Patent Application
20220029798
The disclosure relates to the technical field of quantum information and optical communication, and more particularly relates to an OAM measurement device independent quantum key distribution system based on real-time tracking compensation and method thereof.
Since the first Quantum Key Distribution protocol was introduced in 1984, Quantum Key Distribution (QKD) has been considered as a very feasible technique in Quantum information science. QKD allows two remote users (Alice and Bob) to generate a key with theoretically unconditional security according to the law of quantum physics. However, in real-world environments, there is a gap between the ideal model and the actual device. For example, an ideal QKD protocol requires an ideal single photon source and detector to ensure its safety. It is hard to achieve an ideal single photon source and detector with current technology. The non-ideality of these devices makes QKD systems vulnerable to various attacks, such as photon number splitting attacks, time-shifting attacks, blinding attacks, etc.
To overcome these difficulties, a concept of Device independent Quantum Key Distribution (DI-QKD) has been proposed. The security of the DI-QKD is not dependent on the characteristics of the device, which means that a quantum hacker cannot exploit this deficiency to steal any information, even if the device is not ideal. Therefore, DI-QKD can always guarantee unconditional theoretical safety. However, the implementation of DI-QKD is a difficult challenge, which requires perfect Bell-state measurements and very efficient single photon detection techniques, which are difficult to achieve with the existing technologies. However, the recently proposed Measurement Device Independent Quantum Key Distribution protocol (MDI-QKD) shortens the distance between DI-QKD and practical use, achieves partial QKD Device Independent Quantum communication, and eliminates all security holes related to detection. Meanwhile, the protocol introduces a scheme of decoy state, converts the photon state into a mixed state of photon number by using phase randomization, which can well prevent photon number splitting attack. Various MDI-QKD implementations have been developed, such as polarization-coding, phase-coding, and time-bin-coding.
The MDI-QKD protocol solves all loopholes of a quantum key system measuring end at one time, but there is still loopholes influencing safety in a light source part, a modulation part, a side channel part and the like, for example, the traditional MDI-QKD (patent: CN106712940) introduces a weak coherent light source in combination with a decoy state, which reduces the requirement of the MDI-QKD system on the light source, but both parties of users use independent light sources respectively, and the spectrums of the emitted light are inconsistent. By utilizing the difference, a quantum hacker can distinguish the source of the photon and further steal the key information of the user. To solve the problem of inconsistent spectrum, plug-and-play MDI-QKD is proposed (Article: Liu, C. Q. at. (2016) Polarization-Encoding-Based Measurement-Device-Independent Quantum Key Distribution with a Single unordered source, Chinese Physics Letters, 33 (10)), but the modulation scheme has the problem of incomplete matching of a measuring base reference system, which increases the error rate. In view of the above, recently proposed MDI-QKD scheme based on Orbital Angular Momentum (OAM) coding solves the problem of incomplete matching of reference system (Article: Wang L, Zhao S M, Gong L Y, et al, Free-space measurement-device-independent quantum-key-distribution protocol using with orthogonal irregular absorption spectrum [J] Chinese Physics B, 2015, 24(12): 120307), reduces bit error rate, but has the problem of spectrum inconsistency, and there is no good monitoring method and signal compensation method for channel environment, so the performance of the weak signal quantum key distribution system is very easily affected by external environment.
The present disclosure is directed to overcome the above-mentioned deficiencies of the prior art, and to provide an OAM measurement device independent quantum key distribution system based on real-time tracking compensation, in which a measuring unit transmits an intensive light pulse to a user side by using a pulse laser, a polarization beam splitter, and a beam splitter. The user side utilizes a Charge coupled device (CCD) and a beam splitter for monitoring and synchronization, performs phase distortion compensation through a deformable mirror, and utilizes an intensity modulator and a spatial light modulator to randomly generate decoy state photons and signal state photons of orbital angular momentum with the number of the photons less than 1, and sends the photons to a middle measuring unit. The measuring unit measures the photon state sent by the user and publishes the measuring result, and the user locally generates a consistent key after the processes of base comparison, key agreement and the like according to the response condition of the measurement.
