System for providing EPR quantum channels

Abstract

There is disclosed a system for providing an EPR quantum channel, comprising: a transmitter of entangled photons, the transmitter comprising a source configured to generate entangled photon pairs, a first receiver and a second receiver, the first receiver and the second receiver each comprising: a unit for storing quantum bits, the unit is arranged to store quantum bits carried by the received photons; -a photonic switch arranged to send the received photons to the storage unit; -a photon pass-through detector configured to control the photonic switch and to record the time at which a photon is received; the invention relates to a device for receiving photons, comprising a plurality of receivers, an information processor arranged to control the photon switches of said receivers, a communication system connecting the two receivers to each other, said communication system being arranged to communicate the time at which the photons are received to determine an entangled photon pair, the two photons of which have each arrived at the receiver to which it is transmitted.

Description

TECHNICAL FIELD

[0001] The present invention relates to methods of quantum communication, and more specifically, to those that allow for the teleportation of quantum information. BACKGROUND

[0002] Currently, long distance transmission of information is limited to classical information, not quantum information (called qubits). However, the long distance transmission of qubits would allow quantum computers to be connected to each other. For example, this would allow low power computers to use more powerful computers for computation, while maintaining the confidentiality of the data transmitted and computed. This would also allow the use of a network of quantum computers to overcome the short lifetime of quantum memory (typically around one second) by working together to collectively fill a quantum database that, when integrated into a central computer, can be polled.

[0003] At short distances, quantum teleportation would allow the implementation of quantum computers, for example, allowing the transmission of qubits and controlling the transmission of qubits to units for performing quantum operations.

[0004] In the context of quantum cryptography, it is known to use pairs of entangled photons to securely generate and transmit codes.

[0005] By entangled photons, it is meant a pair of photons whose quantum state (e.g. polarization) of one photon depends on the quantum state of the other photon of the pair, regardless of the distance between them. The quantum entanglement phenomenon has been observed and demonstrated experimentally on several occasions, for example in the article by Shashi Prabhakar et al. entitled "Quantum Entanglement: A Review of the Recent Experimental Progress" published in Advances in Physics. Two-photon quantum interference and entanglement at 2.1 μm ” (Sci. Adv. 6, eaay 5195, 2020).

[0006] The article by Wang, R (2005) entitled "Quantum Communication System" published in the arXiv: Quantum Physics section describes a quantum communication system that allows for the superluminal transmission of information by sending pairs of entangled photons to two receivers wishing to communicate with each other. The photons are entangled and the linear polarization of the photon that reaches the first receiver is measured in different directions at 45° to each other. At the second receiver, the second photon is de-multiplexed and the average polarization of the de-multiplexed flux is measured to determine the polarization direction of the first photon measured. However, this system does not allow for the transmission of quantum states. Superluminal telecommunication: an observable contradiction between quantum entanglement and relativistic causality The article by Wang, R (2005) entitled "Quantum Communication System" published in the arXiv: Quantum Physics section describes a quantum communication system that allows for the superluminal transmission of information by sending pairs of entangled photons to two receivers wishing to communicate with each other. The photons are entangled and the linear polarization of the photon that reaches the first receiver is measured in different directions at 45° to each other. At the second receiver, the second photon is de-multiplexed and the average polarization of the de-multiplexed flux is measured to determine the polarization direction of the first photon measured. However, this system does not allow for the transmission of quantum states.

[0007] The polarization of a photon is not necessarily binary (as in the case of spin), or even quaternary. In particular, it can be represented on a Jones sphere, which characterizes the orientation and ellipticity of polarization: polarization can be linear, where the electric field is always parallel to an axis perpendicular to the direction of photon propagation; it can also be circular, where the electric field rotates around that axis; or it can be somewhere in between, where the electric field moves along an elliptical trajectory around the propagation axis. In cases where the polarization is not circular, orientation measures the direction of the axis, and eccentricity measures the flattening of the ellipse. Patent FR 3125658 utilizes this property and allows non-quantum information to be transmitted over long distances (e.g., greater than 200 km) at near-light speeds by using optical fibers or photons for propagation in space.

[0008] Furthermore, there exist systems for teleporting quantum information, for example, in Nature Communications (2023) entitled " Long distance multiplexed quantum teleportation from a telecom photon to a solid-state qubit The article describes a system for teleporting qubits between photons and physical atoms. However, these systems are limited to short distances, and the teleportation does not occur between two physical atoms, but rather between photons carried by an optical fiber and photons stored in a crystal.

[0009] Furthermore, existing systems for teleporting quantum information are limited by photon loss during transmission and by the speed of photon transmission.

[0010] Finally, the article titled "Nature" (2021) Nondestructive detection of photonic qubits The article discloses a method for detecting photons without destroying them; however, it does not describe how it can be used to achieve teleportation of qubits. Summary of the Invention

[0011] There is a need for further improvements to quantum communication systems and methods, especially those that allow EPR (Einstein-Podolsky-Rosen) quantum channels to remote users hundreds of kilometers away or even further (if optical fibers are used, especially if optical links through free space are used). Invention Overview

[0013] The object of the present invention is to meet this need, and according to its first aspect, the present invention achieves this by means of a system for providing an EPR quantum channel, the system comprising: An emitter of entangled photons, said emitter comprising a source configured to produce at least one pair of entangled photons, said at least one pair of entangled photons comprising a first photon emitted on a first propagation path, and a second photon emitted, preferably simultaneously, on a second propagation path different from the first propagation path; A first receiver, said first receiver being disposed on the first propagation path, said first receiver comprising: - at least one unit for storing a quantum bit, this unit being arranged to store the quantum bit carried by the photon received by the first receiver; - a photon switch, this photon switch being arranged to send the photon received by the first receiver to the storage unit, or optionally to another channel able to deliver it to a storage unit or to a photon release path; - a photon passage detector, this photon passage detector being configured to monitor the photon switch and to record the time at which the photon is received by the first receiver, and optionally, where applicable, the identifier of the storage unit to which the photon is sent; A second receiver, said second receiver being disposed on the second propagation path so as to be reached by the second photon, said second receiver comprising: - at least one unit for storing a quantum bit, this unit being arranged to store the quantum bit carried by the photon received by the second receiver; - a photon switch, this photon switch being arranged to send the photon received by the second receiver to the storage unit, or optionally to another channel able to deliver it to a storage unit or to a photon release path; - a photon passage detector, this photon passage detector being configured to monitor the photon switch and to record the time at which the photon is received by the second receiver, and optionally, where applicable, the identifier of the storage unit to which the photon is sent; At least one information processor, for example an electronic microprocessor, included in the first receiver and / or in the second receiver, arranged to control the photon switch of the receiver; A communication system connecting the two receivers together, said communication system being notably arranged to inform the information processor of the times of reception of the photons at the first receiver and at the second receiver, in order to determine the pair of entangled photons, the two photons of which have each reached the receiver to which they were sent.

[0014] The system for providing an EPR quantum channel according to the application allows the use of optical fibers, notably by using spatial optical communication, to transmit information over long distances, notably distances greater than 100 km, for example between 100 km and 400 km or more.

[0015] The loss of photons during the transmission is very high due to the very large distance between the receiver and the transmitter. In optical fibers, the loss of photons is about 0.2 dB / km. The unit for storing the qubits of the two receivers only allows to retain those qubits carried by the photons received by the first receiver within a waiting duration corresponding to the duration necessary to know whether the qubit carried by the photon entangled with said photon has been received and stored in another receiver, plus the duration necessary for said first receiver to provide to the user said qubit received at the first receiver.

[0016] The system according to the application thus allows to transmit information including a minimized error rate, while removing most of the error sources.

[0017] The system can allow the transmission of quantum information with a delay time independent of the distance between the two locations wishing to communicate, and only using photons, which requires little energy.

[0018] The system is for example used for communication networks and / or quantum computer networks in the Earth, the sky and / or space, notably in order to communicate with systems located far from the Earth, such as satellites or spacecraft.

[0019] The first receiver and / or the second receiver can comprise at least one additional channel, notably downstream of the switch, which can lead to a storage unit or to a photon release channel.

[0020] Each receiver preferably has at least one interface, for example an electronic interface, notably allowing it to communicate with the outside and / or allowing it to display the presence of qubits entangled with the qubits carried by the storage unit of the other receiver in one of its units for storing qubits.

[0021] Photonic memory cell

[0022] The storage unit of the first receiver and / or of the second receiver can be chosen from the following: an optical path, notably an optical fiber or a spatial path using a mirror arrangement, or a carrier of physical qubits, notably ions interacting indirectly with the incident photons.

[0023] The photon storage unit of the first receiver and / or of the second receiver can be located upstream of the photonic switch of the first receiver and / or of the second receiver, respectively. The one or more photon storage units of the first receiver and / or of the second receiver can be located downstream of the photonic switch of the first receiver and / or of the second receiver, respectively.

[0024] The at least one storage unit can be an optical fiber, wherein the photons received in the optical fiber are received while keeping their time of travel in said optical fiber. The length of the optical fiber is preferably short enough to limit the loss of photons inside, in particular less than 1%, and long enough to be able to store photons for a time allowing the first receiver to determine whether the other receiver has received an entangled photon. The length of the optical fiber can be between 0.2 m and 500 m. For example, the length of the optical fiber is substantially equal to 200 m, which allows the photons to be stored for about 1 microsecond.

