CN116094713A - Dual-field quantum key distribution method and system - Google Patents
Dual-field quantum key distribution method and system Download PDFInfo
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- H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
- H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
- H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
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- H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
- H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
- H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
- H04L9/0838—Key agreement, i.e. key establishment technique in which a shared key is derived by parties as a function of information contributed by, or associated with, each of these
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- H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
- H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
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Abstract
The invention discloses a double-field quantum key distribution method, which comprises the following steps: transmitting a first optical signal generated by a first transmitting end to a detecting end through a first channel, and transmitting a second optical signal generated by a second transmitting end to the detecting end through a second channel, wherein the first optical signal and the second optical signal comprise a quantum frame part for encoding and a reference frame part not for encoding, and the quantum frame part comprises an X base vector and a Z base vector for representing an original key; the first optical signal and the second optical signal are processed through a detection end to obtain single photon detection information of the optical signal and a global phase difference of a quantum frame, and the global phase difference is sent to a first sending end and a second sending end through an authenticated classical channel; and processing the random numbers held by the first transmitting end and the second transmitting end respectively according to the global phase difference and the single photon detection information of the optical signals to obtain a safe shared secret key. The invention also discloses a system for distributing the double-field quantum key.
Description
Technical Field
The present invention relates to the field of quantum key distribution, and in particular, to a two-field quantum key distribution method, an electronic device, and a storage medium.
Background
Quantum key distribution (Quantum Key Distribution, QKD) is the use of quantum mechanical properties to guarantee communication security. It enables both parties to the communication to generate and share a random, secure key to encrypt and decrypt messages. QKD is increasingly gaining attention by researchers because of its unconditional security. The method solves the security problem of key distribution, and can ensure unconditional secure communication of both parties by combining a one-time encryption mode. The technique is therefore widely applicable to high confidentiality authorities.
Since the advent of the first QKD protocol, long-range communications of QKD have been an important and difficult task for research in the quantum communications field. Since the security of QKD derives from the unclonable principle, signal amplification by an optical amplifier is not possible as in classical communication, and therefore the transmission of a photon signal from one party must be attenuated as the channel length increases. Those skilled in the art have shown that the upper bound of the rate of formation R in a non-relay point-to-point QKD with respect to the channel transmission η, at a greater distance, η < 1,
this theoretically limits the furthest communication distance that can be achieved by a practical QKD. The related experiments also show that in the measurement equipment independent QKD experiment of 404km, the data accumulation time is as long as 3 months, and the code rate is only 3.2×10 -4 bps, indicating difficulties in implementation of remote QKD.
In recent years, aiming at the difficulty of QKD remote quantum communication, a novel QKD protocol, namely a two-field quantum key distribution protocol, is proposed by scientific researchers in the field; the code rate of the protocol
It is expected that the existing QKD code-separation will be doubled. At the same time, the two-field QKD has measurement device independent properties. By means of the two-field QKD, the number of trusted relays in a trusted relay scheme can be significantly reduced, and the rate of the resultant code is also improved in magnitude at the same distance (> 300 km). However, based on doubleThe quantum communication scheme of the field quantum key distribution protocol needs to use a light source phase locking technology and an optical fiber phase compensation technology, the existing light source phase locking technology needs to establish an additional servo channel for transmitting phase-locked light, and a transmitting end held by a user needs an additional phase locking device, so that the practical development of double-field QKD is greatly limited.
Disclosure of Invention
In view of the foregoing, the present invention provides a two-field quantum key distribution method and system, so as to solve at least one of the foregoing problems.
According to a first aspect of the present invention, there is provided a two-field quantum key distribution method comprising:
transmitting a first optical signal generated by a first transmitting end to a detecting end through a first channel, and transmitting a second optical signal generated by a second transmitting end to the detecting end through a second channel, wherein the first transmitting end and the second transmitting end have optical fields with random phases, the optical fields are determined according to random numbers held by the first transmitting end and the second transmitting end respectively, the first optical signal and the second optical signal comprise a quantum frame part for encoding and a reference frame part not for encoding, and the quantum frame part comprises an X-base vector and a Z-base vector for representing an original key;
The first optical signal and the second optical signal are processed through the detection end to obtain single photon detection information of the optical signal and a global phase difference of a quantum frame, and the global phase difference is sent to the first sending end and the second sending end through authenticated classical channels;
and according to the global phase difference and the single photon detection information of the optical signal, the first transmitting end and the second transmitting end respectively carry out key screening, key error correction and key privacy amplification on the random numbers held by the first transmitting end and the second transmitting end to obtain a safe shared key.
According to an embodiment of the present invention, according to the global phase difference and the single photon detection information of the optical signal, the first transmitting end and the second transmitting end respectively perform key screening, key error correction and key privacy amplification on the random numbers held by the first transmitting end and the second transmitting end, so as to obtain a secure shared key, which includes:
based on single photon detection information of a reference frame part, the detection end carries out frequency recovery on a single-frequency beat signal, and recovers initial phases of the first optical signal and the second optical signal to obtain the global phase difference of the first optical signal and the second optical signal, wherein the single photon detection information of the optical signal comprises single photon detection information of the reference frame part and single photon detection information of a quantum frame part;
The first sending end and the second sending end screen the random numbers held by the first sending end and the second sending end respectively according to the single photon detection information of the quantum frame part and the global phase difference to obtain the original secret key, and the global phase difference is used for screening the original secret key, correcting the secret key and amplifying the secret key privacy to obtain the safe shared secret key.