Another objective of the present disclosure is to provide an OAM measurement device independent quantum key distribution method based on real-time tracking compensation, which can naturally implement matching of spectrum modes, and can conveniently implement real-time channel monitoring, pulse intensity measurement and atmospheric turbulence intensity measurement, clock synchronization, and the like.
In order to achieve the purpose of the disclosure, the technical scheme of the disclosure is as follows:
an OAM measurement device independent quantum key distribution system based on real-time tracking compensation, comprising: a user side Alice, a user side Bob and a measuring unit;
the user side Alice and the user side Bob are connected with the measuring unit through quantum channels, wherein:
the measuring unit comprises: the system comprises a first telescope system, a second telescope system, a first 50/50 beam splitter, a first polarization beam splitter, a pulse laser, a first reflector, a second reflector, a third reflector and a fourth reflector, a first M-Z interferometer and second M-Z interferometer, and a first single photon detector, a second single photon detector, a third single photon detector and a fourth single photon detector; when a pulse laser of the measuring unit emits a fundamental mode Gaussian beam, the fundamental mode Gaussian beam with the polarization mode of vertical polarization is reflected to a first 50/50 beam splitter and splitted into 2 beams through screening of the first polarization beam splitter, then is respectively reflected by the first reflector and the second reflector, and afterwards is collimated by the first telescope system and the second telescope system and is finally respectively transmitted to the user side Alice and the user side Bob through quantum channels;
the user side Alice and the user side Bob respectively perform channel environment real-time monitoring, phase distortion compensation and orbital angular momentum encoding on the strong pulse laser from the measuring unit and then send the strong pulse laser to the test unit;
when the first telescope system and the second telescope system of the measuring unit respectively receive signal pulses from a user side Alice and a user side Bob, the signal pulses are reflected by the first reflector and the second reflector, then are interfered at a third 50/50 beam splitter, the interfered pulses respectively enter a first M-Z interferometer and a second M-Z interferometer after being respectively reflected by the third reflector and the fourth reflector; and then the pulses enter the first single photon detector, the second single photon detector, the third single photon detector and the fourth single photon detector to cause response and output measuring results after being separated by the first M-Z interferometer and the second M-Z interferometer; and the user side Alice and the user side Bob locally generate consistent keys after the processes of base comparison, key agreement and the like according to the measured response condition.
Preferably, the user side Alice comprises: a third telescope system, a first narrow band filter, a first beam splitter, a first Charge coupled device (CCD), a first delayer, a second polarization beam splitter, a first deformable mirror, a second deformable mirror, a first half-wave plate, a first spatial light modulator and a first intensity modulator;
the user side Bob comprises: a fourth telescope system, a second narrow-band filter, a second beam splitter, a second Charge coupled device (CCD), a second delayer, a third polarization beam splitter, a third deformable mirror, a fourth deformable mirror, a second half-wave plate, a second spatial light modulator and a second intensity modulator.
Preferably, the first spatial light modulator, the second spatial light modulator and the first intensity modulator, the second intensity modulator randomly modulate pulses;
when the first spatial light modulator and the second spatial light modulator encode orbital angular momentum, the first spatial light modulator and the second spatial light modulator randomly select one of four states
for encoding; wherein {|o, |e
} is X base;
is Y base, and |o and
represents bit 0; and |e and
represents bit 1; and |o and |e
respectively represent orbital angular momentum states of odd topological charge numbers and orbital angular momentum states of even topological charge numbers; the first intensity modulator and the second intensity modulator accurately generate the photons in the decoy state and the signal state with different average photon number intensities.
Preferably, the third telescope system and the fourth telescope system each comprise two confocal convex lenses for controlling the size of the laser pulse and the far-field divergence angle of the laser beam; the first narrow-band filter and the second narrow-band filter are provided for filtering light out of a communication waveband; the first beam splitter and the second beam splitter divide incident pulse laser into two paths of strong pulse laser and weak pulser laser, namely a strong upper branch and a weak lower branch; the first Charge coupled device (CCD) and the second Charge coupled device (CCD) are provided 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 of the lower branch; the second polarization beam splitter and the third polarization beam splitter transmit the horizontal polarization light and reflect the vertical polarization light; the first deformable mirror, the second deformable mirror, the third deformable mirror and the fourth deformable mirror are also called wavefront correctors, which may change the optical path of the wave front transmission or change the refractive index of a transmission medium to change the phase structure of the wave front of the incident light according to the reference information of phase distortion, so as to achieve the purpose of compensating the wave phase of the light wave; the principal sections of the first half-wave plate and the second half-wave plate are provided at an angle of 45 degrees with the polarization surface of incident light, and the polarization direction of the incident light may be rotated by 90 degrees; the first spatial light modulator and the second spatial light modulator are phase-only reflective liquid crystal spatial light modulators, which are active digital optical devices based on liquid crystal molecule electro-birefringence effect, and provided for modulating orbital angular momentum of laser beams; the first intensity modulator and the second intensity modulator may accurately generate the decoy state photons and the signal state photons with different average photon number intensities.
