CN210839604U - M-Z type OAM entanglement modulation key distribution system - Google Patents
M-Z type OAM entanglement modulation key distribution system Download PDFInfo
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Abstract
The utility model provides an M-Z type OAM entanglement modulation key distribution system, which comprises an OAM-OAM entanglement generation unit, a first multiplexing module, a second multiplexing module, an OAM modulation unit, a Bob user side and a coincidence measurement unit; the OAM-OAM entanglement generation unit is used for generating orbital angular momentum and orbital angular momentum mixed entangled quantum states; the first multiplexing module and the second multiplexing module are used for separating any OAM state; the OAM modulation unit is used for carrying out phase deflection modulation on the orbital angular momentum and loading coding information; the coincidence measurement unit is used for performing coincidence measurement on the signal light and the idle light and decoding quantum bit information. The utility model provides high quantum key distribution system's security utilizes arbitrary OAM of M-Z interferometer separation, has expanded quantum coding's capacity, has obtained the quantum key distribution system of high-efficient code, can clock synchronization, carries out real-time supervision, has eliminated the leak of all detector sides to effectively solved the problem that reference system aimed at and mode matching.
Description
Technical Field
The utility model relates to a free space communication and quantum communication network field, concretely relates to M-Z type OAM entangles modulation key distribution system.
Background
The security of the traditional password technology depends on the computational complexity in mathematics, a computer with strong computing power plays an extremely important role in password cracking, and the security of the traditional password technology is greatly threatened along with the improvement and improvement of the current computing power. Quantum Key Distribution (QKD) security sources rely on physical principles rather than the solution complexity of mathematical problems. Therefore, theoretically, no more computing resources can effectively help an eavesdropper to break the key, so that the QKD has theoretically unconditional security. In short, the security of QKD comes from two characteristics of quantum mechanics: the method is characterized in that the quantum world is truly random in nature; the second is quantum unclonable theorem.
Photons can carry two types of angular momentum: spin Angular Momentum (SAM) and Orbital Angular Momentum (OAM). The spin angular momentum is related to the polarization state, so that the spin state of a single photon is used for coding, and only one quantum bit can be realized; the eigen state of the orbital angular momentum is | l >, l is OAM quantum number, and any integer is allowed to be taken theoretically, so that the multi-bit quantum state coding in a high-dimensional Hilbert space can be realized by utilizing the orbital angular momentum of a single photon, the information capacity carried by the photon can be obviously increased, the coding safety is improved, the defect that the quantum information is easily interfered by the environment in the optical fiber transmission process is overcome better by phase coding, and the method is very important in the field of the quantum information.
In a quantum key distribution system, there are two types of carriers that encode quantum information: single photon and entangled photon pairs. The entangled photon pair has higher safety relative to a single photon, in a quantum key distribution mechanism, two particles in quantum entanglement are given, and two communication parties respectively receive one particle, and any eavesdropping action can be detected and discovered by the two communication parties because the quantum entanglement of the pair of particles can be destroyed by measuring any one particle. But other present quantum key distribution schemes can not separate arbitrary OAM to input in the arbitrary user of Bob user side, the utility model discloses the improvement has designed scalable multi-user OAM high dimension coding quantum key distribution system.
SUMMERY OF THE UTILITY MODEL
An object of the utility model is to overcome prior art's is not enough, provides a M-Z type OAM entangles modulation key distribution system, has improved quantum key distribution system's security, utilizes M-Z interferometer can separate arbitrary OAM, has expanded quantum encoding's capacity, has obtained the quantum key distribution system of high-efficient code.
The technical scheme of the utility model is realized like this: an M-Z type OAM entanglement modulation key distribution system comprises an Alice control end, a multiplexing module and a Bob user end; the Alice control end comprises an OAM-OAM entanglement generation unit, an OAM modulation unit and a coincidence measurement unit; the multiplexing module comprises a first multiplexing module and a second multiplexing module, and the entanglement generating unit is respectively connected with the first multiplexing module and the second multiplexing module; the first multiplexing module, the OAM modulation unit and the coincidence measurement unit are sequentially connected; the second multiplexing module, the Bob user side and the coincidence measurement unit are sequentially connected;
the OAM-OAM entanglement generation unit is used for generating orbital angular momentum and orbital angular momentum mixed entangled quantum states;
the OAM modulation unit is used for carrying out phase deflection modulation on the orbital angular momentum and loading coding information;
the coincidence measurement unit is used for performing coincidence measurement on the signal light and the idle light and decoding quantum bit information;
the first multiplexing module and the second multiplexing module are both used for separating any OAM state;
the OAM-OAM entanglement generation unit generates an OAM-OAM entangled-state signal optical path and an idle optical path; the signal light path enters a first multiplexing module for polarization separation, then enters an OAM modulation unit for phase deflection modulation and loading coding information, and then is sent to a coincidence measurement unit for measurement;
the idle optical path enters a second multiplexing module for polarization separation, and then is modulated and loaded with coding information by the Bob user side and then is sent to a coincidence measurement unit for measurement;
the coincidence measurement unit performs coincidence measurement on signal photons and idle photons with the same wavelength and arriving in unit time, recovers an encoded secret key according to a coincidence measurement result, establishes a sequence of random passwords as an original password, and obtains a safe secret key through secret key screening and privacy amplification, thereby completing multi-user secret key distribution and sharing.
