CN117792517A - System and method based on multi-user measurement device independent QKD - Google Patents
System and method based on multi-user measurement device independent QKD Download PDFInfo
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Abstract
The invention discloses a system based on multi-user measurement equipment independent QKD, which comprises a synchronization unit, a transmission unit, a sending unit, a control unit and a measurement unit; the synchronous unit sends synchronous light pulses to the sending unit respectively, calculates time delay between links after testing the returned pulses, and sets parameters of the control unit according to the time delay so as to control the light pulses reaching the measuring unit to be synchronous; the sending unit prepares three photons with polarization states and three photons with GHZ entangled states, and enables the photons to enter the beam splitter of the measuring unit synchronously after passing through the transmission unit respectively for two-photon interference to generate Bell state trigger detector response, and an original secret key is formed according to the detector response condition. The invention adopts a synchronous mode to solve the problem of asynchronous photon arrival caused by the difference of link lengths, provides guarantee for the signal synchronization of the subsequent arrival measuring end, and has simple structure and low realization cost.
Description
Technical Field
The invention relates to the technical field of quantum secret communication and optical communication, in particular to a system and a method based on multi-user measurement equipment independent QKD.
Background
The quantum cipher realized by the intersection method of cryptography, quantum mechanics and physics has good safety performance and application prospect due to the safety and the detectability to eavesdropping. Quantum key distribution (Quantum Key Distribution, QKD) is an important branch of quantum cryptography, and uses single photons, entangled photons, coherent optical fields, etc. as carriers to transmit key information, which enables legal communication parties (sender called Alice and receiver called Bob) to share a set of keys unconditionally secure in information theory.
Because various vulnerabilities exist in an actual system with the incompleteness of the device, an eavesdropper Eve attacks the communication process, and most of attack means are considered to be aimed at a detection end of the QKD system, such as a pseudo-state attack, a detector time-shift attack, a detector blinding attack and the like, the proposal of a measurement device independent (Measurement device independent, MDI) protocol is quite significant. In the MDI protocol Alice and Bob are responsible for preparing the quantum states, which are measured by a third party to generate the key.
Most QKD studies are currently focused mainly on the two parties, but with the continued development of technology, the current demands have not been met. The multiparty quantum key distribution can break through the limitation of single-way communication, so that the quantum secret communication is truly practical. This scheme of multiparty participation in key distribution is also called quantum cryptography conference (Quantumcryptograph conference, QCC), and the principle of this scheme is mainly to use the characteristic of entanglement of multiple particles to make particles among multiple participants present a certain relationship for key distribution.
The GHZ (Greenberger-horn-zeilinger) state is a multiple quantum entanglement state proposed by Greenberger et al in 1989 and is a commonly used entanglement state in multi-party quantum secure communications today. GHZ is applied to MDI-QKD, and is mainly used in quantum key sharing and quantum cryptography conference.
In the prior art, the improved GHZ analyzer can enable the system redundancy to be better and the system can be controlled more easily. Meanwhile, a flexible optical cross module is adopted, so that a GHZ analyzer can be shared by a plurality of quantum key distribution. However, the method cannot solve the problem of photon arrival asynchronism caused by the difference of link lengths, and has the advantages of complex structure and high realization cost.
Accordingly, there is a need to improve upon the deficiencies of the prior art by proposing a system and method based on multi-user measurement device independent QKD.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a system and a method based on multi-user measurement device independent QKD, which aim to solve the problems of photon arrival asynchronism caused by link length difference and system realization cost.