Preferably, the third telescope system of the user side Alice receives the pulse laser from the measuring unit, then filters light out of a communication band through the first narrow band filter, and divides the incident pulse laser into two paths of strong pulse laser and weak pulser laser through the first beam splitter, namely a strong upper branch and a weak lower branch; the upper branch is connected with a first charge coupled device 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 lower branch is provided for modulating pulse loading phase information and is sequentially connected with a first delayer, a second polarization beam splitter, a first deformable mirror, a first half-wave plate, a first spatial light modulator, a first intensity modulator and a second deformable mirror; the pulse laser splitted into the lower branch enters a first delayer, and enters a second polarization beam splitter after a certain time delay, the second polarization beam splitter reflects the pulse laser to a first deformable mirror, and the first deformable mirror performs distortion compensation on a wavefront phase according to reference information provided by the upper branch; the compensated pulse laser is reflected to a first half-wave plate, the first half-wave plate turns the polarization state of the pulse laser by 90 degrees and then enters a first spatial light modulator, and the first spatial light modulator encodes the pulse with orbital angular momentum; the coded pulses are modulated into an orbital angular momentum signal state and a decoy state with different average photon number intensities by a first intensity modulator, the orbital angular momentum signal state and the decoy state enter the second deformable mirror for phase correction, then it is transmitted from a second polarization beam splitter, and reaches a third telescope system through a first delayer, a first beam splitter and a first narrow-band filter; and finally, it is collimated by the third telescope system and sent to the measuring unit.
Preferably, the fourth telescope system of the user side Bob receives the pulse laser from the measuring unit, filters light outside a communication band through a second narrowband filter, and divides the incident pulse laser into two paths of strong pulse laser and weak pulse laser through a second beam splitter, namely a strong upper branch and a weak lower branch; the upper branch is connected with a second charge coupled device provided 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 lower branch is provided for modulating pulse loading phase information and is sequentially connected with a second delayer, a third polarization beam splitter, a third deformable mirror, a second half-wave plate, a second spatial light modulator and a second intensity modulator; the pulse laser splitted into the lower branch enters a second delayer, and enters a third polarization beam splitter after a certain time delay, the third polarization beam splitter reflects the pulse laser to a third deformable mirror, and the third deformable mirror performs distortion compensation on a wavefront phase according to reference information provided by the upper branch; the compensated pulse laser is reflected to a second half-wave plate, the second half-wave plate turns the polarization state of the pulse laser by 90 degrees and then enters a second spatial light modulator, and the second spatial light modulator encodes the pulse with orbital angular momentum; the coded pulses are modulated into an orbital angular momentum signal state and a decoy state with different average photon number intensities by a second intensity modulator, the orbital angular momentum signal state and the decoy state enter the fourth deformable mirror for phase correction, then it is transmitted from a third polarization beam splitter, and reaches a fourth telescope system through a second delayer, a second beam splitter and a second narrow-band filter; and finally, it is collimated by the fourth telescope system and sent to the measuring unit.
Preferably, the first charge coupled device (CCD) and the second charge coupled device (CCD) are provided 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, and the first deformable mirror, the second deformable mirror, the third deformable mirror and the fourth deformable mirror are respectively provided for performing distortion compensation on the wavefront phase according to the reference information provided by the first charge coupled device (CCD) and the second charge coupled device (CCD).
