CN109560880B

CN109560880B - Quantum communication system

Info

Publication number: CN109560880B
Application number: CN201811625728.8A
Authority: CN
Inventors: 李雨轩; 宋俊峰
Original assignee: Jilin University
Current assignee: Jilin University
Priority date: 2018-12-28
Filing date: 2018-12-28
Publication date: 2021-12-07
Anticipated expiration: 2038-12-28
Also published as: CN109560880A

Abstract

The application provides a quantum communication system, includes: the light source module is used for emitting pulses containing a plurality of different frequency components, the sender encoding module is used for dividing the pulses at the same working frequency into pulses to be encoded and reference pulses, and the pulses to be encoded are subjected to phase encoding to obtain encoded pulses; transmitting the reference pulse and the coded pulse to a receiver decoding module; the receiver decoding module is used for carrying out phase decoding on the coded pulse to obtain a decoded pulse; and the receiver data reading module is used for carrying out same-frequency pulse interference on the decoding pulse and the reference pulse and obtaining communication data based on an interference result. According to the method and the device, the pulses with different frequencies are introduced as the information carriers, so that the information quantity carried by a single information bit is effectively increased, the communication efficiency is improved, the sensitivity of a quantum communication system to the relative phase of the adjacent pulses is weakened, and the effective communication distance is obviously increased.

Description

Quantum communication system

Technical Field

The invention relates to the technical field of quantum communication, in particular to a quantum communication system.

Background

The quantum communication has the characteristics of high communication speed, low signal-to-noise ratio requirement, good reading stealing visibility and communication confidentiality and the like, and has important application in various fields such as national organs, military national defense, financial securities and the like.

At present, a quantum communication system is mainly formed by building an independent optical fiber device on an optical platform, and the system generally has the defects of large volume, high energy consumption, short communication distance, easy information leakage, low coding and decoding speed, low coding rate, poor stability and the like, and is not suitable for the development of future quantum communication.

Although the separation device is integrated into the quantum communication chip by adopting the silicon-based photoelectron integration technology, the system can be greatly optimized in the aspects of volume, energy consumption, safety, stability and the like; however, the existing quantum communication system still generally has the defects of small information carrying amount of a single information bit and low communication efficiency, and the problems of large difficulty in controlling relative phases of adjacent pulses and short effective communication distance.

Disclosure of Invention

In view of the above, the present invention provides a quantum communication system to improve the communication efficiency and effective communication distance of quantum communication.

The technical scheme is as follows:

a quantum communication system, comprising: the optical fiber communication system comprises a sender communication module and a receiver communication module, wherein the sender communication module comprises a light source module and a sender coding module connected with the light source module, the receiver communication module comprises a receiver decoding module used for optical fiber communication with the sender coding module and a receiver data reading module connected with the receiver decoding module, and the receiver data reading module comprises:

the light source module is used for emitting pulses containing a plurality of different frequency components;

the sender coding module is used for dividing the pulse at the same working frequency into a pulse to be coded and a reference pulse, and carrying out phase coding on the pulse to be coded to obtain a coded pulse; transmitting a working pulse to the receiver decoding module, wherein the working pulse comprises the reference pulse and a coding pulse;

the receiver decoding module is used for carrying out phase decoding on the coded pulse in the working pulse to obtain a decoded pulse and transmitting the decoded pulse and the reference pulse to the receiver data reading module;

and the receiver data reading module is used for carrying out same-frequency pulse interference on the decoding pulse and the reference pulse and obtaining communication data based on an interference result.

Preferably, the sender encoding module includes a first frequency-division delay phase shifter, an intensity modulator, a beam splitter, and a second frequency-division delay phase shifter, which are sequentially connected to the light source module, wherein:

the first frequency-division delay phase shifter is used for determining at least two working frequencies and separating the pulses with the working frequencies from the pulses with different frequency components emitted by the light source; controlling the pulses with different working frequencies to be sequentially output, wherein the output time interval between any two adjacent output pulses is a preset time interval;

the intensity modulator is used for adjusting the light intensity of the pulse output by the first frequency-division delay phase shifter, ensuring that the pulses with different working frequencies separated from the same pulse have the same average photon number, and realizing the preparation of a signal state and a decoy state;

the beam splitter is used for respectively splitting the pulse of each working frequency output by the intensity modulator into a pulse to be coded and a reference pulse;

the second frequency-dividing delay phase shifter is connected with the first port of the beam splitter, which is used for outputting the pulse to be coded, and is used for receiving the pulse to be coded and carrying out phase modulation on the pulse with a specific frequency in the pulse to be coded to obtain a coded pulse; the coded pulse and the reference pulse output by the second port of the beam splitter for outputting the reference pulse form a working pulse.

Preferably, the receiving-side decoding module includes: a third frequency division delay phase shifter for fiber connection with the second frequency division delay phase shifter, the third frequency division delay phase shifter being configured to:

receiving the coded pulse output by the second frequency-dividing delay phase shifter, carrying out phase modulation on the pulse with a specific frequency in the coded pulse to obtain a decoded pulse, and outputting the decoded pulse; the decoding pulses include pulses of a specific frequency of the encoding pulses that are phase-modulated and pulses of the encoding pulses that are not phase-modulated.

Preferably, the method is characterized in that,

the second frequency-dividing delay phase shifter is also used for controlling the simultaneous output of the pulses of all the working frequencies in the coded pulses;

the third frequency division delay phase shifter is further configured to control pulses with different working frequencies in the decoded pulses to be sequentially output, an output time interval between any two adjacent output pulses is the preset time interval, and pulses with the same working frequency in the reference pulses in the beam splitter and pulses with the same working frequency in the decoded pulses arrive at the data reading module at the same time.

