CN112039668A - Quantum conference key negotiation method and system based on coherent detection - Google Patents
Quantum conference key negotiation method and system based on coherent detection Download PDFInfo
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Abstract
The invention discloses a quantum conference key negotiation method and system based on coherent detection, which comprises five stages of preparation, measurement, modulation, parameter estimation and post-processing, wherein data under a time basis vector is used for extracting a quantum conference key, and data under an interference basis vector is used for calculating contrast. The quantum conference key negotiation system comprises a continuous laser, an intensity modulator, a beam splitter and a single photon detector. The continuous laser generates phase-stabilized continuous light; the intensity modulator is used for pulse preparation of the passed optical signal; transmitting the pulse signal to a detection end, and splitting the optical signals of the first beam splitter and the second beam splitter at the transmitting end; the beam splitter is used for combining optical signals; the fourth beam splitter and the fifth beam splitter form a Mach-Zehnder interferometer; the detector detects the optical signal at a detection end. The invention has strong operability and simpler experimental equipment, does not need phase randomization and different intensity modulation, reduces the security risk and breaks the linear limitation of the code rate and the transmission distance in the key agreement protocol of the unrepeatered quantum conference.
Description
Technical Field
The invention relates to the technical field of quantum communication, in particular to a quantum conference key negotiation method and system based on coherent detection.
Background
Since the twenty-first century, the internet has been rapidly developed, information security is increasingly important, and private communication between users is one of the basic requirements of the modern information society. With the development of various types of computers, especially quantum computers, the computing power is continuously improved, the encryption algorithm based on the computation complexity is no longer safe, and the information security faces increasingly serious challenges. Quantum communication has come into play. Quantum communication is an emerging research field of cross-derivation of quantum mechanics and informatics, and information safety is guaranteed by means of the basic principle of quantum mechanics. The quantum communication branch fields are numerous, including the fields of quantum key distribution, quantum secret sharing, quantum digital signature, quantum conference key negotiation and the like.
Quantum Key Distribution (QKD) enables unconditionally secure key sharing between two users. However, in more application scenarios, such as network meeting, online course, etc., there are far more than two users who need to share the secret key. At this time, the Conference Key Agreement (Conference Key Agreement) is needed to realize the Key sharing among a plurality of trusted users, and the security of the classic Conference Key is based on the computational complexity, and the security cannot be ensured by the classic protocol with the continuous development of the quantum computer. Thus, it becomes especially important to develop quantum conference key agreement, also referred to as multi-party quantum key distribution.
The key distribution among multiple parties can be repeatedly realized between every two parties through quantum key distribution, and can also be realized through distribution of a multi-party entangled state. The overhead of the various quantum conference negotiation schemes recently proposed has been significantly less than the overhead required for repeated quantum key distribution.
The earliest quantum conference key agreement protocol was proposed in 1998 (phys. rev.a 57,822). Through the development of more than twenty years, scholars have proposed various quantum conference key agreement implementation methods, such as a distribution multi-particle GHZ (Greenberger-Horne-Zeilinger) state, a W-state QCKA, a continuous variable QCKA, a device-independent QCKA, and the like, but not all methods are sufficient. However, these protocols have problems such as severe experimental conditions and long distance from practical use.
At present, the most advanced scheme with the highest practical degree is proposed by the inventor group in 2020, the scheme in the patent CN202010348916.1 breaks the linear limitation of the transmission capability of the quantum link for the first time, realizes the transmission distance of more than 500 km, and realizes the sharing of the unconditional security key between three parties. However, the required instruments and equipment are relatively complex, a continuous laser, an intensity modulator, a phase modulator and a signal attenuator are required for a transmitting end, complex operations such as phase randomization, different light intensity modulation and the like are required, and the safety risk is increased.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the defects, the invention provides a quantum conference key negotiation method and system based on coherent detection, which are easy to realize and simple in equipment, realize that the key forming code rate linearly changes along with the square root of the channel transmission rate, break the linear limit of the transmission forming code rate and distance of quantum conference key negotiation, and improve the key transmission forming code rate and the transmission distance.