Preferably, the first deformable mirror and the third deformable mirror perform distortion compensation on the wavefront phase according to phase distortion information provided by the upper branch, and the compensated laser recovers to a state without phase distortion; the second deformable mirror and the fourth deformable mirror correct the wavefront phase according to the phase distortion information provided by the upper branch, so that the incident light generates a conjugate phase conjugated with the distortion phase, when the laser beam returns to the measuring unit through the original light path, the phase distortion caused by the environment such as atmospheric turbulence and the like is counteracted, and the laser beam recovers to the state without phase distortion.
Preferably, the first M-Z interferometer comprises a second 50/50 beam splitter, a third 50/50 beam splitter, a fifth mirror, a sixth mirror, a first dove prism and a second dove prism; the second M-Z interferometer comprises a fourth 50/50 beam splitter, a fifth 50/50 beam splitter, a seventh mirror, an eighth mirror, a third dove prism and a fourth dove prism.
Preferably, the quantum channel is a free space channel or a fiber channel.
When the measuring unit receives the signal pulses from the user side Alice and the user side Bob and performs interferometric measurement on the signal pulses, the first 50/50 beam splitter of the measuring unit erases photon state path information, so that photon states are indistinguishable. Due to the HOM effect, the same photon state will be output from the same output port of the first 50/50 splitter, while different photon states are output independently of each other.
Specifically, after the signal pulses are interfered by a first 50/50 beam splitter of the measuring unit, the signal pulses are output from the upper port and the lower port of the first 50/50 beam splitter, reflected by the reflector and enter a first M-Z interferometer and a second M-Z interferometer.
Taking the first M-Z interferometer as an example, the function of the first M-Z interferometer on the input photons is represented as follows:
assuming the photon state incident to the input port of the M-Z interferometer is provided as follows:
|ϕin=|0
|1
Wherein, |0 represents a vacuum state and |1
represents a single photon state. After passing through the second 50/50 beam splitter, the photon state becomes:
|ϕBS1=
(|0
|1
+i|1
|0
)
the above equation shows that the probability of photons being output from the transmissive end and reflective end of the second 50/50 splitter is respectively 50%, where i represents the half-wave phase shift caused when the photons are output from the reflective end. After the photon state is acted by the Dove prism module, the phase difference ϕ=lα generated by the two optical paths, the photon state becomes:
|ϕ=
(|0
|1
+ieiϕ(|1
|0
)
after passing through a third 50/50 beam splitter, the photon state becomes:
|ϕBS2=(1−eiϕ)|0
|1
+i/2(1+eiϕ)|1
|0
Assuming α=π,
when the orbital angular momentum order l is odd numbers, |ϕBS2 becomes |0
|1
, photons are transmitted from the third 50/50 beam splitter;
when the orbital angular momentum order l is even numbers, |ϕBS2 becomes |1
|0
, the photons become reflected from the third 50/50 beam splitter.
And finally, the states output by the M-Z interferometer are detected by a single photon detector, and a result is output in response. Specifically, the response of measuring unit is listed as follows:
As shown in the list, the first single photon detector or the third single photon detector is called as “A response” when they responds, and the orbital angular momentum order l of the responding photon is an odd number; the second single photon detector or the fourth single photon detector is called as “B response” when they responds, and the orbital angular momentum order l of the responding photon is an even number; it can be seen that only “A and B response under different interferometers” can be coded. In particular, when photons from the user end Alice and the user end Bob enter the same interferometer at the same time, it may not form a single photon interference phenomenon, and thus, the orbital angular momentum order l cannot be effectively subjected to odd-even separation, which causes a random response of the detector, resulting in failure of code formation. “A and B response under different interferometers” is referred to as a successful detection event.
And finally, the user side Alice and the user side Bob locally generate consistent keys after the processes of base comparison, key agreement and the like according to the response condition of the measuring unit.
