WO2020140851A1 - Quantum communication and quantum time-frequency transmission fusion network system and method - Google Patents

Abstract

Disclosed are a quantum communication and quantum time-frequency transmission fusion network system and method. The method comprises: a quantum relay unit emitting an entangled photon pair and respectively sending same to two quantum terminal units via a transmission unit, and each quantum terminal unit reflecting input photons and returning same to the quantum relay unit via the transmission unit; the quantum relay unit performing HOM interference measurement on the entangled photon pair and adjusting an optical path delay, and obtaining the maximum HOM dip value after multiple measurements, so as to realize optical path balance; then, a signal laser sending a laser pulse and sending same to the quantum terminal unit via the transmission unit; the quantum terminal unit coding the input laser pulse and transmitting same back to the quantum relay unit via a transmission channel; the quantum relay unit obtaining and publishing a measurement result; the quantum terminal unit performing clock synchronization by means of a classical channel and by using an optical channel monitor after obtaining a key by means of the classical channel; and time-frequency information being encrypted by means of a key distributed through QKD, so that the information security problem of the time-frequency information is solved, and fusion between quantum communication and quantum time-frequency transmission is realized.

Description

Quantum communication and quantum time-frequency transmission fusion network system and method Technical field

The invention relates to the technical field of quantum information and optical communication, in particular to a fusion network system and method of quantum communication and quantum time-frequency transmission.

Background technique

Time-frequency is a very important parameter; time-frequency standard transmission is also very important in high-precision time service systems, and is widely used in many fields such as positioning, navigation, and communication. Time-frequency synchronization technology refers to the process of comparing time-frequency signals generated by a clock in a different place by some means and forming a unified time-frequency reference. Precision navigation is inseparable from accurate time service, and the basic requirement of time service is clock synchronization.

With the continuous development of atomic clock technology, the frequency uncertainty of optical frequency atomic clocks has reached 10 ^-18 . The existing time-frequency synchronization technology has been unable to meet the requirement of high-precision clock comparison, and it is necessary to develop a time-frequency synchronization method with higher transmission stability. Relying on the rapid development of optical fiber communication technology, time-frequency synchronization technology based on optical fiber came into being. Optical fiber, as a large-bandwidth, high-speed transmission medium, has become the world's largest communications infrastructure. In 2017, the length of newly built optical cable lines in my country was 7.05 million kilometers, and the total length of national optical cable lines reached 37.47 million kilometers. Taking advantage of low transmission loss of optical fiber, isolation of electrical noise, and wide distribution, it is of practical and important significance to build a time-frequency network based on optical fiber.

Quantum communication is considered to be the future development direction of communication. Quantum key distribution (Quantum Key Distribution, QKD allows legal users Alice and Bob to share theoretically secure passwords, combined with a one-time encryption system to achieve the current The only safe communication that can be proved. After more than 30 years of development, QKD has now entered the stage of measurement equipment independent protocol (MDI), combined with deceptive technology, MDI-QKD has closed the detector's defects at one time. It also solves the problem of multi-photon composition of weakly coherent state single photon source, and has become the most practical solution at present. The network fusion of quantum communication and quantum time-frequency transmission is currently a key technical problem that needs to be solved for precise timing and timing security. Important exploration.

However, the quantum state emitted by the Alice and Bob ends in the measurement device-independent protocol was successfully measured by the third-party Charlie. It requires that the modes of time, spectrum, and polarization to reach the photon must match exactly. First of all, the distance between the Alice and Bob ends and Charlie is not exactly the same, it is necessary to accurately delay so that the photon arrival time is fully aligned. Secondly, different lasers are used at Alice and Bob, and the spectrum is not exactly the same. Third, because of the birefringence effect of optical fibers, it is difficult to ensure stable transmission of photon polarization. Although phase encoding can be used, phase drift and time jitter limit the performance of the QKD system and the key rate is low.

At the same time, in the prior art, for example, the patent 201510008068.9 attempts to solve the problem of the stability of the irrelevant protocol of the measurement equipment of the phase modulation polarization encoding, but it artificially reduces the communication distance by half.

Among the existing technologies, such as the Gisin group of the University of Geneva, Switzerland, which first proposed a plug-and-play solution (Document: Muller A, Herzog T, Huttner B, etal. "plug and play" systems" for quantum cryptography [J]. Applied physics Letters, 1997,70:793-795) adopts the phase encoding method, the patent 201610700278.9 is further improved, and the time phase encoding method is used. The main purpose is to solve the problem of polarization jitter compensation in the optical fiber, but it does not involve the measurement equipment irrelevant solution.

The plug-and-play solution can use the same laser to achieve the consistency of the photon spectrum and other parameters, but because the distance between the two communication parties and the relay is not completely symmetrical, the HOM interference contrast decreases. In the current experiment, independent optical pulses of different wavelengths are generally used to achieve synchronization between the two parties of communication using wavelength division multiplexing, which consumes wavelength resources. However, with the increase of network users, especially in the fusion of classical and quantum communication networks, each wavelength is a precious resource, and the above method is obviously not economical and feasible.