The method is realized by the following technical scheme:
a system based on multi-user measurement device independent QKD, the system comprising a synchronization unit, a transmission unit, a control unit, and a measurement unit;
the synchronous unit, the transmission unit, the sending unit and the measuring unit are sequentially connected through optical signals, wherein an output port of the sending unit is also connected with an input port of the synchronous unit;
the output port of the synchronous unit is also connected with the input port of the control unit, and the output port of the control unit is connected with the transmission unit to form a closed loop;
the synchronous unit is used for generating optical pulses, the optical pulses are reflected after entering the sending unit through the transmission unit, pulse delay signals are obtained, and the pulse delay signals are input to the control unit;
the transmission unit is used for transmitting the light pulse;
the control unit is used for setting delay driving chip parameters according to the pulse delay signals to control pulse synchronization reaching the sending unit;
the transmitting unit is used for generating photons with polarization states and photons with GHZ entangled states, inputting the photons into the transmitting unit and then entering the measuring unit;
the measuring unit is used for triggering the detector to respond after two-photon interference is carried out on photons with polarization states and photons with GHZ entangled states, and generating a quantum key according to a response result;
the synchronization unit comprises a synchronization laser, a first beam splitter, a second beam splitter, a third beam splitter, a first circulator, a second circulator, a third circulator, a fourth circulator, a photoelectric detector and a synchronization controller;
the synchronous laser is connected with a first beam splitter, and the first beam splitter is respectively connected with a first circulator and a second beam splitter; the second beam splitter is connected with the second circulator and the third beam splitter respectively; the third beam splitter is respectively connected with the third circulator and the fourth circulator; the first circulator, the second circulator, the third circulator and the fourth circulator are respectively connected with a photoelectric detector, an output port of the photoelectric detector is connected with an input port of a synchronous controller, and an output port of the synchronous controller is connected with an input port of a control unit.
Preferably, the transmission unit comprises a wavelength division multiplexer and a wavelength division demultiplexer which are sequentially connected.
Preferably, the control unit comprises 4 delay driving chips and 4 lasers; the 1 delay driving chip is connected with 1 corresponding laser and then connected to the input port of the transmission unit.
Preferably, the transmitting unit includes a first transmitter Alice, a second transmitter Bob, a third transmitter Charlie … …, and an nth transmitter DavidN; the output ports of the N senders are connected with the input ports of the transmission unit through optical signals.
Preferably, the transmitting unit includes a first sender Alice, a second sender Bob, a third sender Charlie, and a fourth sender David; the output ports of the first sender Alice, the second sender Bob, the third sender Charlie and the fourth sender David are connected with the input port of the transmission unit through optical signals.
Preferably, the measuring unit is composed of N measuring units, each measuring unit including a beam splitter, a first polarizing beam splitter, a second polarizing beam splitter, a first vertical polarization state detector, a first horizontal polarization state detector, a second vertical polarization state detector, and a second horizontal polarization state detector;
the output port of the beam splitter is respectively connected with the input ports of the first polarization beam splitter and the second polarization beam splitter; the two output ports of the first polarization beam splitter are respectively connected with the first vertical polarization state detector and the first horizontal polarization state detector, and the two output ports of the second polarization beam splitter are respectively connected with the second vertical polarization state detector and the second horizontal polarization state detector.
Preferably, the synchronization unit sends synchronization light pulses to each sender, calculates time delay between links after testing the returned pulses, and controls synchronization of the light pulses reaching the measurement unit according to parameters of the delay driving chip.
Preferably, the first sender Alice, the second sender Bob and the third sender Charlie prepare photons with polarization states, and the fourth sender David prepares three photons with GHZ entangled states, and the three photons with GHZ entangled states and the single photon with polarization states enter a beam splitter of a measuring unit to perform two-photon interference after entering the transmitting unit synchronously, so as to generate Bell state trigger detector response; the first sender Alice, the second sender Bob and the third sender Charlie then form the original key according to the initially agreed GHZ state and the probe response situation.