Preferably, the orbital angular momentum mixing and entangling unit includes a pump light source LD, a lens, a BBO crystal, a first holophote and a second holophote, the BBO crystal is connected with the lens and the pump light source LD in sequence, and is configured to generate signal photons and idle photon orbital angular momentum entangled photon pairs, which are expressed as:
wherein S and I respectively represent signal photons and idle photons, and m represents OAM topological charge.
Preferably, the first multiplexing module comprises a first M-Z interferometer comprising first to fourth 1/4 wave plates, first and second half wave plates, first to third polarizing beam splitters, first and second dove prisms, third and fourth total reflection mirrors; the second multiplexing module comprises a first M-Z interferometer, the first M-Z interferometer comprises fifth to eighth 1/4 wave plates, third and fourth half-wave plates, fourth to sixth polarizing beam splitters, third and fourth dove prisms, fifth and sixth total reflection mirrors; the signal light and the idle light coming out of the BBO crystal enter a first multiplexing module and a second multiplexing module after being reflected by a first total reflector and a second total reflector respectively, and incident photons are horizontally polarized spiral light"photons enter the first M-Z interferometer and the second M-Z interferometer respectively to realize two arbitrary orbital angular momentum states | M1>And | m2>Separation of (4).
Specifically, the first multiplexing module is provided with a first dove prism and a second dove prism at a long arm and a short arm for realizing the rotation of the phase of the photon, and if the relative orientation angle of the first and second dove prisms is set to α, the absolute value of the absolute value m of the orbital angular momentum state is>A phase difference exp (im2 α) between the two arms, | m1>The photon will have β1＝m1α spin deflection of angle, | m2>Will have β2＝m2α, the polarization directions of the two signal photons will result in an angle Δ β ═ m1-m2) α, preset α ═ pi/2 (m)1-m2) Then Δ β ═ m (m)1-m2) α pi/2, the two signal photons will have orthogonal polarizations, thus resulting in a topological charge m1And m2Two different paths communicate securely with two arbitrary Bob users.
Preferably, the OAM modulation unit includes a first beam splitter, a first charge coupled device, a first retarder, a polarization beam splitter, a first wavefront corrector, a first spatial light modulator, a first single mode fiber, a second beam splitter, a second charge coupled device, a second retarder, a second wavefront corrector, a second spatial light modulator, a second single mode fiber, and a seventh total reflection mirror.
Preferably, the Bob user terminal comprises Bob1And Bobm2A user; bobm1And Bobm2The user comprises a third beam splitter, a third charge coupled device, a third retarder, a ninth polarization beam splitter, a third wavefront corrector, a third spatial light modulator, a third single-mode fiber, a fourth beam splitter, a fourth charge coupled device, a fourth retarder, a tenth polarization beam splitter, a fourth wavefront corrector, a fourth spatial light modulator, an eighth total reflector and a fourth single-mode fiber; the first wave-front corrector to the fourth wave-front corrector can change the optical path of the wave-front transmission of the light wave or change the transmission medium according to the reference information of the phase distortionThe refractive index of the light source changes the phase structure of the wave front of the incident light wave, thereby achieving the purpose of compensating the wave surface phase of the light wave; the first charge coupling element, the second charge coupling element, the third charge coupling element, the fourth charge coupling element and the fourth charge coupling element are used for monitoring the intensity of laser pulses and wavefront phase distortion caused by atmospheric turbulence in real time and providing reference information for clock synchronization and phase distortion compensation; the first to fourth spatial light modulators perform deflection phase modulation on OAM carried by signal light and idle light with topological charge of m, and the modulated quantum-state signal light and idle light are represented as follows:
wherein, thetas、θIA deflection phase orientation angle that is orbital angular momentum;
the first to fourth single-mode fibers are used for coupling and transmitting Gaussian mode signal photons and idle photons.
Preferably, when combined with Bobm1When a user communicates, the OAM topological load is m1The signal light enters a first spatial light modulator, and the first spatial light modulator has a topological charge of m1Modulating OAM carried by the signal light; when it is in contact with Bobm2When a user communicates, the OAM topological load is m2Enters a second spatial light modulator, and the second spatial light modulator has a topological charge of m2The OAM carried by the signal light is phase-code modulated.
Preferably, the coincidence measurement unit includes first to fourth single photon detectors, and first and second coincidence counters, the single photon detector is configured to record signal photons and idle photon numbers arriving in a unit time and send detection data thereof to the coincidence counter, and the coincidence counter is configured to perform coincidence measurement.
Specifically, when Alice control end and Bobm1When the user communicates, the signal photons arriving in unit time are recorded by the first single photon detector and are recordedAnd sending the lower detection data to a first coincidence counter, simultaneously recording idle photons arriving in unit time by a third single-photon detector, sending the recorded detection data to the first coincidence counter, and finally performing coincidence measurement and decoding by the first coincidence counter according to modulation information transmitted by the two single-photon detectors. When Alice control terminal and Bobm2And when a user communicates, a second single-photon detector is used for recording signal photons arriving in unit time, recorded detection data are sent to a second coincidence counter, a fourth single-photon detector is used for recording idle photons arriving in unit time, recorded detection data are sent to the second coincidence counter, and finally the coincidence counter performs coincidence measurement and decoding according to modulation information transmitted by the two single-photon detectors.