MDI-QKD has high requirements for clock synchronization, and the security of time-frequency transmission cannot be fully guaranteed at present. Combining the advantages of QKD information security and the high accuracy of time-frequency transmission synchronization, the network that combines quantum communication and quantum time-frequency transmission is temporarily No relevant proposals have been proposed.

Summary of the invention

The present invention is made in view of the above problems, and the purpose is to overcome the shortcomings of the prior art, to provide a quantum communication and quantum time-frequency transmission fusion network system and method, to solve the MDI-QKD clock synchronization problem and time-frequency network in practical applications Information security issues.

In order to achieve the above object, the present invention provides the following technical solutions: a fusion network system of quantum communication and quantum time-frequency transmission, including a quantum relay unit, a transmission unit, a quantum terminal unit Alice and a quantum terminal unit Bob;

The quantum relay unit emits signal photon and idle frequency photon entangled photon pair pulses, wherein the signal photon reaches the quantum terminal unit Alice through the transmission unit, and the idle frequency photon reaches the quantum terminal unit Bob through the transmission unit. Alice and Bob respectively reflect signal photons and idle frequency photons, and then return to the quantum relay unit through the original link. The quantum relay unit performs HOM (Hong-Ou-Mandel) interference on the reflected signal photons and idle frequency photons to obtain an interference pattern. . The transmission unit adjusts the delay between the two optical paths multiple times, and gradually approaches the maximum value of the HOM depression. At this time, it is considered that the optical paths of the two optical paths are exactly the same, and the time for Alice and Bob to reach the quantum relay unit Charlie is exactly the same. Alice and Bob use optical monitoring channels for clock synchronization.

Next, perform quantum key distribution:

The quantum relay unit emits two communication laser pulses. The two communication laser pulses are sent to Alice and Bob of the quantum terminal unit through the transmission unit, and are encoded and reflected in the quantum terminal unit. After reflection, they are returned by the transmission unit. The quantum relay unit.

The quantum relay unit Charlie analyzes the communication laser pulse encoded by the quantum terminal unit to obtain a measurement result, and publishes the measurement result through a classic channel, where the classic channel is a common channel, such as broadcast.

Among them, the entangled photon pair pulse is used to correct the optical path balance to achieve clock synchronization, and the communication laser pulse is used for quantum key distribution.

The multiple quantum terminal units compare the measurement results and the locally prepared quantum state information to obtain a screening code, and perform a bit error rate detection on the screening code. If it is considered safe, the communication is successful, and if it is considered unsafe, give up this time Communication, start again.

The quantum relay unit and the transmission unit are connected through a fiber channel;

The quantum terminal unit and the transmission unit are connected through a fiber channel;

The quantum terminal unit and the quantum relay unit are connected by a transmission unit.

Preferably, the quantum entangled light source includes a pump laser, a nonlinear crystal, a first narrow-band filter, and a second narrow-band filter. The pump laser emits a pump pulse laser at 790 nm, enters a nonlinear crystal to generate entangled photon pairs with similar frequencies, and enters the transmission unit through the first narrowband filter and the second narrowband filter, respectively.

Preferably, the transmission unit receives the entangled photon pairs generated by the quantum relay unit, wherein the signal photons enter the first circulator through the first beam combiner, and then enter the optical fiber through the first wavelength division multiplexer and the electronically controlled optical delay line The link is transmitted to the quantum terminal unit Alice, the idle frequency photons enter the second circulator through the second beam combiner, enter the fiber link through the second wavelength division multiplexer, and manually adjustable optical delay line to transmit to the quantum Terminal unit Bob, the two quantum terminal units reflect the pulses, and after the reflected pulses are transmitted through the quantum channel, they are transmitted to the quantum relay unit via the first circulator and the second circulator respectively;

Preferably, the quantum communication light source includes a laser and a polarization beam splitter. The laser emits pulsed laser light in the 1550 nm band. After passing through the polarization beam splitter, the horizontally polarized light enters the transmission unit.

Preferably, the transmission unit receives the communication optical pulse of the quantum relay unit, and is divided into two paths by the first beam splitter, wherein one pulse passes through the first beam combiner and enters the first circulator, and then passes through the first wave The device and the electronically controlled optical delay line enter the optical fiber link and are transmitted to the quantum terminal unit Alice. Another pulse enters the second circulator through the second beam combiner, and is manually dimmable through the second wavelength division multiplexer The delay line enters the optical fiber link and is transmitted to the quantum terminal unit Bob. The quantum terminal units Alice and Bob reflect the pulse. After being transmitted through the quantum channel, the reflected pulse passes through the first circulator and the third Two circulators, transmitting the quantum relay unit;

The quantum relay unit includes a measuring instrument. The measuring instrument performs projection measurement on the incoming pulse of the transmission unit to obtain a quantum state determined by measurement. The quantum terminal unit measures the determined quantum state and locally prepared quantum state. Information comparison, get the screening code, pass the authenticated classic channel communication, select a part of the screening code to estimate the bit error rate, and calculate the theoretical value according to the deceptive mode. If the bit error rate is lower than the theoretical value, it is considered safe and continue to follow up Treatment, if the bit error rate is higher than the theoretical value, it is considered that there is a security risk, and this communication is abandoned.

Preferably, the measuring instrument is used to perform HOM interference measurement on the signal photons and idle frequency photons introduced by the transmission unit to obtain the relationship between the delay time and the interference contrast.