The technical scheme is as follows:
a quantum conference key negotiation method based on coherent detection comprises two sending ends and a detecting end; the two sending ends are respectively marked as a first sending end and a second sending end; the method comprises the following steps:
(1) the two sending ends respectively send random optical pulses and send the random optical pulses to the detection end through a quantum channel;
(2) splitting beams by the optical pulses sent by two sending ends of the first beam splitter and the second beam splitter respectively, and sending one of the optical pulses to the first detector and the second detector of the detection end respectively to perform time basis vector measurement; the other beam is sent to a third beam splitter for beam combination after the pulse polarization is modulated to be the same through a polarization controller; the distance from the first beam splitter to the third beam splitter is longer than the distance from the second beam splitter to the third beam splitter by a set distance so as to delay odd number of half cycles, and the set distance is equal to the odd number of half cycles multiplied by the light speed;
(3) sending the pulses combined in the step (2) to a detector for interference basis vector measurement after interference;
(4) the detection end publishes the response time of the detector and publishes the selected basis vector, if the first detector responds and the second detector does not respond, the logic bit of the detection end is 1; if the first detector does not respond and the second detector responds, the logic bit of the detection end is 0; if the two detectors under the time basis vector both respond, the detection end randomly selects a logic bit value; if the detector responses exist under the two basis vectors, the data is removed;
(5) and (4) reserving the data under the time basis vector in the partial data and the data of the two corresponding sending ends as original keys according to the step (4), and extracting the conference keys through classical error correction, error verification and privacy amplification.
In the step (3), the combined pulse is interfered by a Mach-Zehnder interferometer composed of two beam splitters, and then is detected under the interference basis vector through a detector.
In the step (4), the detection end publishes the corresponding strength information of the response of the detector under the interference basis vector, and only when the two adjacent quantum states are not in the vacuum state, the corresponding part of data of the response of the detector under the interference basis vector is used for calculating the contrast of the response of the detector under the interference basis vector, and the contrast is used for calculating the final code forming rate;
the contrast expression is as follows:
p (D1) and P (D2) represent the probability of two detector responses making interferometric basis vector measurements, respectively.
In the step (4), the two sending ends and the detecting end respectively publish the logic bit values of the corresponding parts of the sending ends and the detecting end, and the logic bit values are used for calculating the gain of the quantum state of the code.
And the detection end adopts passive basis vector detection.
A quantum conference key negotiation method based on coherent detection comprises two sending ends and a detecting end; the two sending ends are respectively marked as a first sending end and a second sending end; the method comprises the following steps:
(1) the two sending ends respectively send random optical pulses and send the random optical pulses to the detection end through a quantum channel;
(2) pulses of the two sending ends are respectively modulated into the same pulse polarization by the polarization controller and then sent to the first beam splitter for beam combination; the distance from the first sending end to the first beam splitter is longer than the distance from the second sending end to the first beam splitter by a set distance so as to delay odd number of half cycles, and the set distance is equal to the odd number of half cycles multiplied by the light speed;
(3) the first beam splitter outputs two beams of continuous pulses, and one beam of continuous pulses is sent to the fourth detector to carry out time basis vector measurement; the other string is sent to the beam splitter II for beam splitting, one beam is sent to the detector three-purpose for time basis vector detection, and the other beam is sent to the detector for interference basis vector measurement after interference;
(4) the detection end publishes the response time of the detector and publishes the selected basis vector, the time basis vector measurement of the detection end is equivalent to the sequence of detecting the state arrival time of | alpha >, and |0 > | alpha > corresponds to a logic bit 1 and | alpha > |0 > corresponds to a logic bit 0 under the time basis vector; if the third detector or the fourth detector responds twice in a period, a bit value is randomly selected; if the detector responses exist under the two basis vectors, discarding the part of data;
(5) and (4) reserving the data under the time basis vector in the partial data and the data of the two corresponding sending ends as original keys according to the step (4), and extracting the conference keys through classical error correction, error verification and privacy amplification.
A quantum conference key negotiation method based on coherent detection comprises two sending ends and a detecting end; the two sending ends are respectively marked as a first sending end and a second sending end; the method comprises the following steps:
(1) the two sending ends respectively send random optical pulses and send the random optical pulses to the detection end through a quantum channel;
(2) pulses of the two sending ends are respectively modulated into the same pulse polarization by the polarization controller and then sent to the fast optical switch for beam combination; the distance from the first sending end to the fast optical switch is longer than the distance from the second sending end to the fast optical switch by a set distance so as to delay odd number of half cycles, and the set distance is equal to the odd number of half cycles multiplied by the optical speed;
(3) the pulse combined by the fast optical switch is sent to a beam splitter for beam splitting, wherein one beam is sent to a detector for time basis vector measurement, and the other beam is sent to the detector for interference basis vector measurement after interference;
(4) the detection end publishes the response time of the detector and publishes the selected basis vector, the time basis vector measurement of the detection end is equivalent to the sequence of detecting the state arrival time of | alpha >, and |0 > | alpha > corresponds to a logic bit 1 and | alpha > |0 > corresponds to a logic bit 0 under the time basis vector; if the detectors under the two basis vectors have responses, removing the part of data;
(5) and (4) reserving the data under the time basis vector in the partial data and the data of the two corresponding sending ends as original keys according to the step (4), and extracting the conference keys through classical error correction, error verification and privacy amplification.