Preferably, the transmitting side encoding module further includes a fourth frequency-division delay phase shifter connected to the second port of the beam splitter, and the receiving side decoding module further includes a fifth frequency-division delay phase shifter connected to the fourth frequency-division delay phase shifter, where:

the fourth frequency division delay phase shifter is used for controlling the simultaneous output of the pulses with the working frequencies in the reference pulses;

and the fifth frequency-division delay phase shifter is used for controlling the pulses with different working frequencies in the reference pulse to be sequentially output, the output time interval between any two adjacent output pulses is the preset time interval, and the pulse with each working frequency in the reference pulse and the pulse with the same working frequency in the decoding pulse in the third frequency-division delay phase shifter are simultaneously output.

Preferably, the sender encoding module further comprises a first variable optical attenuator,

the variable optical attenuator is used for adjusting the light intensities of the pulse to be coded and the reference pulse which are output by the beam splitter and have the same working frequency to be the same.

Preferably, the receiver decoding module further comprises a second variable optical attenuator,

the second variable optical attenuator is used for ensuring that the number of photons when the decoding pulse and the reference pulse with the same working frequency are input to the receiving side data reading module is the same.

Preferably, the receiving-side data reading module includes an interferometer and a first single-photon detector connected to the interferometer for reading the communication data based on the interference result.

Preferably, the first frequency-division delay phase shifter, the second frequency-division delay phase shifter, the third frequency-division delay phase shifter, the fourth frequency-division delay phase shifter, and the fifth frequency-division delay phase shifter are formed by frequency-division delay phase shifters, and the frequency-division delay phase shifter includes:

the array waveguide grating is provided with different sub-channels matched with different frequency pulses, the length of a delay line of each sub-channel is distributed in an arithmetic progression, and each sub-channel is integrated with one phase modulator;

alternatively, the first and second electrodes may be,

the phase modulator is connected with the circulator; the bragg reflectors are arranged to distribute pulses of different frequencies to different time bits, the time interval between any two adjacent time bits being the same as the time interval between any other two adjacent time bits.

Preferably, the first single-photon detector is further operable to measure an average photon count of the interference result pulses to determine whether the system is under a first attack, the first attack being indicative of a photon-number-separation attack,

the receiver data reading module further comprises a second single-photon detector connected with the interferometer, the second single-photon detector is used for determining whether the system is attacked or not based on the interference result, and the second attack indicates phase modulation attack.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

Fig. 1 is a schematic structural diagram of a quantum communication system according to an embodiment of the present application;

fig. 2 is a schematic structural diagram of a sender encoding module according to an embodiment of the present disclosure in detail;

fig. 3 is a schematic structural diagram of a receiver decoding module according to an embodiment of the present disclosure;

fig. 4 is a schematic structural diagram of another quantum communication system provided in an embodiment of the present application;

fig. 5 is a schematic structural diagram of another quantum communication system provided in an embodiment of the present application;

fig. 6 is a schematic diagram illustrating a detailed structure of a data reading module of a receiving party according to an embodiment of the present disclosure;

FIG. 7 is a detailed structural diagram of an interferometer provided in an embodiment of the present application;

fig. 8(a) - (b) are schematic structural diagrams of a frequency division delay phase shifter according to an embodiment of the present application;

fig. 9(a) - (b) are schematic structural diagrams of another fractional-n delay phase shifter provided in the embodiments of the present application;

fig. 10 is a schematic structural diagram of another fractional-n delay phase shifter according to an embodiment of the present application;

fig. 11 is a schematic structural diagram of another receiver data reading module according to an embodiment of the present disclosure;

fig. 12 is a schematic structural diagram of another quantum communication system according to an embodiment of the present application.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Fig. 1 is a schematic structural diagram of a quantum communication system according to an embodiment of the present application.

As shown in fig. 1, the system includes: a sender communication module 11 and a receiver communication module 12; the sender communication module 11 includes a light source module 111 and a sender encoding module 112 connected to the light source module 111, and the receiver communication module 12 includes a receiver decoding module 121 for optical fiber communication with the sender encoding module 112 and a receiver data reading module 122 connected to the receiver decoding module 121.

in the embodiment of the present application, the light source module is configured to emit a pulse including a plurality of pulses with different frequencies.

The sender coding module is used for dividing the pulse at the same working frequency into a pulse to be coded and a reference pulse, and carrying out phase coding on the pulse to be coded to obtain a coded pulse; the working pulse is transmitted to a receiver decoding module, and comprises a reference pulse and a coding pulse;

in this embodiment, after the sender coding module receives the pulses sent by the light source, the pulses at the operating frequency can be determined from the pulses. For example, the pulses emitted by the light source include pulses of 3 frequencies, which are a first frequency pulse, a second frequency pulse and a third frequency pulse; if the working frequency is the first frequency and the third frequency, the sender coding module determines that the first frequency pulse is a pulse at the working frequency and determines that the third frequency pulse is a pulse at the working frequency from the pulses sent by the light source.

Correspondingly, the sender coding module divides the first frequency pulse into a pulse to be coded and a reference pulse; and dividing the third frequency pulse into a pulse to be encoded and a reference pulse.

The method for dividing the pulse at the same working frequency into the pulse to be coded and the reference pulse by the sender coding module is as follows: the photon number of the pulse at the same working frequency is averagely divided into two parts, one part is used as a pulse to be coded, and the other part is used as a reference pulse.

In this embodiment, after determining each pulse at the operating frequency, the sender encoding module may perform the following process for each pulse at the same operating frequency: the pulses at the same operating frequency are divided into pulses to be encoded and reference pulses.

Correspondingly, the sender encoding module can perform phase encoding on the pulse to be encoded to obtain an encoded pulse; and the coded pulse and the reference pulse are used as working pulses and are sent to a receiver decoding module.

To facilitate understanding of a quantum communication system provided in the embodiments of the present application, a detailed structural diagram of a transmitting-side encoding module is now provided, please refer to fig. 2 specifically.