[0025] The storage unit of the first receiver and / or of the second receiver can be a carrier of physical qubits, for example atoms, in particular atoms located in an optical cavity. The carrier of physical qubits can be physically moved so as to be replaced by another carrier of physical qubits, preferably initialized in a pure state before or after its movement, thus allowing it to interact with a new incoming photon. The carrier of physical qubits can be stimulated so as to emit a photon entangled with it before being reset, in order to be ready to interact with a new photon from the emitter of the entangled photons, wherein said photon entangled with it interacts in particular with the control port of a CNOT gate. Said movement or said stimulation of the carrier of physical qubits is advantageously controlled by an external device.

[0026] The storage unit of the first receiver and / or of the second receiver is preferably arranged to be usable to store a new qubit at the request of one of the information processors or periodically, in particular in the case where the unit for storing qubits needs to be processed in order to be able to store a new qubit.

[0027] If the unit for storing qubits allows the detection of the reception of a photon, said unit for storing qubits can also allow the detection of the passage of a photon.

[0028] The duration for which each storage unit is able to maintain a qubit is preferably greater than the time difference between the arrival of the two entangled photons between the two receivers, plus the time taken by the communication system to communicate information relating to the time of arrival of the entangled photons, the time taken by the processor to decide whether the two entangled qubits are present in one of the storage units of the receivers, and the time taken by the processor to inform the interface.

[0029] The communication system can be arranged to transfer information faster than the speed at which the photons are transported in the optical fibre. This can allow for a reduction in the number of storage units required to store each qubit carried by a photon for the same rate of reception of photons. This can also allow for a reduction in the duration for which a qubit is stored in a storage unit. This can therefore allow the optical fibre to be used as a storage unit and / or improve the fidelity of the stored qubits.

[0030] The system for providing an EPR quantum channel can comprise a single unit for storing a qubit in each receiver.

[0031] Each unit for storing a qubit can have an identifier.

[0032] Photonic switch

[0033] The photon switch of the first receiver and / or the second receiver can be an optical switch.

[0034] The photon switch of the first receiver and / or the second receiver can comprise a mirror, the axis of which can be mechanically controlled by a sensor or an electrically controlled device, or alternatively, the photon switch can comprise a prism or a plate made of a material whose refractive index depends on the electric field (Pockels cell), or a transparent material with a non-linear refractive index, by another light flux (for example transverse and preferably of a different wavelength than the photons, and not capable of generating photons of the same wavelength as the photons), causing a change in the refractive index of the non-linear material, thereby controlling the position of the photons in the material and optionally controlling the direction of exit of the photons from the material.

[0035] The photon switch of the first receiver and / or the second receiver can be an optical microcavity, i.e. a cavity formed by a reflective surface surrounding an optical medium, which is in particular configured to be used as an optical CNOT gate as described below, in which a succession of atoms is transported to interact with each photon. At least two holes can be formed in the cavity to allow at least two light rays to pass through, which are used as optical tweezers and allow the atoms to be transported and positioned within the cavity. The use of optical tweezers in particular allows the atom to be moved after interacting with a first one of the two photons for which the CNOT operation must be performed. This atom can in particular be moved into another cavity and can be replaced by a new atom, thereby allowing a new photon to be received, which carries the qubit used as the control qubit for another CNOT gate.

[0036] The photons enter and exit the microcavity in particular through an optical fibre, the end of which is shaped in the form of a lens.

[0037] As a variant, the photonic switch of the first receiver and / or of the second receiver is an acousto-optic deflector. The acousto-optic deflector can comprise an acousto-optic material, in particular belonging to the group consisting of quartz glass, lithium niobate, arsenic trisulfide, tellurium dioxide, more generally tellurium glass, flint glass, mercury amalgam, lead (II) bromide. As a variant, the acousto-optic material is water. The acousto-optic deflector can comprise an electro-acoustic transducer, in particular a piezoelectric material. The refractive index of the acousto-optic deflector undergoes a change as a function of the acoustic wave propagating in the deflector. The direction in which the acousto-optic deflector transmits the photons depends on the refractive index of the deflector, and thus on the acoustic wave propagating therein. Thus, the acousto-optic deflector allows the photons to be sent to a predetermined storage unit by a suitable acoustic wave.

[0038] The photonic switch of the first receiver and / or of the second receiver advantageously has the possibility of directing the received photons towards a photon absorber.

[0039] Photons passing through a detector

[0040] The passage of the photons by the detector of the first receiver and / or of the second receiver can comprise a non-destructive photonic qubit detector, for example using parametric conversion of the incident photons, which produces two photons of smaller frequency from a single photon, in which one of the produced photons indicates the presence of a qubit and the other provides information relating to said qubit, or, alternatively, the passage of the photons by the detector can comprise a photonic detector as described in the article entitled "Non-invasive photonic qubit detection" by Niemietz, D., Ferrara, P., Langenfeld, S. et al. Nature 591, 570-574 (2021). Nondestructive detection of photonic qubits The non-destructive photonic qubit detector allows the passage of the photons to be detected without absorbing them, and thus without destroying their properties.

[0041] The non-destructive photonic qubit detector can comprise a QED cavity in which a rubidium atom is trapped. This atom has two interesting energy levels defining observable values, and is in a quantum superposition of these two values. When a photon is reflected by the cavity, it can modify the quantum superposition state of the atom by applying a Pauli-Z gate to it, leaving a measurable trace. This change of state can be detected by applying a microwave pulse that rotates the quantum state by Pi / 2, in order to place it in the observable state 1 without having applied the Pauli-Z gate, or in the state 0 if the Pauli-Z gate has been applied. By measuring the change of state of the atom, it is then possible to detect the passage of the photon without destroying it, where the application of an electromagnetic microwave pulse allows the atom to be restored to its initial superposition state after having detected that the superposition state of the atom has been modified.

[0042] As a variation, photons from the first and / or second receivers passing through the detector may include, as in the paper titled "Brekenfeld, M., Niemietz, D., Christesen, JD et al. published in Nature Physics, 16, 647-651 (2020)". A quantum network node with crossed optical fiber cavities The device described in the article stores qubits transported by incident photons across physical atoms and allows detection of the storage.

[0043] The photon-pass detectors of the first and second receivers can each include a clock, and these two clocks are synchronized with each other. Therefore, the photon-pass detectors of the first and second receivers can respectively record the time when the first and second receivers receive photons.

[0044] Preferably, the clocks of the two receivers are configured to take into account the phenomenon of different time flows at different locations (especially the different heights of each component).

[0045] The timing accuracy of photon detectors can be improved by using multiple photon detectors, with arriving photons oriented sequentially towards these detectors using a photon switch, where another photon switch advantageously allows photons that have passed through each photon detector to return via the same optical path. For example, a clock can command these switches to change the photon detectors used at regular time intervals.

[0046] For example, if the time precision of the photon detector is t1, where t1 corresponds to the reciprocal of its operating frequency (i.e., the verification frequency of the quantum state of the atom, for example, if it is a cavity detector as described above), and the required time precision t2 is less than t1, then t1 / t2 photon detectors (or integers above them) can be used, with the photon oriented towards a different photon detector every t2. This allows the photon detector to have time t1 to detect or not detect the passage of a photon. At the end of time t1, a photon may have already been detected, and the quantum state of the photon detector can be reset to allow the detection of a new photon.

[0047] Information processor

[0048] Each of the two receivers may include at least one information processor.

[0049] An information processor that has identified two entangled photons that have each arrived at the receiver, or one of the information processors, can notify the interface of each receiver of the identifier of the storage unit containing the qubits carried by the entangled photons.

[0050] The information processor or one of the information processors that has identified a pair of photons of which at least one photon has not yet reached one of the two receivers can make a new quantum bit available to the memory of the storage unit in which the quantum bit carried by the other photon has already been stored, and if necessary, control the operation to make it available.

[0051] The one or more information processors can order the receiver that is furthest from the photon emitter to direct the photon of which the entangled photon has not yet been received by the other receiver towards the photon absorber.

[0052] Communication unit

[0053] The photon-by-detector of the first receiver can comprise a communication unit, the photon-by-detector of the second receiver can comprise a communication unit, the two communication units preferably communicating with each other via a communication system.

[0054] The exchange of the time of reception of the photons allows each receiver that has received a first photon to determine whether the other receiver has received a photon entangled with this first photon.

[0055] The communication system advantageously allows the speed of transmission of information between each receiver to be faster than the speed of transport of the photons between the emitter and each receiver. The quantum communication system is for example the system described in patent FR 3125658. As a variant, the communication system is an optical communication system (especially a communication system using optical fibers), a radio communication system, or a power line communication system.

[0056] The high speed of the communication system can allow the number of storage units of the receivers to be reduced. Especially, if the time taken by the two receivers to communicate via the communication system plus the time taken to control the switch is less than the time interval between the arrival of the two photons at the respective receivers, the number of units for storing quantum bits can be reduced to one, then the storage unit is located upstream of the photon switch, forming a link between the photon-by-detector and the photon switch.

[0057] If the information communication system does not allow the speed of transmission of information between each receiver to be faster than the speed of transport of the photons between the emitter and each receiver, the system for providing an EPR quantum channel comprises at least two units for storing quantum bits at each receiver.

[0058] The travel time of the photons in the photon storage unit can be lengthened, especially by using a storage unit with a high refractive index or a length greater than the distance between the photon-by-detector and the photon switch.

[0059] The communication unit advantageously comprises means for exchanging classical information between the two receivers, notably allowing them to exchange classical bits required for implementing quantum teleportation.

[0060] Control unit

[0061] The photon passage detector of the first receiver can comprise a control unit, notably configured to control the photon switch of the first receiver.

[0062] The photon passage detector of the second receiver can comprise a control unit, notably configured to control the photon switch of the second receiver.