An OAM measurement device independent quantum key distribution method based on real-time tracking compensation is applied to the OAM measurement device independent quantum key distribution system based on real-time tracking compensation, comprising the following steps:
S1, monitoring signal channel environment: the measuring unit emitting strong laser pulses to the user side Alice and the user side Bob, the user side Alice and the user side Bob performing clock synchronization and anti-eavesdropping monitoring by using the pulses, and meanwhile estimating the atmospheric turbulence intensity according to the dispersion degree of the light spots of the incident Gaussian pulses; executing the next step when the intensity of the atmospheric turbulence is lower than a threshold value and no eavesdropping is monitored;
S2, bit encoding: the user side Alice and the user side Bob randomly selecting an X base or a Y base to perform information coding, randomly coding bit information into 4 orbital angular momentum states by using a spatial light modulator, and then transmitting the bit information to a middle measuring unit; wherein X base represents {|o, |e
}; y base represents
and |o and
represent bit 0; |e and
represent bit 1; |o and |e
respectively represent an orbital angular momentum state of odd topological charge numbers and an orbital angular momentum state of even topological charge numbers;
S3, Bell measurement: the measuring unit performing the measuring operation, then declaring which bits being successfully detected, and simultaneously publishing the measuring result; the user side Alice and the user side Bob reserving the above data and discarding the data of other code bits;
S4, pairing base: the user side Alice and the user side Bob performing base pairing through a public channel, selecting bits prepared under the same base, and negotiating to perform bit inversion, thus ensuring the consistency of the bits of both communication sides; after these operations are completed, the reserved data being used as the original key;
S5, error code estimation: the user side Alice and the user side Bob generating a final security key by using an original key obtained from the X base, the original key obtained from the Y base being used as a test bit, detecting the error rate, if the error rate is higher than a threshold value, which indicates the fact that eavesdropping exists, abandoning the communication process, and otherwise, reserving the remaining data to execute the next step;
S6, key agreement: the user side Alice and the user side Bob performing error correction and private key amplification on the screened data by using the public classical channel, and after data coordination, the user side Alice and the user side Bob having consistent security keys.
Preferably, when the bit encoding is performed, the user side Alice and the user side Bob randomly selecting the orbital angular momentum states or the superposition states of odd topology charges numbers or orbital angular momentum states or the superposition states of even topology charges numbers to perform encoding, and allowing a group of mutually unbiased bases to be formed by any odd-numbered or even-numbered orbital angular momentum states to perform encoding.
Compared with the prior art, the disclosure has the following beneficial effects:
1. the user side of the OAM measurement device independent quantum key distribution system based on real-time tracking compensation utilizes the two deformable mirrors and the CCD to form the self-adaptive optical system, which can perform real-time tracking monitoring on phase distortion caused by atmospheric turbulence, estimate the degree of the atmospheric turbulence, compensate distortion phase in real time, and improve the anti-interference capability of the OAM measurement device independent quantum key distribution system.
2. In the OAM measurement device independent quantum key distribution system based on real-time tracking compensation, pulse signals of both user parties come from the same laser, the spectrum modes of the pulse signals are naturally the same, and the pulse signals have extremely high fidelity during interferometry; by using the light source, it can be conveniently to realize real-time channel monitoring, to prevent Trojan horse attack, and to conveniently perform clock synchronization.
3. The OAM measurement device independent quantum key distribution system based on real-time tracking compensation and method thereof of the present disclosure, utilizes photons with Orbital Angular Momentum (OAM) as information carriers, which can perform device independent quantum key distribution under the condition without aligning a reference system of a base, and improve the key rate; and the orbital angular momentum state has the characteristic of infinite dimensionality, so that the disclosure has extremely strong expansion capability, which may be conveniently combined with an orbital angular momentum multiplexing/separating device and improve the channel capacity.
The following description of the embodiments of the present disclosure will be made with reference to the accompanying drawings.
As shown in
The user side Alice and the user side Bob are connected with the measuring unit through quantum channels, wherein:
the quantum channel is a free space channel or an optical fiber channel, and the embodiment takes the free space channel as an example for explanation.
The measuring unit generates strong Gaussian pulses by using a pulse laser, the Gaussian pulses are transmitted to a user side through a polarization beam splitter and a beam splitter, the user side utilizes a charge coupled device (CCD) and a beam splitter for monitoring and synchronization, performs phase distortion compensation through a deformable mirror, and utilizes an intensity modulator and a spatial light modulator to randomly generate decoy state photons and signal state photons of orbital angular momentum with the number of the photons less than 1, and sends the photons to a middle measuring unit. The measuring unit measures the photon state emitted by the user with time multiplexed single photon detector. The measuring unit measures the photon state sent by the user and publishes the measuring result, and the user locally generates a consistent key after the processes of base comparison, key agreement and the like according to the response condition of the measurement.