A method based on multi-user measurement device independent QKD, to which the above-mentioned multi-user measurement device independent QKD system is applied, characterized in that the method comprises the steps of:
step 1: system synchronization time setting: the synchronization unit sends synchronous light pulses which are respectively transmitted to the first generating party Alice, the second transmitting party Bob and the third transmitting party Charlie, tests returned pulses, calculates time delay between links, and adjusts parameters of a delay driving chip according to the time delay so that the light pulses of the links synchronously reach a measurement unit after being processed by the delay driving chip;
step 2: preparing photons to be measured: the first sender Alice, the second sender Bob and the third sender Charlie prepare photons with polarization states, and the fourth sender David prepares three photons with GHZ entanglement states, and the three photons with GHZ entanglement states and the single photon with polarization states enter a transmission unit at the same time and then enter a measurement unit;
step 3: measurement: the single photon with the polarization state and the photon with the GHZ entangled state enter a beam splitter of a measuring unit to generate Bell state after two-photon interference, and the detector is triggered to respond;
step 4: key screening: the first sender Alice, the second sender Bob and the third sender Charlie generate an original secret key according to the initially agreed GHZ state and the response condition of the detector;
step 5: and (3) detecting the error rate: the first sender Alice, the second sender Bob and the third sender Charlie publicly calculate the error rate of part of the original secret key and compare the error rate with the theoretical error range;
if the error rate exceeds the trusted range, terminating the round protocol and jumping to the step 2;
if the error rate is in the trusted range, jumping to the step 6;
step 6: post-processing data: error correction is carried out on the residual screening codes through classical communication among the first sender Alice, the second sender Bob and the third sender Charlie by adopting a Hash algorithm to obtain error correction codes;
if the error correction is successful, security enhancement is carried out to obtain a safe quantum key;
if the error correction fails, the step 2 is skipped.
Preferably, in step 4, the case of forming the original key is as follows:
when Alice sends a vertical polarization state |V > and first interferes with photons in a GHZ entangled state prepared by David;
if photons of GHZ entangled state prepared by David collapse intoThe code cannot be formed;
if photons of GHZ entangled state prepared by David collapse intoTriggering the vertical polarization state detector and one horizontal polarization state detector of the first measuring party to generate a response;
when the detection results of the second measuring party and the third measuring party are also a response to one vertical polarization state detector and one horizontal polarization state detector, an original secret key is formed.
The beneficial effects of the invention are as follows:
1. the synchronization mode adopted by the invention can solve the problem of photon arrival asynchronism caused by the difference of link lengths, and provides a guarantee for the signal synchronization of the subsequent arrival at the measuring end.
2. The invention is a measuring equipment irrelevant system, which can resist the attack to the measuring equipment and eliminate the safety problem brought by the detector side.
3. The invention has simple structure and low realization cost.
Drawings
FIG. 1 is a system block diagram of the present invention;
FIG. 2 is a system schematic block diagram of the present invention;
FIG. 3 is a block diagram of a control unit of the present invention;
fig. 4 is a block diagram of a transmitter in a transmitting unit of the present invention;
fig. 5 is a block diagram of David in the transmitting unit of the present invention;
FIG. 6 is a block diagram of a measurement tip of the present invention;
fig. 7 is a flow chart of the method of the present invention.
Detailed Description
The present invention will be further described in detail with reference to the following examples, for the purpose of making the objects, technical solutions and advantages of the present invention more apparent, but the scope of the present invention is not limited to the following specific examples.
