Quantum communication system using correction of photon polarization

Abstract

The invention relates to a quantum communication system using correction of photon polarization. The invention proposes a receiver (20-m) for receiving a multiplexed signal (S10-n) and an optical signal (S10-h) transmitted independently over a transmission channel (50), the multiplexed signal comprising a first quantum signal (Qn) and at least one polarization state control signal (Rn1), said signals comprising a second quantum signal (Qh), the receiver comprises a processing chain (Cm) and a correlation module (260) associated with a polarization basis of at least one polarization state, the chain being designed to determine the polarization state of the control signal and to modify the polarization of the multiplexed signal in order to align the determined state with the state of the basis, the module is configured to perform a correlation measurement between the first quantum signal and the second quantum signal and to generate, based on the measurement, at least one information signal (Imk) regarding an entangled state of the first quantum signal and the second quantum signal.

Description

Technical Field

[0001] Broadly speaking, the present invention relates to quantum telecommunications, and more particularly, the present invention relates to a transmitter for transmitting an optical signal including an entangled quantum signal, a receiver for receiving an optical signal including a quantum signal, a system including such a transmitter and a receiver, and an associated method implemented. Background Art

[0002] The main application of current quantum telecommunications systems is to distribute cryptographic keys (or encryption keys) between two telecommunications devices (i.e., two users) via specific quantum protocols using quantum information theory, with the aim of subsequently encrypting the communication between these two devices in a secure manner. The obtained secret cryptographic keys have a higher degree of security compared to keys obtained using conventional protocols.

[0003] In a quantum telecommunications system, two users may be physically too far apart to simply share such an encryption key using the usual steps of the QKD (Quantum Key Distribution) quantum protocol. In this context, quantum-state-teleportation and entanglement-sharing quantum protocols make it possible to link two distant quantum devices to each other in order to share an encryption key.

[0004] Such quantum-state-teleportation and entanglement-sharing quantum protocols consist in interfering quantum particles with each other, the quantum particles originating from two entangled quantum signals, each particle belonging to an entangled pair of quantum particles.

[0005] The information for generating the encryption key is obtained by measuring the encoded variable of a quantum particle (also called a "qubit") that has been pre-encoded (usually corresponding to a photon). This encoded variable has a random value, but is the same for two entangled particles, thus making it possible to share the same information. The encoded variable of a qubit corresponds to the degree of freedom of the quantum particle and can be the polarization of a photon. However, the polarization state of the quantum particle undergoes random rotations between the various devices in the system during its propagation. These may be due to the birefringence of the various media traversed or indeed due to the movement of the transmitter device relative to the receiver device, such as the movement of a satellite (transmitter or receiver) relative to a ground station in the case where the communication of one of its legs passes through outer space.

[0006] To avoid such random rotation of the polarization state, some known quantum systems use only free-space propagation, where the polarization of the photon is stable during its propagation through the transmission channel (or communication channel). However, in some applications, it is necessary to use guided optics transmission as the transmission channel, for example, in the case of propagation through a terrestrial network or on a satellite, in order to relax the constraints on the construction of the payload.

[0007] To compensate for (or correct) the random rotation of the polarization state, some known systems use a single polarization reference at the start of the implementation of the quantum protocol. This single polarization reference allows an initial estimation of the polarization rotation induced during propagation and aligns the polarization of the transmitted photons with the measurement base at the receiving end. However, this single reference does not allow correction of new polarization rotations after the initial estimation phase. Instead, other existing systems alternatively use the following approach: a reference signal is periodically generated by the quantum signal source in the encoding base, and the reference signals are entangled and thus time-division multiplexed with the qubits, which reduces the bandwidth of the system available for the payload.

[0008] Therefore, there is a need for an improved quantum communication system capable of correcting in real time the rotation of the polarization state of the qubits. Summary of the Invention

[0009] To this end, the present invention proposes a receiver configured to receive a multiplexed optical signal and an optical signal independently transmitted through a transmission channel. The multiplexed optical signal includes a first quantum signal, the optical signal includes a second quantum signal, the multiplexed optical signal further includes at least one polarization state control signal. The receiver includes a processing chain associated with a polarization base composed of at least one polarization state, and the processing chain is designed to determine the polarization state of the at least one polarization state control signal and modify the polarization of the multiplexed optical signal so as to align the determined polarization state with one of the at least one polarization states of the associated base. The receiver further includes a correlation module designed to perform a correlation measurement between the first quantum signal of the multiplexed optical signal resulting from the polarization modification and the second quantum signal. The correlation module is associated with the polarization base and is further designed to generate at least one information signal based on the correlation measurement, the information signal including information about the entanglement of the polarization states of the first quantum signal and the second quantum signal.

[0010] In some embodiments, the processing chain may include a control signal detection module and an analysis device. The control signal detection module is configured to demultiplex the at least one control signal and the first quantum signal from the multiplexed optical signal. The detection module is further configured to transmit the demultiplexed control signal to a polarization analysis device, which includes at least one detection unit. The at least one detection unit is designed to detect the control signal according to one of the at least one polarization states of the associated basis.

[0011] According to some aspects, the detection module may further include a processor configured to analyze the determined polarization state and generate a servo signal applied to a polarization correction module for correcting the polarization of the multiplexed optical signal.

[0012] In some embodiments, the receiver may be formed of polarization maintaining fiber and / or single mode fiber.

[0013] The present invention further provides a transmitter configured to transmit an optical signal. The transmitter includes:

[0014] - a signal generator configured to generate a first quantum signal, a second quantum signal, and a polarization state control signal, where the first quantum signal and the second quantum signal are entangled quantum signals with each other,

[0015] - a signal integrator configured to generate a multiplexed optical signal, where the multiplexed signal includes the first control signal and the first quantum signal.

[0016] The transmitter is configured to transmit the multiplexed optical signal and an optical signal including the second quantum signal through a transmission channel.

[0017] Therefore, embodiments of the present invention provide a quantum communication system including a plurality of transmitters and at least one receiver.

[0018] In some embodiments, the plurality of transmitters may include at least a first transmitter and a second transmitter, and the system may further include a plurality of auxiliary receivers including a first auxiliary receiver and a second auxiliary receiver. The first auxiliary receiver is configured to receive an optical signal including a quantum signal transmitted by the first transmitter, and the second auxiliary receiver is configured to receive an optical signal including a quantum signal transmitted by the second transmitter. Each auxiliary receiver is associated with a measurement polarization basis consisting of at least one polarization state and is designed to measure the associated quantum signal according to at least one of the at least one polarization state of the associated measurement polarization basis. Each auxiliary receiver may be configured to receive an entanglement information signal, where the entanglement information signal includes information about the entanglement of the polarization state of the quantum signal transmitted by at least one receiver. Each auxiliary receiver is configured to determine a shared quantum encryption key based on the measurement of the associated quantum signal and the information about the entanglement of the polarization state of the quantum signal.

[0019] According to some aspects, for one or both of the auxiliary receivers, the optical signal received by the auxiliary receiver may be a multiplexed optical signal that further includes a polarization state control signal. One or more of the auxiliary receivers include a processing chain associated with the measurement polarization basis, and the processing chain is designed to determine the polarization state of the polarization state control signal and modify the polarization of the multiplexed optical signal so as to align the determined polarization state with one of the at least one polarization state of the associated measurement polarization basis.

[0020] In some embodiments, the multiplexed signal may be a frequency multiplexed signal.

[0021] Advantageously, the absolute value of the wavelength difference between the quantum wavelength of the quantum signal and the reference wavelength of the control signal may be greater than or equal to a minimum wavelength difference value.

[0022] The present invention also proposes a method for determining at least one information signal in response to receiving a multiplexed optical signal and an optical signal transmitted independently through a transmission channel, the multiplexed optical signal including a first quantum signal, the optical signal including a second quantum signal, the multiplexed optical signal further including at least one polarization state control signal, the method including a processing stage associated with a polarization basis consisting of at least one polarization state, the processing stage being for determining the polarization state of the at least one polarization state control signal and for modifying the polarization of the multiplexed optical signal so as to align the determined polarization state with one of the at least one polarization states of the associated basis. The method further includes a correlation step that includes measuring the correlation between the first quantum signal and the second quantum signal of the multiplexed optical signal resulting from the polarization modification, the correlation measurement being associated with the polarization basis, the correlation step further including generating the at least one information signal based on the correlation measurement, the information signal including information about the entanglement of the polarization states of the first quantum signal and the second quantum signal.

[0023] Thus, embodiments of the present invention make it possible to correct the polarization rotation of qubits transmitted between the emitter and the receiver of entangled quantum signals so as to establish a quantum key, in particular, between two remote receivers.

[0024] In particular, embodiments of the present invention provide an emitter of an optical signal associated with a pair of entangled quantum particles, making it possible to robustly integrate one or more polarization state reference signals of these quantum particles.

[0025] Such a reference can be generated at any power independently of the generation of qubits to form an effective solution accessible in terms of hardware complexity. According to an embodiment of the present invention, the guided optical emitter advantageously has a small volume and weight, as well as an optimized footprint and robustness. Furthermore, frequency multiplexing such a reference with qubits makes it possible to maintain a high bandwidth for transmitting payload information (i.e., qubits).

[0026] One or more receivers according to embodiments of the present invention make it possible to correct in real time the polarization rotation experienced by qubits before detection. In particular, such receivers make it possible to independently analyze the qubits and the reference signal so as to optimally align the polarization of the qubits with the measurement basis of the receiver. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Other features, details, and advantages of the present invention will become apparent upon reading the description given with reference to the accompanying drawings, which are given by way of example.