A quantum conference key negotiation system comprises two sending ends and a detection end; the two sending ends are respectively marked as a first sending end and a second sending end;
the transmitting end comprises a continuous laser used for generating phase-stable continuous light and an intensity modulator used for modulating the phase-stable continuous light generated by the continuous laser into light pulses with different intensities;
the detection end comprises a first beam splitter, a second beam splitter, a third beam splitter, a fourth beam splitter, a fifth beam splitter, a first detector, a second detector, a third detector and a fourth detector;
the first beam splitter and the second beam splitter are respectively arranged on the light paths of the two sending ends and are used for splitting the pulses of the two sending ends and respectively sending one of the pulses to the first detector and the second detector for time basis vector measurement; the other beam is sent to a third beam splitter through a polarization controller;
the third beam splitter combines pulses sent by the first beam splitter and the second beam splitter, and the distance from the first beam splitter to the third beam splitter is longer than the distance from the second beam splitter to the third beam splitter by a set distance so as to delay odd number of half cycles, wherein the set distance is equal to the odd number of half cycles multiplied by the light speed;
and the fourth beam splitter and the fifth beam splitter form a Mach-Zehnder interferometer, and pulses after the third beam splitter is combined are interfered and then are sent to the third detector and the fourth detector for interference basis vector measurement.
A quantum conference key negotiation system comprises two sending ends and a detection end; the two sending ends are respectively marked as a first sending end and a second sending end;
the transmitting end comprises a continuous laser used for generating phase-stable continuous light and an intensity modulator used for modulating the phase-stable continuous light generated by the continuous laser into light pulses with different intensities;
the detection end comprises a first beam splitter, a second beam splitter, a third beam splitter, a fourth beam splitter, a first detector, a second detector, a third detector and a fourth detector; polarization controllers are arranged on the light paths from the two transmitting ends to the first beam splitter;
the first beam splitter is used for modulating the pulses of the two sending ends by the polarization controller, keeping the pulses consistent, then combining the pulses, and outputting two continuous series of pulses, wherein one continuous series of pulses is sent to the fourth detector for time basis vector detection; the other string is sent to a second beam splitter; the distance from the first sending end to the beam combiner is prolonged by a set distance compared with the distance from the second sending end to the beam combiner to delay odd number of half cycles, and the set distance is equal to the odd number of half cycles multiplied by the light speed;
the two beam splitters split the pulse sent by the first beam splitter, one beam is sent to the detector for three-purpose time basis vector detection, and the other beam is used for interference basis vector detection;
the third beam splitter and the fourth beam splitter form a Mach-Zehnder interferometer, and interfere the pulse sent by the second beam splitter;
and the first detector and the second detector perform interference basis vector measurement on the interfered pulses.
A quantum conference key negotiation system comprises two sending ends and a detection end; the two sending ends are respectively marked as a first sending end and a second sending end;
the transmitting end comprises a continuous laser used for generating phase-stable continuous light and an intensity modulator used for modulating the phase-stable continuous light generated by the continuous laser into light pulses with different intensities;
the detection end comprises a fast optical switch, a first beam splitter, a second beam splitter, a third beam splitter, a first detector, a second detector and a third detector; polarization controllers are arranged on the light paths from the two transmitting ends to the quick optical switch;
the rapid optical switch is used for modulating pulses of the two sending ends by the polarization controller, keeping the pulses consistent, combining the pulses and sending the pulses to the first beam splitter; the distance from the first sending end to the fast optical switch is longer than the distance from the second sending end to the fast optical switch by a set distance so as to delay odd number of half cycles, and the set distance is equal to the odd number of half cycles multiplied by the optical speed;
the beam splitter splits the pulses sent by the fast optical switch, one beam is sent to the detector for three-purpose time basis vector detection, and the other beam is used for interference basis vector detection;
the second beam splitter and the third beam splitter form a Mach-Zehnder interferometer, and interfere the pulse sent by the first beam splitter;
and the first detector and the second detector perform interference basis vector measurement on the interfered pulses.
Due to the adoption of the technical scheme, the invention has the following technical effects:
(1) the invention can realize the key sharing between any two senders and one receiver, namely, realizes the key sharing between three parties, and realizes the unconditional safe conference key distribution between the parties.
(2) The conference key coding rate is not linearly attenuated along with the channel transmission rate any more, and the linear attenuation of the key coding rate along with the square root of the channel transmission rate is realized, so that the key transmission coding rate and the transmission distance are improved.
(3) By using the laser source and the single-photon detector, the quantum conference key negotiation system can break the rate-distance limitation, and can realize transmission of hundreds of kilometers under the practical condition.
(4) The invention has simple required equipment, simpler sending end equipment, strong operability and only needs a laser source and an intensity modulator.
(5) Compared with the latest protocol, the method removes the processes of phase randomization and different light intensity modulation, reduces the security risk, and effectively promotes the practical process of quantum conference key negotiation.