A system based on multi-user measurement device independent QKD, as shown in fig. 1, comprising a synchronization unit 1, a transmission unit 2, a transmission unit 5, a control unit 4, and a measurement unit 3;
the synchronous unit 1, the transmission unit 2, the sending unit 5 and the measuring unit 3 are sequentially connected through optical signals, wherein the output port of the sending unit 5 is also connected with the input port of the synchronous unit 1;
the output port of the synchronization unit 1 is also connected with the input port of the control unit 4, and the output port of the control unit 4 is connected with the transmission unit 2 to form a closed loop;
the synchronization unit 1 is configured to generate an optical pulse, and the optical pulse is reflected after entering the transmission unit 5 through the transmission unit 2, so as to obtain a pulse delay signal caused by a fiber link difference, and the pulse delay signal is input to the control unit 4;
the transmission unit 2 is used for transmitting light pulses;
the control unit 4 is used for setting delay driving chip parameters according to the pulse delay signals to control the pulse synchronization reaching the transmitting unit 5;
the sending unit 5 is configured to generate photons with polarization states and photons with entangled states of GHZ, and input the photons to the transmission unit 2 and then enter the measurement unit 3;
the measuring unit 3 is used for triggering the detector to respond after two-photon interference is carried out on photons with polarization states and photons with GHZ entangled states, and generating a quantum key according to a response result;
as shown in fig. 2, the synchronization unit 1 includes a synchronization laser 101, a first beam splitter 102, a second beam splitter 103, a third beam splitter 104, a first circulator 105, a second circulator 106, a third circulator 107, a fourth circulator 108, a photodetector 109, and a synchronization controller 110;
the synchronous laser 101 is connected with a first beam splitter 102, and the first beam splitter 102 is respectively connected with a first circulator 105 and a second beam splitter 103; the second beam splitter 103 is respectively connected with a second circulator 106 and a third beam splitter 104; the third beam splitter 104 is respectively connected with a third circulator 107 and a fourth circulator 108; the first circulator 105, the second circulator 106, the third circulator 107 and the fourth circulator 108 are respectively connected with a photoelectric detector 109, an output port of the photoelectric detector 109 is connected with an input port of a synchronous controller 110, and an output port of the synchronous controller 110 is connected with an input port of the control unit 4;
as shown in fig. 3, the control unit 4 includes 4 delay driving chips and 4 lasers, which are a first delay driving chip 401, a second delay driving chip 402, a third delay driving chip 403 and a fourth delay driving chip 404, respectively, and a first laser 411, a second laser 412, a third laser 413 and a fourth laser 414; the 1 delay driving chip is connected with 1 corresponding laser and then connected to the input port of the transmission unit 2;
the transmission unit 2 comprises a wavelength division multiplexer and a wavelength division demultiplexer which are sequentially connected, as shown in fig. 2, the transmission unit 2 comprises 3 first wavelength division multiplexers 201, 1 second wavelength division multiplexer 202, 3 first wavelength division demultiplexers 211 and 1 second wavelength division demultiplexer 212; specifically, the 3 first wavelength division multiplexers 201 and the 3 corresponding second wavelength division multiplexers 202 are respectively connected and then respectively connected to the transmitting unit 5, and the second wavelength division multiplexers 202 are connected and then connected to the second wavelength division demultiplexer 212 and then connected to the transmitting unit 5;
the transmitting unit 5 includes a first transmitting party Alice, a second transmitting party Bob, a third transmitting party Charlie … … and an nth transmitting party DavidN; the output ports of the N senders are connected with the input port of the transmission unit 2 through optical signals; the measuring unit 3 is composed of N measuring units, each measuring unit comprises a beam splitter BS, a first polarization beam splitter PBS1, a second polarization beam splitter PBS2 and a first vertical polarization state detector D 1V First horizontal polarization detector D 1H Second vertical polarization detector D 2V And a second horizontal polarization detector D 2H 。
In this embodiment, as shown in fig. 2, the transmitting unit 5 includes a first sender Alice, a second sender Bob, a third sender Charlie, and a fourth sender David; the output ports of the first sender Alice, the second sender Bob, the third sender Charlie and the fourth sender David are connected with the input port of the transmission unit 2 through optical signals.
As shown in fig. 4, the first sender Alice, the second sender Bob, and the third sender Charlie each include the structure shown in fig. 4, where the first sender Alice, the second sender Bob, and the third sender Charlie each include a faraday lens 501, a polarization modulator 502, an intensity modulator 503, a polarization beam splitter 504, and a beam splitter 505, and an attenuator 506.
As shown in fig. 5, the fourth sender David is a GHZ entanglement source having three output ports for producing GHZ entanglement from the light pulses generated by the fourth laser 414 in the control unit 4.