[0028] Figure 1 is a diagram showing a quantum communication system according to some embodiments of the present invention.

[0029] Figure 2 FIG. is a diagram showing a quantum communication system according to some embodiments of the present invention.

[0030] Figure 3 FIG. is a diagram showing a transmitter of a quantum communication system according to some embodiments of the present invention.

[0031] Figure 4 FIG. is a diagram showing a transmitter of a quantum communication system according to some embodiments of the present invention.

[0032] Figure 5 FIG. is a diagram showing a signal generator of a transmitter of a quantum communication system according to some embodiments of the present invention.

[0033] Figure 6 FIG. is a diagram showing an intermediate receiver of a quantum communication system according to some embodiments of the present invention.

[0034] Figure 7 FIG. is a diagram showing an intermediate receiver of a quantum communication system according to some embodiments of the present invention.

[0035] Figure 8 FIG. is a diagram showing a processing chain of an intermediate receiver of a quantum communication system according to some embodiments of the present invention.

[0036] Figure 9 FIG. is a diagram showing a detection module for detecting a control signal of an intermediate receiver of a quantum communication system according to some embodiments of the present invention.

[0037] Figure 10 FIG. is a diagram showing a detection module for detecting a control signal of an intermediate receiver of a quantum communication system according to some embodiments of the present invention.

[0038] Figure 11 FIG. is a diagram showing an end receiver of a quantum communication system according to some embodiments of the present invention.

[0039] Figure 12 FIG. is a diagram showing a quantum photon analysis module of an end receiver of a quantum communication system according to some embodiments of the present invention.

[0040] Figure 13 FIG. is a flowchart showing a method for transmitting an optical signal implemented by a transmitter of a quantum communication system according to some embodiments of the present invention.

[0041] Figure 14 FIG. is a flowchart showing a method for intermediate reception of an optical signal implemented by a receiver of a quantum communication system according to some embodiments of the present invention.

[0042] Figure 15It is a flowchart showing a method for final reception of an optical signal implemented by a receiver of a quantum communication system according to some embodiments of the present invention.

[0043] Identical or similar elements have been denoted by the same reference numerals in the drawings. For the sake of clarity, the elements shown are not drawn to scale. Detailed Description

[0044] Figure 1 and Figure 2 Schematically shown is a quantum communication system 1 according to some embodiments of the present invention, which includes a first set of devices 10, a second set of devices 20, and a third set of devices 30 that are capable of communicating with each other.

[0045] The first set of devices 10 of the system 1 includes a plurality of transmitter devices 10-n. The index "n" is associated with the n-th transmitter device of the system 1 and is an integer between 1 and N, where the value of N is greater than or equal to 2.

[0046] The second set of devices 20 of the system 1 includes one or more receiver devices 20-m, also referred to as "intermediate receivers". The index "m" is associated with the m-th receiver device of the system 1 and is an integer between 1 and M, where the value of M is greater than or equal to 1.

[0047] The third set of devices 30 of the system 1 includes two receiver devices, also referred to as "end receivers", labeled 30-1 and 30-2 (or more generally, labeled 30-k, where the index "k" is an integer equal to 1 or 2).

[0048] The quantum communication system 1 can be used in various applications. For example and without limitation, the quantum communication system 1 can be used in the space domain and includes transmitters 10-n and / or receivers (20-m and / or 30-k) mounted on satellites. In this exemplary application of the present invention in the space domain, the system 1 can also include transmitters 10-n and / or receivers (20-m and / or 30-k) on the ground, which can be housed in one or more ground devices. The system 1 can also be used in avionics applications, in which case at least one of the transmitter devices 10-n and / or receiver devices (20-m and / or 30-k) is an avionics device. The system 1 can also be used in fiber optic network applications, where at least one of the transmitter devices 10-n and / or one receiver (20-m and / or 30-k) is a fiber optic device integrated in a ground network.

[0049] The devices of the system 1 can be fixed or mobile relative to another device with which it communicates.

[0050] As a non-limiting example, some devices of the quantum communication system 1 can be quantum computers or quantum sensor arrays.

[0051] The transmitter 10-n includes a signal generator 120 (also referred to as a "signal generation module") and at least one signal integrator (also referred to as a "signal integration module"), as Figure 3 and Figure 4 shown, Figure 3 and Figure 4 illustrate some embodiments of the present invention.

[0052] As used herein, for example, an "optical signal" (also simply referred to as a "signal") is produced by one or more pulses of coherent light generated by a light source such as a laser beam. The laser beam can be characterized in particular by its pulse rate f and by the laser pulses (i.e., the signals), and the laser pulses are defined by their frequency ω, their intensity I, their polarization P, and their phase. The "frequency ω" of the laser beam represents "the optical frequency of the laser pulse multiplied by "2π" and is defined as a function of the wavelength λ of the light beam, such that c represents the speed of light.

[0053] The transmitter 10-n in the first set of devices 10 of system 1 is configured to generate two different transmitted optical signals (labeled S 10-n1 and S 10-n2 (also referred to as the "first transmitted optical signal" and the "second transmitted optical signal" respectively) and transmit them through a transmission channel (commonly labeled 50).

[0054] Depending on the application field of the present invention, the transmission channel 50 can be, for example, free space or an optical fiber (or guided optics) device for transmitting information, for example, for the purpose of communicating using optical fiber components.

[0055] The transmission channel 50 connects the transmitter to a given receiver.

[0056] For example, the transmission channel 50 E-R1 connects the transmitter E to the first receiver R1 for the transmission of the first signal.

[0057] The transmission channel 50 E-R2 can connect the same transmitter E to the second receiver R2 for the transmission of a second signal (independent of the first signal transmitted by the transmitter E).

[0058] Similarly, a given receiver R can be connected through the transmission channel 50 E1-R to the first transmitter E1 to receive the first signal, while it is connected to the transmission channel 50 E2-R to receive a second signal (independent of the first signal) from a second transmitter E2 different from the first transmitter E1. Examples of this are shown in Figure 1 and Figure 2 .

[0059] Each transmitted optical signal delivered by transmitter 10-n includes quantum signals labeled as Q n1 and Q n2 respectively. The two quantum signals Q n1 and Q n2 are entangled with each other, and each photon of the quantum signals respectively originates from an entangled photon pair generated by signal generator 120. The first quantum signal Q n1 is associated with a polarization state labeled as P Q-n1 , and the second quantum signal Q n2 is associated with a polarization state labeled as P Q-n2 .

[0060] As used herein, the expression "quantum signal" may refer to a pulsed optical signal in which each pulse has a small number of photons. The measurement of a quantum signal provides a measurement of the detection of a photon (or "particle"), which depends on the "detection probability" of that photon.

[0061] In addition, "quantum signal" may refer to an optical signal including at least one photon that is entangled with another photon of another "quantum signal". Then these two quantum signals are called "entangled quantum signals". An "entangled photon pair" refers to two photons that form a linked system and exhibit quantum states that are correlated with each other regardless of the distance between them. There is a correlation between the measurable physical properties of these different particles (especially between their polarization states). The entanglement of a pair of photons stems from the fact that these photons respectively contained in a specific quantum signal are all generated from the same pump photon. Entangled quantum signals can be pulsed optical signals or continuous optical signals.

[0062] In some embodiments, the polarization states P n1 of the first quantum signal Q n2 and the second quantum signal Q Q-n1 and P Q-n2 can be the same (i.e., correlated) and / or mutually orthogonal (i.e., anti-correlated) respectively. Advantageously, the polarization states P Q-n1 and P Q-n2 of the entangled quantum signals are not separate polarization states that are well-defined when the signals are generated, but can be defined only during the entanglement measurement.

[0063] The first transmitted optical signal S 10-n1 delivered by transmitter 10-n is a multiplexed optical signal (also referred to as a "multiplexed optical signal" or a "multiplexed communication signal") including the first quantum signal Q n1 and a first integrated optical polarization control signal labeled as R n1 . Such a signal is also referred to as a "first control signal" or a "first reference signal".

[0064] In some embodiments, it can be in polarization basis BQ-n1 Define the first control signal R in (also known as the "first control polarization basis") n1 The polarization state of. For example and without limitation, the polarization basis B Q-n1 Can be the H / V polarization basis, which includes the H type (i.e., "horizontal") linearly polarized state and the V type (i.e., "vertical") linearly polarized state. In other embodiments, the polarization basis B Q-n1 Can be the D / A polarization basis, which includes the D type (i.e., "diagonal") linearly polarized state and the A type (i.e., "anti-diagonal") linearly polarized state.

[0065] In some embodiments, the first multiplexed optical signal S delivered by the transmitter 10-n 10-n1 May also include a second integrated optical polarization control signal labeled R n2 Such a signal is also referred to as the "second control signal" or "second reference signal". Advantageously, the polarization state of the second control signal R n2 Can be defined in the polarization basis B Q-n2 (Also known as the "second control polarization basis"). In particular, the polarization basis B Q-n2 Can be a polarization basis that is not orthogonal to the polarization basis B of the first control signal R n1 Q-n1

[0066] In some embodiments, the second transmitted optical signal S delivered by the transmitter 10-n 10-n2 May also be a multiplexed optical signal, in addition to the second quantum signal Q n2 This multiplexed optical signal also includes the first control signal R n1 And / or the second control signal R n2

[0067] The intermediate receiver 20-m in the second set of devices 20 of the system 1 is configured to first receive the multiplexed optical signal S transmitted by the first transmitter 10-n in the first set of devices 10 from the transmission channel 50 10-n (I.e., the signal S 10-n1 Or S 10-n2 ), and secondly receive the transmitted optical signal S transmitted by the second transmitter (labeled 10-h) different from the first transmitter 10-n in the first set of devices 10 10-h (Corresponding to the signal S 10-h1 Or S 10-h2 ), the index "h" is an integer between 1 and N and is different from the index "n". Therefore, as Figure 1 And Figure 2 ​​​As shown, the intermediate receiver 20-1 is configured to first receive a first transmitted optical signal transmitted by the first transmitter 10-1, and second to receive a transmitted optical signal transmitted by the second transmitter 10-2. The first transmitted optical signal received by the intermediate receiver 20-1 is the first transmitted optical signal S corresponding to a multiplexed optical signal including the quantum signal Q n (or Q n1 ) and at least one first control signal R n1 transmitted by the first transmitter 10-1. 10-11 . In addition, the transmitted optical signal transmitted by the second transmitter 10-2 may be the first transmitted optical signal S corresponding to the multiplexed optical signal 10-21 or may also be the second transmitted optical signal S corresponding to the multiplexed optical signal 10-22 , or may only include the quantum signal Q h (or Q 22 , as in the examples shown in Figure 1 and Figure 2 ).