Drawings
Fig. 1 is a schematic structural diagram of a first embodiment of the present invention.
Fig. 2 is a schematic structural diagram of a second embodiment of the present invention.
Fig. 3 is a schematic structural diagram of a third embodiment of the present invention.
FIG. 4 is a graph of the simulated code rate of the present invention.
Detailed Description
The invention is further elucidated with reference to the drawings and the embodiments.
The invention relates to a quantum conference key negotiation system based on coherent detection, which comprises two sending ends and a detecting end which are connected through an unsafe quantum channel; the sending end comprises a continuous laser and an intensity modulator, the continuous laser generates phase-stable continuous light, the intensity modulator converts a continuous optical signal in time into optical pulses at a specific moment and modulates the amplitude of the pulses to form optical pulses with different intensities;
the first embodiment is as follows:
as shown in fig. 1, the two light paths of the two transmitting ends are respectively provided with a beam splitter for splitting the pulses of the two transmitting ends, one beam is sent to the first detector and the second detector for time basis vector detection, and the other beam is modulated and polarized by the polarization controller to make the polarization of the pulses of the two transmitting ends consistent, and then sent to the beam splitter for interference basis vector detection after the three beams are combined; the first beam splitter and the second beam splitter correspond to the first sending end and the second sending end respectively; the polarization controller corresponds to the pulse signal of the first sending end, and the polarization controller corresponds to the pulse signal of the second sending end; after the beam splitter III is combined, interference is carried out through a Mach-Zehnder interferometer formed by the beam splitter IV and the beam splitter V, and then the interference is respectively sent to the detector III and the detector IV to carry out interference basis vector detection on the pulse signals after interference. And the optical pulse at the first sending end is delayed for an odd number of half cycles between the beam splitter and the third beam splitter by the length of the increased optical fiber, wherein the length of the increased optical fiber is the length of the extended distance which is the delay time multiplied by the optical speed.
In the specific implementation process, three parties are respectively Alice, Bob and Charlie, wherein Alice and Bob are sending ends, the equipment is the same, the two parties use a continuous laser to generate stable and constant light with full phase, an intensity modulator is used for pulse preparation, coherent state | alpha > corresponding to logic bit 1 is sent, and vacuum state |0 > represents logic bit 0. Bob makes logic bit inversion after sending out signal; charlie is a detection end, wherein if a detector I responds and a detector II does not respond, the Charlie takes a logic bit value as 1; and if the first detector does not respond and the second detector responds, the Charlie logical bit value takes 0, and if the first detector and the second detector both respond, one logical bit value is randomly selected. If the detectors under both basis vectors are responsive, this portion of the data is removed.
Charlie performs passive basis vector measurements.
Both Alice and Bob send quantum states with a period of 2T (in this example, T ═ 1 nanosecond), and the quantum states occupy one period. Pulses sent by Alice are divided into two beams by the beam splitter, one beam is sent to the detector I for measurement under time basis vectors, and the other beam is sent to the beam splitter III for beam combination. Pulses sent by Bob are divided into two beams by the beam splitter, one beam is sent to the second detector for measurement under the time basis vector, and the other beam is sent to the third beam splitter for beam combination. The pulses of the two persons are polarized by the polarization controller to be the same before the three beams of the beam splitter are combined;
and Alice pulses are subjected to delay (2k +1) T (k belongs to Z) between the first beam splitter and the third beam splitter by increasing the length of the optical fiber, and after the two-side pulses are combined, the two-side pulses are subjected to interference by a Mach-Zehnder interferometer formed by the fourth beam splitter and the fifth beam splitter and then are sent to the third detector and the fourth detector to perform measurement under interference basis vectors.
The method comprises the following specific steps:
(1) the preparation stage comprises the following steps: alice (Bob) sends a pulse | α > with light intensity μ with a probability of t (0 < t < 1), and sends a vacuum state with a probability of (1-t); in this example, t is 6%.
(2) And (3) a measuring stage: and the Charlie at the detection end respectively carries out measurement under a time basis vector and an interference basis vector. If the first detector responds and the second detector does not respond, the logic bit of the detection end is 1; if the first detector does not respond and the second detector responds, the logic bit of the detection end is 0; if the two detectors both respond under the time basis vector, randomly selecting a logic bit value; if the response exists under the two basis vectors, the part of data is removed;
(3) a modulation stage: the Charlie at the detection end publishes the response time of the detector and publishes the selected basis vector; the detection end Charlie publishes corresponding intensity information of detector response under the interference basis vector (intensity information of three moments before and after publishing is needed), and only when two adjacent quantum states are not in a vacuum state (namely, the intensity information is published)
Or
) When the code rate is higher than the first threshold value, the corresponding part of data of the detector response under the interference basis vector is used for calculating the contrast of the detector response under the interference basis vector, and the contrast can be used for calculating the final code rate;
the contrast expression is as follows:
p (D3) and P (D4) are probabilities of detector three and detector four responses;
(4) parameter estimation: the three adopt time basis vector data as an original key, randomly publish a part of logic bit values of two sending ends and a detecting end under time basis vectors, and calculate the quantum state gain for coding;
(5) and in the post-processing stage, the conference key is extracted through classical error correction, error verification and privacy amplification.