Preferably, the signal light with the topological load of m and OAM carried by idle light are subjected to deflection phase modulation; when it is in contact with Bobm1When a user communicates, the OAM topological load is m1The signal light enters a first spatial light modulator, and the first spatial light modulator has a topological charge of m1The OAM carried by the signal light is modulated, and the first spatial light modulator is connected with the first single-mode fiber and then connected with the first single-photon detector; when it is in contact with Bobm2When a user communicates, the OAM topological load is m2Enters a second spatial light modulator, and the second spatial light modulator has a topological charge of m2The OAM carried by the signal light is subjected to phase coding modulation, and the second spatial light modulator is connected with the second single-mode fiber and then connected with the second single-photon detector.
Preferably, the signal optical path line: OAM entanglement states output from the BBO crystal are sequentially input into the first total reflector to change an optical path, horizontally polarized spiral photons pass through a 45-degree first 1/4 wave plate, left-handed and right-handed circular polarization components are respectively converted into horizontal and vertical polarization components, are separated by the first polarization beam splitter, and are respectively transmitted along two arms of the first M-Z interferometer; one beam of signal light passes through the first Daff prism to realize the phase rotation of the photons, the polarization state of the photons is kept unchanged by using the second 1/4 wave plate, and then the signal light is directly transmitted to the second polarizationA beam splitter. And the other beam of signal light passes through a second Dff prism after the light path of the signal light is changed by a third total reflector to realize the rotation of the phase of the photon, the polarization state of the photon is kept unchanged by utilizing a third 1/4 wave plate, and then the signal light passes through a fourth total reflector to change the light path and reaches a second polarization beam splitter. The two components are recombined at the second polarizing beam splitter, passed through a-45 ° fourth 1/4 waveplate to recover the change from circular to linear polarization using the orientation angles
And
the combination of the first half-wave plate and the second half-wave plate and the third polarization beam splitter can conveniently realize two arbitrary orbital angular momentum states | m1>And | m2>Separation of (4). And the signal light coming out of the third polarization beam splitter enters an OAM modulation unit and finally enters the coincidence measurement unit for measurement.
Preferably, the idle optical path is: OAM entanglement states output from the BBO crystal are sequentially input into the second total reflecting mirror to change an optical path, pass through a fifth 1/4 wave plate, and left-handed and right-handed circular polarization components are respectively converted into horizontal and vertical polarization components, separated by a fourth polarization beam splitter, and respectively transmitted along two arms of a second interferometer. One of the idle light beams is used for realizing the rotation of the phase of the photon through the third davit prism, the polarization state of the photon is kept unchanged by utilizing the sixth 1/4 wave plate, and then the idle light beam is directly transmitted to the fifth polarization beam splitter. The other beam of idle light passes through the fourth Dff prism after changing the light path through the fifth holophote to realize the rotation of the phase of the photon, the polarization state of the photon is kept unchanged by utilizing the seventh 1/4 wave plate, and then the idle light passes through the sixth holophote to change the light path and reaches the fifth polarization beam splitter. At the fifth polarizing beam splitter the two components are recombined, passing through an eighth 1/4 waveplate of-45 DEG, recovering the change from circular polarization to linear polarization, with the orientation angles respectively
And
the combination of the third half-wave plate and the fourth half-wave plate and the sixth polarization beam splitter can conveniently realize two arbitrary orbital angular momentum states | m |1>And | m2>Separation of (4). And the idle light from the sixth polarization beam splitter enters a modulation unit and finally enters the coincidence measurement unit together with the signal light for measurement.
Preferably, in the coincidence measurement of the coincidence measurement decoding, the coincidence measurement value satisfies the relation, depending on the phase deflection modulation information of the signal photons and the idle photons:
in the determination of the coincidental measurement decoded bit information, the specific method for recovering the coded key according to the coincidental measurement result is as follows: for example: the relative coincidence count value is '1', and the demodulation code is '0'; the relative coincidence count value is '0.5', and the demodulation code is '1'; the relative coincidence count value is "0", and the demodulation code "2". A random codebook sequence of 0, 1, 2 is established as the codebook.
Compared with the prior art, the beneficial effects of the utility model are that:
1. the utility model discloses mix the entanglement photon with OAM-OAM to the information carrier who regards as the coding and decoding, improved the security of multi-user orbit angular momentum wavelength division multiplexing QKD network system.
2. The utility model can load multi-bit coding information quantity for each OAM-OAM mixed entangled photon pair, and realizes 1-2N quantum coding and decoding channel;
3. the utility model discloses well M-Z type multiplexing technique has guaranteed the independence between each user, and can be based on the one-to-two QKD network communication system of OAM entanglement modulation codec simultaneously. Can conveniently realize two arbitrary orbital angular momentum states | m1>And | m2>So that it is possible to separateTopological charge m1And m2Two different paths communicate securely with two arbitrary Bob users.
4. The QKD network has the advantages of good security, simple devices, and easy implementation. The system has reasonable design and good expansibility.