According to an embodiment of the present invention, based on single photon detection information of a reference frame portion, the detecting end performs frequency recovery on a beat signal of a single frequency, and recovers initial phases of the first optical signal and the second optical signal to obtain the global phase difference between the first optical signal and the second optical signal, including:
the first transmitting end and the second transmitting end respectively conduct numerical conversion on single photon detection information of the reference frame part to obtain a numerical conversion result;
according to a preset sampling time window, the first sending end and the second sending end sample the numerical conversion result respectively, and calculate the sampling result to obtain a discrete array;
according to preset conditions, the detection end carries out pretreatment on the discrete values, and carries out Fourier transformation on the pretreatment result to obtain the frequency spectrum of the single-frequency beat signal;
And the detection end screens the frequency spectrum of the single-frequency beat signal according to preset screening conditions, and obtains the global phase difference of the first optical signal and the second optical signal according to the screening result and the initial phases of the first optical signal and the second optical signal.
According to an embodiment of the present invention, the preprocessing the discrete values by the detection end according to the preset condition includes:
in the case that the data information amount in the discrete array cannot obtain the initial phases of the beat signal of the single frequency and the first optical signal and the second optical signal, the detection end combines the single photon detection information of the reference frame part of other time windows so as to increase the data information amount in the discrete array;
and under the condition that the length of the discrete array does not reach the preset length, the detection end carries out zero padding operation on the discrete array.
According to an embodiment of the present invention, the preset screening condition is determined by the following formula:
|cos(2πνt+φ 0 +(φ a -φ b ))|≥Δ
wherein v represents the frequency of the single-frequency beat signal, phi 0 Is the initial phase difference phi of the first optical signal and the second optical signal a And phi b And the random phases of the first transmitting end and the second transmitting end are respectively represented, and delta is a parameter obtained by optimizing according to the code rate.
According to an embodiment of the present invention, the first transmitting end and the second transmitting end screen the random numbers held by the first transmitting end and the second transmitting end respectively according to the single photon detection information of the quantum frame portion and the global phase difference to obtain the original key, and screen the original key, correct the key and amplify the key privacy by using the global phase difference to obtain a secure shared key, including:
the detection end publishes a single photon response event through the authenticated classical channel;
based on the single photon response event, the first sending end screens the self base vector information and the base vector information corresponding to the second optical signal, and random numbers corresponding to the same parts of the two base vector information are reserved as original keys;
based on the single photon response event, the second sending end screens the own base vector information and published base vector information corresponding to the first optical signal, and random numbers corresponding to the same parts of the two base vector information are reserved as original keys;
the first transmitting end and the second transmitting end respectively screen the respective basic vector information by utilizing the global phase difference to obtain data for parameter estimation;
The first sending end and the second sending end respectively calculate preset safety key quantity through data used for parameter estimation;
and the first sending end and the second sending end respectively use the preset safe key quantity to correct the original key and amplify the privacy so as to obtain the safe shared key.
According to a second aspect of the present invention, there is provided a two-field quantum key distribution system, applied to a two-field quantum key distribution method, including a first transmitting end, a second transmitting end, and a detecting end;
the first transmitting end and the second transmitting end have the same structure and comprise a quantum random number generator, a light source, a phase modulator, an intensity modulator and an optical attenuator;
the detection end comprises a polarization controller, a dense wavelength division multiplexer, a polarization beam splitter, a beam splitter with a preset beam splitting ratio and a single photon detector.
According to an embodiment of the present invention, the light source generator of the first transmitting end generates continuous weak coherent light, so as to obtain an optical signal for encoding;
the first intensity modulator of the first transmitting end carries out chopping processing on the optical signal to obtain a pulse optical signal for quantum key distribution;
The second intensity modulator of the first transmitting end carries out decoy state intensity random modulation on the pulse optical signal to obtain the intensity of the pulse optical signal with various amplitude values;
the third intensity modulator of the first transmitting end decomposes the pulse optical signal in the time domain to obtain a phase reference frame and a quantum frame of the pulse optical signal;
according to a preset optical signal amplitude range and a preset equal division number, the first phase modulator and the second phase modulator of the first transmitting end carry out phase randomization and phase encoding on the pulse optical signal to obtain a pulse optical signal with intensity and phase encoding;
and the attenuator of the first transmitting end attenuates the pulse optical signal with the intensity and the phase code to obtain a first optical signal with single photon magnitude.
According to an embodiment of the present invention, the polarization controller of the detection end performs a polarization reference system alignment process on the first optical signal and the second optical signal, where the first optical signal is generated by the first transmission end and the second optical signal is generated by the second transmission end;
the polarization beam splitter of the detection end respectively performs beam splitting treatment on the first optical signal after alignment treatment and the second optical signal after alignment treatment to obtain a first part of the first optical signal after alignment treatment and a second part of the first optical signal after alignment treatment and a first part of the second optical signal after alignment treatment and a second part of the second optical signal after alignment treatment;
The optical detector of the detection end respectively measures the first part of the first optical signal after the alignment treatment and the first part of the second optical signal after the alignment treatment, and feeds back the obtained detection result to the polarization controller of the detection end;
the beam splitter of the preset beam splitting ratio of the detection end respectively carries out interference processing on the second part of the first optical signal after alignment processing and the second part of the second optical signal after alignment processing to obtain an interference result;
and the single photon detector of the detection end detects the interference result respectively to obtain single photon detection information, and the obtained single photon detection information is sent to the first sending end and the second sending end through authenticated classical channels.