As shown in fig. 2, the sender encoding module includes: a first frequency-division delay phase shifter 1121, an intensity modulator 1122, a beam splitter 1123 and a second frequency-division delay phase shifter 1124 which are sequentially connected with the light source module; wherein:

the first frequency-division delay phase shifter 1121 is configured to determine at least two operating frequencies, and separate pulses with the operating frequencies from pulses with different frequency components emitted from the light source; controlling the pulses with different working frequencies to be sequentially output, wherein the output time interval between any two adjacent output pulses is a preset time interval;

for example, if the pulses emitted by the light source include pulses of 3 frequencies, the pulses are respectively a first frequency pulse (the frequency of the first frequency pulse is a first frequency), a second frequency pulse (the frequency of the second frequency pulse is a second frequency), and a third frequency pulse (the frequency of the third frequency pulse is a third frequency); the first frequency-division delay phase shifter is used for outputting and determining at least two working frequencies, if the two working frequencies are determined by the first frequency-division delay phase shifter at the moment and are respectively a first frequency and a third frequency, the first frequency-division delay phase shifter separates a first working frequency pulse and a third working frequency pulse from pulses with different frequency components emitted by the light source, and controls the first frequency pulse and the third frequency pulse to be sequentially output, and the output time interval between the first frequency pulse and the third frequency pulse is a preset time interval. For example, the first frequency pulse may be output first and then the third frequency pulse, or the third frequency pulse may be output first and then the first frequency pulse, but it is necessary to ensure that the time interval between the output time of the first frequency pulse and the output time of the third frequency pulse is a preset time interval.

The intensity modulator 1122 is configured to adjust the light intensity of the pulse output by the first frequency-division delay phase shifter 1121, so as to ensure that the pulses with different working frequencies separated from the same pulse have the same average photon number, and implement preparation of a signal state and a decoy state;

in this embodiment, the intensity modulator is configured to adjust the light intensity of the pulse output by the first frequency-division delay phase shifter 1121, ensure that the pulses of the operating frequencies (the pulses are weak coherent pulses) separated from the same pulse have the same average photon number, and implement preparation of a signal state and a decoy state.

As described above, the intensity modulator is configured to receive the first frequency pulse and the third frequency pulse output by the first frequency-division delay phase shifter, and adjust the light intensities of the first frequency pulse and the third frequency pulse to output the first frequency pulse and the third frequency pulse having the same average photon number.

Furthermore, the intensity modulator is also used for realizing the preparation of the signal state and the decoy state.

The beam splitter 1123 is configured to divide the pulse of each operating frequency output by the intensity modulator into a pulse to be encoded and a reference pulse, respectively;

in an embodiment of the application, a beam splitter is used to split the pulses of each operating frequency output by the intensity modulator into a pulse to be encoded and a reference pulse. As above, the beam splitter receives the first frequency pulse and the third operating frequency pulse, divides the first frequency pulse into a pulse to be encoded and a reference pulse, and divides the third frequency pulse into a pulse to be encoded and a reference pulse.

The beam splitter has two ports, namely a first port and a second port, wherein the first port is used for outputting the pulse to be encoded (as above, the pulse to be encoded output from the first port comprises the pulse to be encoded separated from the first frequency pulse and the pulse to be encoded separated from the third frequency pulse), and the second port is used for outputting the reference pulse (as above, the reference pulse output from the second port comprises the reference pulse separated from the first frequency pulse and the reference pulse separated from the third frequency pulse).

The second frequency-dividing delay phase shifter 1124 is connected to the first port of the beam splitter 1123, which is used for outputting the pulse to be encoded, and is used for receiving the pulse to be encoded and performing phase modulation on the pulse with the specific frequency in the pulse to be encoded to obtain an encoded pulse; the coded pulse and the reference pulse output by the second port of the beam splitter for outputting the reference pulse form a working pulse.

In the embodiment of the present application, the second frequency-dividing delay phase shifter is connected to the first port of the beam splitter, and is configured to receive a pulse to be encoded output by the beam splitter, and perform phase modulation on a pulse with a specific frequency in the pulse to be encoded, so as to obtain an encoded pulse. As above, when the operating frequency is the first frequency and the third frequency, the specific frequency may be the first frequency or the third frequency. For example, the second frequency-dividing delay phase shifter may encode the pulse to be encoded, which is separated from the first frequency pulse, to obtain an encoded pulse (at this time, the encoded pulse includes the pulse to be encoded, which is encoded in the first frequency pulse, and also includes the pulse to be encoded, which is separated from the third frequency pulse), and may also encode the pulse to be encoded, which is separated from the third frequency pulse, to obtain an encoded pulse (at this time, the encoded pulse includes the pulse to be encoded, which is encoded in the third frequency pulse, and also includes the pulse to be encoded, which is separated from the first frequency pulse).

In this embodiment, the coded pulse output by the second frequency-dividing delay phase shifter and the reference pulse output by the second port of the beam splitter may be regarded as working pulses, so that the receiving-side communication module obtains communication data based on the working pulses.

Further, in order to more clearly describe the quantum communication system, the embodiment of the present application provides a detailed structural schematic diagram of the receiver decoding module.

As shown in fig. 3, the receiving-side decoding module 121 includes a third division delay phase shifter 1211 for connecting to the second division delay phase shifter optical fiber.

The third frequency division delay phase shifter 1211 is configured to receive the coded pulse output by the second frequency division delay phase shifter, perform phase modulation on a pulse with a specific frequency in the coded pulse, obtain a decoded pulse, and output the decoded pulse; the decoding pulses include pulses of a specific frequency of the encoding pulses that are phase-modulated and pulses of the encoding pulses that are not phase-modulated.

Further, in the quantum communication system provided in the embodiment of the present application, if the second frequency-division delay phase shifter is further configured to control the pulses of each working pulse in the coded pulses to be output simultaneously; correspondingly, the third frequency division delay phase shifter in the quantum communication system is also used for controlling the pulses with different working frequencies in the decoding pulses to be output in sequence, the output time interval between any two adjacent output pulses is a preset time interval, and the pulses with the working frequencies in the decoding pulses and the pulses with the same working frequency in the reference pulses in the beam splitter are output simultaneously.