Specifically, the first circulator and the second circulator are used to isolate the outgoing light and the reflected light.

Preferably, the quantum terminal unit includes a four-port circulator, a fourth polarization beam splitter, a Faraday lens, a second beam splitter, an optical channel monitor, an optical isolator, a phase randomizer, an intensity modulator, and a polarization modulator And variable optical attenuator;

After the pulse enters the quantum terminal unit, it first enters the four-port circulator, then transmits to the fourth polarization beam splitter, and then is reflected by the Faraday lens, and returns to the four-port circulator to enter the second beam splitter, which is divided into two paths, one path Enter the optical channel monitor, and enter the optical isolator, phase randomizer, polarization modulator, intensity modulator and variable optical attenuator in turn.

Specifically, the four-port circulator is used to adjust the walking path of the photon.

Faraday lenses are used to automatically compensate for polarization jitter during transmission.

The second beam splitter is a 10:90 beam splitter, the transmitted light is used for quantum key distribution, and an optical channel monitor.

The optical channel monitor is used to monitor the optical power level in the channel, and is used to adjust the variable optical attenuator to ensure that the average photon number is the specified value; after the optical path adjustment is completed, the optical channel monitor is used for time synchronization.

The optical isolator is used to ensure the unidirectional transmission of light and isolate the reflected light.

The phase randomizer randomly modulates the phase of the optical pulse between [0, 2π] to meet the requirements of the photon number state.

The polarization modulator can randomly modulate light pulses into horizontal, vertical, +45 degree and -45 degree polarization states.

The intensity modulator is used to adjust the light pulse to a signal state or a decoy state. The variable optical attenuator guarantees that the average number of photons reflected in the quantum channel is less than one.

Preferably, the measuring instrument includes a third beam splitter, a first polarization beam splitter, a second polarization beam splitter, a first single photon detector, a second single photon detector, a third single photon detector, a fourth Single photon detector and coincidence counter;

The pulse reflected by the Faraday lens passes through the second beam splitter, optical isolator, phase randomizer, polarization modulator, and intensity modulator, and then enters the adjustable attenuator. The attenuated pulse is transmitted to the measuring instrument.

The third beam splitter receives the entangled photon pairs from the transmission unit, and the quantum interference formed on the third beam splitter enters the first single photon through the evolution of the first polarization beam splitter and the second polarization beam splitter The detector, the second single photon detector, the third single photon detector and the fourth single photon detector respond; the coincidence counter counts the photons and performs coincidence measurement to obtain the HOM interference pattern.

Specifically, the third beam splitter is a 50:50 beam splitter.

The first polarization beam splitter and the second polarization beam splitter transmit horizontally polarized light and reflect vertically polarized light.

The first single photon detector, the second single photon detector, the third single photon detector, and the fourth single photon detector are threshold detectors, which are used to detect whether a photon arrives.

The coincidence counter judges the measurement result based on the response of the single photon detector.

The fusion network system and method according to the foregoing quantum communication and quantum time-frequency transmission include:

The laser included in the quantum relay unit sends laser pulses with adjustable wavelengths, which are divided into two optical pulses with the same intensity by the first beam splitter.

The two optical pulses are connected to the quantum channel after passing through the first circulator and the second circulator respectively.

The quantum channel sends light pulses to the quantum terminal unit.

Regardless of the normalization factor, at this time, the quantum state of the photon is:

|ψ>=|H>+|V>.

Among them, H represents the horizontal polarization state, V represents the vertical polarization state.

The fourth polarization beam splitter transmits the horizontal polarization component in the input pulse as the photon to be modulated, and the quantum state becomes:

|ψ>=|H>.

After being reflected by Faraday lens, it is converted into vertically polarized light, and then isolated and reflected by an optical isolator. The phase modulator randomly modulates the photon phase [0, 2π] to satisfy the condition of photon number state (Fock state).

The polarization modulator is randomly modulated into one of four polarization states: horizontal, vertical, +45 degrees, and -45 degrees. The quantum state becomes:

|ψ>={|H>, |V>, |+>, |->}.

The intensity modulator randomly sets the pulse to the signal state or decoy state, and the adjustable attenuator sets the average photon number to the specified value according to the line attenuation and input optical power, such as the signal photon is 0.4 per pulse, and the decoy photon is 0.05 per pulse. .

Assume that the two input quantum states are:

|ψ>=|H>.

Then the joint quantum state output from the tunable optical attenuator is:

When the photon returns to the quantum relay unit through the quantum channel and reaches the measuring instrument (the measuring instrument uses a Bell measuring instrument), the joint quantum state evolution is:

among them:

φ _i , i=a, b is the phase randomly modulated by the phase modulator;

μ, ν are the average number of photons output by the two quantum terminal units respectively;

η _i , i=a, b is the total loss caused by optical devices and fiber channels in the optical path.

The measuring instrument measures the input quantum state.

when:

The first single photon detector and the fourth single photon detector;

The second single photon detector and the third single photon detector;

The simultaneous response of any group indicates that the quantum state is:

when:

The first single photon detector and the second single photon detector;

The third single photon detector and the fourth single photon detector;

The simultaneous response of any group indicates that the quantum state is:

In the above two cases, the measurement is successful. The quantum relay unit Charlie publishes the measurement results through the public channel.

