unit 30 identifies the index position i of top' and the index position j of bot' in the photon sequence as the result of the recursive process (S32). Then, the control unit 30 determines the positional relationship between i and j (S33).

[0086] If top' is in the front (upper), that is, i < j, the control unit 30 sets the switch point corresponding to the path l through which top' passes and the path left + i to straight (S34). Then, it proceeds to step S39.

[0087] If bot' is in the front (upper), that is, j < i, the control unit 30 swaps i and j, updates the i-th in the photon sequence to top' and the j-th to bot' (S35). After that, the control unit 30 performs the following conditional branch process based on the position of i, that is, the positions of top' and bot' (S36).

[0088] If i belongs to the first half of the waveguide array, the control unit 30 sets the (left + i - 1)-th switching element in the switch layer l to straight. Then, in the photon sequence, the control unit 30 inserts top immediately before top' (one position above). Also, the control unit 30 removes bot' from the photon sequence once and inserts bot' and bot into the central position in order (S37).

[0089] If i belongs to the first half of the waveguide array, the control unit 30 sets the left+j+1th switching element in the switch layer l to straight. Then, the control unit 30 inserts bot immediately after bot' (one lower) in the photon train. The control unit 30 also temporarily removes top' from the photon train, and inserts top and top' into the center position in that order (S38).

[0090] As a result, bot is guided to the output port Y(n) adjacent to bot', and the photon train is adjusted so that the corresponding pair configuration is established. Through this process, top and bot are rearranged into the virtual pair top' and bot' so that they are sandwiched between each other on the top and bottom of the waveguide, and are output to the paired output port Y(n).

[0091] Switching element SW that is not set in the switch layer lj As described above, after the arrangement of the paired photons (top and bot) and the switch settings in the switch layer are all completed, the updated photon sequence and switch settings are returned to the routing process in the upper layer.

[0092] This completes the alignment process for photon pairs, and similar processes are applied across each layer until all photons are output adjacent to the photon to be paired.

[0093] This routing algorithm realizes a configuration in which all photon pairs are output adjacently in a reconfigurable non-blocking chevron architecture.

[0094] This embodiment is a recursive routing optimized for a V-shaped switch layout that assumes a central merging structure. By temporarily introducing virtual pairs to ensure structural consistency, recursive processing can proceed without interfering with actual pairing. As with the first embodiment, the amount of calculation required for processing is at most N 2 can be kept to.

[0095] <Third embodiment> (Brickwork Design) The switching elements SW of the quantum switching system 1 according to the third embodiment of the present disclosure are arranged to form a brickwork design as exemplified in FIG.

[0096] In this embodiment, the switching elements SW li The arrangement of the indexes is alternating between odd and odd depending on the layer. The brickwork structure is made up of N / 2 layers. At this time, the switching elements SW kj When the layer number k is an even number, the index j∈{0, 2, 4, ..., N-2}, and when the layer number k is an odd number, the index j∈{1, 3, 5, ..., N-3}. kj The installation position of the will shift by one index for each layer.

[0097] This causes the switching element SW kj In the index space, the positions of the switching elements are alternately offset between odd and even layers, forming a brickwork structure. This structure has the design effect of increasing routing flexibility when crossing specific photon pairs and avoiding local concentration of switch density. Furthermore, as with other embodiments, the minimum number of switches, {N(N-2)} / 4, is achieved.

[0098] FIG. 11 shows the switching element SW kj 12 is a diagram for explaining a control algorithm of the switching element SW1 in the third embodiment. kj 12 is a flowchart illustrating the control process of Fig. 11. The flowchart shown in Fig. 12 shows an example of a process flow for realizing the control algorithm shown in Fig. 11. In the brickwork architecture, the control unit 30 performs photon routing based on the algorithm shown in Fig. 12.

[0099] In the third embodiment, the predetermined adjacent output condition for routing includes moving the higher-order photon of two photons to be paired to the lower-order one first and then to the higher-order one of the two adjacent output ports, moving the lower-order photon to the higher-order one after the movement of the higher-order photon and then to the lower-order one of the two adjacent output ports, deleting the route used for the movement, and repeating the above process for the remaining brick-shaped structures. Below, the routing process of the quantum switching system 1 according to the third embodiment, performed by the control unit 30, will be described using a specific example of the predetermined adjacent output condition.