The optical signal sent by the sending unit enters the measuring unit 3 through the transmission unit 2, in this embodiment, as shown in fig. 6, the measuring unit 3 is composed of 3 measuring units, namely a first measuring unit 301, a second measuring unit 302 and a third measuring unit 303, each measuring unit comprises a beam splitter BS, a first polarizing beam splitter PBS1, a second polarizing beam splitter PBS2 and a first vertical polarization state detector D 1V First horizontal polarization detector D 1H Second vertical polarization detector D 2V And a second horizontal polarization detector D 2H ；
The output ports of the beam splitters BS are respectively connected with the input ports of the first polarization beam splitter PBS1 and the second polarization beam splitter PBS 2; the two output ports of the first polarization beam splitter PBS1 are respectively connected with a first vertical polarization state detector D 1V First horizontal polarization detector D 1H Respectively connected with two output ports of the second polarization beam splitter PBS2 and a second vertical polarization state detector D 2V Second horizontal polarization detector D 2H Are respectively connected.
The principle and the process of the system are as follows:
the synchronization unit 1 sends synchronous light pulses to each sender respectively, calculates time delay between links after testing returned pulses, and sets parameters of first to fourth delay driving chips according to the time delay to control the synchronization of the light pulses reaching the measurement unit 3; specifically, as shown in fig. 2, the laser pulse emitted by the synchronization laser 101 enters the first beam splitter 102, the second beam splitter 103 and the third beam splitter 104 respectively, and is split into four light pulses with equal light intensity, and the four light pulses are transmitted to the transmitting unit 5 through the transmitting unit 2 through the first circulator 105, the second circulator 106, the third circulator 107 and the fourth circulator 108 respectively.
The faraday mirror 501 in the four transmitters in the transmitting unit 5 reflects the four light pulses into the photo-detector 109 in the synchronization unit 1; the photodetector 109 measures the pulse delay data caused by the difference of the optical fiber links, and sends the delay data to the synchronization controller 110 for synchronization processing, and then inputs the delay data to the control unit 4. By adopting the synchronization mode, the problem of asynchronous photon arrival caused by the difference of link lengths can be solved, and the guarantee is provided for the signal synchronization of the subsequent arrival at the measuring end.
Setting parameters of the first delay driving chip 401, the second delay driving chip 402, the third delay driving chip 403 and the fourth delay driving chip 404 according to the delay data so as to control the first laser 411, the second laser 412, the third laser 413 and the fourth laser 414 to emit pulse light;
the pulse light reaches the transmitting unit 5 through the transmitting unit 2 to be modulated, and then enters the measuring unit 3 to be measured; specifically, the first laser 411, the second laser 412, and the third laser 413 respectively emit light pulses, and then respectively transmit the light pulses to the 3 wavelength division multiplexers 201 in the transmission unit 2 after passing through the fifth circulator 421, the sixth circulator 422, and the seventh circulator 423; the fourth laser 414 sends out the optical pulse and then directly sends the optical pulse to the wavelength division multiplexer 202 in the transmission unit 2;
the wavelength division multiplexer 201 multiplexes the optical pulses with different wavelengths into the same optical fiber channel, and the wavelength division multiplexer 211 separates the optical pulses with different wavelengths in the optical fiber channel and then transmits the separated optical pulses to the first generating party Alice, the second transmitting party Bob and the third transmitting party Charlie; similarly, the wavelength division multiplexer 202 multiplexes the optical pulses with different wavelengths into the same optical fiber channel, and the wavelength division demultiplexer 212 separates the optical pulses with different wavelengths in the optical fiber channel and then transmits the separated optical pulses to the fourth sender David;
the first generating party Alice, the second transmitting party Bob and the third transmitting party Charlie respectively receive the light pulses sent by the control unit 4, modulate the polarization states of the light pulses through the polarization modulator 502, then enter the intensity modulator 503 to modulate single photons with different intensities, and adjust the attenuator 506 to attenuate the single photons to a specified value after marking the different single photons as a decoy state or a signal state, and then output a photon signal 1 with the average photon number smaller than 1 to enter the measuring unit 3 through the transmission unit; wherein the polarization state of the photon signal is horizontal, vertical, +45°, or-45 °.