According to the results published by the quantum relay unit Charlie, the Alice and Bob sides of the communication parties compare the local information, and do not operate or perform bit flip operations on the bit information represented by the local quantum state. MDI-QKD (Measurement Device Independent) -Quantum Key Distribution Quantum key distribution) Complete key distribution, the specific method is shown in the following table.

It should be noted that if the +45° and -45° polarization states of the diagonal base are used, the theory shows that the error rate of the diagonal base is greater than that of the linear base, so the diagonal base can be used to estimate the bit error, but it is not used to generate Key.

In the same way, it can be analyzed when the polarization modulator modulates two quantum terminal units into other quantum states.

According to the above principle, the two quantum terminal units obtain the initial key and estimate the bit error rate. If the verification is passed, the two quantum terminal units obtain the final key through security error correction and enhancement.

Further, a fusion network system and method for quantum communication and quantum time-frequency transmission is provided, which is characterized by comprising the following steps,

S1. System initialization: check the hardware/software of the quantum terminal unit, quantum relay unit and transmission unit to be communicated, check whether the device is operating normally, and set the initial conditions;

S2. Optical path calibration: The quantum relay unit sends the entangled photon pairs to the quantum terminal unit through the transmission unit. The quantum terminal unit directly reflects the entangled photons back to the quantum relay unit through the transmission unit. The quantum relay unit measures the HOM depression between the entangled photon pairs , Find the maximum value of HOM depression according to the delay adjusted by the transmission unit, at this time it is considered that the two optical paths are balanced;

S3. Quantum information coding: the quantum relay unit sends signal pulses to multiple quantum terminal units through quantum channels, and the quantum terminal units are randomly loaded with horizontal, vertical, +45 degrees and -45 degrees polarized light pulses through polarization modulators. The decoy state component is added after the intensity modulator, and then modulated by an adjustable attenuator into a number of coherent laser pulses with an average photon number of less than 1, and returned to the quantum relay unit via the original link;

S4. Bell state analysis: The quantum relay unit analyzes the pulses returned by the quantum terminal unit through a measuring instrument, and determines the projected Bell state based on the simultaneous response results of multiple single photon detectors, and publicly announces the measurement results;

S5. Key screening: the quantum terminal unit compares the measurement results with local information to obtain a screening code;

S6. Detection of bit error rate: the quantum terminal unit randomly selects a part of the signal state to detect the bit error rate, QBER=Nerr/Nsift, if the measured QBER value is greater than the theoretical calculation of the decoy state, it is considered that the communication is unsafe and gives up This communication starts again;

S7. Error correction and security enhancement: The classic communication between the quantum terminal units through authentication uses the Hash algorithm to correct the remaining screening codes to obtain an error correction code. If the error correction is successful, security enhancement is performed.

S8. Clock synchronization: The quantum terminal unit performs clock synchronization through the optical channel monitor to realize time-frequency transmission; the generated key is used to encrypt and transmit time-frequency synchronization information.

The beneficial effects of the invention are:

1. The present invention uses the same physical network for quantum communication and quantum time-frequency transmission at the same time, saving physical fiber resources. The present invention uses Faraday lens automatic compensation, and the design returns to the optical path to eliminate the birefringence problem caused by the fiber link. The device is simple and the cost low.

2. The laser light source of the present invention adopts a single laser, which has good stability and consistency and reduces costs; the present invention adopts a method independent of measurement equipment, which can eliminate the QKD security problem caused by the side channel of the detector.

3. The present invention uses quantum clock synchronization to achieve the optical path balance required by the measurement equipment independent protocol and improves the synchronization accuracy. The present invention uses the key generated by QKD to encrypt the quantum time-frequency transmission information to ensure the security of time-frequency information.

BRIEF DESCRIPTION

FIG. 1 is a structural block diagram of the MDI-QKD quantum terminal unit of the present invention;

2 is a structural block diagram of the measuring instrument of the present invention;

3 is a structural block diagram of the quantum entangled light source of the present invention;

4 is a structural block diagram of the quantum communication light source of the present invention;

5 is a block diagram of the transmission unit structure of the present invention;

6 is a block diagram of the overall structure of the working principle of the system of the present invention;

7 is a block diagram of the overall structure of the detailed working principle block diagram of the system of the present invention;

8 is a flowchart showing the operation of the network system of the embodiment.