[0068] Then, the intermediate receiver 20-m is configured to estimate the received first control signal R n1 via the transmitted optical signal transmitted by the first transmitter 10-n, thereby providing an estimated first control signal labeled R mn1 .

[0069] In an embodiment where the multiplexed optical signal S 10-n transmitted by the first transmitter 10-n and received by the intermediate receiver 20-m includes a second control signal R n2 , the intermediate receiver 20-m may also be configured to estimate the received second control signal R n2 transmitted by the first transmitter 10-n, thereby providing an estimated second control signal labeled R mn2 .

[0070] In some embodiments where the transmitted optical signal S 10-h transmitted by the second transmitter 10-h and received by the intermediate receiver 20-m is a multiplexed optical signal including a first control signal R h1 and / or a second control signal R h2 , the intermediate receiver 20-m may also be configured to estimate the received first and / or second control signal R h1 and / or R h2 transmitted by the second transmitter 10-h, thereby providing estimated third and / or fourth control signals labeled R mh1 and R mh2 respectively.

[0071] In addition, the intermediate receiver 20-m is configured to perform a correlation measurement of quantum signals, the correlation measurement being related to the quantum signal Q of the multiplexed optical signal S received from the first transmitter 10-n 10-n and being related to the quantum signal Q of the transmission optical signal S received from the second transmitter 10-h n (i.e., S 10-h or S 10-h1 respectively), and being related to the quantum signal Q 10-h2 (i.e., Q h or Q h1 respectively). In addition, the correlation measurement of the quantum signal is performed based on the estimated first control signal R h2 estimated by the intermediate receiver 20-m mn1 .

[0072] In some embodiments, the correlation measurement of the quantum signal may also be performed based on the estimated second control signal R mn2 , based on the estimated third control signal R mh1 and / or based on the estimated fourth control signal R mh2 .

[0073] Each of the quantum particles sourced from two quantum signals (i.e., Q n and Q h ) separately received by the intermediate receiver 20-m is associated with an independently generated entangled photon pair. In addition, the particles of the first quantum signal Q 10-n1 of the multiplexed optical signal S sent by the first transmitter 10-n to the receiver 20-m belong to an entangled pair associated with the particles of the second quantum signal Q n1 of the transmission optical signal S sent by the first transmitter 10-n 10-n2 . Similarly, the particles of the quantum signal Q n2 of the transmission optical signal S sent by the second transmitter 10-h to the receiver 20-m 10-h1 (e.g., and without limitation, the first quantum signal Q h ) belong to an entangled pair associated with the particles of the second quantum signal Q h1 of the transmission optical signal S sent by the second transmitter 10-h 10-h2 .

[0074] Advantageously, the correlation measurement of the quantum signal performed by the intermediate receiver 20-m may be a Bell measurement, and the Bell measurement correlates these received quantum particles Q h2 and Q n and Q hProjected onto a polarization-entangled Bell state. Such a projection induces an entanglement (or correlation) among these received particles, called "resultant entanglement". Thus, such resultant entanglement induces an entanglement, called "teleportation entanglement" (or "induced entanglement" or "consequent entanglement"), among the quantum particles entangled with the particles Q n and Q h , namely, respectively, among the following:

[0075] - If the intermediate receiver 20-m is configured to receive the multiplexed optical signal S 10-h1 , then between the particles of the second quantum signal Q 10-n2 of the transmitted optical signal S n2 sent by the first transmitter 10-n (i.e., not received by the receiver 20-m) and the particles of the second quantum signal Q 10-h2 of the transmitted optical signal S h2 sent by the second transmitter 10-h (i.e., not received by the receiver 20-m), or

[0076] - If the intermediate receiver 20-m is configured to receive the transmitted optical signal S 10-h2 , then between the particles of the second quantum signal Q 10-n2 of the transmitted optical signal S n2 sent by the first transmitter 10-n (i.e., not received by the receiver 20-m) and the particles of the first quantum signal Q 10-h1 of the multiplexed optical signal S h1 sent by the second transmitter 10-h (i.e., not received by the receiver 20-m).

[0077] In some embodiments, two end receivers 30-1 and 30-2 (also referred to as "extra receivers" or "auxiliary receivers") in the third set of devices 30 of the system 1 can both be configured to receive different transmitted optical signals from the transmission channel 50. These two transmitted optical signals (both received by the end receiver 30-k) are independently transmitted by two different transmitters from the first set of devices 10. Thus, no intermediate receiver 20-m in the second set of devices 20 pre-receives these transmitted optical signals.

[0078] In some embodiments, the first end receiver 30-1 can then be configured to receive the transmitted optical signal S 10-n (and specifically S 10-n2 ), while the second end receiver 30-2 can be configured to receive the transmitted optical signal S transmitted by another transmitter 10-h in the first set of devices 1010-h (and specifically S 10-h2 or S 10-h1 ). Thus, each end receiver 30-k can be configured to estimate a quantum signal originating from the received transmitted optical signal, thereby providing an estimated received quantum signal, labeled S Qk (i.e., S Q1 for the first end receiver 30-1, or S Q2 for the second end receiver 30-2).

[0079] By way of example and not limitation, as Figure 1 and Figure 2 shown, the first end receiver 30-1 can be configured to receive a transmitted optical signal S 10-12 (optionally a multiplexed optical signal) transmitted by the first transmitter 10-1, and is thus configured to determine an estimated received quantum signal S Q1 (i.e., estimate a second quantum signal Q 10-12 originating from signal S 12 ).

[0080] In the example shown in Figure 1 , the second end receiver 30-2 can be configured to receive a transmitted optical signal S 10-22 (optionally a multiplexed optical signal) transmitted by the second transmitter 10-2, while in the example shown in Figure 2 , the second end receiver 30-2 can be configured to receive a transmitted optical signal S 10-32 (optionally a multiplexed optical signal) transmitted by the third transmitter 10-3 in the first set of devices 10. The second end receiver 30-2 can also be configured to determine an estimated received quantum signal S Q2 (i.e., for example, estimate a second quantum signal Q 10-22 originating from signal S 22 or Q 10-32 originating from signal S 32 ).

[0081] Furthermore, in an embodiment where the second set of devices 20 of the system 1 includes a single intermediate receiver (which is then labeled 20-1), as Figure 1 shown, the single receiver 20-1 can also be configured to generate two information signals, each information signal including the result of a correlation measurement of the quantum signal performed by the single receiver 20-1 (i.e., including the result of the projection of quantum particles received independently in Bell polarization states). Each information signal (labeled I 12 or I 22 ) including the result entanglement information derived from the performed correlation measurement can be sent to one of the two end receivers 30-1 or 30-2, respectively.

[0082] Thus, as used herein, one of ordinary skill in the art will readily understand that the expression "result entanglement information" refers to the "correlation information" between quantum signals (i.e., between received quantum particles Q n and Q h ), which are not from an entanglement signal generation operation, unlike, for example, quantum signals entangled with each other generated by the same emitter 10-n, labeled Q n1 and Q n2 respectively), that is derived from the measurement of the correlation between these independent optical signals.

[0083] Alternatively, in an embodiment where the second set of devices 20 of system 1 includes a plurality of intermediate receivers, as Figure 2 shown, a predetermined receiver 20-m from the second set 20 can be configured to generate a first information signal including the result of the correlation measurement of the quantum signal performed by the predetermined receiver 20-m, while another receiver labeled 20-p predetermined from the second set 20 can be configured to generate a second information signal including the result of the correlation measurement of the quantum signal performed by another predetermined receiver 20-p. In this case, the index "p" is an integer between 1 and M and is different from the index "m". The first information signal labeled, for example, I mk includes result entanglement information derived from the correlation measurement performed by the predetermined receiver 20-m and can be sent to one of the two end receivers, receiver 30-k, while the second information signal labeled, for example, I pq includes result entanglement information derived from the correlation measurement performed by the predetermined receiver 20-p and can be sent to the other receiver 30-q of the two end receivers of system 1. In this embodiment, the index "q" is an integer equal to 1 or 2 and is different from the index "k".

[0084] The information signal generally labeled I mk can be sent by the intermediate receiver to the end receiver of system 1 through the transmission channel 50. In addition, the result entanglement information value to be included in the information signal to be sent can, for example and without limitation, correspond to an entanglement value equal to 1 or alternatively correspond to an entanglement value equal to 0, where the entanglement value equal to 1 is associated with received photons of quantum signals Q n and Q h having the same (i.e., correlated) polarization states with each other, and the entanglement value equal to 0 is associated with received photons having different (i.e., anti-correlated) polarization states with each other.