As shown in
as shown in
As shown in
The third telescope system 101 and the fourth telescope system 201 each comprise two confocal convex lenses for controlling the size of the laser pulse and the far-field divergence angle of the laser beam; the first narrow-band filter 102 and the second narrow-band filter 202 are provided for filtering light out of a communication waveband; the first beam splitter 103 and the second beam splitter 203 divide incident pulse laser into two paths of strong pulse laser and weak pulser laser, namely a strong upper branch and a weak lower branch; the first charge coupled device (CCD) 104 and the second Charge coupled device (CCD) 204 are provided 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 of the lower branch; the second polarization beam splitter 106 and the third polarization beam splitter 206 transmit the horizontal polarization light and reflect the vertical polarization light; the first deformable mirror 107, the second deformable mirror 111, the third deformable mirror 207 and the fourth deformable mirror 211 are also called wavefront correctors, which may change the optical path of the wave front transmission or change the refractive index of a transmission medium to change the phase structure of the wave front of the incident light according to the reference information of phase distortion, so as to achieve the purpose of compensating the wave phase of the light wave; the principal sections of the first half-wave plate 108 and the second half-wave plate 208 are provided at an angle of 45 degrees with the polarization surface of incident light, and the polarization direction of the incident light may be rotated by 90 degrees; the first spatial light modulator 109 and the second spatial light modulator 209 are phase-only reflective liquid crystal spatial light modulators, which are active digital optical devices based on liquid crystal molecule electro-birefringence effect, and provided for modulating orbital angular momentum of laser beams; the first intensity modulator 110 and the second intensity modulator 210 may accurately generate the decoy state photons and the signal state photons with different average photon number intensities.
As shown in
as shown in
As shown in
when the first spatial light modulator 109 and the second spatial light modulator 209 encode orbital angular momentum, the first spatial light modulator 109 and the second spatial light modulator 209 may randomly select one of four states
for encoding; wherein {|o, |e
} is X base;
is Y base, and |o and
represents bit 0; and |e and
represents bit 1; and |o and |e
respectively represent orbital angular momentum states of odd topological charge numbers and orbital angular momentum states of even topological charge numbers.
The first telescope system 301 and the second telescope system 302 of the measuring unit respectively receive signal pulses from the user side Alice and the user side Bob, the signal pulses firstly intervene at the first 50/50 splitter 305 after reflecting by the first reflector 303 and the second reflector 304. the first 50/50 beam splitter 305 erases photon state path information, so that photon states are indistinguishable. Due to the HOM effect, the same photon state will be output from the same output port of the first 50/50 splitter 305, while different photon states are output independently of each other.
The signal pulses are output from the upper port and the lower port of the first 50/50 beam splitter 305, reflected by the third reflector 308 and the fourth reflector 309, and enter a first M-Z interferometer 340 and a second M-Z interferometer 341. Taking the first M-Z interferometer 340 as an example, the function of the first M-Z interferometer on the input photons is represented as follows:
assuming the photon state incident to the input port of the M-Z interferometer is provided as follows:
|ϕin=|0
|1
Wherein, |0 represents a vacuum state and |1
represents a single photon state. After passing through the second 50/50 beam splitter 320, the photon state becomes:
|ϕBS1=
(|0
|1
+i|1
|0
)
the above equation shows that the probability of photons being output from the transmissive end and reflective end of the second 50/50 splitter 320 is respectively 50%, where i represents the half-wave phase shift caused when the photons are output from the reflective end. After the photon state is acted by the first Dove prism 322, the second Dove prism 324, the phase difference ϕ=lα generated by the two optical paths, the photon state becomes:
|ϕD=
(|0
|1
+ieiϕ|1
|0
)
after passing through a third 50/50 beam splitter 325, the photon state becomes:
|ϕBS2=
(1−eiϕ)|0
|1
+i/2(1+eiϕ)|1
|0
Assuming α=π,
when the orbital angular momentum order l is odd numbers, |ϕBS2 becomes |0
|1
, photons are transmitted from the third 50/50 beam splitter 325; when the orbital angular momentum order l is even numbers, |ϕ
BS2 becomes |1
|0
, the photons become reflected from the third 50/50 beam splitter 325.