The names of the parts corresponding to the reference numbers in the drawings are as follows:

Quantum terminal unit 1, four-port circulator 101, fourth polarization beam splitter 102, Faraday lens 103, second beam splitter 104, optical channel monitor 105, optical isolator 106, phase modulator 107, polarization modulator 108 , Intensity modulator 109, adjustable attenuator 110, clock 111;

Measuring instrument 2, third beam splitter 201, first polarization beam splitter 202, second polarization beam splitter 203, first single photon detector 211, second single photon detector 212, third single photon detector 213 , The fourth single photon detector 214, in accordance with the counter 221;

Quantum entangled light source 3, pump laser 301, nonlinear crystal 302, first narrowband filter 303, second narrowband filter 304;

Quantum communication light source 4, communication laser 401, third polarization beam splitter 402;

Transmission unit 5, first beam splitter 501, first beam combiner 511, second beam combiner 512, first wave demultiplexer 513, second wave demultiplexer 514, first circulator 521, Two circulators 522, electronically controlled optical delay line (531,533), manually adjustable optical delay line (532,534), fiber link (541-544).

detailed description

The specific implementation of the present invention will be further described below with reference to the drawings:

As shown in FIGS. 1 to 7, this embodiment provides a fusion network system of quantum communication and quantum time-frequency transmission. The working steps are as follows:

The pump laser (Titanium sapphire mode-locked pulsed laser, FemtoLasers) 301 emits a 790nm laser pulse, which is incident on the nonlinear crystal 302 (TypeII phase matching PPKTP), generating entangled photon pairs, in which signal photons and idle frequency photons enter the first The narrowband filter 303 and the second narrowband filter 304 filter the pump light and the stray light, and then enter the transmission unit 5. The transmission unit 5 sends the signal photons and idle frequency photons to the first circulator 521 and the second circulator 522 through the first beam combiner 511 and the second beam combiner 512, respectively, and then to the power The optically controlled delay line 531 and the optical fiber link 541, the wave demultiplexer 514 to the manually tunable optical delay line 532 and the optical fiber link 542 are sent to the quantum terminal units Alice and Bob.

Preferably, by using different pump wavelengths, entangled photon pairs can be routed to different quantum terminal units by wavelength. For example, the signal photon arrives at Alicen through the electronically controlled optical delay line 533 and the optical fiber link 543 through the wave demultiplexer 513, and the idle frequency photon arrives through the electronically controlled optical delay line 534 and the optical fiber link 544 through the wave demultiplexer 514 Bobn.

The signal photon and the idle frequency photon respectively pass through the circulator 101 and the fourth polarization beam splitter 102, are reflected by the Faraday lens 103, and then return to the quantum relay unit 6 along the original optical path.

The measuring instrument 2 of the quantum relay unit 6 receives and measures the HOM effect of entangled photon pairs. Specifically, the signal photons and idle frequency photons enter the measuring instrument through the input port of the third beam splitter 201 respectively. Interference occurs, evolved by the first polarization beam splitter 202 and the second polarization beam splitter 203, respectively, and enters the first single photon detector 211, the second single photon detector 212, the third single photon detection 213, and the fourth single photon The detector 214 detects and recognizes, and finally the coincidence measurement is performed by the coincidence counter 221.

The transmission unit 5 adjusts the electronically controlled optical delay line, sets the time delay between the quantum relay unit and the two quantum terminal units, and the measuring instrument 2 performs measurement again. Repeated many times, gradually after all the HOM depression maximum.

When the coincidence counter obtains the maximum HOM depression, it can be considered that the two optical paths are balanced and the photons reach the two quantum terminal units at the same time. The next step is quantum key distribution.

The signal laser (PDL808 Sepia, Picoquant) 401 emits a 1550 nm laser pulse. After passing through the third polarization beam splitter 402, the pulse transmits horizontally polarized light and enters the transmission unit 5. The transmission unit 5 receives the pulse and divides it into two channels by the second beam splitter 501, one channel enters the first circulator 521 through the first beam combiner 511, and then passes through the first wavelength division multiplexer 513 and the electronically controlled optical delay The line 531 and the optical fiber link 541 are sent to the quantum terminal unit Alice, the other way enters the second circulator 522 through the second beam combiner 512, and then passes through the second wavelength division multiplexer 514, the manually adjustable optical delay line 532 and the optical fiber The link 542 is sent to the quantum terminal unit Bob.

The quantum terminal unit Alice end and the quantum terminal unit Bob end are used to receive the signal pulse of the quantum relay unit 6. The four-port circulator 101 is used to form a photon travel path, the fourth polarization beam splitter 102 is used to form horizontally polarized light, the Faraday lens 103 is used to compensate polarization jitter in the optical fiber link, and the second beam splitter 104 is used to separate parts The photon is used for monitoring, the optical channel monitor is used to monitor the optical power level in the channel, the phase modulator (Photline MPZ) 107 is randomly loaded with the pulse phase [0,2π] is used to meet the requirements of the photon number state, and the polarization modulator (General Photonics MPC) 108 is used to randomly modulate the input photons to:

|ψ>={|H>, |V>, |+>, |->},

The intensity modulator (Photline MXAN) 109 marks the pulse as a deceptive state or a signal state, the adjustable attenuator 110 ensures that the average number of photons is the specified value, the optical channel monitor 105 analyzes the photon number distribution of the pulse according to the optical power, and the Faraday lens 103 will The polarization state of the input light is rotated by 90° to compensate for the birefringence effect in the fiber. Finally, the quantum terminal unit will output photons with an average photon number less than 1, randomly modulated into horizontal, vertical, +45 degrees, and -45 metric photon states, some of which are marked as deceptive states, and some are marked as signal states. The photon returns to the quantum relay unit 3 through the quantum channel 4 and enters the measuring instrument 2 synchronously.

The quantum relay unit 3 receives the modulated photons of the two quantum terminal units and inputs them to the measuring instrument 2.