Drawings
Fig. 1 is a schematic structural diagram of an M-Z OAM entangled modulation key distribution system according to the present invention;
fig. 2 is a detailed device diagram of an M-Z OAM entangled modulation key distribution system according to the present invention;
FIG. 3 is a diagram of a spin polarization orbital angular momentum-based M-Z interferometer unit of the present invention;
fig. 4 is a schematic diagram of the orbital angular momentum dependent deflection according to the present invention;
fig. 5 is a diagram of an extended orbital angular momentum cascade separation network according to the present invention;
the technical characteristics corresponding to the marks in the attached drawings are as follows: 1-OAM-OAM entanglement generation unit, 100-laser, 101-lens, 102-BBO crystal, 103-first total reflector, 104-second total reflector; 2-a first multiplexing module, 201-a first 1/4 wave plate, 202-a first polarization beam splitter, 203-a first dove prism, 204-a second 1/4 wave plate, 205-a second polarization beam splitter, 206-a third total reflection mirror, 207-a second dove prism, 208-a third 1/4 wave plate, 209-a fourth total reflection mirror, 210-a fourth 1/4 wave plate, 211-a first half wave plate, 212-a second half wave plate, 213-a third polarization beam splitter; 3-a second multiplexing module, 301-a fifth 1/4 waveplate, 302-a fourth polarization beam splitter, 303-a third dove prism, 304-a sixth 1/4 waveplate, 305-a fifth polarization beam splitter, 306-a fifth holophote, 307-a fourth dove prism, 308-a seventh 1/4 waveplate, 309-a sixth holophote, 310-an eighth 1/4 waveplate, 311-a third half waveplate, 312-a fourth half waveplate, 313-a sixth polarization beam splitter; 4-signal light OAM modulation unit, 401-first beam splitter, 402-first charge coupled device, 403-first retarder, 404-seventh polarization beam splitter, 405-first wavefront corrector, 406-first spatial light modulator, 407-first single mode fiber, 408-second beam splitter, 409-second charge coupled device, 410-second retarder, 411-eighth polarization beam splitter, 412-second wavefront corrector, 413-second spatial light modulator, 414-seventh total reflector, 415-second single mode fiber; 5-an idle optical OAM modulation unit, 501-a third beam splitter, 502-a third charge coupled device, 503-a third retarder, 504-a ninth polarization beam splitter, 505-a third wavefront corrector, 506-a third spatial light modulator, 507-a third single mode fiber, 508-a fourth beam splitter, 509-a fourth charge coupled device, 510-a fourth retarder, 511-a tenth polarization beam splitter, 512-a fourth wavefront corrector, 513-a fourth spatial light modulator, 514-an eighth total reflection mirror, 515-a fourth single mode fiber; 6-coincidence measuring unit, 601-first single-photon detector, 602-second single-photon detector, 603-ninth total reflecting mirror, 604-third single-photon detector, 605-fourth single-photon detector, 606-tenth total reflecting mirror, 607-first coincidence counter, 608-second coincidence counter.
Detailed Description
The following description of the embodiments of the present invention will be made with reference to the accompanying drawings 1-5:
referring to fig. 1, the M-Z OAM entanglement modulation key distribution system includes an Alice control end, an M-Z multiplexing module, and a Bob user end. The Alice control end comprises an OAM-OAM entanglement generation unit, a modulation unit and a coincidence measurement unit;
referring to fig. 2, the Alice control end includes an OAM-OAM entanglement generating unit 1, an OAM modulating unit 4, and a coincidence measuring unit 6; the OAM entanglement generation unit 1 comprises a pump light source LD, a lens 101, a BBO crystal 102, a first total reflector 103 and a second total reflector 104; the pump light source LD is a laser 100.
The OAM modulation unit 4 includes a first beam splitter 401, a first charge coupled device 402, a first retarder 403, a seventh polarization beam splitter 404, a first wavefront corrector 405, a first spatial light modulator 406, a first single mode fiber 407, a second beam splitter 408, a second charge coupled device 409, a second retarder 410, an eighth polarization beam splitter 411, a second wavefront corrector 412, a second spatial light modulator 413, a seventh total reflection mirror 414, a second single mode fiber 415;
the coincidence measuring unit 6 comprises a first single-photon detector 601, a second single-photon detector 602, a ninth total reflection mirror 603, a third single-photon detector 604, a fourth single-photon detector 605, a tenth total reflection mirror 606, a first coincidence counter 607 and a second coincidence counter 608;
the M-Z multiplexing module comprises a first multiplexing module 2 and a second multiplexing module 3; wherein the first multiplexing module comprises a first M-Z interferometer, the first M-Z interferometer comprises a first 1/4 wave plate 201, a first polarization beam splitter 202, a first davit prism 203, a second 1/4 wave plate 204, a second polarization beam splitter 205, a third total reflection mirror 206, a second davit prism 207, a third 1/4 wave plate 208, a fourth total reflection mirror 209, a fourth 1/4 wave plate 210, a first half wave plate 211, a second half wave plate 212, a third polarization beam splitter 213;
the second multiplexing module 3 comprises a second M-Z interferometer comprising a fifth 1/4 waveplate 301, a fourth polarizing beamsplitter 302, a third davit prism 303, a sixth 1/4 waveplate 304, a fifth polarizing beamsplitter 305, a fifth total reflecting mirror 306, a fourth davit prism 307, a seventh 1/4 waveplate 308, a sixth total reflecting mirror 309, an eighth 1/4 waveplate 310, a third half waveplate 311, a fourth half waveplate 312, a sixth polarizing beamsplitter 313;
the OAM-OAM entanglement generation unit 1 is used for generating signal light and idle light carrying OAM entangled state; the first multiplexing module 2 is connected with the OAM-OAM entanglement generating unit 1 and separates different topological charge values; the OAM modulation unit 4 is connected with the first multiplexing module 2, respectively performs phase coding modulation on OAM carried by the signal light according to different OAM topological charge values, and sends coding information to the coincidence measurement unit 6; the second multiplexing module 3 is connected with the OAM-OAM entanglement generating unit 1, the Bob user end 5 is connected with the second multiplexing module 3, respectively performs phase coding modulation on OAM carried by idle light according to different OAM topological charge values, and sends coding information to the coincidence measuring unit 6; the lens 101 is used for collimating and focusing the light beam; the BBO crystal 102 is used to generate OAM entangled photon pairs.