In the specific embodiment, the following parameters are adopted:
| Pd | μ | t | ηd | α | f |
| 1×10-8 | 0.09 | 6％ | 56％ | 0.167 | 1.1 |
Pdfor the dark counting rate of the single-photon detector, t is the probability of two sending ends selecting to send coherent state | alpha >, and μ is the light intensity (actually, the light intensity and t can be adjusted according to different distances, and μ ═ α |, can be distributed to the field2)，ηdFor the detection efficiency of the detector, α is the fiber attenuation rate, and f is the error correction efficiency.
The conference key coding rate R can be calculated by the following formula:
where t is the probability of sending coherent state | α > is 6% in this embodiment, and in practice, the optimal value, Q, may be taken according to different distances0αAnd Qα0To deliver gain in the relevant quantum state, ETIs the time basis vector error rate, h (x) is the Shannon entropy and the expression is
Wherein the content of the first and second substances,
for visibility, μ is the intensity of light, Qμfh(Eμ) I.e. error correction part, QμTo total gain, EμThe maximum of the error rate between Alice and Charlie and the error rate between Bob and Charlie.
Wherein E isμThe calculations are actually symmetrical, the error rate is the same, and only AC may be considered. For AC and BC, as long as AB sends the same state | α > or |0 >, Charlie and detects, it will cause a necessary error. Since A is symmetrical to B, the AC and BC error counts are half each, i.e., 0.5 × [ (1-t)2Q00+t2Qαα]. In the case of only AC, the error rate also needs to consider the case where AB transmission |0 > | α > and | α > |0 > have errors, which are the same, E0α＝Eα0. Therefore, we can consider only the error rate E when state is |0 > | α > (the latter state is sent by Alice), which is actually equal to the error rate E when |0 > | α > is sent0αThe calculation method is the same as ET. Finally, can be obtained, Eμ＝{0.5×[(1-t)2Q00+t2Qαα]+E0αt(1-t)Q0α+Eα0t(1-t)Qα0}/μ。
In summary, we can obtain a rate-forming graph, which is ideally like fig. 4, and we compare it with the linear constraint of the transmission capability of the quantum link (i.e. the speed-distance limit), which is linear constraint
η1＝ηd*10-αL/10. Specific references are found in: arXiv: 1912.03645. The system linearly attenuates the rate of code rate with the square root of distance, and can make eta1＝ηd*10-αL/20And L is the transmission distance, from which fig. 4 is drawn.
With reference to fig. 4, it can be found that the protocol can break the linear constraint of the transmission capability of the quantum link, and theoretically can achieve a transmission distance of more than 500 km.
Example two:
the device structure in this embodiment is greatly modified, but is substantially the same as in the first embodiment.
With reference to fig. 2, the following description is made: the embodiment comprises two sending ends and a detecting end which are connected through an unsafe quantum channel; the sending end comprises a continuous laser and an intensity modulator; the continuous laser is used for generating phase-stable continuous light; the intensity modulator changes a continuous optical signal in time into an optical pulse at a specific moment and modulates the amplitude of the pulse to form an optical pulse with different intensities;
the detection end comprises a polarization controller, a beam splitter and a detector; in this embodiment, a first beam splitter is arranged on the light paths of the two transmitting ends, and the optical fiber distance from one of the transmitting ends to the first beam splitter is longer for delaying odd number of half cycles; polarization controllers are arranged on light paths between the two sending ends and the first beam splitter, wherein the first sending end corresponds to the first polarization controller, and the second sending end corresponds to the second polarization controller; the polarization controller corresponds to the pulse signal of the first sending end, the polarization controller corresponds to the pulse signal of the second sending end, and the pulse polarization of the two sending ends is modulated by the polarization controller and then keeps consistent;
the first beam splitter is used for combining the light pulses sent by the two sending ends modulated by the polarization controller and outputting two continuous pulse strings, wherein one continuous pulse string is sent to the fourth detector for time basis vector detection; the other string is sent to the beam splitter II for beam splitting, one beam is sent to the detector three-purpose for time basis vector detection, and the other beam is respectively sent to the detector one and the detector two-purpose for interference basis vector detection after being interfered by a Mach-Zehnder interferometer composed of the beam splitter three and the beam splitter four; the time basis vector data is used for coding, and the interference basis vector data is used for calculating contrast, so that the error rate and the safety risk are estimated.