[0085] Thus, each end receiver 30-k (30-1 and 30-2) in the third set of devices 30 of system 1 can be configured to receive a single entanglement information signal I mk, and determine (i.e., derive therefrom) one or more associated items of resultant entanglement information.

[0086] According to one aspect of the present invention, the first end receiver 30-1 and the second end receiver 30-2 in the third set of devices 30 of the system 1 may be configured to use the received quantum signal S estimated by the first end receiver 30-1 Q1 and the received quantum signal S estimated by the second end receiver 30-2 Q2 to determine (i.e., establish) a quantum encryption key. In particular, such quantum key distribution is also based on the entanglement information signal I received by the end receiver 30-k m1 and I m2 (or for example I m1 and I q2 ), and thus is performed based on the associated resultant entanglement information, and the two estimated received quantum signals S Qk are respectively associated with teleportation entanglement generated by one or more resultant entanglements from one or more intermediate receivers 20-m. Therefore, the system 1 may be a quantum encryption key distribution system based on quantum "teleportation". In other words, the system 1 may be configured to perform quantum key distribution using one or more quantum repeaters respectively corresponding to one or more intermediate receivers, and the one or more quantum repeaters are configured to "relay" the resultant entanglement information initially derived from a plurality of independently generated entangled photon pair emitters. Quantum key distribution may be implemented especially within space or terrestrial communication services for the purpose of protecting some or all of the communications exchanged between end receivers, for example.

[0087] Figure 3 and Figure 4 Schematically shows a transmitter 10-n in the first set of devices 10 according to some embodiments of the present invention, and the transmitter 10-n is configured to form at least one multiplexed optical signal.

[0088] The multiplexed optical signal transmitted by the transmitter 10-n is generated by a signal integrator of the transmitter 10-n using at least one control signal and a quantum signal delivered by a signal generator 120.

[0089] In some embodiments, the transmitter 10-n may include a single signal integrator labeled 140-1 (or 140), which is configured to generate a multiplexed optical signal S 10-n1 .

[0090] Advantageously, the transmitter 10-n may include two signal integration modules labeled 140-1 and 140-2, and each signal integration module is configured to generate a multiplexed optical signal. The first integrator 140-1 may be configured to generate a first multiplexed optical signal S 10-n1and the second integrator 140-2 can be configured to generate a second multiplexed optical signal S 10-n2 .

[0091] A single (or first) signal integrator 140-1 is configured to generate a (first) multiplexed optical signal S n1 using the first quantum signal Q n1 and (at least) the control signal R 10-n1 , as Figure 3 and Figure 4 shown.

[0092] In some embodiments where the transmitter 10-n is configured to generate two control signals R n1 and R n2 , as Figure 4 shown, the first (or single) signal integrator 140-1 can be configured to also generate a (first) multiplexed optical signal S n2 using the second control signal R 10-n1 .

[0093] In some embodiments, Figure 4 the second signal integrator 140-2 shown can be configured to generate a second multiplexed optical signal S n2 using the second quantum signal Q n1 and / or using the first control signal R n2 and / or using the second control signal R 10-n2 .

[0094] Thus, in other words, the integration module of the transmitter 10-n configured to generate a multiplexed optical signal is designed to optically multiplex (or optically combine) a quantum signal with one or more control signals on the same optical path.

[0095] In embodiments where the transmitter 10-n is a guided optics (or all-optical) device (i.e., including an optical signal transmission channel composed of optical fibers and / or so-called integrated waveguides (commonly used in integrated photonics)), one or more transmission devices of the transmitter can be composed of polarization-maintaining fiber (PMF) and / or single-mode fiber (SMF).

[0096] In some embodiments, the multiplexed optical signal generated by the transmitter 10-n in the first set of devices 10 can be frequency multiplexed. In this case, the signal generator 120 of the transmitter can be configured to generate an entangled quantum signal Q Q having a wavelength labeled λ Qn1 (or having corresponding wavelengths λ Qn2 and λ n1 and also referred to as the "quantum wavelength") n2 and Q Rn1at least a first control signal R of the “reference wavelength” n1 , one or more quantum wavelengths being different from the control wavelength.

[0097] In some embodiments, the signal generator 120 may also be configured to generate a second control signal R having a control wavelength labeled λ Rn2 , all three wavelengths λ n2 , λ Q , λ Rn1 and λ Rn2 being different from each other. Figure 5 Schematically shows such a signal generator 120 according to some embodiments of the present invention.

[0098] Advantageously, the signal generator 120 may include a first laser source 122-0 that emits a laser beam (or “pump laser”) having a wavelength λ pump . The laser emits a pump wavelength λ pump that may be in the visible or infrared. For example and without limitation, the first laser source 122-0 may be a DFB (distributed feedback) laser diode using a Bragg grating, thereby allowing selection of the emission wavelength λ pump . For example, the selected emission wavelength λ pump of the laser diode may be equal to 780 nm. In particular, such a laser diode emits a continuous wave laser beam. Alternatively, the first laser source 122-0 may be a pulsed laser unit, i.e., a gain-switched laser unit.

[0099] The signal generator 120 may also include one or two other additional laser sources labeled 122-1 and 122-2, as Figure 5 shown, which are configured to emit a laser beam having a wavelength λ R1 and a laser beam having a wavelength λ R2 , respectively. The laser emission wavelengths λ R1 and λ R2 may be in the visible or infrared. For example and without limitation, one or more of the additional laser sources 122-1 and 122-2 may be DFB laser diodes or gain-switched laser units.

[0100] According to some embodiments, the signal generation module 120 may also include one or more intensity modulation units 124, which are configured to modulate the intensity of the laser pulses generated at the output of the first laser source 122-0 and form quantum pulses.

[0101] The intensity modulation unit 124 may also be configured to modulate the rate of the laser pulses (e.g., which is on the order of several kilohertz to several tens of gigahertz) and / or the time width of the laser pulses (e.g., which is up to several nanoseconds).

[0102] AsFigure 5 As shown, the signal generation module 120 may further include an entanglement unit 126 configured to receive a single initial optical signal labeled S n0 and deliver two entangled quantum signals corresponding to a first quantum signal Q n1 and a second quantum signal Q n2 including an entangled photon pair. Advantageously, such an entanglement unit 126 may be arranged at the output of the intensity modulation unit 124.

[0103] By way of example and without limitation, the entanglement unit 126 may be implemented in the form of a Sagnac loop, where the initial optical signal S n0 generates a pair of polarization-entangled photons through a non-linear crystal (or micro-resonator), particularly in two different directions. Such a non-linear crystal may be a PPLN (periodically poled lithium niobate) crystal.

[0104] Advantageously, the quantum wavelengths λ Qn1 and λ Qn2 (or λ Q ) of the entangled quantum signals may be determined according to the pump wavelength λ n0 of the initial optical signal S pump . In particular, since energy conservation is obeyed during the generation of the entangled photon pair, the sum of the frequencies of the entangled photons is equal to the frequency of the initial pump photon. By way of illustration, for a wavelength λ pump equal to 780 nm, the quantum wavelength may be equal to approximately 1560 nm in order to obey energy conservation.

[0105] In some embodiments, according to the following inequality (01), the frequency difference between the quantum wavelength λ Q and the reference wavelength (λ R1 and / or λ R2 ) may be greater than or equal to a first minimum wavelength difference δλ:

[0106] |λ Q - λ R1 / R2 | ≥ δλ (01)

[0107] Furthermore, in embodiments where the generator 120 includes two different laser sources 122-1 and 122-2, according to the following inequality (02), the frequency difference between the reference wavelengths (λ n1 and λ n2 ) of the respective control signals in the control signals R R1 and R R2 may be greater than or equal to a second minimum wavelength difference δλ':

[0108] |λ R1 - λ R2|≥δλ′ (02)

[0109] Advantageously, the first minimum wavelength difference δλ and the second minimum wavelength difference δλ′ can be predefined and, for example and without limitation, be equal to 1.6 nm and 0.8 nm respectively.

[0110] In an embodiment where the transmitter 10-n is a device including a free-space signal transmission device, the entanglement unit 126 of the signal generator 120 may include one or more dichroic filters that make it possible, in particular, to direct the initial optical signal S n0 towards the Sagnac loop and / or separate (i.e., filter) the two photons of each formed pair of entangled photons on two different optical paths in order to deliver two entangled quantum signals Q n1 and Q n2 .

[0111] In an embodiment where the multiplexed signal generated by the transmitter 10-n is frequency multiplexed (i.e., the quantum wavelength λ Q and the reference wavelength λ R1 and / or λ R2 are different from each other), the signal integrator (140-1 and / or 140-2) of the transmitter 10-n may include one or two wavelength division multiplexing (WDM) units, each unit being designed to combine one of the quantum signal under consideration and a control signal on the same optical path (R n1 or R n2 ) into a resulting signal.

[0112] In some embodiments, such a signal integrator may alternatively include one or two dichroic filters, each filter being designed to combine one of the quantum signal under consideration and a control signal on the same optical path (R n1 or R n2 ) into a resulting signal.

[0113] In some embodiments, the multiplexed optical signal generated by the transmitter 10-n in the first set of devices 10 may be time multiplexed. In this case, such a multiplexed signal may be a signal including a set of two or three temporally distinct pulses, the set repeating with a period T, the different pulses corresponding respectively to the entangled quantum signals Q n1 or Q n2 , the first control signal R n1 and / or the second control signal R n2 .

[0114] Advantageously, the entangled quantum signals and control signals generated by the signal generator 120 may be pulsed signals characterized by a period T that is the same as the period of the multiplexed signal delivered by the transmitter 10-n.