The Bob user terminal 5 comprises Bob1And Bobm2A user, wherein the bob user includes a third beam splitter 501, a third charge-coupled device 502, a third retarder 503, a ninth polarization beam splitter 504, a third wavefront corrector 505, a third spatial light modulator 506, a third single-mode fiber 507, a fourth beam splitter 508, a fourth charge-coupled device 509, a fourth retarder 510, a tenth polarization beam splitter 511, a fourth wavefront corrector 512, a fourth spatial light modulator 513, an eighth all-mirror 514, and a fourth single-mode fiber 515; the Bobm1The user is connected with the second multiplexing module 3 and used for carrying out topology load m1The OAM carried by the idle light is modulated, the coding information is loaded, and the coding information is sent to the coincidence measurement unit 6; the Bobm2The user is connected with the second multiplexing module 3 and used for carrying out topology load m2The OAM carried by the idle light is modulated, the coding information is loaded, and the coding information is sent to the coincidence measurement unit 6; the coincidence measurement unit 6 is located between the OAM modulation unit 4 and the Bob client 5, and is configured to record the coding information of the same topology load of the signal light sent by the OAM modulation unit 4 and the idle light sent by the Bob client 5, and perform coincidence measurement decoding.
The utility model discloses specific theory of operation is as follows, laser instrument 100 launches 355nm laser and just incides in BBO crystal 102 after lens 101 focuses on, under the excitation of incident laser, BBO crystal 102 produces 710 nm's signal photon and idle photon through spontaneous parametric down-conversion, and the photon of production is to entangling in orbital angular momentum degree of freedom, and the photon of entangling this moment is to the quantum attitude:
in equation (1), S and I represent signal photons and idle photons, respectively, m represents OAM topological charge, | Cm|2Representing the probability of generating OAM entangled photon pairs.
The signal light coming out of the BBO crystal 102 is reflected by the first total reflection mirror 103 and enters the first multiplexing module 2, as shown in fig. 3, the incident photons coming out of the BBO crystal 102 are all horizontally polarized "spiral" photons, and it is noted that
Wherein the horizontal polarization state can be regarded as coherent superposition of left-handed and right-handed circularly polarized light of equal amplitude, i.e.
Through the first 1/4 waveplate 201 at 45 °, the left-and right-handed circular polarization components are converted into horizontal and vertical polarization components, respectively:
wherein
Is a Jones matrix corresponding to the 1/4 wave plate,
is a matrix expression of left and right hand circular polarization states.
If the relative orientation angle of the first and second dove prisms 203, 207 is set to α, then for the orbital angular momentum state | M >, a phase difference exp (im2 α) is introduced between the two arms, three consecutive reflections between the first and second dove prisms 203, 207 result in a phase shift of 90 ° so we compensate this phase shift with the second 1/4 waveplates 204, 208, keeping the polarization state of the photon constant.A polarization state of the photon constant is maintained.A phase shift of 90 ° is obtained from equation (2):
at the second polarizing beam splitter 205 the two polarization components are recombined, passing through a-45 o fourth 1/4 waveplate 210, restoring the change from circular polarization to linear polarization:
wherein,
is a Jones matrix corresponding to the lambda/4 wave plate.
And finally obtaining:
obtained as
Equation (5) indicates that our interferometer can simulate the effect of optical rotation to achieve a rotation of polarization state, and the angle of rotation is proportional to the orbital angular momentum of the photon, thus, OAM dependent spin polarization operation can be achieved. For example: we need to separate two arbitrary orbital angular momentum states | m1>And | m2>. From equation (5), we know | m1>The photons will have β1＝m1α spin deflection of angle, | m2>Will have β2＝m2α angle of spin polarization, the polarization directions of the two photons will result in an angle Δ β ═ m (m)1-m2) α, as shown in fig. 4, if α ═ pi/[ 2 (m) is preset1-m2)]Then the two photons will have polarizations perpendicular to each other, as shown in fig. 4, and then the angles of orientation are used to be
And
the combination of the first half-wave plate 211 and the second half-wave plate 212, and the third polarization beam splitter 213 can conveniently realize two arbitrary orbital angular momentum states | m1>And | m2>Separation of (4). This allows the topology to be loaded m, as shown in FIG. 51And m2Two different paths communicate securely with two arbitrary Bob users.