The fourth sender David is a GHZ entanglement source, which has three output ports; the fourth sender David receives three light pulses generated by the fourth laser 414 in the control unit 4, and then prepares a photon signal 2 in a GHZ entangled state, and enters the measurement unit 3 through the transmission unit.
As can be seen from the above, each of the measurement units 3 comprises a beam splitter BS, a first polarizing beam splitter PBS1, a second polarizing beam splitter PBS2, a first vertical polarization state detector D 1V First horizontal polarization detector D 1H Second vertical polarization detector D 2V And a second horizontal polarization detector D 2H ；
Photon signals 1 respectively output by a first generating party Alice, a second transmitting party Bob and a third transmitting party Charlie and three photon signals 2 with GHZ entangled state output by a fourth transmitting party David respectively carry out two-photon interference in a beam splitter BS in a first measuring unit to a third measuring unit after passing through a transmission unit 2 to generate Bell state trigger detector responses; the first sender Alice, the second sender Bob and the third sender Charlie then form the original key according to the initially agreed GHZ state and the probe response situation.
Specifically, the photon signals 1 respectively output by the first producer Alice, the second sender Bob and the third sender Charlie and the three photon signals 2 with the GHZ entangled state output by the fourth sender David arrive at the beam splitter BS to generate two-photon interference; based on the physical principle of a half-mirror and a half-mirror, when two particles are subjected to two-photon interference, the response of the Bell state trigger detector is generated, and the corresponding response result is the same as that of a classical MDI-QKD;
the response results are as follows: when the first generating party Alice transmits the vertical polarization state |v > and first interferes with the entangled state prepared by the fourth transmitting party David, the entangled state prepared by the fourth transmitting party David is collapsed intoCannot be coded, if it is collapsed to +>It is possible to trigger the first vertical polarization detector D 1V First horizontal polarization detector D 1H In response, if the detection results of the second measurement unit and the third measurement unit are also a vertical polarization state detector and a horizontal polarization state detector, a quantum key can be formed, so that according to the responses of the three measurement units, the polarization states of the photon signals 1 output by the first sender Alice, the second sender Bob and the third sender Charlie are the same, and the code value represented by the polarization states, namely, the bit 1, can be obtained; similarly, a piece of original key shared by the first producer Alice, the second sender Bob and the third sender Charlie can be obtained. And forming a final shared security key by carrying out steps such as error code detection, confidentiality enhancement and the like on the original key.
A method based on multi-user measurement device independent QKD, to which said multi-user measurement device independent QKD system is applied, said method comprising the steps of:
step 1: system synchronization time setting: the synchronization unit 1 sends synchronous light pulses which are respectively transmitted to the first generating party Alice, the second transmitting party Bob and the third transmitting party Charlie, tests returned pulses, calculates time delay between links, and adjusts parameters of a delay driving chip according to the time delay so that the light pulses of the links synchronously reach a measurement unit after being processed by the delay driving chip;
step 2: preparing photons to be measured: the first sender Alice, the second sender Bob and the third sender Charlie prepare photons with polarization states, and the fourth sender David prepares three photons with GHZ entanglement states, and the three photons with GHZ entanglement states and the single photon with polarization states enter the transmission unit 2 at the same time and then enter the measurement unit 3;
step 3: measurement: the single photon with polarization state and the photon with GHZ entangled state enter into the beam splitter of the measuring unit 3 to generate Bell state after two-photon interference, and trigger the detector to respond;
step 4: key screening: the first sender Alice, the second sender Bob and the third sender Charlie generate an original secret key according to the initially agreed GHZ state and the response condition of the detector;
wherein, the original key is formed as follows:
when Alice sends a vertical polarization state |V > and first interferes with photons in a GHZ entangled state prepared by David;
if photons of GHZ entangled state prepared by David collapse intoThe code cannot be formed;
if photons of GHZ entangled state prepared by David collapse intoTriggering the vertical polarization state detector and one horizontal polarization state detector of the first measuring party to generate a response;
when the detection results of the second measuring party and the third measuring party are also a response to one vertical polarization state detector and one horizontal polarization state detector, an original secret key is formed.