[0115] In some embodiments, the signal generator 120 may be configured to generate entangled pairs of particles (Q n1 and Q n2 ) and control signals R n1 and R n2 , where there is a predefined time shift between each pulse. Alternatively (or additionally), the signal integrator (140-1 and / or 140-2) may be configured to apply a predefined time offset between the quantum signal and the control signal in order to obtain time-division multiplexed signal pulses.

[0116] It should be noted that in embodiments involving time-division multiplexing, the same pair of entangled particles (Q n1 and Q n2 ) are not time-shifted.

[0117] Thus, according to the following inequalities (03) and (04), the resulting time difference between the individual pulses in consecutive different pulses in the multiplexed signal can be strictly less than the repetition period T of the resulting signal (or quantum signal):

[0118] |t Q -t R1 / R2 |<T (03)

[0119] |t R1 -t R2 |<T (04)

[0120] In these embodiments where the multiplexed signal generated by the transmitter 10-n is time-division multiplexed, the quantum wavelength λ Q and the reference wavelength (λ R1 and / or λ R2 ) may be equal to each other.

[0121] In this case, the first laser source 122-0 and one or more additional laser sources 122-1 and 122-2 may correspond, for example, to a single laser source 122-0, and the signal generator 120 may further include a beam splitting unit (not shown in the figure), the beam splitting unit being configured to provide one or two signal components associated with the control signals R n1 and R n2 , and also to provide another signal component associated with the initial optical signal S n0 . Such a beam splitting unit may include one or more symmetric or asymmetric optical couplers, such as polarization-maintaining optical couplers. The beam splitting unit may also be an optical selector that generates a predefined time shift between each delivered signal component.

[0122] In some embodiments, the beam splitting unit of the signal generator 120 may be arranged at the output of the first laser source 122-0, and the resulting control signals R n1 and R n2 then correspond to a conventional (i.e., non-quantum) optical pulse signal. Alternatively, the beam splitting unit may be arranged at the output of the intensity modulation unit 124, and the resulting control signals R n1 and R n2 then correspond to signals with low emission intensity.

[0123] Figure 6 and Figure 7 Schematically shows an intermediate receiver 20-m according to some embodiments, including at least one received multiplexed optical signal processing chain and a correlation module 260.

[0124] The correlation module 260 of the intermediate receiver 20-m is configured to perform a correlation measurement of a received first quantum signal Q originating from a first transmitter 10-n m1 with a received second quantum signal Q originating from a second transmitter 10-h m2 .

[0125] In particular, the correlation module 260 may be implemented in the form of an optical instrument (e.g., by way of example, an optical interferometer) in order to perform a Bell measurement (corresponding to a Bell measurement module). Such a correlation module 260 particularly includes a plurality of detection units. Each detection unit may be designed to measure one or more quantum signals according to a predefined measurement polarization state in a polarization basis B 260 (also referred to as the "measurement polarization basis", and for example and without limitation, corresponding to the H / V basis or the D / A basis).

[0126] The processing chain labeled Cm of the intermediate receiver 20-m is configured to receive the multiplexed optical signal and deliver the received quantum signal Q m . For example, as shown in Figure 6 and Figure 7 , the processing chain Cm may be configured to receive the multiplexed optical signal S 10-n (or S 10-n1 ) transmitted by the first transmitter 10-n, and deliver the received first quantum signal Q associated with the signal Q 10-n (or Q n ) transmitted by the first transmitter 10-n via the signal S n1 . m1 m1 .

[0127] The processing chain Cm is also designed to determine the polarization state of one or more control signals originating from the received multiplexed optical signal. For example, the processing chain Cm may be associated with a first control polarization basis B Q-n1associated and designed to measure in this basis the polarization state of a first control signal R transmitted by the first transmitter 10-n via the multiplexed optical signal S 10-n sent n1 The processing chain Cm can also be associated with a second control polarization basis B Q-n2 and designed to measure in this second basis the polarization state of a second control signal R transmitted by the first transmitter 10-n via the multiplexed optical signal S 10-n sent n2 .

[0128] The processing chain Cm is also designed such that the determined polarization state is aligned with one of the predetermined measurement polarization states of the correlation module 260. In some embodiments, the measurement polarization basis B 260 can correspond to the first control polarization basis B Q-n1 . Alternatively, the measurement polarization basis B 260 can correspond to the second control polarization basis B Q-n2 . As used herein, the expression "the polarization state is aligned with the polarization basis" refers to the rotation of the polarization state of the signal such that it corresponds to a specific detection axis of the basis determined by the quantum signal detection device.

[0129] Thus, the processing chain Cm of the intermediate receiver 20-m can be designed to rotate the polarization state of all signals originating from the received multiplexed optical signal at the input of the processing chain Cm in order to ensure that the particles of the quantum signal Q m at the output of the processing chain Cm are aligned with the measurement polarization basis B 260 .

[0130] In some embodiments, as Figure 7 shown, the intermediate receiver 20-m can include two processing chains Cm, each processing chain Cm being configured to process the multiplexed optical signal S 10-n sent by the first transmitter 10-n or the multiplexed optical signal S 10- sent by the second transmitter 10-h

[0131] In other embodiments, the intermediate receiver 20-m can include a single processing chain Cm configured to process the multiplexed optical signal S 10-n sent by the first transmitter 10-n, as Figure 6 shown. In this case, the transmitted optical signal S 10-h sent by the second transmitter 10-h is not a multiplexed signal and includes only the quantum signal Q m2 directly corresponding to the received second quantum signal Q h originating from the second transmitter 10-h.

[0132] Advantageously, the processing chain Cm can include a servo loop between the polarization state correction module 220 and the control signal detection module 240. AsFigure 8 As shown, calibration module 220 may be arranged upstream of detection module 240.

[0133] The calibration module 220 of the intermediate receiver 20-m may be configured to modify the polarization of the signal passing through it in response to a setpoint signal. Thus, the calibration module 220 may be configured to receive a multiplexed optical signal (e.g., S 10-n , or more precisely, S 10-n1 ) transmitted by the first transmitter 10-n, and deliver a multiplexed optical signal with modified polarization labeled S m .

[0134] For example, the setpoint signal of the calibration module 220 may be an electrical signal or a radio frequency signal. Advantageously, the calibration module 220 may be an optical fiber polarization controller, which particularly includes one or more polarization rotation optical fibers, and one or more stress axes of the polarization rotation optical fibers (which are designed to rotate the polarization of the signal) are controlled (or adjusted) based on the setpoint signal. For example and without limitation, such a controllable stress axis may be implemented in the form of a wound fiber component with an adjustable geometry, or implemented using a piezoelectric element that induces mechanical stress on the optical fiber. Alternatively, the calibration module 220 may include one or more components called active retarder plates, i.e., the plate rotation (i.e., the rotation of its optical axis) is controlled (or adjusted) based on the setpoint signal. For example and without limitation, the calibration module 220 may be a triple of active retarder plates, which successively includes a quarter-wave plate, a half-wave plate, and a quarter-wave plate.

[0135] In some embodiments, the transmission means of the intermediate receiver 20-m (particularly, the processing chain Cm) may be a single-mode optical fiber SMF and / or advantageously a polarization-maintaining optical fiber PMF.

[0136] Figure 9 and Figure 10 Schematically shows a detection module 240 of a processing chain Cm including a signal demultiplexing unit 242 and an analysis device DA for analyzing the polarization of a control signal according to some embodiments of the present invention.

[0137] The signal demultiplexing unit 242 may receive a multiplexed optical signal S with modified polarization at the input m , and may be configured to separate from this signal the received quantum signal component Q m related to the quantum signal originating from the received multiplexed signal, and one or two received control signal components R mFor example, for a received multiplexed optical signal S that is transmitted by the first transmitter 10-n and includes a quantum signal Q n (or Q n1 ) and a control signal R n1 , the demultiplexing unit 242 may be configured to determine a signal quantum component Q 10-n related to the quantum signal Q n1 and a signal control component R m related to the control signal R n1 . m .

[0138] The demultiplexed quantum component Q m of the signal S m at the output of the unit 242 may then be transmitted to the correlation module 260 of the intermediate receiver 20-m, while the control component R m may be transmitted to the analysis device DA.

[0139] In an embodiment where the received multiplexed optical signal S 10-n includes a quantum signal Q n1 and two control signals R n1 and R n2 , the demultiplexing unit 242 may be configured to isolate a quantum component Q n1 related to the quantum signal Q m , a first signal control component R n1 related to the first control signal R m1 and a second signal control component R n2 related to the second control signal R m2 . In this case, the first control component R m1 may be transmitted to the first analysis device, while the second control component R m2 may be transmitted to a second analysis device (not shown in the figure). The two analysis devices are similarly configured, each analysis device being matched to the characteristics of the control component to be processed (i.e., the control polarization bases (B Q-n1 and B Q-n2 )) to be used) and optionally to the reference wavelength under consideration. Using two different analysis devices enables a better estimate of the polarization rotation (or distortion) experienced by the multiplexed optical signal S 10-n between transmission and reception on the transmission channel. For example and without limitation, the second analysis device may be used to confirm the polarization analysis of the control signal as determined by the first analysis device.

[0140] In an embodiment involving time-division multiplexing (where the received multiplexed optical signal S 10-n includes a quantum signal Q n1 and two control signals R n1 and Rn2 ),the first and second signal control components R after demultiplexing m1 and R m2 can be transmitted to a single analysis device, which is configured to alternately analyze these components based on the time difference between successive different pulses associated with the control signals.

[0141] The demultiplexing unit 242 of the detection module 240 can in particular include one or more demultiplexing elements, which are determined according to the type of multiplexing of the signals by the transmitter under consideration (i.e., frequency division multiplexing and / or time division multiplexing).