[0063] The control unit of the first receiver and / or of the second receiver can comprise one or more information processors.

[0064] For example, the control unit is configured to control the electric current sent to the electro-acoustic transducer of the photon switch, to modify the refractive index of the acousto-optic material, and thus the transmission direction of the photon.

[0065] The control unit of the first receiver can be configured to order the photon switch of the first receiver to send the photon to a first quantum bit carrier outside the system, if the photon passage detector of the first receiver receives information indicating that the second receiver has received a photon entangled with said photon.

[0066] The control unit of the first receiver can be configured to order the photon switch of the first receiver to send the photon to a photon release channel of the first receiver, if the photon passage detector of the first receiver receives information indicating that the second receiver has not received a photon entangled with said photon.

[0067] The control unit of the second receiver can be configured to order the photon switch of the second receiver to send the photon to a second quantum bit carrier outside the system, if the photon passage detector of the second receiver receives information indicating that the first receiver has received a photon entangled with said photon.

[0068] The control unit of the second receiver can be configured to order the photon switch of the second receiver to send the photon to a photon release channel of the second receiver, if the photon passage detector of the second receiver receives information indicating that the first receiver has not received a photon entangled with said photon.

[0069] Antireflection layer

[0070] In order to avoid photon losses, antireflection layers are preferably arranged at the interfaces between adjacent transparent media having different refractive indices through which the photons pass, and at the interfaces of prisms and birefringent plates through which the photons pass, the antireflection layers preferably adapting to the refractive index of the material and / or to the angle of incidence and the direction of polarization, and to the wavelength of the photons that have to pass through it.

[0071] Dichroic filter

[0072] The first and / or second receiver preferably comprises one or more dichroic filters that only allow photons having a given wavelength to pass, in particular prisms made of a dispersive transparent material, in particular if the refractive index of the nonlinear material is modified by applying a strong light flux.

[0073] Method for providing an epr quantum channel

[0074] Another object of the application is to provide a method for providing an EPR quantum channel using the system described above for providing an EPR quantum channel, comprising the following steps: (a) generating from the emitter an entangled pair of photons, a first photon of the pair being emitted towards the first receiver, a second photon of the pair being preferably emitted simultaneously towards the second receiver, the first and second photons being entangled; (b) the photons being detected at each receiver by a photon pass detector possibly; (c) the photon reception times being transmitted between the two photon pass detectors of the first and second receivers; if the communication between the two photon pass detectors is shorter than the time taken by the photon switch of the receiver receiving the photons to transport the photons from the photon pass detector to that receiver, the method comprises: (d) the photons being transported from the photon pass detector to the photon switch by a single temporary storage unit of the receiver; if the photon pass detector receiving the photons receives information indicating that the other photon pass detector has already received a photon entangled with the said photon, the method comprises: (d1) the photon switch sending the photon to a quantum bit carrier outside the system; if the photon pass detector receiving the photons receives information indicating that the other photon pass detector has not yet received a photon entangled with the said photon, the method comprises: (d2) the photon switch sending the photon to a photon release path; if the communication between the two photon pass detectors is longer than the time taken by the photon switch of the receiver receiving the photons to transport the photons from the photon pass detector to that receiver, the method comprises: (e) the photon is transported from the photon passage detector to a photon switch, which sends the photon to a unit for storing a quantum bit; If the photon passage detector receiving the photon receives information indicating that another photon passage detector has received a photon entangled with said photon, the method comprises: (e1 ) if the unit for storing a quantum bit is an optical device, the switch of the unit for storing a quantum bit sends the photon to a quantum bit carrier outside the system, or if the unit for storing a quantum bit is not an optical device, the quantum bit contained in the unit for storing a quantum bit is provided to a user, wherein said providing is notified to said user, for example, by an electronic device of a receiver; If the photon passage detector receiving the photon receives information indicating that another photon passage detector has not received a photon entangled with said photon, the method comprises: (e2) the photon switch of the optical unit for storing a quantum bit sends the photon to a photon release path, or, if the unit for storing a quantum bit is not an optical device, the unit for storing a quantum bit is reset so that it is ready to receive a new photon.

[0075] Multiphoton transmission

[0076] When a photon reaches a photon passage detector, it can be counted. If the count shows that more than one photon has reached within a predetermined time interval, at least some of these photons can be transported to a photon release channel within that interval.

[0077] Assembly for teleporting quantum information

[0078] According to another aspect of the invention, it is another object of the invention to provide an assembly for teleportation of quantum information, the assembly comprising at least two systems for providing an EPR quantum channel as described above linked one after the other, and especially comprising at least one optical CNOT gate between each system.

[0079] The assembly can comprise 1 to 10 systems for providing an EPR quantum channel as described above linked one after the other.

[0080] If said systems benefit from an error correction system, the assembly can comprise 1 to 30 systems for providing an EPR quantum channel as described above linked one after the other.

[0081] The systems for providing an EPR quantum channel in the chain are preferably chained to each other in the chain by the same devices operating according to the same process.

[0082] The first photon exiting from the first system of the assembly for providing an EPR quantum channel is advantageously sent to the control port of the CNOT gate. The second photon exiting from the second system of the assembly for providing an EPR quantum channel is advantageously sent to the controlled port of the CNOT gate.

[0083] The assembly can comprise one or more devices arranged to perform a Bell measurement of the first photon and of the second photon at the output of the CNOT gate, wherein the first photon passes through a Hadamard gate at the output of the CNOT gate before its Bell measurement. Preferably, the result of this measurement is sent to a set of quantum unitary gates at the output of the last system of the chain for providing an EPR quantum channel, in particular using a communication unit associated with the two systems for providing an EPR quantum channel.

[0084] The set of quantum unitary gates at the output of the last system of the chain is preferably formed by a linear optical system that applies the following operations to the photons leaving the last system in the chain: no modification, a NOT gate, or a combination of gates (in particular a NOT gate followed by a Pauli-Z gate).

[0085] The photons exiting from the receiver of the last system of the chain for providing an EPR quantum channel are advantageously sent to a unitary gate that is the product of the quantum unitary gates obtained by each Bell measurement at the interface of each system of the chain for providing an EPR quantum channel, in the case where the receiver is not connected to any other receiver in another system.

[0086] The quantum unitary gate is in particular: if D1 = 0 and D2 = 0, the quantum unitary gate is the identity gate; if D1 = 0 and D2 = 1, the quantum unitary gate is the Pauli-Z gate; if D1 = 1 and D2 = 0, the quantum unitary gate is the NOT gate; if D1 = 1 and D2 = 1, the quantum unitary gate is the NOT gate followed by the Pauli-Z gate; wherein D1 is the measurement of the quantum state of the first photon leaving the CNOT gate through the port associated with the control photon, and D2 is the measurement of the quantum state of the second photon leaving the CNOT gate through the port associated with the controlled photon, for example if the quantum state of the photon is measured in vertical polarization, the measurement D of the quantum state of the photon is 1, and 0 if it is measured in horizontal polarization.

[0087] CNOT gate

[0088] The CNOT gate can comprise a cavity in which a neutral atom, in particular a rubidium atom, is trapped.

[0089] a first photon, which is a "control" photon, which can be linearly polarized in particular when entering the CNOT gate.

[0090] a second photon, which is a "target" photon, which is preferably linearly polarized when entering the CNOT gate. The second photon, which optionally passes through the cavity, optionally has a phase shift of π imposed on it. The CNOT gate advantageously comprises a first polarization converter, which allows to convert the polarization of the second photon into circular polarization in one direction if said photon is horizontally polarized and in the other direction if it is vertically polarized, for example, before sending the second photon to the cavity.

[0091] The CNOT gate can comprise a director arranged to direct the first photon and the second photon towards the polarization filter.

[0092] The polarization filter can be arranged to send the first photon to the mirror, in particular if it is vertically polarized, or to the cavity containing rubidium atoms, in particular if it is horizontally polarized.

[0093] The polarization filter can be arranged to send the second photon to the mirror, in particular if it is vertically polarized, or to the cavity containing rubidium atoms, in particular if it is horizontally polarized.

[0094] The external device can apply an electromagnetic pulse to the atom, causing its quantum state to change / 2.

[0095] The polarization filter can further be arranged to return the first photon and / or the second photon reflected by the mirror and / or the cavity to the director, in particular the vertically polarized component of the second photon not changing phase and the horizontally polarized component being phase shifted , thereby causing the circular polarization of the second photon to change direction.

[0096] The director can further be arranged to send the first photon to the output of the CNOT gate.

[0097] The CNOT gate advantageously comprises a second polarization converter at the output of the director for converting the circular polarization of the second photon into linear polarization.

[0098] The distances between the polarization filter and the mirror and between the polarization filter and the cavity can be adjusted so that the optical paths of the first photon and the second photon are identical when returning to the director, regardless of their reflection location (mirror or cavity).

[0099] The first polarization converter and the second polarization converter are for example quarter- wave plates adapted to the wavelength of the second photon or quarter- wave plates interposed between two outputs of two multiplexers associated with the same wavelength and adapted to said same wavelength.

[0100] The guide can be composed of an electro-controlled element, such as a liquid crystal or a Pockels cell, so as to be able to control the trajectory of the photons as a function of the date of passage of the photons.

[0101] The two photons can have different wavelengths. The guide can comprise a material and / or a dichroic filter.

[0102] Method for teleporting quantum information

[0103] Another object of the application is a method for teleportation of quantum information using an assembly for teleportation of quantum information as described above, comprising: transmitting a quantum bit from a first receiver to a second receiver, the first receiver being called the input receiver and the second receiver being called the output receiver.