For example, if the pulses emitted by the light source include a first frequency pulse (the frequency of the first frequency pulse is a first frequency), a second frequency pulse (the frequency of the second frequency pulse is a second frequency), and a third frequency pulse (the frequency of the third frequency pulse is a third frequency); when the working frequency determined by the first frequency-division delay phase shifter is a first frequency and a third frequency, the first frequency-division delay phase shifter separates a pulse (a first frequency pulse) with the first frequency and a pulse (a third frequency pulse) with the third frequency from pulses emitted by the light source, and controls the first frequency pulse and the third frequency pulse to be sequentially output; correspondingly, the beam splitter also receives the first frequency pulse and the third frequency pulse in sequence, divides the first frequency pulse into a first pulse to be coded and a first reference pulse, and divides the third frequency pulse into a third pulse to be coded and a third reference pulse; correspondingly, the second frequency-dividing delay phase shifter also receives the first pulse to be coded and the third pulse to be coded in sequence (the first pulse to be coded and the third pulse to be coded form the pulse to be coded), and the second frequency-dividing delay phase shifter performs phase modulation on the pulse with the specific frequency (the pulse with the specific frequency is the first pulse to be coded or the third pulse to be coded) to obtain a coded pulse and outputs the coded pulse; that is, the coded pulses in the second frequency-dividing delay phase shifter include pulses of two different operating frequencies.

If the second frequency-dividing delay phase shifter does not synchronously control the output time of the pulses with the two different working frequencies, the pulses with the two working frequencies in the coded pulses are sequentially output, and correspondingly, the third frequency-dividing delay phase shifter controls the pulses with the first frequency and the pulses with the third frequency in the decoded pulses to be sequentially output after the pulses with the specific frequency in the coded pulses are subjected to phase modulation to obtain the decoded pulses. At this time, it is noted that: the data reading module is controlled to simultaneously output the first frequency pulse in the decoding pulse output by the third frequency division delay phase shifter and the first reference pulse output by the second port of the beam splitter, simultaneously output the third frequency pulse in the decoding pulse output by the third frequency division delay phase shifter and the third reference pulse output by the second port of the beam splitter to the data reading module, and the time for the first frequency pulse in the decoding pulse output by the third frequency division delay phase shifter and the time for the third frequency pulse in the decoding pulse output by the third frequency division delay phase shifter to reach the data reading module are different.

If the second frequency-division delay phase shifter is also used for controlling the simultaneous output of the two pulses with different working frequencies in the coded pulse, the third frequency-division delay phase shifter is also used for controlling the sequential output of the two pulses with different working frequencies in the decoded pulse, and the pulse with each working frequency in the decoded pulse and the reference pulse with the working frequency output by the second port of the beam splitter need to be controlled to simultaneously reach the data reading module.

For example, if the second frequency-dividing delay shifter controls the pulse of the first frequency and the pulse of the third frequency in the coded pulse to be output simultaneously, the third frequency-dividing delay shifter needs to control the pulse of the first frequency and the pulse of the third frequency in the decoded pulse to be output sequentially, the first frequency pulse in the decoded pulse output by the third frequency-dividing delay shifter and the first reference pulse output by the second port of the beam splitter reach the data reading module simultaneously, the third frequency pulse in the decoded pulse output by the third frequency-dividing delay shifter and the third reference pulse output by the second port of the beam splitter reach the data reading module simultaneously, and the first frequency pulse in the decoded pulse output by the third frequency-dividing delay shifter and the third frequency pulse in the decoded pulse output by the third frequency-dividing delay shifter reach the data reading module at different times.

The embodiment of the present application further provides a schematic structural diagram of another quantum communication system, please refer to fig. 4 in detail.

As shown in fig. 4, the sender encoding module of another quantum communication system provided in this embodiment of the present application further includes a fourth frequency-division delay phase shifter 1125 connected to the second port of the beam splitter, and the receiver decoding module further includes a fifth frequency-division delay phase shifter 1212 connected to the fourth frequency-division delay phase shifter.

In the embodiment of the application, the fourth frequency division delay phase shifter is used for controlling the simultaneous output of the pulses with the working frequencies in the reference pulses;

as above, after the first reference pulse and the third reference pulse are sequentially output from the second port of the beam splitter, the fourth frequency-division delay phase shifter is configured to receive the first reference pulse and the third reference pulse sequentially output from the second port of the beam splitter, and control the first reference pulse and the third reference pulse to be output from the fourth frequency-division delay phase shifter at the same time.

And the fifth frequency division delay phase shifter is used for controlling the pulses with different working frequencies in the reference pulse to be sequentially output, the output time interval between any two adjacent output pulses is a preset time interval, and the pulse with each working frequency in the reference pulse and the pulse with the same working frequency in the decoding pulse in the third frequency division delay phase shifter are simultaneously output.

For example, after receiving the first reference pulse and the third reference pulse output by the fourth frequency-division delay phase shifter at the same time, the fifth frequency-division delay phase shifter controls the first reference pulse and the third reference pulse to be output from the fifth frequency-division delay phase shifter in sequence, and the time for the fifth frequency-division delay phase shifter to output the first reference pulse is the same as the time for the third frequency pulse in the decoded pulses output by the third frequency-division delay phase shifter, and the time for the fifth frequency-division delay phase shifter to output the third reference pulse is the same as the time for the third frequency pulse in the decoded pulses output by the third frequency-division delay phase shifter.

The embodiment of the present application further provides a schematic structural diagram of another quantum communication system, please refer to fig. 5 in detail.

As shown in fig. 5, the sender encoding module of another quantum communication system provided in the embodiments of the present application further includes a first variable optical attenuator 1126, where the first variable optical attenuator 1126 is configured to adjust the light intensities of the pulse to be encoded and the reference pulse, which have the same operating frequency and are output by the beam splitter, to be the same.

As shown in fig. 5, the first variable optical attenuator 1126 may be disposed between the first port of the beam splitter and the second frequency-dividing delay phase shifter.