The invention is a three-party protocol, and the three parties are respectively Alice, Bob and Charlie. Where Alice and Bob devices are identical, both of them use a continuous laser to produce a full-phase steady light, use an intensity modulator to pulse, send coherent state | α > corresponding to logical bit 1, and send empty state |0 > representing logical bit 0. Bob makes a logic bit flip after signaling. Charlie corresponds to logical bit 1 with |0 > | α > and logical bit 0 with | α > |0 >.
The method comprises the steps that Alice and Bob send quantum states in a period of 2T (T is 1 nanosecond), and pulse signals of the Alice and the Bob are modulated by a first polarization controller and a second polarization controller, and then are polarized to be consistent; the fiber distance from Alice to the first beam splitter is longer, so that Alice arrives at the beam splitter just later (2k +1) T (k. epsilon. Z) than Bob's signal; the two square pulses are combined by a beam splitter, two continuous pulses are output, and the continuous pulses are sent to a detection end Charlie through an unsafe quantum channel.
In the second embodiment, the time base vector measurement at the detecting end is equivalent to detecting the time of arrival of the state | α >, and |0 > | α > corresponds to logic bit 1 and | α > |0 > corresponds to logic bit 0 under the time base vector; if the detector III or the detector IV responds twice in a period, a bit value is randomly selected; if both the time basis vector and the detector under the detection basis vector are responsive, then this portion of data is discarded.
The rest of the process is the same as the first embodiment.
Because the detector response probability is small after long-distance transmission, the probability that the detector three and the detector four respond simultaneously is negligible. However, since this is the case, the coding rate performance of the second embodiment is slightly worse than that of the first embodiment.
Example three:
another beam combining approach is described in conjunction with fig. 3, using a fast optical switch.
Compared with the embodiment, the present embodiment is different from the present embodiment in that the beam combining is performed using the fast optical switch.
The embodiment comprises two sending ends and a detecting end which are connected through an unsafe quantum channel; the sending end comprises a continuous laser and an intensity modulator; the continuous laser is used for generating phase-stable continuous light; the intensity modulator changes a continuous optical signal in time into an optical pulse at a specific moment and modulates the amplitude of the pulse to form an optical pulse with different intensities;
the detection end comprises a polarization controller, a fast light switch, a beam splitter and a detector; in this embodiment, the fast light switches are arranged on the light paths of the two transmitting ends, and the optical fiber distance from one of the transmitting ends to the fast light switch is longer for delaying an odd number of half periods (2k +1) T (T ═ 1 nanosecond, k ∈ Z)); polarization controllers are arranged on light paths between the two sending ends and the quick light opening, wherein the first sending end corresponds to the first polarization controller, and the second sending end corresponds to the second polarization controller; the polarization controller corresponds to the pulse signal of the first sending end, the polarization controller corresponds to the pulse signal of the second sending end, and the pulse polarization of the two sending ends is modulated by the polarization controller and then keeps consistent; a first beam splitter is arranged after the fast light is switched on;
when a pulse signal of the second sending end arrives, the fast optical switch is connected with the optical path from the second sending end to the first beam splitter, and the path from the first sending end to the first beam splitter is cut off; when a signal of a first sending end arrives, a light path from the first sending end to a first beam splitter is connected, and a path from a second sending end to the first beam splitter is cut off; the pulse combination of the two sending ends can be realized by operating according to the process. The first beam splitter splits the pulses after the rapid light is switched on and switched off, wherein one beam is sent to the third detector for time basis vector detection; the other beam is interfered by a Mach-Zehnder interferometer composed of a second beam splitter and a third beam splitter and then respectively sent to a first detector and a second detector for interference basis vector detection; the time basis vector data is used for coding, and the interference basis vector data is used for calculating contrast, so that the error rate and the safety risk are estimated.
In the third embodiment, the time base vector measurement at the detecting end is equivalent to detecting the time of arrival of the state | α >, and |0 > | α > corresponds to logic bit 1 and | α > |0 > corresponds to logic bit 0 under the time base vector; if the detectors under different basis vectors all respond, this portion of the data is removed.
The rest is the same as in the first and second embodiments.
Although the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the details of the foregoing embodiments, and various equivalent changes (such as number, shape, position, etc.) may be made to the technical solution of the present invention within the technical spirit of the present invention, and the equivalents are protected by the present invention.