[0104] The assembly for teleportation of quantum information advantageously assigns an identifier to each pair, comprising the input photon arriving at the input receiver and the output quantum bit carrier of the output end of the output receiver, and makes this identifier accessible to a user of the assembly, for example by writing it in a memory accessible to the user.

[0105] The output receiver can have an indicator that allows to inform one or more users thereof of the provision of the output quantum bit carrier associated with the photon arriving at the input receiver.

[0106] The input receiver advantageously has a register that, for each input photon whose entangled photon has been identified as having arrived at another receiver of the input system, indicates the estimated output time of the input receiver of said input photon, so that a user of the input receiver can prepare for a possible manipulation thereof.

[0107] The input receiver also advantageously indicates to the user the available time to manipulate said input photon before the entangled photon of said input photon interacts with the external carrier of the physical quantum bit or leaves said input receiver. For example, the manipulation involves the passage of the photon through a controlled non-quantum logic gate, i.e. a CNOT, or a Toffoli logic quantum gate.

[0108] If the carrier of the output quantum bit is physical and searchable, in particular by optical excitation, the output system advantageously uses a memory searchable by a user of the output receiver to store the optical reading command of the carrier of the output quantum bit with the estimated time between the arrival of the photon emitted by the carrier of the output quantum bit after optical excitation, wherein the path traveled by the photon is possibly different depending on the position of the carrier of the physical quantum bit within the output receiver.

[0109] Teleportation

[0110] Teleportation can be performed between a first quantum bit and a second quantum bit separated by a system for providing an EPR quantum channel as described above or by a component for teleporting quantum information as described above, wherein the carriers of the first and second quantum bits can be, in particular, respectively: a photon and a photon, a rubidium 87 a neutral atom and a photon, a rubidium 87 a neutral atom and another rubidium 87 a neutral atom.

[0111] Method for teleporting quantum bits carried by rubidium atoms over long distances onto photons

[0112] Another object of the application is a method for teleporting a quantum bit carried by a neutral atom, such as a rubidium atom, onto a photon over long distances using a system for providing a quantum channel as described above, comprising the following steps: - generating an entangled pair of photons from an emitter, a first photon of the pair being emitted towards a first receiver, a second photon of the pair being emitted, preferably simultaneously, towards a second receiver, the first and second photons being entangled, these photons having, in particular, a wavelength of 780 nm, the first photon encoding a quantum bit, in particular according to a linear polarization basis; - sending the first photon received by the first receiver into a CNOT gate comprising a cavity in which a neutral atom is trapped, in particular a cavity as described above; - sending an electromagnetic wave pulse in the microwave domain onto the neutral atom, thereby applying a Hadamard gate to it; - measuring the excited state of the neutral atom and the polarization of the first photon at the output of the CNOT gate; - transmitting the measurements to the second receiver; - modifying the polarization of the second photon according to the measurements of the state of the neutral atom and of the polarization direction of the first photon, i.e. the state 0 or 1 of the quantum bit carried by each of them.

[0113] If the measurement of the quantum bit carried by the neutral atom is 0 and the measurement of the quantum bit carried by the first photon is 0, i.e. it is, for example, vertically polarized, no operation is applied to the second photon.

[0114] If the measurement of the quantum bit carried by the neutral atom is 0 and the measurement of the quantum bit carried by the first photon is 1, i.e. it is, for example, horizontally polarized, the second photon can be sent through a Pauli-Z gate.

[0115] If the measurement of the quantum bit carried by the neutral atom is 1 and the measurement of the quantum bit carried by the first photon is 0, i.e. it is, for example, horizontally polarized, the second photon can be sent through a NOT gate.

[0116] If the measurement of the quantum bit carried by the neutral atom is 1 and the measurement of the quantum bit carried by the first photon is 1, i.e. it is for example horizontally polarized, the second photon can be sent through a CNOT gate and a Pauli-Z gate in this order.

[0117] For example, the CNOT gate consists of two birefringent prisms and two half- wave plates.

[0118] For example, the Pauli-Z gate consists of a half-wave plate.

[0119] Method for teleporting quantum bits carried by a first neutral atom onto a second neutral atom

[0120] Another object of the application is a method for teleportation of a quantum bit carried by a first neutral atom, such as a rubidium atom, onto a second neutral atom, such as a rubidium atom, over a long distance, using a system for providing a quantum channel as described above, comprising the following steps: - generating an entangled pair of photons from the emitter, a first photon of the pair being emitted towards the first receiver, a second photon of the pair being emitted, preferably simultaneously, towards the second receiver, the first and second photons being entangled, these photons having in particular a wavelength of 780 nm, the first photon encoding in particular a quantum bit according to the linear polarization basis; - exciting the first neutral atom located at the first receiver until it emits a photon, and directing the emitted photon towards the control port of a first CNOT control gate, then to a first Hadamard gate; - sending the first photon of the entangled pair of photons to the controlled port of the first CNOT gate; - measuring the polarization direction of the photon emitted by the first neutral atom at the output of the Hadamard gate and the polarization direction of the first photon at the output of the CNOT gate; - transmitting the measurements to the second receiver; - modifying the polarization of the second photon received by the second receiver in the entangled pair of photons according to the measurements of the state of the neutral atom and of the polarization direction of the first photon, i.e. the state 0 or 1 of the quantum bit carried by each; - sending the modified second photon to the control port of a second CNOT gate, then to a second Hadamard gate; - exciting the second neutral atom located at the second receiver until it emits a photon, and directing the emitted photon towards the controlled port of the second CNOT gate; - measuring the polarization direction of the photon emitted by the second neutral atom at the output of the second CNOT gate and the polarization direction of the second photon at the output of the second Hadamard gate; - sending at least one microwave electromagnetic pulse onto the second neutral atom in order to apply to it a quantum unitary gate, characterized in particular as follows: If the measured value of the polarization direction of the photon emitted by the second neutral atom is 0, and the measured value of the polarization direction of the second photon is 0, then for example, no operation is applied to the second neutral atom; If the measured value of the polarization direction of the photon emitted by the second neutral atom is 1, and the measured value of the polarization direction of the second photon is 0, then the Pauli-Z gate can be applied to the second neutral atom. If the measured value of the polarization direction of the photon emitted by the second neutral atom is 0, and the measured value of the polarization direction of the second photon is 1, then a NOT gate can be applied to the second neutral atom. If the measured value of the polarization direction of the photon emitted by the second neutral atom is 1, and the measured value of the polarization direction of the second photon is 1, then the NOT gate and the Pauli-Z gate can be applied to the second neutral atom accordingly.

[0121] Alternatively, the entangled photons emitted by the transmitter have a wavelength different from 780 nm, and are converted to 780 nm photons by a mixer before reaching the photon receiver, for example, as in the paper titled "..." published in Physical Review on October 26, 2022. Entanglement between a trapped ion qubit and a 780-nm photon via quantum frequency conversion As stated in the article.

[0122] Method for teleporting quantum bits carried by carriers of physical quantum bits in parallel to realize error correction algorithm when transmitting quantum bits using a communication system Figure 1

[0123] Another object of the present invention is a method for teleporting qubits carried by a carrier of physical qubits in parallel, to implement an error correction algorithm during qubit transmission. This method uses the system described above for providing an EPR quantum channel, and includes: - Emit entangled photon pairs, wherein the first photon in each pair is emitted toward a first receiver, and the second photon in each pair is preferably emitted simultaneously toward a second receiver, each receiver containing at least one neutral atom (e.g., a rubidium atom), such as nine neutral atoms, one or more neutral atoms being arranged to be able to emit photons and having a quantum unitary gate applied thereto, wherein each neutral atom of one receiver is paired with a neutral atom of the other receiver; - At each receiver, a photon emitted by a neutral atom of the receiver is simultaneously sent to a single photon pass detector of the receiver (the single photon pass detector is located upstream of a single CNOT gate of the receiver) until the neutral atom of the receiver has become entangled with a neutral atom paired with it in another receiver; - Once each neutral atom pair is entangled, an error reduction algorithm is applied, such as the Schor algorithm. BRIEF DESCRIPTION OF DRAWINGS

[0124] The application will be better understood by reading the following detailed description of non-limiting embodiments of the application, given only by way of example, and in reference to the attached drawings, wherein: Figure 2 A system for providing an EPR quantum channel according to the application is schematically and partially described; Figure 3A Another system for providing an EPR quantum channel according to the application is schematically and partially described; Figure 3B An example of a CNOT gate adapted for linearly polarized photons is schematically and partially described; Figure 3C An example of a CNOT gate adapted for circularly polarized photons is schematically and partially described; Figure 3D An example of a CNOT gate between two non-synchronized photons with wavelengths close to 780 nm is schematically and partially described; Figure 3E An example of storing a quantum bit carried by a photon in a rubidium atom is schematically and partially described; Figure 4 An example of extracting a quantum bit carried by a rubidium atom to a photon is schematically and partially described; Figure 5 A method for teleporting quantum information from a quantum memory consisting of rubidium atoms Rb located in a first receiver to a second receiver according to the application is schematically and partially described; Figure 6 A method for teleporting quantum information to a quantum memory consisting of neutral atoms according to the application is schematically and partially described; Figure 7 An assembly for teleporting quantum information according to the application is schematically and partially described; Figure 1 A method for teleporting nine quantum bits carried by the carriers of physical quantum bits in parallel to allow the implementation of a Schor algorithm to correct errors during the transmission of quantum bits using a system of Figure 8 Figure 9 A method for generating entangled photons from the polarization of entangled photons is schematically and partially described; Figure 10 A method for measuring the result of the teleportation of quantum information is schematically and partially described; Figure 11 ​It is schematically and partially described to transfer a database stored in a memory of a computer to a quantum memory of the same computer; and Figure 1 It is schematically and partially described an optical cavity with interchangeable atoms. DETAILED DESCRIPTION

[0125] Shaping frequency entangled qubits A system 1 for providing an EPR quantum channel according to the present application is shown. The system comprises an emitter 2 of pairs of entangled photons (P1, P2), wherein a first photon P1 propagates on a propagation path C1 and a second photon C2 propagates on a propagation path C2 different from path C1.