According to the embodiment of the invention, the detection event obtained by the single photon detector at the detection end is used for coding, and the detection event obtained by the light detector at the detection end is used for polarization feedback and time delay alignment.
Compared with the double-field QKD method in the prior art, the double-field quantum key distribution method and system provided by the invention have the advantages that the system complexity and cost brought by a phase-locked light source in the traditional double-field QKD are reduced, an additional phase-locked light path is not needed, the requirement of an optical fiber channel is reduced, and the expansion is easy; meanwhile, a frequency and phase estimation algorithm based on the fast Fourier transform can obtain a higher signal to noise ratio under a small sample, and is beneficial to realizing fast and accurate frequency estimation; in addition, phase modulation and chopping of the phase reference light are not needed, so that the modulation complexity and the peak power of the reference light are reduced, and the scattering noise is reduced.
Drawings
FIG. 1 is a flow chart of a two-field quantum key distribution method according to an embodiment of the present invention;
FIG. 2 is a flow chart of acquiring a secure shared key according to an embodiment of the invention;
FIG. 3 is a flow chart of acquiring a global phase difference according to an embodiment of the present invention;
FIG. 4 is a flow chart of a data process for acquiring a global phase difference according to an embodiment of the present invention;
FIG. 5 is a base-vector comparison flow chart according to an embodiment of the invention;
fig. 6 is a schematic structural diagram of a two-field quantum key distribution system according to an embodiment of the present invention.
Detailed Description
The present invention will be further described in detail below with reference to specific embodiments and with reference to the accompanying drawings, in order to make the objects, technical solutions and advantages of the present invention more apparent.
The technical difficulty of the two-field QKD experiment is far higher than that of the traditional point-to-point QKD, and a certain distance is still kept from the actual practical application. The biggest difficulty in a two-field QKD experiment is single photon interference between two independent light sources, which requires the following two conditions to be met: (1) the phase between two light sources needs to be correlated. At present, the phase correlation is realized mainly by laser phase locking, and the modes comprise an optical phase-locked loop, a time-frequency transmission technology and an injection locking technology. The time-frequency transmission technology needs an ultra-stable cavity, and has high technical difficulty; the injection locking technology has lower difficulty, but because the phase of the internal light source is controlled directly by the external light source, the actual safety has a larger risk; the technical difficulty of the optical phase-locked loop is moderate, and the safety risk is avoided; (2) The phase change after transmission through the fiber can be estimated or compensated. In order to compensate the influence of the optical fiber on the phase, two schemes of real-time compensation and post-selection are divided. These two schemes divide the transmitted pulse light into phase reference light and quantum light for encoding, and the light intensity of the reference light is large in order to accumulate sufficient counts in a short time. The real-time compensation scheme is that a phase modulator is utilized at a detection end to enable phase reference light to be in a complete phase state all the time, so that two sending ends and the detection end establish the same phase reference system; the phase post-selection does not need real-time feedback, but estimates the phase difference of the phase reference light during post-processing, and the compensation purpose can be achieved. The prior art provides a scheme of multiplexing the phase reference strong light and the quantum light wave, reduces the optical fiber scattering noise of the phase reference strong light, and further improves the code forming distance.
In summary, the optical source phase-locking technology and the optical fiber phase compensation technology are key technologies and core difficulties of the two-field QKD experimental scheme. The existing light source phase locking technology needs to establish an additional servo channel for transmitting phase locked light, and a transmitting end held by a user needs an additional phase locking device, which greatly limits the practical development of double-field QKD.
The invention provides a non-phase-locking double-field QKD scheme for solving the practical problem of light source phase locking in the double-field QKD, which can reduce the complexity of a double-field QKD transmitting end device and the use of optical fiber channels, expand the application fields of the device, such as integrating a chip transmitting end, a free space double-field QKD and the like, further promote the practical process of the double-field QKD and provide a feasible technical route for remote QKD.
The user end, namely the transmitting end, comprises a light source, a quantum random number generator, a phase modulator, an intensity modulator, an attenuator and the like. The light source is used for generating continuous weak coherent light, and chopping is carried out through the first intensity modulator; the second intensity modulator performs decoy state modulation to generate intensities with random multiple amplitudes; the third intensity modulator temporally separates the transmitted light into phase reference frames and quantum frames. The first and second phase modulators are used together for phase randomization and phase encoding. The attenuator is used to attenuate the light intensity to the single photon level. The transmitted quantum state is transmitted to the detection end through the single mode fiber for interference and single photon detection.
The detection end comprises an electric control polarization controller, a dense wavelength division multiplexer, a polarization beam splitter and 50:50 spectral ratio beam splitters, and single photon detectors. The detection events of the first and second single photon detectors are used for encoding. The detection events of the third and fourth single photon detectors are used for polarization feedback and time delay alignment. The user filters, corrects errors and amplifies privacy of the original key according to the QKD protocol content, ultimately producing a secure shared key.
Fig. 1 is a flow chart of a two-field quantum key distribution method according to an embodiment of the present invention.
As shown in fig. 1, the above-described two-field quantum key distribution method includes operations S110 to S130.