As just described above, the inventor may further dispose the first variable optical attenuator 1126 between the second port of the beam splitter and the fourth frequency-dividing delay phase shifter, or dispose two first variable optical attenuators 1126, wherein one of the first variable optical attenuators 1126 may be disposed between the first port of the beam splitter and the second frequency-dividing delay phase shifter, and the other of the first variable optical attenuators 1126 may be disposed between the second port of the beam splitter and the fourth frequency-dividing delay phase shifter.

As shown in fig. 5, the receiver decoding module of another quantum communication system provided in the embodiment of the present application further includes a second variable optical attenuator 1213.

The second variable optical attenuator is used for ensuring that the number of photons when the decoding pulse and the reference pulse with the same working frequency are input to the receiving-side data reading module is the same.

As shown in fig. 5, the second variable optical attenuator 1213 may be disposed between the second and third division delay phase shifters of the beam splitter.

As described above, only in the preferred embodiment of the present invention, the second variable optical attenuator may be disposed between the fourth frequency-dividing delay phase shifter and the fifth frequency-dividing delay phase shifter, or two second variable optical attenuators may be disposed, one of the second variable optical attenuators may be disposed between the second frequency-dividing delay phase shifter and the third frequency-dividing delay phase shifter, and the other of the second variable optical attenuators may be disposed between the fourth frequency-dividing delay phase shifter and the fifth frequency-dividing delay phase shifter.

In order to realize reading of communication data, the embodiment of the present application provides a detailed structural schematic diagram of a receiving-side data reading module.

In the embodiment of the present application, it is preferable that the receiver-side data reading module 122 includes an interferometer 1221, and a first single-photon detector 1222 connected to the interferometer 1221 for reading communication data based on the interference result.

In the quantum communication system shown in fig. 3 provided in the embodiment of the present application, the interferometer is configured to be connected to the second ports of the third fractional delay phase shifter and the beam splitter, respectively.

In the quantum communication system provided in the embodiment of the present application and shown in fig. 4 to 5, the interferometer is configured to be connected to the third frequency-division delay phase shifter and the fifth frequency-division delay phase shifter, respectively.

In order to facilitate understanding of the working principle of a quantum communication system provided in the embodiments of the present application, the mach-zehnder interferometer is taken as an example for description, and please refer to fig. 7 for the structure of the mach-zehnder interferometer.

The two ends of the Mach-Zehnder interferometer are 50:50 directional couplers, and a thermo-optic phase modulator (TOPM) integrated with an upper arm is used for ensuring that the phase difference of the upper arm and the lower arm of the interferometer is strictly 90 degrees; the Mach-Zehnder interferometer is used for interfering the same-frequency pulses of the upper path and the lower path, and outputting new pulses generated after interference from the upper arm and the lower arm of the interferometer. Correspondingly, the upper arm of the interferometer can be connected with a single-photon detector, the lower arm of the interferometer can also be connected with the single-photon detector, and the single-photon detector is used for converting detected optical pulse signals into electric signals and realizing the conversion and reading of the signals.

In the embodiment of the application, the first single-photon detector can be used for being connected with the lower arm of the interferometer to realize the detection of the pulse output by the lower arm of the interferometer.

When the first single-photon detector is connected to the lower arm of the interferometer, the principle of the quantum communication system provided by the embodiment of the application can be as follows:

the pulse sent by the light source of the sender communication module comprises a first frequency pulse (the frequency of the first frequency pulse is a first frequency), a second frequency pulse (the frequency of the second frequency pulse is a second frequency) and a third frequency pulse (the frequency of the third frequency pulse is a third frequency); when the working frequency determined by the first frequency-division delay phase shifter is the first frequency and the third frequency, the first frequency-division delay phase shifter separates a pulse with the first frequency (a first frequency pulse) and a pulse with the third frequency (a third frequency pulse) from the pulses emitted by the light source, and controls the first frequency pulse and the third frequency pulse to be output in sequence.

Correspondingly, the beam splitter receives the first frequency pulse and the third frequency pulse in sequence, divides the first frequency pulse into a first pulse to be encoded (referred to as pulse 1) and a first reference pulse (referred to as pulse 3), and divides the third frequency pulse into a third pulse to be encoded (referred to as pulse 2) and a third reference pulse (referred to as pulse 4).

Correspondingly, the second frequency-division delay phase shifter also receives the first pulse to be encoded (pulse 1) and the third pulse to be encoded (pulse 2) in sequence, and after performing phase modulation on the pulse with the specific frequency (if the sending-side communication module wants to send data 0, the first frequency can be used as the specific frequency, the pulse 1 is subjected to phase modulation, so as to modulate the phase of the pulse 1 by 90 degrees), so as to obtain encoded pulses (the encoded pulses are the pulse 1 with the phase modulated by 90 degrees and the pulse 2 with the phase not modulated), and output the encoded pulses.

Correspondingly, a third frequency-division delay phase shifter in the receiving-side decoding module is used for receiving the coded pulse output by the second frequency-division delay phase shifter, two decoding basis sets, namely a decoding basis set 1 and a decoding basis set 2, exist in the third frequency-division delay phase shifter, the decoding basis set 1 is used for modulating the phase of the pulse 1 by 90 degrees, and the decoding basis set 2 is used for modulating the phase of the pulse 2 by 90 degrees.

At this time, after receiving the coded pulse output by the second frequency-division delay phase shifter, if the decoding basis set 1 is selected, the third frequency-division delay phase shifter in the receiving-side decoding module modulates the phase of the pulse 1 in the coded pulse by 90 degrees with the first frequency as a specific frequency (at this time, the phase of the pulse 1 is modulated by 180 degrees in total through the modulation of the second frequency-division delay phase shifter and the third frequency-division delay phase shifter), and does not modulate the phase of the pulse 2.