[0126] Due to the nature of light and the wave-particle duality of photons, the terms "wave", "electromagnetic wave", "photon", and "particle" can be used interchangeably hereinafter to designate the product emitted by the emitter 2.

[0127] The system 1 comprises a first receiver 3 located on the propagation path C1 of the first photon P1 and a second receiver 4 located on the propagation path C2 of the second photon P2. The photons P1 and P2 are preferably emitted simultaneously and the paths C1 and C2 preferably have the same length, i.e. the photons P1 and P2 emitted by the emitter 2 are entangled when they reach, preferably simultaneously, the receivers 3 and 4.

[0128] In the example considered, the receiver 3 comprises a photon passage detector 31, a photon switch 32, photon storage units 33a to 33c, and a photon release path 34.

[0129] The receiver 4 comprises a photon passage detector 41, a photon switch 42, photon storage units 43a to 43c, and a photon release path 44.

[0130] The photon storage units 33a to 33c and 43a to 43c are for example optical fibers, which preferably have the same length, in particular a length between 1 mm and 200 m. The shorter the length of the optical fibers, the faster the photon reaches the user. The longer the length of the optical fibers, the more time there is to inform the user of the arrival of the photon.

[0131] The transmission of the photons P1 and P2 between the emitter and the first receiver and the second receiver, respectively, can occur in different ways and in different media. For example, the photons propagate in optical fibers or waveguides, or even freely in space, where this space is a vacuum or filled with a gas.

[0132] Photons can cross a plurality of media of different refractive indices. For example, an anti-reflection plate can be inserted between two crossed media, if applicable, to avoid unwanted optical phenomena, in particular Fresnel reflections of the waves emitted by the emitter 2.

[0133] Advantageously, an optical correction device (not shown) can be provided upstream of the passage of the photons through the detectors 31 and 41. The optical correction device is preferably arranged to correct the distortions undergone by the photons between the emitter 2 and said optical correction device. Indeed, when the photons travel on the paths CI and C2, their polarization and shape can both undergo changes. The optical correction device advantageously has phase and photon shape detectors, which are used in particular for photons that said detectors can absorb, so that these photons do not transmit to the photon passage detectors 31 or 41. For example, the phase and photon shape detectors operate intermittently on a sample of incident photons.

[0134] For example, the wavelength of the emitted waves is chosen as a function of the medium or media to be crossed; for example, when the photons must cross the atmosphere or air, it is preferable to use photons in the infrared range.

[0135] The emitter 2 generates pairs of entangled photons, for example by the method of spontaneous parametric conversion (SPDC). Alternatively, the emitter 2 can generate pairs of entangled photons by a CNOT gate, two photons having crossed an optical Hadamard gate being injected into the CNOT gate. The emitter 2 is for example configured to emit at least one pair per unit of time (for example per nanosecond, which corresponds to a photon transmission frequency of 1 GHz).

[0136] The photons PI and P2 are entangled as a function of their polarization. As a variant, the photons PI and P2 can be entangled as a function of their wavelength, as described in the article entitled "Entanglement of the orbital angular momentum of photons", by C. Bernhard, B. Bessire, T. Feurer, A. Stefanov, Physical Review A, vol. 88, 2013. Figure 2 The photons PI and P2 can also be entangled in time (so-called "time-bin" entangled photons).

[0137] When they are emitted, the photons PI and P2 are for example linearly polarized, i.e. the corresponding electromagnetic waves have an electric field with a direction perpendicular to the propagation direction CI or C2 of the photons. The polarization direction is preferably fixed, for example horizontal, so as to allow the devices 30 and 40 to detect and modify any disturbance imposed to said polarization when the photons travel from the emitter 2.

[0138] As long as they are not measured or absorbed, the quantum state corresponding to the polarization of the photons is sometimes indeterminate. Thus, before the measurement, the quantum state of the photons is sometimes considered to be a superposition of possible states, i.e. in the example considered, a polarization at an angle of 45° and a polarization at an angle of -45°.

[0139] As a variant, the emitted photons P1 and P2 are circularly polarized, i.e. the direction of the corresponding electric field varies with a rotational movement, while its modulus remains constant.

[0140] In the considered example, the photon switch 32 is configured to send the photons P1 received by the receiver 3 to the photon storage units 33a, 33b or 33c, and the photon switch 42 is configured to send the photons P2 received by the receiver 4 to the photon storage units 43a, 43b or 43c, wherein the number of photon storage units per receiver is not limited, said storage units being selected by the controller 310 or 410.

[0141] The storage units 33a to 33c, or 43a to 43c, are configured to store the photons P1 or P2 while waiting for said photons to be delivered to one or more users.

[0142] The release channel 34 or 44 is configured to release a photon received by a receiver when the entangled photon P2 of said photon P1 or the entangled photon P1 of said photon P2 has not been received by another receiver.

[0143] Each photon pass detector 31 and 41 comprises a control unit 310 and 410, respectively, and a communication unit 311 and 411, respectively.

[0144] The photon pass detectors 31 and 41 detect the passage of a photon P1 or P2, respectively, and transmit this information to the control units 310 and 410, respectively.

[0145] The control units 310 and 410 each have a clock (not shown), which is preferably synchronized. The control units 310 and 410 communicate with each other via the communication units 311 and 411.

[0146] The two communication units 311 and 411 communicate with each other via the communication system 5, in particular to exchange the reception times of the photons P1 and P2. Exchanging the reception times of the photons allows each of the receivers 3 and 4 that has received a first photon to determine whether the other receiver has received a photon entangled with this first photon.

[0147] The communication system 5 is preferably a communication system as described in patent FR 3125658, or, alternatively, it is an optical communication system (in particular a communication system using optical fibers), a radio communication system, or a power line communication system.

[0148] The control units 310 and 410 are in particular configured to control the photon switches 32 and 42. The control units 310 and 410 are configured to control, for example, the electric current sent to the electroacoustic transducers of the photon switches 32 and 42, in order to modify the refractive index of the acousto-optic material, and thus the direction of transmission of the photons.

[0149] The control unit 310 or 410 can be configured to command the photonic switch 32 or 42 to send the photon to the photonic release channel 34 or 44 if the photon receives information through the detector 31 or 41 indicating that another receiver has not received a photon entangled with said photon.

[0150] As a variant, as shown in Figure 3D The control unit 310 or 410 can be configured to command the switch 32 or 42 to sequentially send the quantum bits carried by the photons P1 or P2 to the quantum bit carrier group 33 incorporating the quantum bit carriers 33a, 33b and 33c, or to the quantum bit carrier group 43 incorporating the quantum bit carriers 43a, 43b and 43c. The control unit 310 or 410 can then be configured to command the system (not shown) surrounding said quantum bit carriers to implement a process for transferring the quantum bits carried by the photons sent to said quantum bit carriers onto said quantum bit carriers themselves, for example as shown in Figure 3E .

[0151] Since the communication units 311 and 411 have communicated with each other, the control units 310 and 410 can then determine that such quantum bits carried by such quantum bit carriers 33a to 33c and 43a to 43c are entangled with the quantum bits of the other receiver. The control units 310 and 410 can then inform the user of the availability of such quantum bits.

[0152] The controllers 35 and 45 can then extract the quantum bits identified as having quantum bits entangled with the other receiver, for example according to the user's request, for example by the process shown in Figures 3A to 3C .

[0153] Figure 3A An example of a CNOT gate is shown.

[0154] A photon- A CNOT gate adapted for linearly polarized photons is shown, for quantum bits encoding photons on a linear polarization basis, converting two quantum bits, quantum bit 0 and quantum bit 1, into two other quantum bits, quantum bit 2 and quantum bit 3, where quantum bit 2 = quantum bit 0, quantum bit 3 = quantum bit 1, unless quantum bit 0 = 1, in which case quantum bit 3 = 0 if quantum bit 1 = 1; quantum bit 3 = 1 if quantum bit 1 = 0.

[0155] The first incident photon Ph1 is a "control" photon and is linearly polarized, which enters the flip control gate CFLIP through the control photon input end E0, in particular as described in the Max Planck Institute 2017 publication entitled "A photonic quantum information processor based on linear optics" by M. Halder et al. photon quantum gate based on a single atom in an optical resonatorFigure 3B as described in the article entitled "Experimental realization of a universal entangling gate operated by a single trained photon", Phys. Rev. Lett. 91, 147901 (2003).

[0156] If the second photon Ph2 is horizontally polarized, it is converted by the polarization converter Conv1 into a circularly polarized photon in one direction, or if the second photon Ph2 is vertically polarized, it is converted by the polarization converter Conv1 into a circularly polarized photon in the other direction.

[0157] The control photon Ph1 exiting the CFLIP gate is sent to the output SO. If the photon Ph1 is vertically polarized, the CFLIP gate allows the second photon Ph2 to exit in the same circularly polarized state, or if the photon Ph1 is horizontally polarized, it allows the second photon Ph2 to exit circularly polarized in the other direction.