Step 5: and (3) detecting the error rate: the first sender Alice, the second sender Bob and the third sender Charlie publicly calculate the error rate of part of the original secret key and compare the error rate with the theoretical error range;
if the error rate exceeds the trusted range, terminating the round protocol and jumping to the step 2;
if the error rate is in the trusted range, jumping to the step 6;
step 6: post-processing data: error correction is carried out on the residual screening codes through classical communication among the first sender Alice, the second sender Bob and the third sender Charlie by adopting a Hash algorithm to obtain error correction codes;
if the error correction is successful, security enhancement is carried out to obtain a safe quantum key;
if the error correction fails, the step 2 is skipped.
The invention adopts a synchronous mode to solve the problem of asynchronous photon arrival caused by the difference of link lengths, and has simple system structure and low realization cost.
The invention is a measuring equipment irrelevant system, which can resist the attack to the measuring equipment and eliminate the safety problem brought by the detector side.
Variations and modifications to the above would be obvious to persons skilled in the art to which the invention pertains from the foregoing description and teachings. Therefore, the invention is not limited to the specific embodiments disclosed and described above, but some modifications and changes of the invention should be also included in the scope of the claims of the invention. In addition, although specific terms are used in the present specification, these terms are for convenience of description only and do not constitute any limitation on the invention.
Claims (10)
1. A system based on multi-user measurement device independent QKD, comprising a synchronization unit, a transmission unit, a control unit, and a measurement unit;
the synchronous unit, the transmission unit, the sending unit and the measuring unit are sequentially connected through optical signals, wherein an output port of the sending unit is also connected with an input port of the synchronous unit;
the output port of the synchronous unit is also connected with the input port of the control unit, and the output port of the control unit is connected with the transmission unit to form a closed loop;
the synchronous unit is used for generating optical pulses, the optical pulses are reflected after entering the sending unit through the transmission unit, pulse delay signals are obtained, and the pulse delay signals are input to the control unit;
the transmission unit is used for transmitting the light pulse;
the control unit is used for setting delay driving chip parameters according to the pulse delay signals to control pulse synchronization reaching the sending unit;
the transmitting unit is used for generating photons with polarization states and photons with GHZ entangled states, inputting the photons into the transmitting unit and then entering the measuring unit;
the measuring unit is used for triggering the detector to respond after two-photon interference is carried out on photons with polarization states and photons with GHZ entangled states, and generating a quantum key according to a response result;
the synchronization unit comprises a synchronization laser, a first beam splitter, a second beam splitter, a third beam splitter, a first circulator, a second circulator, a third circulator, a fourth circulator, a photoelectric detector and a synchronization controller;
the synchronous laser is connected with a first beam splitter, and the first beam splitter is respectively connected with a first circulator and a second beam splitter; the second beam splitter is connected with the second circulator and the third beam splitter respectively; the third beam splitter is respectively connected with the third circulator and the fourth circulator; the first circulator, the second circulator, the third circulator and the fourth circulator are respectively connected with a photoelectric detector, an output port of the photoelectric detector is connected with an input port of a synchronous controller, and an output port of the synchronous controller is connected with an input port of a control unit.
2. The system of claim 1, wherein the transmission unit comprises a wavelength division multiplexer and a wavelength division demultiplexer connected in sequence.
3. The system of claim 1, wherein the control unit comprises 4 delay drive chips and 4 lasers; the 1 delay driving chip is connected with 1 corresponding laser and then connected to the input port of the transmission unit.
4. The system of claim 1, wherein the transmission unit comprises a first transmitter Alice, a second transmitter Bob, a third transmitter Charlie … …, and an nth transmitter DavidN; the output ports of the N senders are connected with the input ports of the transmission unit through optical signals.