In operation S110, a first optical signal generated by a first transmitting end is transmitted to a detecting end through a first channel, and a second optical signal generated by a second transmitting end is transmitted to the detecting end through a second channel, wherein the first transmitting end and the second transmitting end have optical fields of random phases, which are determined according to random numbers held respectively, the first optical signal and the second optical signal include a quantum frame portion for encoding and a reference frame portion not for encoding, and the quantum frame portion includes an X-basis vector and a Z-basis vector characterizing an original key.
The above-mentioned two-field quantum key distribution method provided by the invention needs two sending ends and a detecting end to finish together. The two sending ends are respectively held by two users needing to establish a shared secret key; the two transmitting ends respectively transmit the quantum states of the intensity and phase codes to the detecting end for single photon detection, wherein the quantum states can be a first optical signal and a second optical signal which respectively correspond to the first transmitting end and the second transmitting end. The quantum state is composed of a quantum frame and a reference frame, an X base vector in the quantum frame is suitable for screening an effective single photon response event (detection result), and a Z base vector in the quantum frame is used for a transmitting end to generate a final security key through screening, error correction, privacy amplification and the like through a double-field QKD protocol according to the detection result.
The two user terminals, namely the transmitting terminal, comprise a light source, a quantum random number generator, a phase modulator, an intensity modulator, an attenuator and the like. The light source is used for generating continuous weak coherent light, and chopping is carried out through the first intensity modulator; the second intensity modulator performs decoy state modulation to generate intensities with random multiple amplitudes; the third intensity modulator temporally separates the transmitted light into phase reference frames and quantum frames. The first and second phase modulators are used together for phase randomization and phase encoding. The attenuator is used to attenuate the light intensity to the single photon level. The transmitted quantum state is transmitted to a detection end through a single mode fiber (a first channel or a second channel) for interference and single photon detection. The quantum random number generator may generate a random number that may be used to determine the generation of the light field at the transmitting end and the original key, such as the intensity and the magnitude of the phase modulation at the transmitting end.
The optical signals sent by the two sending ends have intensity information and phase information. Wherein, the reference frame adopts continuous light, does not need intensity and phase modulation. The transition region is pulsed and not phase modulated. The quantum frames are modulated in intensity and phase simultaneously. The intensity and phase modulation are determined by random numbers generated by quantum random number generators in the first transmitting end and the second transmitting end, and the random numbers generated by the first transmitting end and the second transmitting end are mutually independent.
In operation S120, the first optical signal and the second optical signal are processed through the detection end, so as to obtain single photon detection information of the optical signal and a global phase difference of the quantum frame, and the global phase difference is transmitted to the first transmission end and the second transmission end through the authenticated classical channel.
The detection end comprises an electric control polarization controller, a dense wavelength division multiplexer, a polarization beam splitter, a beam splitter with a preset beam splitting ratio (for example, 50:50 beam splitting ratio) and a single photon detector. The detection events of the first and second single photon detectors are used for encoding. The detection events of the third and fourth single photon detectors are used for polarization feedback and time delay alignment.
In operation S130, according to the global phase difference and the single photon detection information of the optical signal, the first transmitting end and the second transmitting end perform key screening, key error correction and key privacy amplification on the random numbers held by the first transmitting end and the second transmitting end respectively, so as to obtain a secure shared key.
The user end screens, corrects errors and privacy amplifies an original secret key based on QKD protocol content according to the global phase difference and single photon detection information of the optical signals, and finally generates a safe shared secret key, wherein the original secret key comprises a Z-base vector and the like determined according to the held random number.
Compared with the double-field QKD method in the prior art, the double-field quantum key distribution method and system provided by the invention have the advantages that the system complexity and cost brought by a phase-locked light source in the traditional double-field QKD are reduced, an additional phase-locked light path is not needed, the requirement of an optical fiber channel is reduced, and the expansion is easy; meanwhile, a frequency and phase estimation algorithm based on the fast Fourier transform can obtain a higher signal to noise ratio under a small sample, and is beneficial to realizing fast and accurate frequency estimation; in addition, phase modulation and chopping of the phase reference light are not needed, so that the modulation complexity and the peak power of the reference light are reduced, and the scattering noise is reduced.
FIG. 2 is a flow chart of acquiring a secure shared key according to an embodiment of the invention.
As shown in fig. 2, according to the global phase difference and single photon detection information of the optical signal, the first transmitting end and the second transmitting end perform key screening, key error correction and key privacy amplification on the random numbers held by the first transmitting end and the second transmitting end respectively to obtain a secure shared key, which includes operations S310 to S320.
In operation S310, based on the single photon detection information of the reference frame portion, the detection end performs frequency recovery on the beat signal of the single frequency, and recovers initial phases of the first optical signal and the second optical signal to obtain a global phase difference of the first optical signal and the second optical signal, where the single photon detection information of the optical signal includes the single photon detection information of the reference frame portion and the single photon detection information of the quantum frame portion.
In operation S320, the first transmitting end and the second transmitting end screen the random numbers held by the first transmitting end and the second transmitting end respectively according to the single photon detection information and the global phase difference of the quantum frame portion, obtain an original key, and screen the original key, correct the key and amplify the key privacy by using the global phase difference respectively, so as to obtain a secure shared key.
By the method, the random numbers held by the two sending ends are screened, so that an original secret key is generated, and the original secret key is screened, corrected and privacy amplified, so that a safe shared secret key can be obtained.
The key of the secure shared key acquisition process is the screening of the key, wherein the screening of the key comprises the basic vector comparison and the frequency and phase recovery.