[0158] The circularly polarized photon Ph2 is then converted by the converter Conv2 into a linearly polarized photon.

[0159] Figure 3C A CNOT gate is shown, suitable for circularly polarized photons, for encoding a photon on a circularly polarized basis, converting two qubits, qubit 0 and qubit 1, into two other qubits, qubit 2 and qubit 3, where qubit 2 = qubit 0, qubit 3 = qubit 1, unless qubit 0 = 1, in which case qubit 3 = 0 if qubit 1 = 1; qubit 3 = 1 if qubit 1 = 0.

[0160] The first photon Ph1 incident is the "control" photon and is circularly polarized, it is converted by the polarization converter Conv3 into a linearly polarized photon, which then passes through the control photon input of the flip control gate CFLIP.

[0161] The control photon Ph1 exiting the CFLIP gate is sent to the polarization converter Conv4, which converts it into a circularly polarized photon.

[0162] The second photon Ph2 is sent through the controlled input of the CFLIP gate, which exits from this input in circular polarization in the same direction or in the opposite direction to the polarization direction of the photon Ph1 that has already passed through the CFLIP gate.

[0163] Figure 3C A CNOT gate is shown between two non-synchronized photons of wavelength close to 780 nm, which carry qubits encoded according to linear polarization (qubit 0 and qubit 1) and a photon of wavelength close to 810 nm, which carries a qubit encoded according to circular polarization (qubit 2). Scalable Photonic Quantum Computation through Cavity-Assisted The CNOT gate shown in Fig. 1 is inspired by the article entitled "Experimental realization of a universal entangling gate operated by a single trained photon", Phys. Rev. Lett. 91, 147901 (2003). Interactions Figure 3D The article entitled "Experimental realization of a universal entangling gate operated by a single trained photon", Phys. Rev. Lett. 91, 147901 (2003).

[0164] The first photon Phl is a "control" photon and is linearly polarized, it enters the CNOT gate at E0. It is guided by the director Ot to the polarization filter Fp which sends it to the mirror Ma if it is vertically polarized or to the cavity Cv containing the rubidium atom Rb if it is horizontally polarized.

[0165] An electromagnetic pulse is applied to the atom Rb, which changes its quantum state / 2.

[0166] Then the photon Phl reflected by the mirror Ma or the cavity Cv is returned by the polarization filter Fp to the director Ot which orients it towards the output So.

[0167] The second photon Ph2 enters the CNOT gate at El. If the photon Ph2 is horizontally polarized, its polarization is converted in one direction to circular polarization by the polarization converter Convl, if it is vertically polarized, it is converted in the other direction to circular polarization.

[0168] The director Ot sends the circularly polarized photon Ph2 to the polarization filter Fp which reflects the vertical component of the polarization without changing the phase but reflects the horizontal component with a phase shift of , thus changing the direction of the circular polarization of the photon Ph2.

[0169] Then the circularly polarized photon Ph2 is converted to a linearly polarized photon by the converter Conv2.

[0170] The distances between the polarization filter Fp and the mirror Ma and between the polarization filter Fp and the cavity Cv are adjusted so that the optical paths of the photons Phl and Ph2 are the same when they return to the director Ot, regardless of their reflection position, mirror Ma or cavity Cv.

[0171] The polarization converters Convl and Conv2 are for example quarter- wave plates adapted to the wavelength of the photon Ph2 or quarter- wave plates interposed between two outputs of two multiplexers associated with the same wavelength and adapted to said same wavelength.

[0172] The director Ot can be composed of electrically controlled elements such as liquid crystals or Pockels cells in order to be able to control the trajectory of the photons according to the date of their passage.

[0173] The wavelengths of the two photons Phl and Ph2 can be different, the director Ot can also comprise materials and / or dichroic filters.

[0174] Figure 3E It is shown that the quantum bits carried by the photons are stored in rubidium 87Method in a quantum memory on an atom Rb. An incoming photon Ph carrying a quantum bit is sent to the control port 50 of a CNOT gate, then to a Hadamard gate H at the output of the CNOT gate. After the passage of the photon Ph through the CNOT gate, the atom Rb is excited by optical pumping by a laser Ls until the passage of the photon is detected by a detector DP. The photon is then directed towards the controlled port 60 of the CNOT gate. A Bell measurement is then performed on the incoming photon Ph and the photon Ph' controlled by the polarisation detectors D and D'. One or more microwave electromagnetic pulses EM are then sent by the antenna 4 on the atom Rb in order to apply a quantum gate thereon. The quantum gate is characterised as follows: - if D=0 and D'=0, the quantum gate is the identity gate; - if D=0 and D'=1, the quantum gate is the NOT gate; - if D=1 and D'=0, the quantum gate is the Pauli-Z gate; - if D=1 and D'=1, the quantum gate is the NOT gate followed by the Pauli-Z gate.

[0175] Figure 4 A method for extracting a quantum bit carried by a rubidium atom Rb onto a photon is shown. 87 A method for extracting a quantum bit carried by a rubidium atom Rb onto a photon is shown.

[0176] Figure 5 A method for providing an EPR quantum channel using the system 1 according to the application is shown, more specifically, the long distance teleportation of a quantum bit from a quantum memory consisting of a rubidium atom Rb located in the receiver 3 onto a photon is shown.

[0177] The rubidium atom is in a combination of two Rydberg states, namely F=1; mF=1 and F=2; mF=2, which represent the low and high energy states of the associated atom on which the quantum bit is encoded, respectively.

[0178] The system 1 for providing an EPR quantum channel sends from its receiver 3 a first photon P1 of wavelength 780 nm encoding a quantum bit according to the linear polarisation basis, entangled with another photon P2 on the path towards the receiver 4. The receiver 3 informs the director Ot of the arrival of the photon P1.

[0179] The photon P1 crosses a polarization converter Conv1 which converts the linear polarization of the photon into a circular polarization. Then, a director Ot directs the photon P1 towards a polarization filter FP which sends it to a mirror Ma if the photon P1 is vertically polarized or to a cavity Cv containing rubidium atoms Rb if the photon P1 is horizontally polarized.

[0180] Then, the photon P1 reflected by the mirror Ma or the cavity Cv returns through the polarization filter FP to the director Ot which orients it towards a polarization converter Conv2 which converts the circular polarization of the photon into a linear polarization.

[0181] One or more pulses of electromagnetic waves in the microwave range are sent to the rubidium atoms, thereby applying a Hadamard gate to them.

[0182] Then, a measurement of the excited state of the rubidium atom Rb and a measurement of the polarization of the photon are made by a photon detector D1. These measurements are sent to the receiver 4, then to the system 1 for providing an EPR quantum channel, then to the second line TL2, by direct communication line TL or by first line TL1.

[0183] According to the measurements of the state of the rubidium atom Rb and of the polarization direction of the photon P1, i.e. of the state 0 or 1 of the quantum bit carried by each of them, the polarization modifier MP actuates the two switches Cm1 and Cm2 before the photon P2 emitted from the second receiver 4 reaches them, making the photon P2 cross the combination of devices Dp1, Dp2 and Dp3, thereby allowing an operation to be performed on the photon P2.

[0184] If the measurement of the quantum bit carried by the rubidium atom is 0 and the measurement of the quantum bit carried by the photon P1 is 0, i.e. it is vertically polarized, no operation is applied to the photon P2.

[0185] If the measurement of the quantum bit carried by the rubidium atom is 0 and the measurement of the quantum bit carried by the photon P1 is 1, i.e. it is horizontally polarized, the photon P2 is sent through a Pauli-Z gate.

[0186] If the measurement of the quantum bit carried by the rubidium atom is 1 and the measurement of the quantum bit carried by the photon P1 is 0, i.e. it is horizontally polarized, the photon P2 is sent through a NOT gate.

[0187] If the measurement of the quantum bit carried by the rubidium atom is 1 and the measurement of the quantum bit carried by the photon P1 is 1, i.e. it is horizontally polarized, the photon P2 is sent through a NOT gate followed by a Pauli-Z gate.

[0188] For example, the NOT gate consists of two birefringent prisms and two half- wave plates.

[0189] For example, the Pauli-Z gate is composed of a half-wave plate.

[0190] ​ A method for providing an EPR quantum channel using the system 1 according to the present application is shown, more specifically, a method for teleporting quantum information using the system 1 to a quantum memory composed of neutral atoms.

[0191] The first rubidium atom Rb1 is excited until a photon Ph is detected by the detector DP1 and is guided towards the control port 50 of the first control gate CNOT1, which sends it, as described above, to the Hadamard gate H, whose polarization direction is then measured by the photon detector D1.

[0192] The receiver 3 of the system 1 sends the first photon P1 having a wavelength of 780 nm to the controlled port 60 of the gate CNOT1, which modifies the first photon P1, whose linear polarization direction is then measured by the photon detector D2.

[0193] The receiver 4 of the system 1 sends the second photon P2 entangled with the first photon P1 to the phase modifier MP, which, as described above, changes the polarization of the second photon P2 according to the measurements of the detectors D1 and D2.

[0194] The second photon P2 is then guided towards the control port 50 of the second gate CNOT2, which, as described above, operates at a wavelength of 780 nm, after which it passes through the Hadamard gate H and its polarization direction is measured by the photon detector D3.

[0195] The second atom Rb2 is excited until the passage of the photon Ph' is detected by the second passage detector DP2, which is then guided towards the controlled port 60 of the second gate CNOT2, after which its linear polarization direction is measured by the photon detector D4.