[0100] Steps S41 to S43 are the same as those in the first embodiment, and therefore will not be described. In step S44, the control unit 30 selects a target pair. Specifically, the control unit 30 fixes the lowest-order photon XN-1 in the current photon string X0 to XN-1 as a fixed target, and identifies its partner X(j) from the pair list. The control unit 30 sets the switches for this pairing (X(j), X(N-1)) to guide both photons to the adjacent output port Y(n).

[0101] Next, the control unit 30 determines the arrival line (S45). The index of the lowest path 10(n) that the photon X(j) can ultimately reach is set to k. Here, if k=N-2 is not met, for example, if the photon X(j) does not reach the second-lowest photon transport path 10, the photon X(j) is configured to reach path 10k+1 by crossing X(N-1) upward.

[0102] In step S46, the control unit 30 sets the switches to follow the following rules: In routing the photon X(j), the control unit 30 moves the photon X(j) to the lower layer (photon transport path 10 with a large index) as early as possible (when the switch depth is shallow). In order to reach the lower layer quickly, the control unit 30 selects, for example, the switching element SW10 closest to the input port E(n). kj Set to the intersection.

[0103] On the other hand, in the routing of X(N-1), the control unit 30 makes the output position arrive at the latest possible timing (timing with a deep switch depth). In order to arrive at the lower port adjacent to the output port of X(j) late, the control unit 30 makes the output position arrive at the switching element SW1 close to the output port Y(n), for example. kj is set to the intersection. In this way, the position where the two photons meet is adjusted.

[0104] Next, the control unit 30 reduces the network configuration (S47). kj and remove the traversed photon transport path 10 from the network. This results in a new photon train with two fewer photons than the initial state and a corresponding reduced brickwork architecture.

[0105] Next, the control unit 30 decreases the number of photons to be processed by two (n←n-2) (S48). Then, the control unit 30 repeats the process from S42 on the updated photon string. The process continues until the condition n>2 is no longer satisfied.

[0106] When the number of photons n becomes 2 or less, the remaining two photons are arranged adjacent to each other, and all pairs reach the adjacent output port Y(n). At this time, the order of the photon train and the switching element SW kj The setting state is the final output.

[0107] The resulting configuration from the recursive process is then adjusted to again maintain the brickwork architecture.

[0108] In addition, when performing adjacent output, an extra switching element SW kj If any remain, they are set to a straight-ahead state to maintain consistency.

[0109] When all pairs have been arranged, the photon sequence will be arranged such that photons with adjacent indices are paired together, such as (X(0),X(1)),(X(2),X(3)),...,(X(N-2),X(N-1)). At the same time, the switching element SW kj The state of is determined, and photon guidance to the adjacent output port Y(n) is realized.

[0110] In a brickwork architecture, the number of switches per layer is fixed, resulting in a uniform layout density, making it suitable for physical implementation of photonic integrated circuits. Furthermore, the maximum number of passes through a switch point (network depth) can be limited to N / 2, which reduces photon loss. Furthermore, the difference in the number of switch passes between pairs of photons is small, suppressing the variation in photon loss. By combining updates to the virtual network structure with recursive processing, non-blocking routing is achieved for any pair list.

[0111] <Fourth embodiment> 13 is a diagram for explaining a quantum switching system 1 according to the fourth embodiment of the present disclosure. The switching element SW lj As shown in FIG. 13, the flow of photons is configured to be the opposite of that in the first to third embodiments.

[0112] In this embodiment, photons are transported from the output port Y(n) side toward the input port E(n). Specifically, in this embodiment, quantum entangled photon pairs generated from a photon source are input to the quantum switching system 1 from a position corresponding to the output port Y(n). The photon pairs input to the quantum switching system 1 are distributed to the input port E(n) through the switching element arrangement section 20 and emitted from the corresponding photon emitter 100.

[0113] In this embodiment, by realizing the reverse transport of photons as described above, it becomes possible to apply the present invention to applications such as distributing photon pairs in a quantum entangled state to arbitrary positions to supply quantum resources.