The process of frequency and phase recovery is described in detail below in conjunction with fig. 3 and 4.
Fig. 3 is a flow chart of acquiring a global phase difference according to an embodiment of the present invention.
As shown in fig. 3, based on single photon detection information of a reference frame portion, a detection end performs frequency recovery on a beat signal of a single frequency, and recovers initial phases of a first optical signal and a second optical signal to obtain a global phase difference of the first optical signal and the second optical signal, which includes operations S410 to S440.
In operation S410, the first transmitting end and the second transmitting end respectively perform numerical conversion on the single photon detection information of the reference frame portion, so as to obtain a numerical conversion result.
In operation S420, according to a preset sampling time window, the first transmitting end and the second transmitting end sample the numerical conversion result respectively, and operate the sampling result to obtain a discrete array.
In operation S430, the detection end performs preprocessing on the discrete values according to the preset conditions, and performs fourier transform on the preprocessing result to obtain a spectrum of the beat signal with a single frequency.
In operation S440, the detection end screens the spectrum of the beat signal of the single frequency according to the preset screening condition, and obtains the global phase difference of the first optical signal and the second optical signal according to the screening result and the initial phases of the first optical signal and the second optical signal.
According to an embodiment of the present invention, the preprocessing, by the detection end, the discrete values according to the preset condition includes:
under the condition that the data information quantity in the discrete array cannot obtain the beat frequency signal of a single frequency and the initial phases of the first optical signal and the second optical signal, the detection end combines single photon detection information of reference frame parts of other time windows so as to increase the data information quantity in the discrete array;
under the condition that the length of the discrete array does not reach the preset length, the detection end carries out zero padding operation on the discrete array.
According to an embodiment of the present invention, the above-mentioned preset screening condition is determined by formula (1):
|cos(2πνt+φ 0 +(φ a -φ b ))|≥Δ (1)，
wherein v represents the frequency of the beat signal of a single frequency, phi 0 Is the initial phase difference of the first optical signal and the second optical signal, phi a And phi b The phases of the first transmitting end and the second transmitting end are respectively represented, delta is a parameter obtained according to code rate optimization, and can be taken here
The global phase difference is 2pi.v t+phi 0 。
The reference frame is used for recovering the phase difference of the optical fields transmitted by the two transmitting ends when the first optical beam splitter of the detecting end interferes. The reference frames are not used for encoding, while the quantum frames are used for encoding. The phase of the reference frame recovery influences the screening of the original key in the manner shown in equation (1) and results in a valid X-basis vector event (i.e., single photon response event).
FIG. 4 is a flow chart of a data process for acquiring a global phase difference according to an embodiment of the present invention.
Transmitting terminalA (i.e. the first transmitting end) and a transmitting end B (i.e. the second transmitting end) recover the initial phase between the optical signals of the two transmitting ends based on the single photon detection information in the reference frame. The light source 1 in the transmitting end a and the light source 12 in the transmitting end B can be considered to be kept stable within a short time, for example, within 5 μs, so that the global phase difference between the two transmitting end light signals can be considered to be a single-frequency beat signal, and the global phase difference between the whole reference frame and the quantum frame can be obtained only by recovering the frequency and the initial phase of the beat signal based on the single photon detection information in the reference frame, and the specific process is shown in fig. 4. Firstly, a transmitting end A and a transmitting end B change single photon detection information in all reference frames into a numerical form x which is easy to process i : if at t i Taking x when the first single photon detector at the moment detection end responds i =1; if at t i The response of the second single photon detector at the moment detection end takes x i = -1. Then, the transmitting end A and the transmitting end B select a proper sampling time window size T, and single photon detection event information under different time in the same time window is added together to obtain a discrete array, as shown in a formula (2):
To further increase accuracy of frequency and phase recovery, phase estimation error and corresponding error rate can be reduced for X k The pretreatment is optionally performed. First judge X k Whether the data information in the reference frames is sufficiently recovered to obtain accurate frequency and phase, and if not, the X can be increased by combining single photon detection information in a plurality of reference frames k Data amount in the data storage unit. Next, judging X k If the data length of (2) is sufficient, if X k If the data length is insufficient, X can be increased by adding 0 at the end k Thereby increasing the recovered spectral resolution. Finally, to X k The frequency spectrum corresponding to the beat frequency signal can be obtained by performing Fourier transform, wherein the frequency component with the largest amplitude can be selected as the frequencyRestoring the result
Amplitude-corresponding argument as initial phase recovery result +.>
Thereby eventually yielding a global phase reference as shown in equation (3):
fig. 5 is a base-vector comparison flow chart according to an embodiment of the invention.
As shown in fig. 5, the first transmitting end and the second transmitting end screen the random numbers held by the first transmitting end and the second transmitting end according to the single photon detection information and the global phase difference of the quantum frame part respectively to obtain an original key, and screen the original key, correct the key and amplify the key privacy by using the global phase difference respectively to obtain a safe shared key, which comprises operations S610 to S660.
In operation S610, the probe end publishes a single photon response event through an authenticated classical channel.
In operation S620, based on the single photon response event, the first transmitting end screens the own base vector information and published base vector information corresponding to the second optical signal, and reserves random numbers corresponding to the same parts of the two base vector information (for example, the two Z base vectors) as the original key.