The measuring instrument 2 analyzes the input photons. The following are the quantum states output by the two quantum terminal units:

That is, the polarization modulator 108 modulates all the photons into horizontal polarization, the phase modulator 107 randomly modulates the phases of the two quantum terminal units 1 to φ _a and φ _b , respectively, and the intensity modulator 109 and the adjustable attenuator 110 work together to make the two The average number of photons of each quantum terminal unit 1 is μ and ν, respectively. The joint quantum state is:

After fiber channel attenuation, the joint quantum state evolution is:

η _a and η _b are the total loss caused by the fiber channel and the device between the two quantum terminal units 1 and the tester 2, respectively.

After the two pulses enter the tester 2, the third beam splitter receives the entangled photon pairs from the transmission unit, and the quantum interference formed on the third beam splitter passes through the first polarization beam splitter, the second The evolution of the polarization beam splitter enters the first single photon detector, the second single photon detector, the third single photon detector, and the fourth single photon detector to generate a response; the coincidence counter counts the photons and performs coincidence measurement.

The measuring instrument 2 measures the above-mentioned combined quantum state when:

The first single photon detector 211 and the fourth single photon detector 214;

The second single photon detector 212 and the third single photon detector 213;

The simultaneous response of any group indicates that the quantum state is:

when:

The first single photon detector 211 and the second single photon detector 212;

The third single photon detector 213 and the fourth single photon detector 214;

The simultaneous response of any group indicates that the quantum state is:

In the above two cases, the measurement is successful. The quantum relay unit 6 publishes the measurement results.

The two quantum terminal units 1 compare the measurement results with the locally prepared quantum state information to obtain the original code, and then discard those data that have not been successfully measured to obtain a screening code.

The two quantum terminal units 1 communicate through the authenticated classic channel, select a part of the screening code to estimate the bit error rate, and calculate the theory according to the decoy mode (weak decoy state + vacuum state, double decoy state, single decoy state) value. If the bit error rate is lower than the theoretical value, it is considered safe and the post-processing is continued. If the bit error rate is higher than the theoretical value, it is considered that there is a security risk, and this communication is abandoned.

After the bit error rate test is passed, the two quantum terminal units 1 communicate through authenticated classic channels, respectively, and use a classic algorithm, preferably a Hash algorithm for error correction.

After the error correction is passed, the two quantum terminal units 1 communicate with each other through the authenticated classic channel to enhance the confidentiality of the retained data, that is, discard a part of the data, so that the information obtained by the eavesdropper is approximately 0, and a secure quantum key is obtained.

Finally, the distribution of quantum keys is realized between the two quantum terminal units 1.

As shown in FIG. 8, a key distribution and sharing method for a plug-and-play measurement device-independent quantum key distribution network system includes the following steps:

S1. System initialization: check the hardware/software of the quantum terminal unit, quantum relay unit and transmission unit to be communicated, check whether the device is operating normally, and set the initial conditions;

S2. Optical path calibration: The quantum relay unit sends the entangled photon pairs to the quantum terminal unit through the transmission unit. The quantum terminal unit directly reflects the entangled photons back to the quantum relay unit through the transmission unit. The quantum relay unit measures the HOM depression between the entangled photon pairs , Find the maximum value of HOM depression according to the delay adjusted by the transmission unit, at this time it is considered that the two optical paths are balanced;

S3. Quantum information coding: the quantum relay unit sends signal pulses to multiple quantum terminal units through quantum channels, and the quantum terminal units are randomly loaded with horizontal, vertical, +45 degrees and -45 degrees polarized light pulses through polarization modulators. The decoy state component is added after the intensity modulator, and then modulated by an adjustable attenuator into a number of coherent laser pulses with an average photon number of less than 1, and returned to the quantum relay unit via the original link;

S4. Bell state analysis: The quantum relay unit analyzes the pulses returned by the quantum terminal unit through a measuring instrument, and determines the projected Bell state based on the simultaneous response results of multiple single photon detectors, and publicly announces the measurement results;

S5. Key screening: the quantum terminal unit compares the measurement results with local information to obtain a screening code;

S6. Detection of bit error rate: the quantum terminal unit randomly selects a part of the signal state to detect the bit error rate, QBER=Nerr/Nsift, if the measured QBER value is greater than the theoretical calculation of the decoy state, it is considered that the communication is unsafe and gives up This communication starts again;

S7. Error correction and security enhancement: The classic communication between the quantum terminal units through authentication uses the Hash algorithm to correct the remaining screening codes to obtain an error correction code. If the error correction is successful, security enhancement is performed.

S8. Clock synchronization: The quantum terminal unit performs clock synchronization through the optical channel monitor to realize time-frequency transmission; the generated key is used to encrypt and transmit time-frequency synchronization information.

According to the disclosure and teaching of the above description, those skilled in the art to which the present invention belongs can also make changes and modifications to the above-mentioned embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the invention should also fall within the protection scope of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the invention.