[0196] One or more microwave electromagnetic pulses are sent onto the second atom Rb2 in order to apply to it a quantum unitary gate characterized as follows: - if D3=0 and D4=0, the quantum unitary gate is the identity gate; - if D3=0 and D4=1, the quantum unitary gate is the Pauli-Z gate; - if D3=1 and D4=0, the quantum unitary gate is the NOT gate; - if D3=1 and D4=1, the quantum unitary gate is the NOT gate followed by the Pauli-Z gate.

[0197] Alternatively, the entangled photons emitted by the photon emitter 2 have a wavelength different from 780 nm and are converted into photons at 780 nm by a frequency mixer before they reach the photon receivers 3 and 4, for example as described in the article entitled “ Entanglement between a trapped ion qubit and a 780-nm photon via quantum frequency conversion ” published on October 26, 2022 in Physical Review.

[0198] The plurality of systems 1 for providing an EPR quantum channel can be concatenated to each other to form an assembly for teleportation of quantum information, allowing the transport of quantum bits over very long distances, for example over 1000 km, using optical fibers. Figure 6 An assembly for providing an EPR quantum channel is shown, comprising two systems 1a and 1b for providing an EPR quantum channel.

[0199] The first system for providing an EPR quantum channel provides the receivers 3a and 4a with two entangled photons P1a and P2a.

[0200] As mentioned above, the photon P2a is directed towards the control port 50 of a CNOT gate operating, for example, in the linear polarization basis.

[0201] The photon P2a exits the CNOT gate so as to pass through the Hadamard gate H, after which its polarization direction is measured by the photon detector Da.

[0202] The controlled port 60 of the CNOT gate is supplied with a third photon P1b originating from the receiver 3b, which is itself entangled with a fourth photon P2b leaving the receiver 4b and provided by the second system 1b for providing an EPR quantum channel.

[0203] The third photon P2b is modified in the CNOT gate, after which its polarization direction is measured by the photon detector Db.

[0204] The measurement results are sent to the polarization modifier MPb through the direct data transmission line TL or through the transmission line TL1 and the transmission line TL2 of the second system 1b.

[0205] The fourth photon P2b leaves the receiver 4b so as to advance towards the polarization modifier MPb.

[0206] According to the measurements of the polarization directions in Da and Db, and therefore according to the state 0 or 1 of each quantum bit carried by the photons P2a and P1b, the polarization modifier MPb actuates the two switches Cm1 and Cm2 before the photon P2b originating from the second receiver 4b reaches them, making the photon P2b pass through the combination of devices Dp1, Dp2, Dp3, allowing the photon P2b to be operated on.

[0207] If the measurement of P2a is 0 and the measurement of P1 b is 0, no operation is applied to the photon P2b.

[0208] If the measurement of P2a is 0 and the measurement of P1 b is 1, the photon P2b is sent through a Pauli-Z gate.

[0209] If the measurement of P2a is 1 and the measurement of P1 b is 0, the photon P2b is sent through a CNOT gate.

[0210] If the measurement of P2a is 1 and the measurement of P1 b is 1, the photon P2b is sent through a CNOT gate and then through a Pauli-Z gate.

[0211] The system thus formed therefore provides the user of the receiver 3a with two entangled photons P1 a and P2b at the output of the polarisation modifier MPb.

[0212] More than two systems for providing an EPR quantum channel according to the application can be linked one after the other to form a quantum transmission chain, each end of which provides a user with a photon entangled with the photon reaching the other end of the chain.

[0213] Figure 7 The emitter 2 of entangled photons is shown sending a pair of entangled photons P1 and P2 to the receivers 3 and 4, which also have a direct transmission line TL, allowing them to exchange conventional information.

[0214] Each receiver 3 and 4 contains, for example, nine rubidium 87 atoms Rb, which are arranged to be able to emit photons and have quantum unitary gates applied to them.

[0215] Each atom Rb of the receiver 3 or 4 is paired with an atom Rb of the other receiver 4 or 3.

[0216] Optical switches (not shown) present on each receiver 3 and 4 allow the photons emitted by any one of the atoms Rb of the receiver to be directed towards a single photon pass detector (not shown) upstream of a single CNOT gate arranged in each of the two receivers.

[0217] The said optical switches of the two receivers 3 and 4 are actuated simultaneously in order to send, within each receiver, the photons emitted by one of the atoms Rb to the photon pass detector until the said atom Rb has entangled with the atom Rb with which it is paired in the other receiver.

[0218] Once each of the nine pairs of atoms Rb has been entangled, an error reduction algorithm, such as the Schor algorithm, can be applied, and then the two receivers 3 and 4 are able to use the same means TL as the communication system uses for transmitting conventional information.

[0219] Figure 8 A method for producing entangled photons is shown. A vertically polarized photon emitter 2 is excited to emit a first photon P1. This first photon P1 passes through a Hadamard gate H, such as a half-wave plate, before reaching the input of a CNOT gate as control photon.

[0220] The photon emitter 2 emits a second vertically polarized photon P2, which is directed towards the controlled port 60 of the CNOT gate.

[0221] The photons P1 and P2 leaving at SO and S1 are entangled and can be used as entangled photons in the system 1.

[0222] Figure 9 A method for measuring the result of the teleportation of a quantum bit of quantum information is shown. This method allows the probability that the quantum bit carried by the photon is read as state 0 or 1 to be measured instantaneously. The particle on which the quantum bit has been teleported, for example a rubidium 87 The atoms Rb or ytterbium ions are stimulated to emit a photon P entangled with them. The photon P is demultiplexed by an optical amplifier 13, for example an erbium-doped fiber amplifier, which preserves its polarization, to form a photon flux F. As mentioned above, the polarization of the photon flux F is measured by a conventional polarization detector D.

[0223] For example, a horizontal polarization indicates that the quantum bit carried by the particle is in state 0, while a vertical polarization indicates that it is in state 1, and an intermediate polarization indicates that the quantum bit is in an indeterminate state.

[0224] Figure 10 A process is shown for transferring a conventional database to a quantum computer 10, the conventional data of which are distributed on three different computers 7, 8 and 9.

[0225] The computers 7, 8 and 9 respectively transfer their conventional data to respective quantum memories 71, 81 and 91, and then the quantum memories of the quantum computers 7, 8 and 9 are transferred to the quantum bit carriers forming the quantum memory 11 of the quantum computer 10 by the method for teleporting quantum information according to the invention.

[0226] The quantum computer 10 can then poll the reconstructed database in its quantum memory 11.

[0227] The photonic switch 32 or 42 can be an optical microcavity 12, i.e. a cavity formed by a reflective surface 13 surrounding an optical medium, which is notably configured to be used as an optical CNOT gate, as shown in Figure 11 The atom that has to interact with each photon is successively delivered into the cavity. At least two holes 14 are formed in the cavity to allow at least two light rays 15 emitted by the laser 16 to pass through, which act as optical tweezers allowing the atom to be delivered and placed inside the cavity. The use of optical tweezers notably allows the atom to be moved after interacting with a first one of the two photons for which the CNOT operation has to be implemented. This atom can notably be moved into another cavity and can be replaced by a new atom, allowing a new photon to be received, which carries the qubit used as the control qubit of another optical CNOT gate. This cavity notably comprises a hole 17 allowing the passage of the photon carrying the incident qubit. It also comprises an input / output end 18 for the atom in the cavity and the photons emitted by the atom, said atom moving along an axis 19.

Claims

1. A system for providing an EPR quantum channel, comprising: An entangled photon emitter, the emitter including a source configured to generate at least one entangled photon pair, the at least one entangled photon pair including a first photon emitted on a first propagation path and a second photon emitted simultaneously on a second propagation path different from the first propagation path; A first receiver, disposed on the first propagation path, includes: - At least one unit for storing qubits, said unit being arranged to store qubits carried by photons received by the first receiver; - A photonic switch, the photonic switch being arranged to transmit photons received by the first receiver to the storage unit; - A photon passes through a detector, which is configured to monitor the photon switching and record the time when the first receiver receives a photon; A second receiver, positioned along the second propagation path to be reached by the second photon, comprises: - At least one unit for storing qubits, the unit being arranged to store qubits carried by photons received by the second receiver; - A photonic switch, which is arranged to send photons received by the second receiver to the storage unit; - A photon passes through a detector configured to monitor the photon switch and record the time when the second receiver receives the photon; Includes at least one information processor, such as an electronic microprocessor, in the first receiver and / or the second receiver, said at least one information processor being arranged to control a photonic switch of the receiver; A communication system that connects two receivers together, the communication system being particularly arranged to notify the information processor of the reception time of photons at the first and second receivers, in order to determine that both photons of the entangled photon pair have arrived at the receiver to which they were sent.

2. The system as claimed in the preceding claim, wherein, The storage units of the first receiver and / or the second receiver are selected from the following: optical paths, especially optical fibers or spatial pathways arranged using mirrors, or carriers of physical qubits, especially ions that indirectly interact with incident photons.

3. The system as described in any one of claims 1 and 2, wherein, Each storage unit can maintain a qubit for a duration greater than the time difference between the arrival of two entangled photons at the two receivers, which also includes the following times: the time spent by the communication system transmitting information related to the arrival time of the entangled photons, the time required for the processor to determine whether the two entangled qubits exist in one storage unit of the receiver, and the time spent by the processor sending a notification to the interface of the receiver.

4. The system as described in any of the preceding claims, wherein, The photonic switch of the first receiver and / or the second receiver is an optical micro-resonant cavity, i.e., a cavity formed by an optical medium surrounded by a reflective surface, in which atoms for interaction with each photon are continuously transported. In particular, at least two holes are formed in the cavity to allow at least two rays of light to pass through, which act as optical tweezers and allow the atoms to be transported and positioned within the cavity.