The signal light coming out of the third polarization beam splitter 213 enters the OAM modulation unit 4, and the incident pulse laser is divided into two paths of strong and weak, which are a stronger upper branch and a weaker lower branch, respectively, by the first beam splitter 401 and the second beam splitter 408; the upper branch is connected with the first charge coupling element 402 and the second charge coupling element 409, and is used for monitoring the intensity of laser pulses and wavefront phase distortion caused by atmospheric turbulence in real time and providing reference information for clock synchronization and phase distortion compensation; the pulse laser separated to the lower branch enters the first delayer 403 and the second delayer 410 firstly, and enters the seventh polarization beam splitter 404 and the eighth polarization beam splitter 411 after a certain time delay, the seventh polarization beam splitter 404 and the eighth polarization beam splitter 411 respectively reflect the pulse laser to the first Wavefront Corrector (WC)405 and the second Wavefront Corrector (WC)412, the first wavefront corrector 405 performs distortion compensation on a wavefront phase according to reference information provided by the upper branch, the compensated pulse laser is reflected to the first incoming Spatial Light Modulator (SLM)406, and the first spatial light modulator 406 performs encoding on orbital angular momentum on pulses. When it is in contact with Bobm1When a user communicates, the OAM topological load is m1Enters a first Spatial Light Modulator (SLM)406, and the first spatial light modulator 406 charges topology m1The OAM carried by the signal light is modulated, and the modulated quantum state can be expressed as:
in equation (6), θsIs the yaw phase orientation angle of orbital angular momentum. Then, the signal light is coupled through a first Single Mode Fiber (SMF)407 and then sent to a first single photon detector 601 in the coincidence measurement unit 6.
When it is in contact with Bobm2When a user communicates, the OAM topological load is m2Enters a second Spatial Light Modulator (SLM)413, and the second SLM 413 has a topological charge of m2The OAM carried by the signal light is modulated by phase coding, and the modulated quantum state can be expressed as:
in equation (7), θsA deflection phase orientation angle of orbital angular momentum, different thetasCorresponding to the corresponding deflection of orbital angular momentum. Then, after the signal light is reflected by the seventh total reflector 414 and coupled by the second single-mode fiber (SMF)415, the second single-mode fiber 415 transmits the quantum state code of the fundamental mode gaussian mode to the second single-photon detector 602, and sends the quantum state code to the second single-photon detector 602 in the coincidence measurement unit through the ninth total reflector 603.
The idle light coming out of the BBO crystal 102 is reflected by the second total reflection mirror 104 and enters the second multiplexing module 3, and two arbitrary orbital angular momentum states | m1>And | m2>After separation, the idle light coming out of the sixth polarization beam splitter 313 enters the Bob client 5, and the incident pulse laser is divided into two paths of strong and weak branches through the third beam splitter 501 and the fourth beam splitter 508, namely a strong upper branch and a weak lower branch; the upper branch is connected with the third charge coupling element 502 and the fourth charge coupling element 509, and is used for monitoring the intensity of the laser pulse and the wavefront phase distortion caused by the atmospheric turbulence in real time and providing reference information for clock synchronization and phase distortion compensation; the pulse laser separated to the lower branch enters a third delayer 503 and a fourth delayer 510, after a certain time delay, the pulse laser enters a ninth polarization beam splitter 504 and a tenth polarization beam splitter 511, the ninth polarization beam splitter 504 and the tenth polarization beam splitter 511 respectively reflect the pulse laser to a third wave front corrector (WC)505 and a third wave front corrector 512, the third wave front corrector (WC)505 performs distortion compensation on a wave front phase according to reference information provided by the upper branch, the compensated pulse laser is reflected to enter a third Spatial Light Modulator (SLM)506, the third spatial light modulator 506 performs encoding on an orbital angular momentum deflection phase of the pulse, and when the encoded pulse laser and the Bobm m deflection phase encode the orbital angular momentum deflection phase1When a user communicates, the OAM topological load is m1Enters a third Spatial Light Modulator (SLM)506, the third SLM 506 having a topological charge of m1The OAM carried by idle light carries out phase coding modulationThe modulated quantum state can be expressed as:
in equation (8), θIIs the yaw phase orientation angle of orbital angular momentum. The idle light is then coupled through a third Single Mode Fiber (SMF)507 and sent to a third single photon detector 604 in the coincidence measurement unit 6.
When it is in contact with Bobm2When a user communicates, the OAM topological load is m2Enters a fourth Spatial Light Modulator (SLM)513, the fourth SLM 513 charges a topology m2The OAM carried by the idle light is modulated by phase coding, and the modulated quantum state can be expressed as:
in equation (9), θIA deflection phase orientation angle of orbital angular momentum, different thetaICorresponding to the corresponding deflection of orbital angular momentum. The idle light is then coupled through a fourth Single Mode Fiber (SMF)515 and sent to a fourth single photon detector 605 in the coincidence measurement unit.
And (3) encoding the quantum bit: the Alice control end and Bob user end 5 perform phase deflection modulation on the orbital angular momentum of the signal light and the idle light by using an orbital angular momentum modulation unit, for example: the Alice control terminal deflects the orbital angular momentum by an orientation angle thetasModulation is pi/4, Bob user terminal 5 randomly modulates the deflection phase orientation angle theta of orbital angular momentumIThe modulation is pi/8 and pi/4.