Claims (10)
1. A quantum conference key negotiation method based on coherent detection is characterized in that: the system comprises two sending ends and a detection end; the two sending ends are respectively marked as a first sending end and a second sending end; the method comprises the following steps:
(1) the two sending ends respectively send optical pulses at random and send the optical pulses to the detection end through an unsafe quantum channel;
(2) splitting beams by the optical pulses sent by two sending ends of the first beam splitter and the second beam splitter respectively, and sending one of the optical pulses to the first detector and the second detector of the detection end respectively to perform time basis vector measurement; the other beam is sent to a third beam splitter for beam combination after the pulse polarization is modulated to be the same through a polarization controller; setting the distance from the first beam splitter to the third beam splitter to be longer than the distance from the second beam splitter to the third beam splitter, delaying odd number of half periods, and setting the extended distance as odd number of half periods multiplied by light speed;
(3) sending the pulses combined in the step (2) to a detector for interference basis vector measurement after interference;
(4) the detection end publishes the response time of the detector and publishes the selected basis vector; if the first detector responds and the second detector does not respond, the logic bit of the detection end is 1; if the first detector does not respond and the second detector responds, the logic bit of the detection end is 0; if the two detectors under the time basis vector both respond, the detection end randomly selects a logic bit value; if the detector responses exist under the two basis vectors, the data is removed;
(5) and (4) reserving the data under the time basis vector in the partial data and the data of the two corresponding sending ends as original keys according to the step (4), and extracting the conference keys through classical error correction, error verification and privacy amplification.
2. The quantum conference key agreement method according to claim 1, characterized in that: in the step (3), the combined pulse is interfered by a Mach-Zehnder interferometer composed of two beam splitters, and then is detected under the interference basis vector through a detector.
3. The quantum conference key agreement method according to claim 1, characterized in that: in the step (4), the detection end publishes the corresponding strength information of the response of the detector under the interference basis vector, and only when the two adjacent quantum states are not in the vacuum state, the corresponding part of data of the response of the detector under the interference basis vector is used for calculating the contrast of the response of the detector under the interference basis vector, and the contrast is used for calculating the final code forming rate;
the contrast expression is as follows:
p (D1) and P (D2) represent the probability of two detector responses making interferometric basis vector measurements, respectively.
4. The quantum conference key agreement method according to claim 1, characterized in that: in the step (4), the two sending ends and the detecting end respectively publish the logic bit values of the corresponding parts of the sending ends and the detecting end, and the logic bit values are used for calculating the gain of the quantum state of the code.
5. The quantum conference key agreement method according to claim 1, characterized in that: and the detection end adopts passive basis vector detection.
6. A quantum conference key negotiation method based on coherent detection is characterized in that: the system comprises two sending ends and a detection end; the two sending ends are respectively marked as a first sending end and a second sending end; the method comprises the following steps:
(1) the two sending ends respectively send random optical pulses and send the random optical pulses to the detection end through a quantum channel;
(2) pulses of the two sending ends are respectively modulated into the same pulse polarization by the polarization controller and then sent to the first beam splitter for beam combination; the distance from the first sending end to the first beam splitter is longer than the distance from the second sending end to the first beam splitter by a set distance so as to delay odd number of half cycles, and the set distance is equal to the odd number of half cycles multiplied by the light speed;
(3) the first beam splitter outputs two beams of continuous pulses, and one beam of continuous pulses is sent to the fourth detector to carry out time basis vector measurement; the other string is sent to the beam splitter II for beam splitting, one beam is sent to the detector three-purpose for time basis vector detection, and the other beam is sent to the detector for interference basis vector measurement after interference;
(4) the detection end publishes the response time of the detector and publishes the selected basis vector, the time basis vector measurement of the detection end is equivalent to the sequence of detecting the state arrival time of | alpha >, and |0 > | alpha > corresponds to a logic bit 1 and | alpha > |0 > corresponds to a logic bit 0 under the time basis vector; if the third detector or the fourth detector responds twice in a period, a bit value is randomly selected; if the detector responses exist under the two basis vectors, discarding the part of data;
(5) and (4) reserving the data under the time basis vector in the partial data and the data of the two corresponding sending ends as original keys according to the step (4), and extracting the conference keys through classical error correction, error verification and privacy amplification.
7. A quantum conference key negotiation method based on coherent detection is characterized in that: the system comprises two sending ends and a detection end; the two sending ends are respectively marked as a first sending end and a second sending end; the method comprises the following steps:
(1) the two sending ends respectively send random optical pulses and send the random optical pulses to the detection end through a quantum channel;
(2) pulses of the two sending ends are respectively modulated into the same pulse polarization by the polarization controller and then sent to the fast optical switch for beam combination; the distance from the first sending end to the fast optical switch is longer than the distance from the second sending end to the fast optical switch by a set distance so as to delay odd number of half cycles, and the set distance is equal to the odd number of half cycles multiplied by the optical speed;
(3) the pulse combined by the fast optical switch is sent to a beam splitter for beam splitting, wherein one beam is sent to a detector for time basis vector measurement, and the other beam is sent to the detector for interference basis vector measurement after interference;
(4) the detection end publishes the response time of the detector and publishes the selected basis vector, the time basis vector measurement of the detection end is equivalent to the sequence of detecting the state arrival time of | alpha >, and |0 > | alpha > corresponds to a logic bit 1 and | alpha > |0 > corresponds to a logic bit 0 under the time basis vector; if the detectors under the two basis vectors have responses, removing the part of data;
(5) and (4) reserving the data under the time basis vector in the partial data and the data of the two corresponding sending ends as original keys according to the step (4), and extracting the conference keys through classical error correction, error verification and privacy amplification.