Claims (10)

1. A fusion network system of quantum communication and quantum time-frequency transmission, which is characterized by comprising a quantum terminal unit, a quantum relay unit and a transmission unit, and the quantum terminal unit includes N Alice terminals and N Bob terminals;

   The quantum relay unit generates signal photon and idle frequency photon entangled photon pair pulses, wherein the signal photon reaches the quantum terminal unit Alice end through the transmission unit, and the idle frequency photon reaches the quantum terminal unit Bob end through the transmission unit; the Alice end and the Bob end are respectively The reflected signal photons and idle frequency photons are returned to the quantum relay unit via the original link; the quantum relay unit performs HOM interference on the reflected signal photons and idle frequency photons to obtain an interference pattern; the transmission unit mediates the two optical paths multiple times The delay between them is gradually approached to obtain the maximum value of the HOM depression. At this time, the time for Alice and Bob to reach the quantum relay unit is completely equal, and the signal photons and idle frequency photons reach the Alice end and Bob end of the quantum terminal unit at the same time;

   The quantum key distribution process is as follows:

   The quantum relay unit generates two communication laser pulses, and the two communication laser pulses are sent to the N Alice terminals and N Bob terminals of the quantum terminal unit through the transmission unit, and the Alice and Bob terminals are randomly loaded through the polarization modulator Horizontal, vertical, +45 degrees and -45 degrees polarized light pulses, decoy state components are added after the intensity modulator, and then modulated by an adjustable attenuator into a number of coherent laser pulses with an average photon number less than 1, and returned to the quantum through the original link Relay unit

   The quantum relay unit performs the Bell state analysis of the returned coherent laser pulse through the measuring instrument, determines the projected Bell state based on the simultaneous response results of multiple single photon detectors, and publicly announces the measurement results;

   The quantum terminal unit Alice end and the quantum terminal unit Bob end respectively compare the measurement result with the locally prepared quantum state information to obtain a screening code, and perform a bit error rate detection on the screening code, if it is deemed safe, then The communication is successful. If you think it is not safe, give up this communication and start again.
2. The fusion network system of quantum communication and quantum time-frequency transmission according to claim 1, wherein the quantum relay unit includes a measuring instrument, a quantum entangled light source and a quantum communication light source;

   The quantum entangled light source is used to generate signal photon and idle frequency photon entangled photon pairs, wherein the signal photon is transmitted to the quantum terminal unit Alice via the transmission unit, and the idle frequency photon is transmitted to the quantum terminal unit Bob via the transmission unit; the quantum terminal unit Alice And Bob reflect the signal photons and idle frequency photons respectively, and the transmission unit returns to the measuring instrument along the original optical path; the measuring instrument measures the signal photons and idle frequency photons;

   The quantum communication light source sends a communication pulse laser. After entering the transmission unit, the communication pulse laser is divided into two channels, one to the quantum terminal unit Alice and the other to the quantum terminal unit Bob; the quantum terminal units Alice and Bob respectively communicate with the laser Pulse coding, the transmission unit returns to the measuring instrument along the original optical path; the measuring instrument performs Bell state analysis on the input communication laser pulse to obtain the measurement result and publish it.
3. The fusion network system of quantum communication and quantum time-frequency transmission according to claim 2, wherein the measuring instrument includes a third beam splitter, a first polarization beam splitter, a second polarization beam splitter, a first Single photon detector, second single photon detector, third single photon detector, fourth single photon detector and coincidence counter;

   The third beam splitter receives the entangled photon pairs from the transmission unit, and the quantum interference formed on the third beam splitter enters the first single photon through the evolution of the first polarization beam splitter and the second polarization beam splitter The detector, the second single photon detector, the third single photon detector and the fourth single photon detector respond; the coincidence counter counts the photons and performs coincidence measurement to obtain the HOM interference pattern.
4. The fusion network system of quantum communication and quantum time-frequency transmission according to claim 2, wherein the quantum entangled light source includes a pump laser, a nonlinear crystal, a first narrow-band filter and a second narrow-band filter;

   The pump laser emits pulsed pump light, and the pulsed pump light is incident on the nonlinear crystal to generate a pair of entangled photons of signal and idle frequency photons with similar frequencies. The signal photons enter the transmission unit through the first narrow-band filter. Two narrow-band filters enter the transmission unit;

   The narrow-band filter is used to filter pump light and stray light.
5. The fusion network system of quantum communication and quantum time-frequency transmission according to claim 2, wherein the quantum communication light source includes a pulse laser and a third polarization beam splitter;

   The pulse laser sends a communication pulse laser with a wavelength of 1550 nm, and the transmitted horizontally polarized light is obtained through the third polarization beam splitter, and the transmitted horizontally polarized light is sent to the transmission unit;

   The third polarization beam splitter is used to transmit horizontally polarized light and reflect vertically polarized light.
6. The fusion network system of quantum communication and quantum time-frequency transmission according to claim 1, wherein the transmission unit includes a first beam splitter, a first beam combiner, a second beam combiner, and a first wavelength division Multiplexer, second wavelength division multiplexer, first circulator, second circulator, electronically controlled optical delay line, manually adjustable optical delay line and fiber link;

   The first beam combiner receives the signal photon from the quantum relay unit, enters the first wavelength division multiplexer through the first circulator, and then transmits it to the quantum terminal unit Alice through the electronically controlled optical delay line and the optical fiber link ;