The Alice control terminal selects different legal users according to the communication requirements, and when the Alice control terminal and the Bobm1When a user communicates, the first single-photon detector 601 is used for recording signal photons arriving in unit time and sending recorded detection data to the first coincidence counter 607, meanwhile, the third single-photon detector 604 is used for recording idle photons arriving in unit time and sending recorded detection data to the first coincidence counter 607, and finally, the first coincidence counter607 performing coincidence measurement and decoding according to the modulation information transmitted by the first single-photon detector 601 and the third single-photon detector 604, wherein the two paths of coincidence probability functions are
When Alice control terminal and Bobm2When a user communicates, a second single-photon detector 602 records signal photons arriving in unit time, recorded detection data are sent to a second coincidence counter 608, a fourth single-photon detector 605 records idle photons arriving in unit time, recorded detection data are sent to the second coincidence counter 608, finally, an eighth coincidence counter 608 performs coincidence measurement and decoding according to modulation information transmitted by the second single-photon detector 602 and the fourth single-photon detector 605, and at the moment, two paths of coincidence probability functions are
And (3) forming a code by using the secret key, and restoring the coded secret key by using the Alice control terminal according to the measurement result, for example: the relative coincidence count value is '1', and the demodulation code is '0'; the relative coincidence count value is '0.5', and the demodulation code is '1'; the relative coincidence count value is "0", and the demodulation code "2". A random codebook sequence of 0, 1, 2 is established as the codebook. The following equations (10) and (11) show that: the coincidence counting function is in cosine square relation with the difference of the orbital angular momentum state deflection orientation angles of the signal light and the idle light. By using the coincidence counting method, the Alice control end and the Bob user end 5 can distribute the quantum key, and the basic idea is as follows: alice one end keeps the deflection orientation angle theta of the modulation orbital angular momentum statesThe deflection orientation angle theta of the orbital angular momentum state is modulated in real time at Bob client 5 without changing (for example, the orientation can be fixed to pi/4)IAnd finally, the Alice recovers the secret key coded by the Bob user terminal 5 from different relative coincidence counting values.
For example, when m is 1, θsWhen pi/4, then phaseFor coincidence with the count value of
Relationship of coded bit value to relative coincidence count value:
| orbital angular momentum deflection angle thetaI | π/4 | π/2 | 3π/4 |
| Relatively matches the count value C (phi)s,m,φI,m) | 1 | 0.5 | 0 |
| |
0 | 1 | 2 |
As shown in fig. 2, Alice's control end manipulates the OAM state of signal photons only in its private domain, as does Bob's user end 5, which handles the OAM state of idle light. In these private areas, the eavesdropper Eve has no chance of getting exposed to photons. Of course, an eavesdropper Eve still has the opportunity to eavesdrop when Alice's control end transmits photons to Bob's user end 5 in free space. The eavesdropper Eve intercepts and measures each idle light, prepares a new photon according to the measurement result, and then retransmits the new photon to the Bob client 5. However, since the idle light and the signal light are in an entangled state, photons remaining after an Eve attack by an eavesdropper will not satisfy equations (10) and (11). Moreover, the Alice control end always has signal light, and the attack behavior of Eve can be detected through the CHSH inequality.
S＝|E(θs,θI)-E(θs,θ'I)+E(θ'S,θI)+E(θ'S,θ'I)|≤2 (12)
E (θ) heres,θI) From the coincidence count we obtain:
if the inequality exists, entanglement will be preserved, and Alice control can ensure that the channel is free from attack.
The above description is only an embodiment of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions within the technical scope of the present disclosure should be covered by the scope of the present application. Variations and modifications to the above-described embodiments may occur to those skilled in the art, in light of the above teachings and teachings. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should fall within the protection scope of the claims of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Claims (7)
1. An M-Z type OAM entanglement modulation key distribution system, characterized by: the system comprises an Alice control end, a multiplexing module and a Bob user end; the Alice control end comprises an OAM-OAM entanglement generation unit, an OAM modulation unit and a coincidence measurement unit; the multiplexing module comprises a first multiplexing module and a second multiplexing module, and the OAM-OAM entanglement generating unit is respectively connected with the first multiplexing module and the second multiplexing module; the first multiplexing module, the OAM modulation unit and the coincidence measurement unit are sequentially connected; the second multiplexing module, the Bob user side and the coincidence measurement unit are sequentially connected;
the OAM-OAM entanglement generation unit is used for generating orbital angular momentum and orbital angular momentum mixed entangled quantum states;
the OAM modulation unit is used for carrying out phase deflection modulation on the orbital angular momentum and loading coding information;
the coincidence measurement unit is used for performing coincidence measurement on the signal light and the idle light and decoding quantum bit information;
the first multiplexing module and the second multiplexing module are used for separating any OAM state;
the OAM-OAM entanglement generation unit generates an OAM-OAM entangled-state signal optical path and an idle optical path; the signal light path enters a first multiplexing module for polarization separation, then enters an OAM modulation unit for phase deflection modulation and loading coding information, and then is sent to a coincidence measurement unit for measurement;
the idle optical path enters a second multiplexing module for polarization separation, and then is modulated and loaded with coding information by the Bob user side and then is sent to a coincidence measurement unit for measurement;
the coincidence measurement unit performs coincidence measurement on signal photons and idle photons with the same wavelength and arriving in unit time, recovers an encoded secret key according to a coincidence measurement result, establishes a sequence of random passwords as an original password, and obtains a safe secret key through secret key screening and privacy amplification, thereby completing multi-user secret key distribution and sharing.