In operation S630, based on the single photon response event, the second transmitting end screens the own base vector information and published base vector information corresponding to the first optical signal, and reserves random numbers corresponding to the same parts of the two base vector information (for example, the two Z base vectors) as the original key.
In operation S640, the first transmitting end and the second transmitting end respectively screen the respective basis vector information by using the global phase difference, so as to obtain data for parameter estimation.
In operation S650, the first transmitting end and the second transmitting end calculate preset security key amounts through data for parameter estimation, respectively.
In operation S660, the first transmitting end and the second transmitting end perform error correction and privacy amplification on the original key by using the preset secure key amount, respectively, to obtain a secure shared key.
In the above-mentioned basic vector comparison process, the transmitting end A (i.e. the above-mentioned first transmitting end) and the transmitting end B (i.e. the above-mentioned second transmitting end) disclose single photon response events through the authenticated classical channel, and screen and get the corresponding original secret key and data used for parameter estimation, calculate and expect the amount of security secret key that can be produced through parameter estimation, and carry on error correction and privacy amplification to the original secret key, finally produce the safe shared secret key. The specific key screening, error correction, and privacy amplification processes are related to the actually implemented two-field QKD protocol, which is illustrated here as a send-no-send (SNS-two-field QKD) protocol.
In the SNS-two-field QKD protocol, a sender a (i.e., the first sender described above) and a sender B (i.e., the second sender described above) keep random encodings corresponding to detection events, both of which select the Z-basis vectors, as original keys, where sender a (sender B) counts the vacuum state (non-vacuum state) as bit 0 (bit 1) and sender a (sender B) counts the non-vacuum state (vacuum state) as bit 1 (bit 0). The transmitting end A and the transmitting end B select phi through phase modulation corresponding to the detection event that they select X base vectors a (φ b ) Disclosure is made for parameter estimation to calculate the amount of information leaked and the amount of security keys expected to be generated. In the parameter estimation process, the transmitting end A and the transmitting end B screen out detection events corresponding to X base vectors which are selected by the transmitting end A and the transmitting end B and modulated by the same intensity, and are further based on global phase reference recovered by the reference frame 
And according to the condition shown in formula (4): />
Screening to obtain effective X-base vector event, wherein phi a (φ b ) Respectively, the phase modulation selection of the transmitting end a (B). In an effective X-basis vector event, the first single photon detector at the detection end responds and
or the second single photon detector of the detection end responds and +.>
The rest are error events corresponding to the correct events. Based on the correct and error event number in the effective X-base vector event, the transmitting end A and the transmitting end B combine the single photon detection information corresponding to each intensity combination disclosed by the Z-base vector and the X-base vector to perform finite code length analysis and parameter estimation, and obtain safe single photon contribution and corresponding single photon phase error rate, so that the expected security key quantity can be calculated. And then, the transmitting end A and the transmitting end B carry out error correction and privacy amplification on the reserved Z-base vector original key based on the result of parameter estimation, and finally generate a safe shared key.
According to a second aspect of the present invention, there is provided a two-field quantum key distribution system, which is applied to the above-mentioned two-field quantum key distribution method, and is characterized by comprising a first transmitting end, a second transmitting end and a detecting end;
the first transmitting end and the second transmitting end have the same structure and comprise a quantum random number generator, a light source, a phase modulator, an intensity modulator and an optical attenuator;
The detection end comprises a polarization controller, a dense wavelength division multiplexer, a polarization beam splitter, a beam splitter with a preset beam splitting ratio and a single photon detector.
According to the embodiment of the invention, the light source generator of the first transmitting end generates continuous weak coherent light to obtain an optical signal for encoding;
the method comprises the steps that a first intensity modulator of a first sending end chops an optical signal to obtain a pulse optical signal for quantum key distribution;
the second intensity modulator of the first transmitting end carries out decoy state intensity random modulation on the pulse optical signal to obtain the intensity of the pulse optical signal with various amplitude values;
the third intensity modulator of the first transmitting end decomposes the pulse optical signal in the time domain to obtain a phase reference frame and a quantum frame of the pulse optical signal;
according to a preset optical signal amplitude range and a preset equal division number, a first phase modulator and a second phase modulator of a first transmitting end carry out phase randomization and phase encoding on a pulse optical signal to obtain a pulse optical signal with intensity and phase encoding;
the attenuator of the first transmitting end attenuates the pulse optical signal with intensity and phase code to obtain a first optical signal with single photon magnitude.
According to the embodiment of the invention, the polarization controller of the detection end performs polarization reference system alignment processing on a first optical signal and a second optical signal, wherein the first optical signal is generated by a first transmission end, and the second optical signal is generated by a second transmission end;
the polarization beam splitter at the detection end respectively carries out beam splitting treatment on the first optical signal after alignment treatment and the second optical signal after alignment treatment to obtain a first part of the first optical signal after alignment treatment and a second part of the first optical signal after alignment treatment and a first part of the second optical signal after alignment treatment and a second part of the second optical signal after alignment treatment;
the optical detector of the detection end respectively measures the first part of the first optical signal after alignment processing and the first part of the second optical signal after alignment processing, and the obtained detection result is fed back to the polarization controller of the detection end;
the beam splitter of the preset beam splitting ratio of the detection end respectively carries out interference processing on the second part of the first optical signal after alignment processing and the second part of the second optical signal after alignment processing to obtain an interference result;
the single photon detectors of the detection ends detect the interference results respectively to obtain single photon detection information, and the obtained single photon detection information is sent to the first sending end and the second sending end through authenticated classical channels.