And finally, the states output by the M-Z interferometer are detected by a single photon detector, and a result is output in response. Specifically, the response of measuring unit is listed as follows:
As shown in the list, the first single photon detector or the third single photon detector is called as “A response” when they responds, and the orbital angular momentum order l of the responding photon is an odd number; the second single photon detector or the fourth single photon detector is called as “B response” when they responds, and the orbital angular momentum order l of the responding photon is an even number; it can be seen that only “A and B response under different interferometers” can be coded. In particular, when photons from the user end Alice and the user end Bob enter the same interferometer at the same time, it may not form a single photon interference phenomenon, and thus, the orbital angular momentum order l cannot be effectively subjected to odd-even separation, which causes a random response of the detector, resulting in failure of code formation. “A and B response under different interferometers” is referred to as a successful detection event.
And finally, the user side Alice and the user side Bob locally generate consistent keys after the processes of base comparison, key agreement and the like according to the response condition of the measuring unit.
As shown in
S1, monitoring signal channel environment: the measuring unit emitting strong laser pulses to the user side Alice and the user side Bob, the user side Alice and the user side Bob performing clock synchronization and anti-eavesdropping monitoring by using the pulses, and meanwhile estimating the atmospheric turbulence intensity according to the dispersion degree of the light spots of the incident Gaussian pulses; executing the next step when the intensity of the atmospheric turbulence is lower than a threshold value and no eavesdropping is monitored;
S2, bit encoding: the user side Alice and the user side Bob randomly selecting an X base or a Y base to perform information coding, randomly coding bit information into 4 orbital angular momentum states by using a spatial light modulator, and then transmitting the bit information to a middle measuring unit; wherein X base represents {|o, |e
}; y base represents
and |o and
represent bit 0; |e and
represent bit 1; |o and |e
respectively represent an orbital angular momentum state of odd topological charge numbers and an orbital angular momentum state of even topological charge numbers; when the bit encoding is performed, the user side Alice and the user side Bob randomly selecting the orbital angular momentum states or the superposition states of odd topology charges numbers or orbital angular momentum states or the superposition states of even topology charges numbers to perform encoding, and allowing a group of mutually unbiased bases to be formed by any odd-numbered or even-numbered orbital angular momentum states to perform encoding;
S3, Bell measurement: the measuring unit performing the measuring operation, then declaring which bits being successfully detected, and simultaneously publishing the measuring result; the user side Alice and the user side Bob reserving the above data and discarding the data of other code bits;
S4, pairing base: the user side Alice and the user side Bob performing base pairing through a public channel, selecting bits prepared under the same base, and negotiating to perform bit inversion, thus ensuring the consistency of the bits of both communication sides; after these operations are completed, the reserved data being used as the original key;
S5, error code estimation: the user side Alice and the user side Bob generating a final security key by using an original key obtained from the X base, the original key obtained from the Y base being used as a test bit, detecting the error rate, if the error rate is higher than a threshold value, which indicates the fact that eavesdropping exists, abandoning the communication process, and otherwise, reserving the remaining data to execute the next step;
S6, key agreement: the user side Alice and the user side Bob performing error correction and private key amplification on the screened data by using the public classical channel, and after data coordination, the user side Alice and the user side Bob having consistent security keys.
The above description is only an embodiment of the present disclosure, but the scope of the present disclosure is not limited thereto, and any changes or substitutions within the technical scope disclosed in the present disclosure should be covered within the scope of the present disclosure. Therefore, the scope of the present disclosure should be determined by the revelation and teaching of the above specification, and the modifications and variations of the above embodiments can be made by those skilled in the art to which the present disclosure pertains. Therefore, the present disclosure is not limited to the specific embodiments disclosed and described above, and modifications and variations of the present disclosure are also intended to fall within the scope of the appended claims. Furthermore, although specific terms are used herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201811634554.1 | Dec 2018 | CN | national |
The present disclosure is a Continuation Application of PCT Application No. PCT/CN2019/129490 filed on Dec. 27, 2019, which claims the benefit of Chinese Patent Application No. 201811634554.1 filed on Dec. 29, 2018. All the above are hereby incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2019/129490 | Dec 2019 | US |
| Child | 17361387 | US |