8. A quantum conference key agreement system using the method of any one of claims 1 to 5, characterized in that: the system comprises two sending ends and a detection end; the two sending ends are respectively marked as a first sending end and a second sending end;
the transmitting end comprises a continuous laser used for generating phase-stable continuous light and an intensity modulator used for modulating the phase-stable continuous light generated by the continuous laser into light pulses with different intensities;
the detection end comprises a first beam splitter, a second beam splitter, a third beam splitter, a fourth beam splitter, a fifth beam splitter, a first detector, a second detector, a third detector and a fourth detector;
the first beam splitter and the second beam splitter are respectively arranged on the light paths of the two sending ends and are used for splitting the pulses of the two sending ends and respectively sending one of the pulses to the first detector and the second detector for time basis vector measurement; the other beam is sent to a third beam splitter through a polarization controller;
the third beam splitter combines pulses sent by the first beam splitter and the second beam splitter, and the distance from the first beam splitter to the third beam splitter is longer than the distance from the second beam splitter to the third beam splitter by a set distance so as to delay odd number of half cycles, wherein the set distance is equal to the odd number of half cycles multiplied by the light speed;
and the fourth beam splitter and the fifth beam splitter form a Mach-Zehnder interferometer, and pulses after the third beam splitter is combined are interfered and then are sent to the third detector and the fourth detector for interference basis vector measurement.
9. A quantum conference key agreement system using the method of claim 6, characterized in that: the system comprises two sending ends and a detection end; the two sending ends are respectively marked as a first sending end and a second sending end;
the transmitting end comprises a continuous laser used for generating phase-stable continuous light and an intensity modulator used for modulating the phase-stable continuous light generated by the continuous laser into light pulses with different intensities;
the detection end comprises a first beam splitter, a second beam splitter, a third beam splitter, a fourth beam splitter, a first detector, a second detector, a third detector and a fourth detector; polarization controllers are arranged on the light paths from the two transmitting ends to the first beam splitter;
the first beam splitter is used for modulating the pulses of the two sending ends by the polarization controller, keeping the polarization consistent, then combining the pulses, and outputting two continuous pulses, wherein one continuous pulse is sent to the fourth detector for time basis vector detection; the other string is sent to a second beam splitter; the distance from the first sending end to the beam combiner is prolonged by a set distance compared with the distance from the second sending end to the beam combiner to delay odd number of half cycles, and the set distance is equal to the odd number of half cycles multiplied by the light speed;
the two beam splitters split the pulse sent by the first beam splitter, one beam is sent to the detector for three-purpose time basis vector detection, and the other beam is used for interference basis vector detection;
the third beam splitter and the fourth beam splitter form a Mach-Zehnder interferometer, and interfere the pulse sent by the second beam splitter;
and the first detector and the second detector perform interference basis vector measurement on the interfered pulses.
10. A quantum conference key agreement system using the method of claim 7, characterized in that: the system comprises two sending ends and a detection end; the two sending ends are respectively marked as a first sending end and a second sending end;
the transmitting end comprises a continuous laser used for generating phase-stable continuous light and an intensity modulator used for modulating the phase-stable continuous light generated by the continuous laser into light pulses with different intensities;
the detection end comprises a fast optical switch, a first beam splitter, a second beam splitter, a third beam splitter, a first detector, a second detector and a third detector; polarization controllers are arranged on the light paths from the two transmitting ends to the quick optical switch;
the rapid optical switch is used for modulating pulses of the two sending ends by the polarization controller, keeping the pulses consistent, combining the pulses and sending the pulses to the first beam splitter; the distance from the first sending end to the fast optical switch is longer than the distance from the second sending end to the fast optical switch by a set distance so as to delay odd number of half cycles, and the set distance is equal to the odd number of half cycles multiplied by the optical speed;
the beam splitter splits the pulses sent by the fast optical switch, one beam is sent to the detector for three-purpose time basis vector detection, and the other beam is used for interference basis vector detection;
the second beam splitter and the third beam splitter form a Mach-Zehnder interferometer, and interfere the pulse sent by the first beam splitter;
and the first detector and the second detector perform interference basis vector measurement on the interfered pulses.
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