2. The M-Z OAM entangled modulation key distribution system of claim 1, wherein: the orbit angular momentum mixing entanglement unit comprises a pump light source LD, a lens, a BBO crystal, a first holophote and a second holophote, wherein the BBO crystal is sequentially connected with the lens and the pump light source LD and is used for generating signal photons and idle photon orbit angular momentum entanglement photon pairs, and the photon orbit angular momentum mixing entanglement unit is represented as follows:
wherein S and I respectively represent signal photons and idle photons, and m represents OAM topological charge.
3. The M-Z OAM entangled modulation key distribution system of claim 2, wherein: the first multiplexing module comprises a first M-Z interferometer, the first M-Z interferometer comprises first to fourth 1/4 wave plates, first and second half-wave plates, first to third polarizing beam splitters, first and second dove prisms, third and fourth total reflection mirrors; the second multiplexing module comprises a first M-Z interferometer, the first M-Z interferometer comprises fifth to eighth 1/4 wave plates, third and fourth half-wave plates, fourth to sixth polarizing beam splitters, third and fourth dove prisms, fifth and sixth total reflection mirrors; the signal light and the idle light coming out of the BBO crystal enter a first multiplexing module and a second multiplexing module after being reflected by a first total reflector and a second total reflector respectively, the incident photons are horizontally polarized spiral photons, and two arbitrary orbital angular momentum states | M are realized by a first M-Z interferometer and a second M-Z interferometer respectively1>And | m2>Separation of (4).
4. An M-Z type OAM entangled modulation key distribution system as recited in claim 3, wherein: the OAM modulation unit comprises a first beam splitter, a first charge coupled device, a first retarder, a polarization beam splitter, a first wavefront corrector, a first spatial light modulator, a first single mode fiber, a second beam splitter, a second charge coupled device, a second retarder, a second wavefront corrector, a second spatial light modulator, a second single mode fiber and a seventh total reflection mirror.
5. The M-Z OAM entangled modulation key distribution system according to claim 4, wherein: the Bob user side comprises Bobm1And Bobm2User, Bobm1And Bobm2The user comprises a third beam splitter, a third charge coupled device, a third retarder, a ninth polarization beam splitter and a third pre-wave correctorThe optical fiber comprises a first spatial light modulator, a first single-mode optical fiber, a first beam splitter, a first charge-coupled element, a first retarder, a first polarization beam splitter, a first wavefront corrector, a first spatial light modulator, a first full mirror and a first single-mode optical fiber; the first wave-front corrector to the fourth wave-front corrector can change the optical path of the wave-front transmission of the light wave or change the refractive index of the transmission medium to change the phase structure of the wave-front of the incident light wave according to the reference information of the phase distortion, thereby achieving the purpose of compensating the wave-front phase of the light wave; the first charge coupling element, the second charge coupling element, the third charge coupling element, the fourth charge coupling element and the fourth charge coupling element are used for monitoring the intensity of laser pulses and wavefront phase distortion caused by atmospheric turbulence in real time and providing reference information for clock synchronization and phase distortion compensation; the first to fourth spatial light modulators perform deflection phase modulation on OAM carried by signal light and idle light with topological charge of m, and the modulated quantum-state signal light and idle light are represented as follows:
wherein, thetas、θIA deflection phase orientation angle that is orbital angular momentum;
the first to fourth single-mode fibers are used for coupling and transmitting Gaussian mode signal photons and idle photons.
6. The M-Z OAM entangled modulation key distribution system of claim 5, wherein: when Alice control terminal and Bobm1When a user communicates, the OAM topological load is m1The signal light enters a first spatial light modulator, and the first spatial light modulator has a topological charge of m1Modulating OAM carried by the signal light; when Alice control terminal and Bobm2When a user communicates, the OAM topological load is m2Enters a second spatial light modulator, and the second spatial light modulator has a topological charge of m2Carried by signal lightOAM performs phase-coded modulation.
7. The M-Z OAM entangled modulation key distribution system of claim 1, wherein: the coincidence measurement unit comprises first to fourth single photon detectors, first and second coincidence counters, the single photon detectors are used for recording the number of arriving signal photons and idle photons in unit time and sending detection data of the arriving signal photons and idle photons to the coincidence counter, and the coincidence counter is used for performing coincidence measurement.
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| CN112865879A (en) * | 2020-12-31 | 2021-05-28 | 华南师范大学 | Spin-orbit angular momentum coupled hybrid entangled state generation system and method |
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| CN111130779A (en) * | 2019-12-31 | 2020-05-08 | 华南师范大学 | OAM entanglement modulation key distribution network system and method for real-time tracking compensation |
| CN111130779B (en) * | 2019-12-31 | 2024-04-26 | 广东尤科泊得科技发展有限公司 | OAM entanglement modulation key distribution network system and method for real-time tracking compensation |
| CN112865879A (en) * | 2020-12-31 | 2021-05-28 | 华南师范大学 | Spin-orbit angular momentum coupled hybrid entangled state generation system and method |
| CN112865879B (en) * | 2020-12-31 | 2022-04-19 | 华南师范大学 | Spin-orbit angular momentum coupled hybrid entangled state generation system and method |
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