Taking the third frequency division delay phase shifter to output the pulse 1 first and then the pulse 2 as an example, the pulse 1 output by the third frequency division delay phase shifter and the pulse 3 output by the beam splitter reach the interferometer at the same time first, and the pulse 2 output by the third frequency division delay phase shifter and the pulse 4 output by the beam splitter reach the interferometer at the same time (for example, assuming that the pulse 1 output by the third frequency division delay phase shifter and the pulse 3 output by the beam splitter reach the interferometer at the time of T1, the pulse 2 output by the third frequency division delay phase shifter and the pulse 4 output by the beam splitter reach the interferometer at the time of T2, and T2 is later than T1); at time T1, the interferometer receives pulse 1 whose phase is modulated by 180 degrees and pulse 3 whose phase is not modulated, the phase difference between pulse 1 whose phase is modulated by 180 degrees and pulse 3 whose phase is not modulated is 180 degrees, and after the interferometer interferes, the interferometer outputs a pulse from the lower arm, at which time the first single-photon detector is turned on; and at time T2, the interferometer receives pulse 2 whose phase is not modulated and pulse 4 whose phase is not modulated, the phase difference between pulse 2 whose phase is not modulated and pulse 4 whose phase is not modulated is 0 degree, and after the interferometer interferes, the interferometer outputs a pulse from the upper arm, at which time the first single-photon detector is not lit.

Further, after receiving the coded pulse output by the second frequency-division delay phase shifter, if the decoding base group 2 is selected, the third frequency-division delay phase shifter in the receiving-side decoding module modulates the phase of the pulse 2 in the coded pulse by 90 degrees with the second frequency as a specific frequency, and does not modulate the phase of the pulse 1.

Taking the third frequency division delay phase shifter to output the pulse 1 first and then the pulse 2 as an example, the pulse 1 output by the third frequency division delay phase shifter and the pulse 3 output by the beam splitter reach the interferometer at the same time first, and the pulse 2 output by the third frequency division delay phase shifter and the pulse 4 output by the beam splitter reach the interferometer at the same time (for example, assuming that the pulse 1 output by the third frequency division delay phase shifter and the pulse 3 output by the beam splitter reach the interferometer at the time of T1, the pulse 2 output by the third frequency division delay phase shifter and the pulse 4 output by the beam splitter reach the interferometer at the time of T2, and T2 is later than T1); at time T1, the interferometer receives pulse 1 whose phase is modulated by 90 degrees and pulse 3 whose phase is not modulated, the phase difference between pulse 1 whose phase is modulated by 90 degrees and pulse 3 whose phase is not modulated is 90 degrees, and after the interferometer interferes, the interferometer outputs pulses from both the upper arm and the lower arm, at which time the first single-photon detector is turned on; at time T2, the interferometer receives pulse 2 whose phase is modulated by 90 degrees and pulse 4 whose phase is not modulated, and the phase difference between pulse 2 whose phase is modulated by 90 degrees and pulse 4 whose phase is not modulated is 90 degrees, and after the interferometer interferes, the interferometer outputs pulses from both the upper arm and the lower arm, at which time the first single-photon detector is turned on.

In this embodiment of the application, the receiving-side communication module may determine that the data sent by the sending-side communication module at this time is data 0 based on results that the first single-photon detector is turned on at time T1 and the first single-photon detector is not turned on at time T2; when the first single-photon detector is turned on at the time T1 and the time T2, the receiving-side communication module cannot definitely determine whether the data sent by the sending-side communication module at this time is 0 or 1.

Note that, in the case where a single-photon detector is also connected to the upper arm of the interferometer, if the interferometer outputs a pulse from the upper arm, the single-photon detector connected to the upper arm of the interferometer can be turned on.

Further, the second frequency-division delay phase shifter receives the first pulse to be encoded (pulse 1) and the third pulse to be encoded (pulse 2) in sequence, and after performing phase modulation on the pulse with the specific frequency (if the sending-side communication module wants to send data 1, the second frequency is taken as the specific frequency, and the pulse 2 is subjected to phase modulation to modulate the phase of the pulse 2 by 90 degrees), obtains an encoded pulse (the encoded pulse includes the pulse 1 with the unmodulated phase and the pulse 2 with the 90-degree modulated phase), and outputs the encoded pulse.

At this time, after receiving the coded pulse output by the second frequency-division delay phase shifter, if the decoding basis group 2 is selected, the third frequency-division delay phase shifter in the receiving-side decoding module modulates the phase of the pulse 2 in the coded pulse by 90 degrees with the second frequency as a specific frequency (at this time, the phase of the pulse 2 is modulated by 180 degrees through the phase modulation by the second frequency-division delay phase shifter and the third frequency-division delay phase shifter), and does not modulate the phase of the pulse 1.

Taking the third frequency division delay phase shifter to output the pulse 1 first and then the pulse 2 as an example, the pulse 1 output by the third frequency division delay phase shifter and the pulse 3 output by the beam splitter reach the interferometer at the same time first, and the pulse 2 output by the third frequency division delay phase shifter and the pulse 4 output by the beam splitter reach the interferometer at the same time (for example, assuming that the pulse 1 output by the third frequency division delay phase shifter and the pulse 3 output by the beam splitter reach the interferometer at the time of T1, the pulse 2 output by the third frequency division delay phase shifter and the pulse 4 output by the beam splitter reach the interferometer at the time of T2, and T2 is later than T1); at time T1, the interferometer receives pulse 1 with unmodulated phase and pulse 3 with unmodulated phase, the phase difference between pulse 1 with unmodulated phase and pulse 3 with unmodulated phase is 0 degree, after the interferometer interferes, the interferometer outputs pulse from the upper arm, and the first single-photon detector is not lighted; at time T2, the interferometer receives pulse 2 whose phase is modulated by 180 degrees and pulse 4 whose phase is not modulated, and the phase difference between pulse 2 whose phase is modulated by 180 degrees and pulse 4 whose phase is not modulated is 180 degrees, and after the interferometer interferes, the interferometer outputs a pulse from the lower arm, at which time the first single-photon detector is turned on.