According to the embodiment of the invention, the detection event obtained by the single photon detector at the detection end is used for coding, and the detection event obtained by the light detector at the detection end is used for polarization feedback and time delay alignment.
To better aid those skilled in the art in understanding the above-described two-field quantum key distribution system, the present invention is described in further detail with reference to fig. 6.
Fig. 6 is a schematic structural diagram of a two-field quantum key distribution system according to an embodiment of the present invention.
As shown in fig. 6, the above-mentioned two-field quantum key distribution system includes a transmitting end a, a transmitting end B, and a detecting end C. The transmitting end A and the transmitting end B comprise a light source, an intensity modulator, a phase modulator and an optical attenuator. Taking the example that the light quantum is sent by the sending end A, the light source 1 of the sending end A generates continuous weak coherent light, and the light signals used for coding are chopped through the first intensity modulator 2 of the sending end A respectively to obtain pulse light signals used for quantum key distribution; the second intensity modulator 3 of the transmitting end A carries out decoy state intensity modulation, and randomly modulates to obtain intensities with various amplitudes; the third intensity modulator 4 of the transmitting end a divides the time domain into a phase reference frame and a quantum frame. The optical signal is then phase randomized and phase encoded by 16 equally divided phases in the range 0-2 pi through the first and second phase modulators 5 and 6 of the transmitting terminal a and attenuated to the single photon level by the attenuator 7 of the transmitting terminal a. The modulated optical signal is transmitted via the first channel 8. The transmitting end B has the same structure as the transmitting end a, and includes a light source 12, a first intensity modulator 13, a second intensity modulator 14, a third intensity modulator 15, a first phase modulator 16, a second phase modulator 17, and an attenuator 18, and the generated light quanta are transmitted to the detecting end C through a second channel 19.
Photons emitted by the transmitting end a and the transmitting end B are detected via the first channel 8 and the second channel 19 to the detecting end C, respectively, and the polarization reference systems of the two users are aligned via the first polarization controller 9 and the second polarizer 20. Then, the two light signals are divided into two parts by the first polarizing beam splitter 10 and the second polarizing beam splitter 21, wherein a small part of the two light signals are measured by the first light detector 11 and the second light detector 22, and the measurement results are fed back to the first polarizing controller 9 and the second polarizer 20 for compensating random drift of polarization of the light signals in the optical fiber; the remaining portions of the two optical signals are interfered by a 50:50 optical beam splitter 23 and then detected by a first single photon detector 24 and a second single photon detector 25. And the measured single photon detection information is sent to a sending end A and a sending end B through authenticated classical channels, and the sending end A and the sending end B carry out key screening, error correction and privacy amplification on an original key according to QKD protocol content to finally generate a safe shared key.
The foregoing embodiments have been provided for the purpose of illustrating the general principles of the present invention, and are not meant to limit the scope of the invention, but to limit the invention thereto.
Claims (10)
1. A method of two-field quantum key distribution, comprising:
transmitting a first optical signal generated by a first transmitting end to a detecting end through a first channel, and transmitting a second optical signal generated by a second transmitting end to the detecting end through a second channel, wherein the first transmitting end and the second transmitting end have optical fields with random phases, the optical fields are determined according to random numbers held by the first transmitting end and the second transmitting end respectively, the first optical signal and the second optical signal comprise a quantum frame part for encoding and a reference frame part not for encoding, and the quantum frame part comprises an X-base vector and a Z-base vector for representing an original key;
the first optical signal and the second optical signal are processed by the detection end to obtain single photon detection information of the optical signal and a global phase difference of a quantum frame, and the global phase difference is sent to the first sending end and the second sending end through authenticated classical channels;
and according to the global phase difference and the single photon detection information of the optical signal, the first sending end and the second sending end respectively carry out key screening, key error correction and key privacy amplification on the random numbers held by the first sending end and the second sending end to obtain a safe shared key.
2. The method according to claim 1, wherein the obtaining, by the first transmitting end and the second transmitting end, the secure shared key by performing key screening, key error correction, and key privacy amplification on the random numbers held by the first transmitting end and the second transmitting end, respectively, according to the global phase difference and the single photon detection information of the optical signal, includes:
based on single photon detection information of a reference frame part, the detection end carries out frequency recovery on a single-frequency beat signal, and recovers initial phases of the first optical signal and the second optical signal to obtain the global phase difference of the first optical signal and the second optical signal, wherein the single photon detection information of the optical signal comprises single photon detection information of the reference frame part and single photon detection information of a quantum frame part;
the first sending end and the second sending end screen the random numbers held by the first sending end and the second sending end respectively according to the single photon detection information of the quantum frame part and the global phase difference to obtain the original secret key, and the global phase difference is used for screening the original secret key, correcting the secret key and amplifying the secret key privacy to obtain the safe shared secret key.
3. The method according to claim 2, wherein the detecting end performs frequency recovery on a beat signal of a single frequency and recovers initial phases of the first optical signal and the second optical signal based on single photon detection information of a reference frame portion, to obtain the global phase difference of the first optical signal and the second optical signal, including:
the first transmitting end and the second transmitting end respectively conduct numerical conversion on the single photon detection information of the reference frame part to obtain a numerical conversion result;
according to a preset sampling time window, the first transmitting end and the second transmitting end sample the numerical conversion result respectively, and operate the sampling result to obtain a discrete array;
according to preset conditions, the detection end carries out pretreatment on the discrete values, and carries out Fourier transformation on the pretreatment result to obtain the frequency spectrum of the single-frequency beat signal;
and according to a preset screening condition, the detection end screens the frequency spectrum of the single-frequency beat signal, and according to a screening result and initial phases of the first optical signal and the second optical signal, a global phase difference of the first optical signal and the second optical signal is obtained.