[0142] In an embodiment where the received multiplexed signal is frequency multiplexed, the demultiplexing unit 242 can include at least one optical filter configured to separate the quantum component Q m from the control component R m . For example and without limitation, such an optical filter can be a band-stop filter, such as an FBG (fiber Bragg grating) filter, or a filter called "drop WDM". The filter can be selected based on, for example, a predetermined frequency difference between the quantum wavelength λ Q and a reference wavelength (λ R1 and / or λ R2 ) defined by equation (01).

[0143] In some embodiments, the demultiplexing unit 242 can also include an optical filter configured to separate the control components from each other. Such an optical filter can be selected based on a predetermined frequency difference (e.g., defined by equation (02)) between the reference wavelengths λ R1 and λ R2 of each control signal.

[0144] The transmission means 240-i and 242-i leading respectively to the correlation module 260 and the analysis device DA at the output of the demultiplexing unit 242 and the transmission means (not shown in the figure) included in the unit 242 can be single-mode optical fibers SMF. Advantageously, these transmission means can be polarization-maintaining optical fibers PMF.

[0145] The analysis device DA for analyzing the polarization of the control signals of the analysis processing chain Cm can be configured to detect the control component R to be processed according to a predefined polarization basis m , in order to provide an estimated control signal.

[0146] It should be noted that at the output of the transmitter 10-n, the control signals (R n1 and / or R n2)Characterized by its polarization state, which is well-defined. During the propagation of the multiplexed signal between the transmitter 10-n and the intermediate receiver 20-m, the polarization state of the considered control signal may have undergone a random rotation, such that the polarization state of the received and detected control component R m associated with the considered control signal may be different from the initially defined polarization state.

[0147] Thus, the analysis device DA for analyzing the polarization of the control signal may include at least one detection unit configured to detect the considered control signal especially according to a predefined polarization in order to provide an estimate of the received control signal (e.g., R mn1 or R mn2 ).

[0148] In some embodiments, the detection unit of the analysis device DA may be designed to detect a conventional optical pulse signal. For example and without limitation, such a unit may be a photodiode configured to deliver a photocurrent based on the measurement of the received control signal component associated with the processing chain Cm.

[0149] Alternatively, the detection unit of the analysis device DA may be a single-photon detection unit. Such a unit may consist of a detection surface configured to detect the "presence" of a single photon at its detection surface (i.e., via photon / surface interaction). Such detection of the presence of a single photon is defined according to a given quantum detection efficiency. For example and without limitation, the single-photon detection unit may be an avalanche photodiode detector (APD) or a superconducting nanowire single-photon detector (SNSPD). In particular, the single-photon detection unit may include an internal amplification mechanism configured to deliver a voltage when a photon is detected.

[0150] In some embodiments, as Figure 9 shown, the analysis device DA may include a polarizer 244-A and a single detection unit 246 for detecting the control component R n1 (or R n2 ) associated with the considered control signal (e.g., R m ). The polarizer 244-A (also referred to as a "polarization filter") may be designed to send only an optical signal defined in a predefined polarization state to the detection unit 246. Thus, the detection unit 246 is configured to detect the light energy related to the control component R m defined only according to the considered polarization state (i.e., the predefined polarization basis processed by the analysis device DA), and provide an estimate of the received control signal, e.g., R mn1 (or R mn2)。According to this configuration, if the polarization state of the received control signal component is equal to the predefined polarization state, the value of the control signal detected (or measured) by the detection unit 246 is maximum. Conversely, if the polarization state of the received control signal component is orthogonal to the predefined polarization state, the detected value of the control signal can be minimum.

[0151] Advantageously, the analysis device DA may include a polarization detection unit that directly groups (i.e., combines) the functions of the polarizer 244 - A and the detection unit 246 together.

[0152] In some embodiments, as Figure 10 shown, the analysis device DA may include a polarization beam splitting unit 244 - B, followed by two different detection units 246 - 1 and 246 - 2. The polarization beam splitting unit 244 - B (also referred to as a "polarization beam splitter") may be designed to provide two polarization signal sub - components related to the control component R m under consideration. Each sub - component may propagate on a transmission device (244 - i1 or 244 - i2) at the output of the beam splitting unit 244 - B to one of the two detection units (246 - 1 or 246 - 2), and then, it is defined only in one of the two polarization states of the predefined polarization basis processed by the analysis device DA. Thus, each detection unit (246 - 1 and 246 - 2) is configured to detect the light energy related to one of the two polarization sub - components of the control component R m in order to provide an estimate of the received control signal. For example and without limitation, according to this configuration, if the polarization state of the control component R m is equal to the initial polarization state of the considered control signal transmitted by the transmitter, the value related to the estimated control signal measured by the first detection unit 246 - 1 may be maximum, and the value measured by the second detection unit 246 - 2 may be minimum. Conversely, if the polarization state of the control component R m is orthogonal to the initial polarization state of the considered control signal transmitted by the transmitter, the value related to the estimated control signal measured by the first detection unit 246 - 1 may be minimum, and the value measured by the second detection unit 246 - 2 may be maximum.

[0153] For example and without limitation, an analysis device DA for analyzing the polarization of the received control component R m associated with the H / V diagonal basis may include a beam splitting unit 244 - B configured to provide a first sub - component with linear polarization of type H propagating on the transmission device 244 - i1 and a second sub - component with linear polarization of type V propagating on the transmission device 244 - i2. In this example, the two corresponding detection units 246 - 1 and 246 - 2 are thus configured to detect the control component R mSub-components related to the H-type linear polarization and the control component R m Sub-components related to the V-type linear polarization.

[0154] In some embodiments, one or more detection units (246 or 246-1 and 246-2) of the analysis device DA may be associated with the control component R to be detected m at the reference wavelength λ Rx (i.e., λ R1 or λ R2 ).

[0155] The intermediate receiver 20-m may also include one or more processors (also referred to as "central computing units") or CPUs (central processing units).

[0156] In some embodiments, each analysis device DA of the receiver 20-m may include a specific processor, typically labeled 248, which is configured to analyze one or more electrical signals corresponding to the estimated control signal from one or more detection units (246 or 246-1 and 246-2) associated with the analysis device DA. The processor 248 may be configured to generate a servo signal labeled S C that corresponds to the polarization correction setpoint signal to be delivered to the correction module 220 associated with the processing chain Cm.

[0157] In some embodiments, the intermediate receiver 20-m may include a single processor 248 configured to analyze all electrical signals from the detection units of the analysis devices of the receiver 20-m. In this case, the processor 248 may be configured to generate servo signals S specific to each correction module 220 of the processing chain Cm C .

[0158] The servo loop of the processing chain Cm (i.e., the polarization correction loop that generates the servo signal) may be implemented continuously or intermittently. The processor 248 may thus be configured to control one or more servo loops of the intermediate receiver 20-m. In particular, the servo loop may be activated periodically and / or after evaluating the polarization state of one or two estimated control signals with respect to one or more associated polarization bases. Additionally, the servo loop may be implemented until the polarization state of one or two estimated control signals is aligned with the associated selected (or reference) polarization state and / or within the selected polarization basis.

[0159] In some embodiments, the processor 248 of the intermediate receiver 20-m may be configured to determine a polarization state difference δP between the polarization state of an estimated control signal under consideration and the polarization state of a polarization basis associated with a particular calibration device D for the particular calibration device D. The processor 248 may also be configured to evaluate whether the polarization state difference δP is strictly greater than (or greater than or equal to) a predefined reference difference δP ref .

[0160] In particular, if the determined polarization state difference δP is greater than or equal to the reference difference δP ref , the servo loop may be activated.

[0161] Advantageously, the servo loop may be implemented to optimize (i.e., maximize or minimize) the detection of the components of one or more control signals based on one or more associated polarization states.

[0162] For example and without limitation, a differentiable optimization algorithm (such as a gradient descent algorithm) may be used to generate a servo signal for the servo loop in order to search (incrementally or iteratively) for an optimal point of an objective function that is particularly associated with the determined polarization state difference of the calibration device D of the receiver 20-m. If the optimal point is found, the servo loop may be stopped.

[0163] For example and without limitation, if the determined polarization state difference δP is evaluated as strictly less than (or less than or equal to) the reference difference δP ref , the servo loop may also be stopped.

[0164] Thus, in some embodiments, a servo signal S may be generated that is related to the setpoint signal of the calibration module 220 C in order to control the module 220 and, in particular, to rotate the polarization of the received multiplexed signal until the value of the estimated control signal measured by the detection unit 240 (e.g., via the first detection unit 246-1) is optimal, i.e., to control the component R m such that the polarization state then equals the initial polarization state of the considered control signal transmitted by the transmitter, or alternatively is orthogonal thereto. Thus, the modification of the polarization of the received multiplexed signal via the servo signal S C causes a modification of the polarization state of the quantum signal Q m demultiplexed from the signal S at the output of the unit 242 and transmitted to the correlation module 260 of the receiver 20-m m .

[0165] Furthermore, the detection unit of the correlation module 260 of the intermediate receiver 20-m may be a single-photon detection unit. For the quantum components Q m1 and Qm2 The detection enables at least one entangled information signal I to be provided mk to be respectively provided to the end receivers 30-k in the third set of devices 30 of the system 1.

[0166] In some embodiments, the correlation module 260 of the intermediate receiver 20-m may include one or two additional demultiplexing units (not shown in the figure) at the input. Each additional demultiplexing unit of the correlation module 260 is associated with one of the quantum components Q m1 or Q m2 and may be equivalent to the signal demultiplexing unit 242 of the detection module 240 of the processing chain Cm, and is configured to send, for example, the considered quantum component to the Bell measurement module. One or more residual components of the control signal from the demultiplexing unit are then directed to the beam absorber.