Further, after receiving the coded pulse output by the second frequency-division delay phase shifter, if the decoding basis set 1 is selected, the third frequency-division delay phase shifter in the receiving-side decoding module modulates the phase of the pulse 1 in the coded pulse by 90 degrees with the first frequency as a specific frequency, and does not modulate the phase of the pulse 2.

Taking the third frequency division delay phase shifter to output the pulse 1 first and then the pulse 2 as an example, the pulse 1 output by the third frequency division delay phase shifter and the pulse 3 output by the beam splitter reach the interferometer at the same time first, and the pulse 2 output by the third frequency division delay phase shifter and the pulse 4 output by the beam splitter reach the interferometer at the same time (for example, assuming that the pulse 1 output by the third frequency division delay phase shifter and the pulse 3 output by the beam splitter reach the interferometer at the time of T1, the pulse 2 output by the third frequency division delay phase shifter and the pulse 4 output by the beam splitter reach the interferometer at the time of T2, and T2 is later than T1); at the time of T1, the interferometer receives a pulse 1 with the phase being modulated by 90 degrees and a pulse 3 with the phase not being modulated, the phase difference between the pulse 1 with the phase being modulated by 90 degrees and the pulse 3 with the phase not being modulated is 90 degrees, after the interferometer interferes, the interferometer outputs pulses from both the upper arm and the lower arm, and at the moment, the first single-photon detector is turned on; at time T2, the interferometer receives pulse 2 whose phase is modulated by 90 degrees and pulse 4 whose phase is not modulated, and the phase difference between pulse 2 whose phase is modulated by 90 degrees and pulse 4 whose phase is not modulated is 90 degrees, and after the interferometer interferes, the interferometer outputs pulses from both the upper arm and the lower arm, at which time the first single-photon detector is turned on.

In this embodiment of the application, the receiving-side communication module may determine that the data 1 is sent by the sending-side communication module at this time based on results that the first single-photon detector is not lighted at time T1 and the first single-photon detector is lighted at time T2; when the first single-photon detector is turned on at the time T1 and the time T2, the receiving-side communication module cannot definitely determine whether the data sent by the sending-side communication module at this time is 0 or 1.

In this embodiment of the application, when the first single-photon detectors are turned on at times T1 and T2, and it cannot be determined explicitly whether the data sent by the sending-side communication module is 0 or 1, the receiving-side communication module may record storage locations of the data, so as to publish the storage locations in a public channel, and then both the communicating sides (the sending-side communication module and the receiving-side communication module) delete the data in the locations at the same time, so as to ensure consistency between the data sent by the sending-side communication module and the data received by the receiving-side communication module.

For one communication process, a set of binary sequences exists in the sender communication module (for convenience of distinction, the binary sequences are temporarily referred to as binary sequences 1), and after the sender communication module sequentially sends each binary number in the set of binary sequences to the receiver communication module, the receiver communication module obtains a set of binary sequences (for convenience of distinction, the binary sequences are temporarily referred to as binary sequences 2). Moreover, the receiver communication module may also publish, in an open channel, a storage location where it is uncertain whether the data sent by the sender communication module is data of 0 or 1, delete, by the sender communication module, the data of the storage location in the binary sequence 1 to obtain a binary sequence 3, and delete, by the receiver communication module, the data of the storage location in the binary sequence 2 to obtain a binary sequence 4.

Further, in order to verify whether the eavesdropping is carried out, the two communication parties can simultaneously disclose a part of the keys in the hands of the two communication parties in a public channel, and the two communication parties disclose the keys in the same position. The presence or absence of eavesdropping is judged by using these keys. Theoretically, keys that are identical in position should be identical, and if there is an eavesdropping, keys that are different from each other appear, it can be judged that there is an eavesdropper present. Furthermore, considering that the actual communication process is not completely idealized, the keys published by the two communication parties cannot be completely the same, but the communication error rate of the two communication parties has an upper bound under the condition that the keys are not intercepted through theoretical calculation, if the key error rate published by the two communication parties exceeds the upper bound, the two communication parties are considered to be intercepted, and if the key error rate published by the two communication parties does not exceed the upper bound, the two communication parties are considered to be not intercepted.

In this embodiment, the binary sequence 1 may be regarded as a secret key of the communication module of the sender, and the binary sequence 2 may be regarded as a secret key of the communication module of the receiver; the binary sequence 3 can also be regarded as a key of the sender communication module and the binary sequence 4 as a key of the receiver communication module.

In the embodiment of the application, if no eavesdropper eavesdrops, the undisclosed binary sequence can be used as the final key for secret communication, and the final key can only be known by both communication parties and cannot be eavesdropped by the eavesdropper.

Furthermore, the first frequency-division delay phase shifter, the second frequency-division delay phase shifter, the third frequency-division delay phase shifter, the fourth frequency-division delay phase shifter and the fifth frequency-division delay phase shifter are formed by frequency-division delay phase shifters, and the frequency-division delay phase shifters can realize the frequency division effect on pulses with different frequencies.

Fig. 8(a) - (b) are schematic structural diagrams of a frequency division delay phase shifter according to an embodiment of the present application.

As shown in fig. 8(a) - (b), the fractional delay phase shifter includes: the system comprises an arrayed waveguide grating and a phase modulator, wherein the arrayed waveguide grating is provided with different sub-channels 81 matched with pulses with different frequencies, the lengths of delay lines of the sub-channels are distributed in an arithmetic progression, and each sub-channel is integrated with one phase modulator 82.

As shown in fig. 8(a) - (b), since different frequency pulses are transmitted from different sub-channels, the different time periods of the different frequency pulses passing through the sub-channels can be controlled by setting different lengths of the delay lines of the sub-channels corresponding to the different frequency pulses, so as to achieve the frequency division effect.

Each subchannel as shown in fig. 8(a) - (b) is provided with a phase modulator, and by phase modulating the phase modulator in the subchannel, encoding/decoding of the pulses transmitted in the subchannel can be achieved. The longer the delay line length in a sub-channel as shown in fig. 8(a) - (b), the later the output time of the pulse in that sub-channel.