4. A method according to claim 3, wherein the preprocessing the discrete values by the detection end according to a preset condition includes:
under the condition that the data information quantity in the discrete array cannot obtain the initial phases of the beat frequency signal of the single frequency and the first optical signal and the second optical signal, the detection end combines single photon detection information of the reference frame part of other time windows so as to increase the data information quantity in the discrete array;
and under the condition that the length of the discrete array does not reach the preset length, the detection end carries out zero padding operation on the discrete array.
5. A method according to claim 3, wherein the preset screening condition is determined by formula (1):
|cos(2πνt+φ 0 +(φ a -φ b ))|≥Δ (1)，
wherein v represents the frequency of the single-frequency beat signal, phi 0 Is the initial phase difference, phi, of the first optical signal and the second optical signal a And phi b And the random phases respectively represent the random phases of the first transmitting end and the second transmitting end, and delta is a parameter obtained by optimizing according to the code rate.
6. The method according to claim 2, wherein the first transmitting end and the second transmitting end screen the random numbers held by the first transmitting end and the second transmitting end respectively according to the single photon detection information of the quantum frame part and the global phase difference to obtain the original key, and screen the original key, correct the key error and amplify the key privacy by using the global phase difference to obtain the safe shared key respectively, including:
The detection end publishes a single photon response event through the authenticated classical channel;
based on the single photon response event, the first transmitting end screens the self base vector information and the base vector information corresponding to the second optical signal, and random numbers corresponding to the same parts of the two base vector information are reserved as original keys;
based on the single photon response event, the second transmitting end screens the self base vector information and published base vector information corresponding to the first optical signal, and random numbers corresponding to the same parts of the two base vector information are reserved as original keys;
the first transmitting end and the second transmitting end screen the respective basic vector information by utilizing the global phase difference respectively to obtain data for parameter estimation;
the first sending end and the second sending end respectively calculate preset safety key quantity through data used for parameter estimation;
and the first sending end and the second sending end respectively use the preset safety key quantity to correct the original key and amplify the privacy so as to obtain the safe shared key.
7. A two-field quantum key distribution system applied to the method of claims 1-6, characterized by comprising a first transmitting end, a second transmitting end and a detecting end;
The first transmitting end and the second transmitting end have the same structure and comprise a quantum random number generator, a light source, a phase modulator, an intensity modulator and an optical attenuator;
the detection end comprises a polarization controller, a dense wavelength division multiplexer, a polarization beam splitter, a beam splitter with a preset beam splitting ratio and a single photon detector.
8. The system of claim 7, wherein the light source generator of the first transmitting end generates continuous weak coherent light to obtain an optical signal for encoding;
the first intensity modulator of the first transmitting end carries out chopping processing on the optical signal to obtain a pulse optical signal for quantum key distribution;
the second intensity modulator of the first transmitting end carries out decoy state intensity random modulation on the pulse optical signal to obtain the intensity of the pulse optical signal with various amplitude values;
the third intensity modulator of the first transmitting end decomposes the pulse optical signal in a time domain to obtain a phase reference frame and a quantum frame of the pulse optical signal;
according to a preset optical signal amplitude range and a preset equal division number, the first phase modulator and the second phase modulator of the first transmitting end carry out phase randomization and phase encoding on the pulse optical signal to obtain a pulse optical signal with intensity and phase encoding;
And the attenuator of the first transmitting end attenuates the pulse optical signal with the intensity and the phase code to obtain a first optical signal with single photon magnitude.
9. The system of claim 7, wherein the system further comprises a controller configured to control the controller,
the polarization controller of the detection end performs polarization reference system alignment processing on the first optical signal and the second optical signal, wherein the first optical signal is generated by the first sending end, and the second optical signal is generated by the second sending end;
the polarization beam splitter of the detection end respectively carries out beam splitting treatment on the first optical signal after alignment treatment and the second optical signal after alignment treatment to obtain a first part of the first optical signal after alignment treatment and a second part of the first optical signal after alignment treatment and a first part of the second optical signal after alignment treatment and a second part of the second optical signal after alignment treatment;
the optical detector of the detection end respectively measures the first part of the first optical signal after alignment processing and the first part of the second optical signal after alignment processing, and feeds back the obtained detection result to the polarization controller of the detection end;
The beam splitter of the preset beam splitting ratio of the detection end respectively carries out interference processing on the second part of the first optical signal after alignment processing and the second part of the second optical signal after alignment processing to obtain an interference result;
and the single photon detectors of the detection ends respectively detect the interference results to obtain single photon detection information and send the single photon detection information to the first sending end and the second sending end through authenticated classical channels.
10. The system of claim 8, wherein the detection events obtained by the single photon detector at the detection end are used for encoding and the detection events obtained by the light detector at the detection end are used for polarization feedback and time delay alignment.
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| CN116633541B (en) * | 2023-07-19 | 2023-09-29 | 济南量子技术研究院 | Double-field light source frequency locking method and system based on air chamber frequency reference |
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