[0167] The additional demultiplexing units of the correlation module 260 may particularly include demultiplexing elements determined according to the multiplexing type of the signal S m . For example, for frequency division multiplexing, the additional demultiplexing unit may be a spectral filter (such as an FBG filter or an add-drop WDM filter), which is configured to separate the quantum signal Q m from two residual components of the integrated signal, and select the spectral filter based on a predetermined frequency difference between the quantum wavelength λ Q and the reference wavelength (λ R1 and / or λ R2 ).

[0168] Such additional demultiplexing units in the correlation module 260 enable, in particular, an increase in the filtering capacity for filtering one or more control signals from one or more multiplexed signals received at the input of the intermediate receiver 20-m, so as to improve the quantum correlation measurement performed by the module 260.

[0169] Figure 11 An end receiver 30-k including a received multiplexed optical signal processing chain and a quantum photon analysis module 360 is schematically shown according to some embodiments. In this case, the end receiver 30-k may be configured to receive a transmitted optical signal, which is a multiplexed signal S 10-n sent by the transmitter 10-n in the first set of devices 10. Such a signal may be, for example, a multiplexed signal S n2 including the quantum signal Q n1 and the first control signal R n2 and / or the second control signal R 10-n2 .

[0170] The processing chain of the end receiver 30-k (labeled Ck) can be configured to receive a multiplexed optical signal and deliver the received quantum signal Q related to the quantum signal originating from the multiplexed signal S 10-n of the multiplexed signal S k . The quantum photon analysis module 360 of the end receiver 30-k can be designed to measure the received quantum signal according to at least one polarization state defined in a polarization basis.

[0171] The processing chain Ck can be designed to determine the polarization state of one or more control signals originating from the multiplexed optical signal received by the end receiver 30-k. The processing chain Ck can also be designed to align the determined polarization state with one of the predefined measurement polarization states of the analysis module 360. Thus, the processing chain Ck can be designed to rotate the polarization states of all signals originating from the received multiplexed optical signal at the input of the processing chain Ck, so as to ensure that the particles of the received quantum signal Qk at the output of the processing chain Ck are correctly aligned in the polarization basis associated with the analysis module 360. Thus, the processing chain Ck can be equivalent to (including similar units) the processing chain Cm of the intermediate receiver 20-m as Figure 8 shown.

[0172] In particular, the processing chain Ck of the end receiver 30-k can include a servo loop arranged between polarization state correction modules upstream of the control signal detection module.

[0173] The correction module of the processing chain Ck (equivalent to the correction module 220 of the processing chain Cm of the receiver 20-m) can be configured to modify the polarization of the signal passing through it in response to a setpoint signal. Thus, the correction module is configured to receive the multiplexed optical signal S received by the end receiver 30-k 10-n (e.g., S transmitted by the first transmitter 10-n 10-n2 ) and deliver the polarization-modified multiplexed optical signal, e.g., labeled S k .

[0174] The detection module of the processing chain Ck (equivalent to the correction module 240 of the processing chain Cm of the receiver 20-m and thus shown in Figure 9 and Figure 10 ) can include a signal demultiplexing unit and at least one analysis device for analyzing the polarization of the control signal. The demultiplexing unit can be configured to separate at least one received quantum signal component Q k from the polarization-modified multiplexed optical signal, and the quantum signal component Q kThen it is transmitted to the quantum photon analysis module 360. The analysis device for analyzing the polarization of the control signal in the processing chain Ck can be configured to process the control signal component received from the multiplexed optical signal modified by polarization, in particular to generate a servo signal corresponding to the polarization correction setpoint signal to be delivered to the correction module of the processing chain Ck.

[0175] In an embodiment where the end receiver 30-k is configured to receive a transmitted optical signal that includes only quantum signals (i.e., non-multiplexed signals), the transmitted optical signal S 10-n thus directly corresponds to the received quantum signal Q to be processed by the analysis module 360. k .

[0176] The analysis module 360 of the end receiver 30-k may include at least one single-photon detection unit. Detecting the received quantum signal Q k makes it possible to provide an estimate of the received quantum signal S Qk , and thus to provide an estimate of the polarization state of the signal for one or more polarization states defined in the polarization basis.

[0177] In some embodiments, the analysis module 360 may include a single single-photon detection unit 366, which is configured to detect the received quantum signal Q defined according to a predefined polarization state. k .

[0178] In other embodiments, as Figure 12 shown, the analysis module 360 may include a switching unit 364, preceded by two single-photon detection units 366-1 and 366-2. The switching unit 364 may be equivalent to the polarization beam splitting unit 244-B of the analysis device DA included in the intermediate receiver 20-m. Thus, the switching unit 364 can be designed to demultiplex the quantum signal Q 10-n from the multiplexed signal S received at the input of the end receiver 30-k k and direct (i.e., route or switch) it to one of the two single-photon detection units (366-1 or 366-2) according to the polarization state of the quantum signal. Thus, each single-photon detection unit (366-1 and 366-2) is configured to detect the presence of a single photon defined according to one of the polarization states of the polarization basis processed by the analysis module 360 (i.e., the end receiver 30-k under consideration).

[0179] By way of illustration, for example and without limitation, the analysis module 360 associated with the H / V basis may include a switching unit 364, which is configured to transmit the received quantum signal Q with horizontal H-type linear polarization via the transmission device 364-i1. kis directed to the first single-photon detection unit 366-1, or the received quantum signal Q having a vertical V-type polarization is directed via the transmission device 364-i2 k to the second single-photon detection unit 366-2.

[0180] In an embodiment where the transmitted optical signal S received by the end receiver 30-k 10-n is a multiplexed signal, the analysis module 360 may include an additional demultiplexing unit 362 at the input, and the additional demultiplexing unit 362 is equivalent to the signal demultiplexing unit 242 of the processing chain Cm or the additional demultiplexing unit of the correlation module 260 included in the intermediate receiver 20-m. The additional demultiplexing unit 362 can thus be configured to send the received quantum signal Q k to the single-photon detection unit 366 or the switching unit 364, as Figure 12 shown. Then, the residual component of the control signal is directed to the beam absorber 362-0, as Figure 12 shown.

[0181] In addition, the analysis module 360 of the end receiver 30-k may include a processor 368, and the processor 368 is configured to analyze one or more electrical signals corresponding to the estimated received quantum signal S from one or more detection units (366 or 366-1 and 366-2). The processor 368 of the end receiver 30-k can be configured to determine a quantum encryption key according to the estimated received quantum signal S Qk and the entanglement information signal I received by the end receiver 30-k Qk i.e., the key shared by the end receiver 30-q and another party. mk The quantum encryption key can be determined using a quantum key distribution protocol (for example, for example, a protocol equivalent to the protocol called BBM92 (as described in the article “Quantum cryptography without Bell's theorem” by C. Bennett, G. Brassard, and D. Mermin, Physical Review Letters 68(5), pp. 557-559, 1992)).

[0182]

[0183] In some embodiments, for example, for example, when the control signal is a quantum signal and the multiplexed signal received by the end receiver 30-k is a time-division multiplexed signal, the processing chain Ck may be composed of at least a part of the polarization state correction module and the analysis module 360. In this case, the processing chain Ck is configured to detect the received quantum signal Q k ​The module 360 can also be configured to detect one or more control signals of the multiplexed optical signal received from the free - end receiver 30 - k. In this case, the processor 368 can also be configured to generate a servo signal corresponding to the polarization correction set - point signal to be delivered to the correction module of the processing chain Ck.

[0184] Figure 13 Illustrated is a method for transmitting an optical signal implemented by the transmitter 10 - n according to some embodiments of the present invention.

[0185] The method for transmitting an optical signal includes a preparatory step 1020 of generating two entangled quantum signals Q n1 and Q n2 and at least one polarization - controlled optical signal R n1 of.

[0186] In step 1040, the polarization - controlled optical signal R n1 is inserted into the optical path for transmitting the first entangled quantum signal Q n1 so as to generate a multiplexed optical signal S 10-n1 .

[0187] In step 1060, the multiplexed optical signal S 10-n1 and a transmission optical signal including the second quantum signal Q n2 are transmitted through the transmission channel 50.

[0188] Figure 14 Illustrated is a method for intermediate reception of an optical signal implemented by the intermediate receiver 20 - m according to some embodiments of the present invention.

[0189] The reception method includes a preparatory step 2020 of receiving the multiplexed optical signal S 10-n (or S 10-n1 ) and a transmission optical signal, each optical signal including an entangled quantum signal, which is independently transmitted by two different transmitters and transmitted through the transmission channel 50.

[0190] In step 2040, the multiplexed optical signal S 10-n1 is directed to the processing chain Cm associated with a predefined polarization basis.

[0191] For the processing chain Cm, the method for intermediate reception of an optical signal further includes a servo loop between steps 2042 and 2044. Step 2044 corresponds to determining the control signal R transmitted by the transmitter 10 - n for the received multiplexed optical signal passing through the chain n1the polarization state of the relevant component, and step 2042 corresponds to modifying the polarization of the received multiplexed optical signal according to the determined polarization state. When the polarization state determined in step 2044 aligns with one of the polarization states of the predefined basis of the processing chain Cm, the servo loop between steps 2042 and 2044 is stopped.

[0192] In step 2060, an interferometry is performed so as to project the particles associated with the quantum component respectively entangled with the received multiplexed optical signal and the entangled quantum signal originating from the received transmitted optical signal onto an entangled polarization state (related to the measurement polarization basis). n1 the quantum component related to the quantum signal Q respectively entangled with the received multiplexed optical signal and the entangled quantum signal originating from the received transmitted optical signal onto an entangled polarization state (related to the measurement polarization basis).