Fig. 9(a) - (b) are schematic structural diagrams of another fractional-n delay phase shifter according to an embodiment of the present application.

As shown in fig. 9(a) - (b), the fractional delay phase shifter includes: a circulator 91, a bragg reflector 92 connected to the circulator 91 and a phase modulator 93; the bragg reflectors are arranged to distribute pulses of different frequencies to different time bits, the time interval between any two adjacent time bits being the same as the time interval between any other two adjacent time bits.

The fractional-n delay phase shifter shown in fig. 9(a) - (b) can achieve the effect of frequency division by distributing pulse signals of different frequencies to different time bits, and by setting the time interval between any two adjacent time bits to be the same as the time interval between any other two adjacent time bits; and the higher the position of the time bit in the bragg reflector, the later the output time of the pulse distributed into the time bit.

Fig. 10 is a schematic structural diagram of another fractional-n delay phase shifter according to an embodiment of the present application.

The fractional delay phase shifter shown in fig. 10 is a modification of the fractional delay phase shifter shown in fig. 9, the fractional delay phase shifter shown in fig. 10 includes a plurality of units 101, a high speed optical switch (HOS) feeds pulses of different operating frequencies separated from one laser pulse into one unit 101 at a time, the different units 101 are used for selecting pulses of different operating frequencies for phase modulation, and the path taken by a selected modulation pulse in each unit 101 is the same as that taken by the other non-selected operating pulses, so that the pulses of different operating frequencies separated from one laser pulse are simultaneously converged to an output point 102.

The first single-photon detector in the receiver data reading module of the above embodiment may be further configured to: the average photon number of the interference result pulse is measured to determine whether the system is under a first attack, and the first attack indicates a photon number separation attack.

Fig. 11 is a schematic structural diagram of another receiver data reading module according to an embodiment of the present disclosure.

As shown in fig. 11, the receiver data read module may further include a second single-photon detector 1223 coupled to the interferometer, the second single-photon detector being configured to determine whether the system is subject to a second attack based on the results of the interference, the second attack being indicative of a phase modulation attack.

In the embodiment of the present application, it is preferable that the second single-photon detector is connected to an upper arm of the interferometer when the interferometer is a mach-zehnder interferometer.

In order to implement information interaction between a sender and a receiver, the embodiment of the present application further provides a schematic structural diagram of another quantum communication system, specifically please refer to fig. 12.

As shown in fig. 12, the quantum communication system includes a sender communication module 11 and a receiver communication module 12, where the receiver communication module 12 may further include a receiver light source module 123 and a receiver encoding module 124 connected to the receiver light source module 123, in addition to the receiver decoding module 121 and the receiver data reading module 122 connected to the receiver decoding module 121 provided in the foregoing embodiment; likewise, the sender communication module 11 may include a sender decoding module 113 and a sender data reading module 114 connected to the sender decoding module 113, in addition to the light source module 111 (for convenience of distinguishing from the receiver light source module 123 in the receiver communication module, the light source module 111 may be referred to as the sender light source module 111) provided in the above embodiment and the sender encoding module 112 connected to the light source module 111; and, the receiving-side encoding module 124 is connected to the transmitting-side decoding module 123.

In the quantum communication system provided in the embodiment of the present application, the processing may implement information transmission to a sender through the sender light source module, the sender encoding module, the receiver decoding module, and the receiver data reading module, and may also implement information transmission to a receiver through the receiver light source module, the receiver encoding module, the sender decoding module, and the sender data reading module, so that the quantum communication system may implement half-duplex communication.

In this embodiment, please refer to the manner for implementing information transmission to the sender based on the sender light source module, the sender encoding module, the receiver decoding module, and the receiver data reading module provided in the above embodiment, which is not described herein again.

Furthermore, the information transmission manner of the receiver to the sender provided in the embodiment of the present application may be improved according to the information transmission manner of the sender to the receiver provided in the above embodiment, and details are not described herein.

The present invention provides a quantum communication system, which is described in detail above, and the principle and the implementation of the present invention are explained by applying specific examples, and the description of the above examples is only used to help understanding the method and the core idea of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.

It should be noted that, in the present specification, the embodiments are all described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments may be referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.

It is further noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include or include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A quantum communication system, comprising: the optical fiber communication system comprises a sender communication module and a receiver communication module, wherein the sender communication module comprises a light source module and a sender coding module connected with the light source module, the receiver communication module comprises a receiver decoding module used for optical fiber communication with the sender coding module and a receiver data reading module connected with the receiver decoding module, and the receiver data reading module comprises:

2. The system of claim 1, wherein the transmitting side coding module comprises a first frequency-division delay phase shifter, an intensity modulator, a beam splitter and a second frequency-division delay phase shifter, which are sequentially connected to the light source module, wherein:

3. The system of claim 2, wherein the receiver decoding module comprises: a third frequency division delay phase shifter for fiber connection with the second frequency division delay phase shifter, the third frequency division delay phase shifter being configured to:

4. The system of claim 3,

5. The system of claim 4, wherein the transmitting-side encoding module further comprises a fourth frequency-division delay phase shifter for coupling to the second port of the beam splitter, and wherein the receiving-side decoding module further comprises a fifth frequency-division delay phase shifter for coupling to the fourth frequency-division delay phase shifter, wherein:

6. The system of claim 2, wherein the sender encoding module further comprises a first variable optical attenuator,

7. The system of claim 3, wherein the receiver decoding module further comprises a second variable optical attenuator,

8. The system of claim 1 wherein said recipient data reading module comprises an interferometer and a first single-photon detector coupled to said interferometer for reading said communication data based on said interference.

9. The system of claim 5, wherein the first, second, third, fourth, and fifth divide-by delay shifters are comprised of divide-by delay shifters, and wherein the divide-by delay shifters comprise:

alternatively, the first and second electrodes may be,

10. The system of claim 8 wherein said first single photon detector is further operable to measure an average photon count of said interference result pulses to determine if said system is under a first attack, said first attack indicating a photon count separation attack,