   The second beam combiner receives idle frequency photons from the quantum relay unit, enters the second wavelength division multiplexer through the second circulator, and then transmits to the quantum terminal unit through the manually adjustable optical delay line and the optical fiber link Bob side

   The first beam splitter receives 1550nm laser pulses from the quantum relay unit, and is divided into two channels. The wire and fiber link are transmitted to the quantum terminal unit Alice, and the other route is transmitted to the quantum terminal via the manually tunable delay line and fiber link through the second beam combiner, second circulator, and second wavelength division multiplexer Unit Bob end;

   After the Alice end of the quantum terminal unit encodes the laser pulse, it is transmitted back to the quantum relay through the optical fiber link, the electronically controlled optical delay line, the first wavelength division multiplexer, and the first circulator unit;

   The Bob terminal of the quantum terminal unit encodes the laser pulse, and then transmits it back to the quantum through the optical fiber link, the manually adjustable optical delay line, the second wavelength division multiplexer, and the second circulator Following the unit.
7. The fusion network system of quantum communication and quantum time-frequency transmission according to claim 1, wherein the quantum terminal unit Alice end and Bob end both include a four-port circulator, a fourth polarization beam splitter, a Faraday lens, The second beam splitter, optical channel monitor, optical isolator, phase randomizer, polarization modulator, intensity modulator and variable optical attenuator;

   The quantum terminal unit Alice end or Bob end receives the laser pulse from the quantum relay unit through transmission, enters the fourth polarization beam splitter through the four-port circulator, and then the Faraday lens compensates the polarization drift caused by the environment, and the reflection enters the four The port circulator reaches the second beam splitter, which is divided into two channels by the second beam splitter: one channel enters the optical channel monitor to monitor the input optical power; the other channel enters the optical isolator to isolate the reflected light, and then enters the phase randomizer , The phase of the randomly modulated light pulse is [0,2π] to meet the requirements of the photon number state, and then the photon is randomly modulated by the polarization modulator to one of the horizontal, vertical, +45 degrees, and -45 degrees partial normal states, and then the intensity The modulator is loaded into a decoy state or a signal state, and finally forms a weak coherent laser pulse signal with an average photon number less than 1 through a variable optical attenuator.
8. The fusion network system of quantum communication and quantum time-frequency transmission according to claim 7, characterized in that the four-port circulator is used to adjust the walking path of the photon; the Faraday lens is used to automatically compensate polarization jitter during transmission .
9. The fusion network system of quantum communication and quantum time-frequency transmission according to claim 7, characterized in that: the second beam splitter is a 10:90 beam splitter, and the beam splitting forms transmitted light and reflected light. Transmitted light is used for quantum key distribution, and reflected light is used for channel monitoring;

   The optical channel monitor is used to monitor the optical power level in the channel, used to adjust the variable optical attenuator to ensure that the average number of photons is a specified value, or the optical channel monitor is used for clock synchronization;

   The optical isolator is used to ensure the unidirectional transmission of light and isolate the reflected light.
10. A fusion network method of quantum communication and quantum time-frequency transmission, which is applied to a fusion network system of quantum communication and quantum time-frequency transmission according to any one of claims 1-8, characterized in that: The method includes the following steps:

    S1. System initialization: check the hardware/software of the quantum terminal unit, quantum relay unit and transmission unit to be communicated, check whether the device is operating normally, and set the initial conditions;

    S2. Optical path calibration: The quantum relay unit sends the entangled photon pairs to the quantum terminal unit through the transmission unit. The quantum terminal unit directly reflects the entangled photons back to the quantum relay unit through the transmission unit. The quantum relay unit measures the HOM depression between the entangled photon pairs , Find the maximum HOM depression according to the delay adjusted by the transmission unit;

    S3. Quantum information coding: the quantum relay unit sends signal pulses to the multiple Alice and Bob terminals of the quantum terminal unit through quantum channels. The Alice and Bob terminals are randomly loaded with a polarization modulator horizontally, vertically, and +45 degrees And -45 degree polarized light pulse, add decoy state component after intensity modulator, and then modulated by adjustable attenuator into a number of coherent laser pulses with average photon number less than 1, and return to quantum relay unit through the original link;

    S4. Bell state analysis: The quantum relay unit analyzes the pulses returned by the quantum terminal unit through a measuring instrument, and determines the projected Bell state based on the simultaneous response results of multiple single photon detectors, and publicly announces the measurement results;

    S5. Key screening: the quantum terminal unit compares the measurement results with local information to obtain a screening code;

    S6. Detection of bit error rate: the quantum terminal unit randomly selects a part of the signal state to detect the bit error rate, QBER=Nerr/Nsift, if the measured QBER value is greater than the theoretical calculation of the decoy state, it is considered that the communication is unsafe and gives up This communication starts again;

    S7. Error correction and security enhancement: The classic communication between the quantum terminal units through authentication uses the Hash algorithm to correct the remaining screening codes to obtain an error correction code. If the error correction is successful, security enhancement is performed.

    S8. Clock synchronization: the quantum terminal unit performs clock synchronization through the optical channel monitor to achieve time-frequency transmission; the generated key is used to encrypt and transmit time-frequency synchronization information;

    The initial condition setting includes the setting of the wavelength, time slot, and optical path that are negotiated by both parties to the communication.

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