[0193] In step 2080, at least one information signal I is generated using the information on the entanglement of the determined polarization state of the received quantum signal mk , and then at least one information signal I is sent through the transmission channel 50 mk .

[0194] Figure 15 Illustrates a method for the final reception of an optical signal implemented by the end receiver 30-k according to some embodiments of the present invention.

[0195] In some embodiments, the method for the final reception of an optical signal may include a preparatory step 3020 of receiving a multiplexed optical signal S 10-n (or S 10-n2 ) sent through the transmission channel 50 and an information signal I on the entanglement of the polarization state of the quantum signal, the multiplexed optical signal S mk (or S 10-n ) including an entangled quantum signal sent by the transmitter. 10-n2

[0196] In step 3040, the multiplexed optical signal S 10-n2 can be directed to a processing chain Ck associated with a predefined polarization basis.

[0197] For the processing chain Ck, the method for the final reception of an optical signal may further include a servo loop between steps 3042 and 3044. Step 3044 corresponds to determining the polarization state of the component of the received multiplexed optical signal passing through the chain related to the control signal R n1 sent by the transmitter 10-n, and step 3042 corresponds to modifying the polarization of the received multiplexed optical signal according to the determined polarization state. When the polarization state determined in step 3044 aligns with one of the polarization states of the predefined basis for the processing chain Ck, the servo loop between steps 3042 and 3044 is stopped.

[0198] In step 3060, the polarization state of the quantum component related to the entangled quantum signal Q of the received multiplexed optical signal can be determined. n2 of the received multiplexed optical signal.

[0199] In step 3080, based on the polarization state of the quantum component related to the entangled quantum signal Q of the received multiplexed optical signal and the entanglement information about the polarization state of the quantum signal derived from the information signal I n2 of the received multiplexed optical signal and the entanglement information about the polarization state of the quantum signal derived from the information signal I mk a quantum encryption key shared with the other end receiver 30-q can be determined.

[0200] Those skilled in the art will readily understand that some steps of the sending and receiving methods can be performed separately, simultaneously, sequentially, independently, or otherwise and / or in a different order, for example, in the order defined by the considered transmitter and receiver.

[0201] The quantum system or a subsystem (transmitter and receiver) of the system according to an embodiment of the present invention and the above method can be implemented in various ways by hardware or a combination of hardware and software, and in particular, in the form of program code that can be released as a program product in various forms. The program code can be released using a computer-readable medium, which can include a computer-readable storage medium and a communication medium. The methods described in this specification can be implemented in particular in the form of computer program instructions executable by one or more processors in a computer-based computing system. These computer program instructions can also be stored on a computer-readable medium.

[0202] The present invention is not limited to the embodiments described above by way of non-limiting examples. The present invention covers any variant embodiments conceivable by those skilled in the art. In particular, those skilled in the art will understand that the present invention is not limited to the various modules of the transmitter and receiver of the quantum system described by way of non-limiting examples.

Claims

1. A receiver (20-m), the receiver (20-m) being configured to receive multiplexed optical signals (S) independently transmitted through a transmission channel (50) 10-n ) and light signal (S 10-h ), The multiplexed optical signal (S 10-n ) includes the first quantum signal (Q n ), the optical signal S 10-h ) includes a second quantum signal (Q h ), the multiplexed optical signal (S 10-n ) also includes at least one polarization control signal (R n1 ), The receiver (20-m) comprises a processing chain (Cm) associated with a polarization basis consisting of at least one polarization state and designed to determine at least one polarization state control signal (R n1 ) and modifying the polarization state of the multiplexed optical signal (S 10-n ) so as to align the determined polarization state with one of the at least one polarization state of the associated basis, The receiver (20-m) further comprises a correlation module (260) designed to perform a correlation analysis of the multiplexed optical signal (S) resulting from polarization modification. 10-n ) of the first quantum signal (Q n1 ) and the second quantum signal (Q h ), the correlation module (260) being associated with the polarization basis, the correlation module (260) being further configured to generate at least one information signal (I mk ), the information signal (I mk ) includes information about the first quantum signal (Q n ) and the second quantum signal (Q h )’s entangled information of the polarization state.

2. The receiver (20-m) according to claim 1, wherein: The processing chain (Cm) comprises a control signal detection module (240) and an analysis device, wherein the control signal detection module (240) is configured to detect the multiplexed optical signal (S 10-n ) demultiplexes at least one of the control signals (R n1 ) and the first quantum signal (Q n ), the detection module (240) is further configured to convert the demultiplexed control signal (R n1 ) is transmitted to a polarization analysis device (DA), the polarization analysis device (DA) comprising at least one detection unit (246), the at least one detection unit (246) being designed to detect the control signal (R) according to one of the at least one polarization state of the associated basis n1 ).

3. The receiver (20-m) according to claim 2, wherein: The detection module (240) further comprises a processor (248) configured to analyze the determined polarization state and generate a signal to be applied to correct the multiplexed optical signal (S 10-n ) of the polarization correction module (220) C ).

4. The receiver (20-m) according to one of claims 1 to 3, wherein: The receiver (20-m) is formed of a polarization-maintaining fiber (PMF) and / or a single-mode fiber (SMF).

5. A transmitter (10-n), the transmitter (10-n) being configured to transmit an optical signal, the transmitter comprising: A signal generator (120) configured to generate a first quantum signal (Q n1 ), the second quantum signal (Q n2 ) and polarization control signal (R n1 ), the first quantum signal (Q n1 ) and the second quantum signal (Q n2 ) are quantum signals that are entangled with each other, A signal integrator (140) configured to generate a multiplexed optical signal (S 10-n1 ), the multiplexed optical signal includes the first control signal (R n1 ) and the first quantum signal (Q n1 ), The transmitter (10-n) is configured to transmit the multiplexed optical signal (S) through a transmission channel (50). 10-n1 ) and includes the second quantum signal (Q n2 ) of the optical signal (S 10-n2 ).

6. A quantum communication system (1) comprising a plurality of transmitters (10-n) according to claim 5 and at least one receiver (20-m) according to one of claims 1 to 4.

7. The quantum communication system (1) according to claim 6, wherein: The plurality of transmitters include at least a first transmitter and a second transmitter, and the quantum communication system (1) further includes a plurality of auxiliary receivers, the plurality of auxiliary receivers include a first auxiliary receiver (30-1) and a second auxiliary receiver (30-2), the first auxiliary receiver (30-1) being configured to receive a quantum signal (Q) transmitted by the first transmitter (10-n) n ) of the optical signal (S 10-n ), the second auxiliary receiver (30-2) is configured to receive a quantum signal (Q h ) of the optical signal (S 10-h ), each auxiliary receiver (30-1; 30-2) is associated with a measurement polarization basis consisting of at least one polarization state and is designed to measure the associated quantum signal (Q) according to at least one of the at least one polarization state of the associated measurement polarization basis n ;Q h ),and Each auxiliary receiver (30-1, 30-2) is configured to receive an entangled information signal (I m1 ;I m2 or I p2 ), the entangled information signal (I m1 ;I m2 or I p2 ) comprises information about the entanglement of the polarization states of the quantum signal transmitted by the at least one receiver (20-m; 20-p), each auxiliary receiver (30-1; 30-2) being configured to receive the quantum signal (Q n ;Q h ) and the information about the entanglement of the polarization states of the quantum signal to determine a shared quantum encryption key.

8. The quantum communication system (1) according to claim 7, wherein: For one or two auxiliary receivers (30-1, 30-2), the optical signal (S) received by the auxiliary receiver (30-1; 30-2) 10-n ; S 10-h ) also includes a polarization control signal (R n1 ), one or more of the auxiliary receivers (30-1; 30-2) comprising a processing chain (Ck), the processing chain (Ck) being associated with the measured polarization basis, and the processing chain (Ck) being designed to determine the polarization state control signal (R n1 ) and modifying the polarization state of the multiplexed optical signal (S 10-n ; S 10-h ) in order to align the determined polarization state with one of the at least one polarization state of the associated measured polarization basis.

9. A quantum communication system (1) according to one of claims 6 to 8, wherein: The multiplexed optical signal is a frequency multiplexed signal.

10. The quantum communication system (1) according to claim 9, wherein: The quantum wavelength (λ Q ) and the reference wavelength (λ R ) is greater than or equal to the minimum wavelength difference (δλ).

11. A method for responding to receiving a multiplexed optical signal (S) independently transmitted through a transmission channel (50) 10-n ) and light signal (S 10-h ) to determine at least one information signal, the multiplexed optical signal (S 10-n ) includes the first quantum signal (Q n ), the optical signal (S 10-h ) includes a second quantum signal (Q h ), the multiplexed optical signal (S 10-n ) also includes at least one polarization control signal (R n1 ), The method comprises a processing phase (Cm) associated with a polarization basis consisting of at least one polarization state, the processing phase (Cm) being used to determine at least one polarization state control signal (R n1 ) and used to modify the multiplexed optical signal (S 10-n ) so as to align the determined polarization state with one of the at least one polarization state of the associated basis, The method further comprises a correlation step, the correlation step comprising measuring the multiplexed optical signal (S) resulting from the polarization modification 10-n ) of the first quantum signal (Q n1 ) and the second quantum signal (Q h ), the measurement of the correlation being associated with the polarization basis, the correlation step (260) further comprising generating the at least one information signal (I mk ), the information signal (I mk ) includes information about the first quantum signal (Q n ) and the second quantum signal (Q h )’s entangled information of the polarization state.

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