[0114] In this case, the ports from which the signals are emitted are not necessarily adjacent to each other.

[0115] In each embodiment, the depth difference Δ of the switching element SW through which two photon pairs pass is as follows:

[0116] Triangular Architecture: N-2 Chevron Architecture: If N / 2 is odd, Δ=N / 2 If N / 2 is even, Δ=(N / 2)-2 Brickwork architecture: Δ≒(N / 4)+1 Therefore, the brickwork architecture minimizes the variation in loss per photon and stabilizes the quality of entanglement. In addition, in networks with nodes of different importance, the switch depth can be adjusted by using the lower ports of the triangular architecture for high-priority connections.

[0117] The disclosed technology is not limited to the above-described embodiment, and can be implemented in various other forms without departing from the spirit of the disclosed technology. Therefore, the above-described embodiment is merely an example in all respects and should not be interpreted as being limiting. For example, the order of the above-described processing steps can be arbitrarily changed or executed in parallel as long as no contradiction occurs in the processing content.

[0118] The program of the embodiment of the present disclosure may be provided in a state stored in a computer-readable storage medium. The storage medium can store the program in a "non-transitory tangible medium." The program includes, but is not limited to, a software program or a computer program. [Explanation of symbols]

[0119] 1...Quantum switching system 10...Photon transport pathway 20...Switching element arrangement section 30...Control unit 100...Photon emitter 200...Photon input section SW...Switching element E(n)...input port Y(n)...Output port

Claims

1. 1. A quantum switching system comprising: A plurality of input ports; a plurality of output ports, the same number as the plurality of input ports; a photon transport path connecting the plurality of input ports and the plurality of output ports; a plurality of two-input, two-output switching elements that are provided across two adjacent photon transport paths and switch the photon propagation paths; a control unit that controls the switching elements to pair photons input to each of the plurality of input ports into any two pairs and output the paired photons to two adjacent pairs of output ports; Equipped with When the number of the plurality of input ports and the plurality of output ports is N, the number of the plurality of switching elements is less than {N(N-2) / 2} and equal to or greater than {N(N-2)} / 4}; the plurality of switching elements are arranged such that any two of the plurality of input ports are connected to two pairs of adjacent output ports; Quantum switching system.

2. The plurality of switching elements are arranged in a plurality of layers in a direction from the input port side toward the output port side, and a different number of switching elements are arranged in any adjacent layers among the plurality of layers, and each switching element in each layer is arranged across the two adjacent paths that are different from each other, the plurality of switching elements are arranged such that any two of the plurality of input ports are connected to two pairs of adjacent output ports; The quantum switching system of claim 1 .

3. The control unit When the photons travel in a direction from the input port side to the output port side, the switching element is controlled so that the photons input to each of the plurality of input ports are paired into any two pairs and output to two adjacent pairs of output ports; When the photon travels in a direction from the output port side toward the input port side, the switching element is controlled so as to output, to the input port, two photons in a quantum entangled state that are to be input to each of the two adjacent pairs of output ports. The quantum switching system of claim 1 .

4. two pairs of adjacent output ports among the plurality of output ports are connected to the same Bell state analyzer; 3. A quantum switching system according to claim 1 or claim 2.

5. the switching element and the photon transport path form a planar structure configured so as not to cross each other; 3. A quantum switching system according to claim 1 or claim 2.

6. One photon of two photons in a quantum entangled state is input to the plurality of input ports.

3. A quantum switching system according to claim 1 or claim 2.

7. One of the two photons in the quantum entangled state is supplied from a quantum memory or a photon pair generation source.

4. The quantum switching system of claim 3.

8. the control unit controls switching between straight and crossing for each of the plurality of switching elements, so that any two of the photons are output to the two pairs of adjacent output ports.

3. A quantum switching system according to claim 1 or claim 2.

9. the plurality of switching elements form a layer structure arranged along an input / output direction of photons, the number of the switching elements included in each layer increasing stepwise from the input port side to the output port side, and the plurality of switching elements as a whole form a triangular layer structure; 3. A quantum switching system according to claim 1 or claim 2.