5. The system as described in any one of the preceding claims, wherein, The photon-pass detector of the first receiver and / or the second receiver includes a non-destructive photonic qubit detector, which, for example, uses a parameter transformation of the incident photon to generate two lower frequency photons from a single photon, wherein one of the generated photons indicates the presence of a qubit, and the other photon provides information related to the qubit.

6. The system as described in any one of claims 1 to 4, wherein, The photon-pass detector of the first receiver and / or the second receiver includes a non-destructive photonic qubit detector, which includes a QED cavity in which rubidium atoms are trapped.

7. A method for providing an EPR quantum channel using a system for providing an EPR quantum channel as described in any of the preceding claims, comprising the following steps: (a) An entangled photon pair is generated from the transmitter, wherein a first photon in the pair is emitted toward a first receiver and a second photon in the pair is simultaneously emitted toward a second receiver, and the first photon and the second photon are entangled; (b) The detector can detect the arrival of photons at each receiver; (c) The photon reception time is transmitted between the detectors for two photons from the first receiver and the second receiver; If the communication between two photons through the detector is shorter than the time taken for the photons received by the receiver to travel from the photons through the detector to the photon switch of the receiver, then the method includes: (d) The photons are transmitted from the photons to the photon switch via a detector through a single temporary storage unit of the receiver; If the photon receiving the photon receives information through a detector indicating that another photon has received a photon entangled with the photon, then the method includes: (d1) The photonic switch sends the photons to a quantum bit carrier outside the system; If the photon receiving the photon receives information through the detector indicating that the other photon has not yet received a photon entangled with the photon, then the method includes: (d2) The photon switch sends the photon to the photon release path; If the communication between two photons through the detector takes longer than the time it takes for the photons received by the receiver to travel from the photons through the detector to the photon switch of the receiver, then the method includes: (e) The photon is transmitted from the photon through a detector to the photon switch, which sends the photon to a cell for storing qubits; If the photon receiving the photon receives information through the detector indicating that another photon has received a photon entangled with the photon, then the method includes: (e1) If the unit for storing qubits is a device, then the switch of the unit for storing qubits sends the photon to a qubit carrier outside the system; or if the unit for storing qubits is not an optical device, then the qubits contained in the unit for storing qubits are provided to the user, wherein the user is notified of the provision, for example, through an electronic device of the receiver. If the photon receiving the photon receives information from the detector indicating that the other photon has not yet received a photon entangled with the photon, then the method includes: (e2) The photon switch of the optical unit for storing qubits sends the photon to the photon release path, or, if the unit for storing qubits is not an optical device, the unit for storing qubits is reset to be ready to receive new photons.

8. A component for teleporting quantum information, comprising at least two systems for providing an EPR quantum channel as described in any one of claims 1 to 6, linked one after the other, said component comprising at least one optical CNOT gate between each system, wherein, A first photon emitted from the first system of the component for providing an EPR quantum channel is sent to the control port (50) of the CNOT gate, and a second photon emitted from the second system of the component after the first system for providing an EPR quantum channel is sent to the controlled port (60) of the CNOT gate.

9. The component as claimed in the preceding claim, wherein, A Bell measurement is performed on the first photon and the second photon at the output of the CNOT gate, the first photon passing through a Hadamard gate at the output of the CNOT gate before its Bell measurement, wherein the result of the measurement is sent to a set of quantum unitary gates at the output of the last system in the chain that provides the EPR quantum channel.

10. The component as claimed in the preceding claim, wherein, The quantum unitary gate enables: - If D1 = 0 and D2 = 0, then the quantum unitary gate is an identity gate; - If D1 = 0 and D2 = 1, then the quantum unitary gate is a Pauli-Z gate; - If D1 = 1 and D2 = 0, then the quantum unitary gate is a NOT gate; - If D1 = 1 and D2 = 1, then the quantum unitary gate is a NOT gate, followed by a Pauli-Z gate; Wherein, D1 is a measurement of the quantum state of the first photon leaving the CNOT gate through the port associated with the control photon, and D2 is a measurement of the quantum state of the second photon leaving the CNOT gate through the port associated with the controlled photon.

11. The component as claimed in any one of claims 9 and 10, wherein, Photons emitted from the receiver of the last system in the chain that provides the EPR quantum channel are sent to a unitary gate, provided that the receiver is not connected to any other receiver in another system. This unitary gate is the product of quantum unitary gates obtained by each Bell measurement at the interface of each system in the chain that provides the EPR quantum channel.

12. The component of any one of claims 8 to 11, comprising 1 to 10 systems linked one after another for providing an EPR quantum channel, or, if the systems benefit from an error correction system, the component comprising 1 to 30 systems linked one after another for providing an EPR quantum channel.

13. The component as claimed in any one of claims 8 to 12, wherein, The CNOT gate includes a cavity in which neutral atoms, particularly rubidium atoms, are trapped.

14. A method for teleporting quantum information using the components for teleporting quantum information as described in any one of claims 8 to 13, comprising: Transferring qubits from the first receiver to the second receiver.

15. A method for long-distance teleportation of a qubit carried by a neutral atom to a photon using a system for providing a quantum channel as described in any one of claims 1 to 6, comprising the following steps: Entangled photon pairs are generated from the transmitter, wherein the first photon in the pair is emitted toward the first receiver, and the second photon in the pair is preferably emitted toward the second receiver simultaneously. The first photon and the second photon are entangled, and these photons have a wavelength of 780 nm in particular. The first photon encodes the qubit, particularly according to a linear polarization basis. The first photon received by the first receiver is sent to a CNOT gate, the CNOT gate including a cavity in which the neutral atom is trapped; An electromagnetic pulse in the microwave domain is sent to the neutral atom, thereby applying a Hadamard gate to it; The excited state of the neutral atom is measured, and the polarization of the first photon at the output of the CNOT gate is measured. The measured value is transmitted to the second receiver; The polarization of the second photon is modified based on the state of the neutral atom and the measured value of the polarization direction of the first photon, i.e., the state of the qubit carried by each atom is 0 or 1.

16. A method for long-distance teleportation of a qubit carried by a first neutral atom to a second neutral atom using a system for providing a quantum channel as described in any one of claims 1 to 6, comprising the following steps: a. An entangled photon pair is generated from a transmitter, wherein a first photon in the pair is emitted toward a first receiver, and a second photon in the pair is preferably emitted simultaneously toward a second receiver, the first photon and the second photon being entangled, the photons having a wavelength of 780 nm in particular, the first photon encoding a qubit, particularly encoding the qubit according to a linear polarization basis; b. Excite the first neutral atom located at the first receiver until it emits a photon, and guide the emitted photon toward the control port of the first CNOT control gate, and then send it to the first Hadamard gate; c. Send the first photon in the entangled photon pair to the controlled port of the first CNOT gate; d. Measure the polarization direction of the photon emitted by the first neutral atom at the output of the Hadamard gate and the polarization direction of the first photon at the output of the CNOT gate; e. Transmit the measured value to the second receiver; f. Modify the polarization of the second photon received at the second receiver in the entangled photon pair based on the state of the neutral atom and the measured value of the polarization direction of the first photon, i.e., the state 0 or 1 of the qubit carried by each. g. Send the modified second photon to the control port of the second CNOT gate, and then send it to the second Hadamard gate; h. Excite the second neutral atom located at the second receiver until it emits a photon, and guide the emitted photon toward the controlled port of the second CNOT gate; i. Measure the polarization direction of the photon emitted by the second neutral atom at the output of the second CNOT gate and the polarization direction of the second photon at the output of the second Hadamard gate; j. Sending at least one microwave electromagnetic pulse to the second neutral atom in order to apply a quantum unitary gate to it, the quantum unitary gate being characterized in particular as follows: i. If the measured value of the polarization direction of the photon emitted by the second neutral atom is 0, and the measured value of the polarization direction of the second photon is 0, then for example, no operation is applied to the second neutral atom; ii. If the measured value of the polarization direction of the photon emitted by the second neutral atom is 1, and the measured value of the polarization direction of the second photon is 0, then apply the Pauli-Z gate to the second neutral atom; iii. If the measured value of the polarization direction of the photon emitted by the second neutral atom is 0, and the measured value of the polarization direction of the second photon is 1, then apply a NOT gate to the second neutral atom; iv. If the measured value of the polarization direction of the photon emitted by the second neutral atom is 1, and the measured value of the polarization direction of the second photon is 1, then apply a NOT gate and a Pauli-Z gate to the second neutral atom accordingly.

17. A method for teleporting qubits carried by a carrier of physical qubits in parallel, for implementing an error correction algorithm during qubit transmission, the method using a system for providing an EPR quantum channel as described in any of the preceding claims, the method comprising: a. Emitting entangled photon pairs, wherein the first photon in each pair is emitted toward a first receiver, and the second photon in each pair is preferably emitted simultaneously toward a second receiver, each receiver containing at least one neutral atom, such as nine neutral atoms, one or more neutral atoms being arranged to be able to emit photons and having a quantum unitary gate applied thereto, wherein each neutral atom of one receiver is paired with a neutral atom of the other receiver; b. At each receiver, a photon emitted by a neutral atom of the receiver is simultaneously sent to a single photon pass detector of the receiver until the neutral atom of the receiver has become entangled with a neutral atom paired with it in another receiver, wherein the single photon pass detector is located upstream of a single CNOT gate of the receiver; c. Once each neutral atom pair is entangled, apply an error reduction algorithm, such as the Schor algorithm.

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