5. The system of claim 4, wherein the transmission unit comprises a first sender Alice, a second sender Bob, a third sender Charlie, and a fourth sender David; the output ports of the first sender Alice, the second sender Bob, the third sender Charlie and the fourth sender David are connected with the input port of the transmission unit through optical signals.
6. The system of claim 1, wherein the measurement unit is comprised of N measurement units, each measurement unit including a beam splitter, a first polarizing beam splitter, a second polarizing beam splitter, a first vertical polarization state detector, a first horizontal polarization state detector, a second vertical polarization state detector, and a second horizontal polarization state detector;
the output port of the beam splitter is respectively connected with the input ports of the first polarization beam splitter and the second polarization beam splitter; the two output ports of the first polarization beam splitter are respectively connected with the first vertical polarization state detector and the first horizontal polarization state detector, and the two output ports of the second polarization beam splitter are respectively connected with the second vertical polarization state detector and the second horizontal polarization state detector.
7. The system of claim 5, wherein the synchronization unit sends synchronized light pulses to each sender separately, calculates the time delay between links after testing the returned pulses, and controls the synchronization of the light pulses to the measurement unit based on the parameters of the delay driver chip.
8. The system of claim 5, wherein the first sender Alice, the second sender Bob and the third sender Charlie prepare photons with polarization states, and the fourth sender David prepares three photons with GHZ entangled states, and the three photons with GHZ entangled states and the single photon with polarization states enter a beam splitter of a measurement unit to perform two-photon interference and then generate Bell state trigger detector response; the first sender Alice, the second sender Bob and the third sender Charlie then form the original key according to the initially agreed GHZ state and the probe response situation.
9. A method based on multi-user measurement device independent QKD, employing a multi-user measurement device independent QKD system according to any of claims 1-8, wherein said method comprises the steps of:
step 1: system synchronization time setting: the synchronization unit sends synchronous light pulses which are respectively transmitted to the first generating party Alice, the second transmitting party Bob and the third transmitting party Charlie, tests returned pulses, calculates time delay between links, and adjusts parameters of a delay driving chip according to the time delay so that the light pulses of the links synchronously reach a measurement unit after being processed by the delay driving chip;
step 2: preparing photons to be measured: the first sender Alice, the second sender Bob and the third sender Charlie prepare photons with polarization states, and the fourth sender David prepares three photons with GHZ entanglement states, and the three photons with GHZ entanglement states and the single photon with polarization states enter a transmission unit at the same time and then enter a measurement unit;
step 3: measurement: the single photon with the polarization state and the photon with the GHZ entangled state enter a beam splitter of a measuring unit to generate Bell state after two-photon interference, and the detector is triggered to respond;
step 4: key screening: the first sender Alice, the second sender Bob and the third sender Charlie generate an original secret key according to the initially agreed GHZ state and the response condition of the detector;
step 5: and (3) detecting the error rate: the first sender Alice, the second sender Bob and the third sender Charlie publicly calculate the error rate of part of the original secret key and compare the error rate with the theoretical error range;
if the error rate exceeds the trusted range, terminating the round protocol and jumping to the step 2;
if the error rate is in the trusted range, jumping to the step 6;
step 6: post-processing data: error correction is carried out on the residual screening codes through classical communication among the first sender Alice, the second sender Bob and the third sender Charlie by adopting a Hash algorithm to obtain error correction codes;
if the error correction is successful, security enhancement is carried out to obtain a safe quantum key;
if the error correction fails, the step 2 is skipped.
10. The method of claim 9, wherein in step 4, the forming the original key is performed as follows:
when Alice sends a vertical polarization state |V > and first interferes with photons in a GHZ entangled state prepared by David;
if photons of GHZ entangled state prepared by David collapse intoThe code cannot be formed;
if photons of GHZ entangled state prepared by David collapse intoTriggering the vertical polarization state detector and one horizontal polarization state detector of the first measuring party to generate a response;
when the detection results of the second measuring party and the third measuring party are also a response to one vertical polarization state detector and one horizontal polarization state detector, an original secret key is formed.
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