10. the plurality of switching elements form a layer structure arranged along a photon input / output direction, and the plurality of switching elements as a whole form a V-shaped structure symmetrically spreading from a central path among the plurality of photon transport paths; 3. A quantum switching system according to claim 1 or claim 2.

11. the plurality of switching elements form a multi-layer structure in which they are alternately arranged between adjacent waveguides, and the plurality of switching elements form a brick-like structure in which the positions of the switching elements are alternately offset between odd-numbered layers and even-numbered layers of the plurality of layers.

3. A quantum switching system according to claim 1 or claim 2.

12. A plurality of input ports; a plurality of output ports, the same number as the plurality of input ports; a photon transport path connecting the plurality of input ports and the plurality of output ports; a plurality of two-input, two-output switching elements that are provided across two adjacent photon transport paths and switch the photon propagation paths; Equipped with When the number of the plurality of input ports and the plurality of output ports is N, the number of the plurality of switching elements is less than {N(N-2) / 2} and equal to or greater than {N(N-2)} / 4}; A method for controlling a quantum switching system, wherein the plurality of switching elements are arranged so that any two of the plurality of input ports are connected to two pairs of adjacent output ports, the method comprising: The control device determining travel paths of any two photons input to each of the plurality of input ports based on a predetermined adjacent output condition regarding output to two adjacent output ports; Controlling switching between straight travel and crossing for each of the plurality of switching elements based on the determined travel path; To execute Control method.

13. When the plurality of switching elements form a layer structure arranged along an input / output direction of photons, the number of the switching elements included in each layer decreases stepwise from the input port side to the output port side, and the plurality of switching elements form a triangular layer structure as a whole, The predetermined adjacent output condition is: for a photon located at the lowest position in the photon sequence, moving its paired photon to a position adjacent to the lowest-positioned photon, causing photons higher than the paired photon to move straight ahead, and moving a photon between the paired photon and the lowest-positioned photon one position higher by crossing, and repeating the process for the lowest-positioned photon for which pairing has not been completed. The control method according to claim 12.

14. When the plurality of switching elements form a layer structure arranged along a photon input / output direction, and the plurality of switching elements as a whole form a V-shaped structure symmetrically spreading from a central path among the plurality of photon transport paths, The predetermined adjacent output condition is: When the most significant and least significant photons in the photon train are a pair, all of the switching elements are crossed to move the pair of photons to two adjacent pairs of output ports in the middle; if the most significant and least significant photons in the photon train are not a pair, extracting a pair partner of each of the most significant and least significant photons, and moving the two photons of the pair partner as a virtual pair to two adjacent output ports that are not a pair, and moving the most significant photon to an output port adjacent to the higher port of the two output ports, and moving the least significant photon to an output port adjacent to the lower port of the two output ports. The control method according to claim 12.

15. When the plurality of switching elements form a multi-layer structure in which they are alternately arranged between adjacent waveguides, and the plurality of switching elements form a brick-like structure in which the positions of the switching elements are alternately offset between odd-numbered layers and even-numbered layers of the plurality of layers, The predetermined adjacent output condition is: Among two photons to be paired, the higher-order photon is first moved to a lower position and moved to a higher-order of two adjacent output ports, and the lower-order photon is moved to a higher position after the movement of the higher-order photon and moved to a lower-order of the two adjacent output ports, deleting the route used for the movement, and repeating the process for the remaining brick-shaped structures. The control method according to claim 12.

16. A plurality of input ports; a plurality of output ports, the same number as the plurality of input ports; a photon transport path connecting the plurality of input ports and the plurality of output ports; a quantum switching system including a plurality of two-input, two-output switching elements that are provided across two adjacent paths of the photon transport paths and switch the photon travel paths, wherein when the number of the plurality of input ports and the number of the plurality of output ports is N, the number of the plurality of switching elements is less than {N(N-2) / 2} and equal to or greater than {N(N-2)} / 4}, and the plurality of switching elements are arranged so that any two of the plurality of input ports are connected to two pairs of adjacent output ports; determining travel paths of any two photons input to each of the plurality of input ports based on a predetermined adjacent output condition regarding output to two adjacent output ports; Controlling switching between straight travel and crossing for each of the plurality of switching elements based on the determined travel path; A program that executes.

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