CN111200494B - Phase compensation method and system for quantum secure direct communication system - Google Patents

Phase compensation method and system for quantum secure direct communication system Download PDF

Info

Publication number
CN111200494B
CN111200494B CN202010151097.1A CN202010151097A CN111200494B CN 111200494 B CN111200494 B CN 111200494B CN 202010151097 A CN202010151097 A CN 202010151097A CN 111200494 B CN111200494 B CN 111200494B
Authority
CN
China
Prior art keywords
voltage
communication information
modulation
phase
photon sequence
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active
Application number
CN202010151097.1A
Other languages
Chinese (zh)
Other versions
CN111200494A (en
Inventor
殷柳国
赵连旭
龙桂鲁
林再盛
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Tsinghua University
Original Assignee
Tsinghua University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Tsinghua University filed Critical Tsinghua University
Priority to CN202010151097.1A priority Critical patent/CN111200494B/en
Publication of CN111200494A publication Critical patent/CN111200494A/en
Application granted granted Critical
Publication of CN111200494B publication Critical patent/CN111200494B/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
    • H04L9/0852—Quantum cryptography
    • H04L9/0858—Details about key distillation or coding, e.g. reconciliation, error correction, privacy amplification, polarisation coding or phase coding
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/70—Photonic quantum communication

Abstract

The invention provides a phase compensation method and a system for a quantum secure direct communication system, wherein the quantum secure direct communication system comprises a communication information receiving end, a communication information sending end, a quantum channel and a classical channel, and the quantum channel and the classical channel are arranged between the two ends, and the phase compensation method comprises the following steps: initializing a quantum secure direct communication system to obtain an initial modulation voltage of a communication information sending end; judging whether the bit error rate of the initialized quantum channel exceeds a threshold value; if not, returning to the step of judging the error rate; if the voltage exceeds the threshold value, judging the drift direction of the initial modulation voltage and estimating the voltage drift amount; the communication information sending end carries out fixed step length scanning with a reduced range according to the drift direction of the initial modulation voltage and the estimated voltage drift amount to obtain a new modulation voltage of the communication information sending end; and loading a new modulation voltage at the communication information sending end, and returning to the step of judging the error rate. The method and the system can be used for quickly adjusting the offset phase.

Description

Phase compensation method and system for quantum secure direct communication system
Technical Field
The invention relates to the technical field of quantum secure communication, in particular to a phase compensation method and system for a quantum secure direct communication system.
Background
Quantum secure direct communication is a form of quantum communication that utilizes classical coding theory and eavesdropping channel theory. The quantum secure direct communication can simply, conveniently, safely transmit information in a quantum channel in real time without a quantum memory and a random key generated in advance, and can theoretically realize absolute security.
Quantum secure direct communication is a great difference compared to conventional optical communication. Conventionally, strong light is used for optical communication, and when the strong light is modulated in phase, polarization, amplitude, and the like, the influence of environmental changes on the system is relatively limited. The quantum secure direct communication uses single photons, and the single photons are greatly influenced by environmental changes and system noise, so that phase drift is easily caused, and therefore, the phase drift needs to be compensated.
Disclosure of Invention
The invention provides a phase compensation method and a phase compensation system for a quantum secure direct communication system, which are used for quickly adjusting the offset phase of the quantum secure direct communication system.
According to an aspect of the present invention, there is provided a phase compensation method for a quantum secure direct communication system including a communication information receiving end, a communication information transmitting end, and a quantum channel and a classical channel between the two ends, the phase compensation method including:
step S1, initializing the quantum secure direct communication system, and obtaining the initial modulation voltage of the communication information sending end;
step S2, generating a photon sequence through the initial modulation voltage phase modulation, obtaining the error rate of a quantum channel according to the transmission of the photon sequence between a communication information receiving end and a communication information sending end, and judging whether the error rate exceeds a threshold value;
step S3, if not, returning to step S2;
step S4, if the threshold value is exceeded, the drift direction of the initial modulation voltage is judged by using the photon sequence sent by the communication information receiving terminal and the basis vector and the classical bit of the photon sequence returned by the communication information receiving terminal, and the voltage drift amount is estimated;
step S5, the communication information sending end carries out fixed step length scanning with reduced range according to the drift direction of the initial modulation voltage and the estimated voltage drift amount to obtain a new modulation voltage of the communication information sending end;
in step S6, a new modulation voltage is applied to the transmission end of the communication information, and the process returns to step S2.
Preferably, the step of obtaining the initial modulation voltage of the communication information transmitting end includes:
setting a first working voltage of a communication information receiving end;
a single photon generated by a communication information receiving terminal is used as an information carrier;
obtaining a first half-wave voltage of a communication information receiving end, comprising: performing fixed-step continuous phase modulation on the single photon in a set phase range by adopting a first working voltage through a first phase modulator at a communication information receiving end to form a continuously-changed photon sequence and a corresponding continuously-changed first modulation voltage, wherein the phase range is in a set range of pi phase; the photon sequence is sent to a second detector of a communication information sending end through a quantum channel, and the second detector counts the received photon sequence; taking the count of the photon sequence received by the second detector as a vertical coordinate, and taking the first modulation voltage of the corresponding communication information receiving end as a horizontal coordinate to construct a coordinate graph; finding a maximum value point and a minimum value point of the coordinate graph, wherein the difference value of first modulation voltages corresponding to the adjacent maximum value point and minimum value point is a first half-wave voltage;
the method for obtaining the initial modulation voltage and the second half-wave voltage of the communication information sending terminal comprises the following steps: performing phase modulation on the single photon by adopting a first working voltage through a first phase modulator of a communication information receiving end to form a photon sequence, and sending the photon sequence to a communication information sending end through a quantum channel; receiving the photon sequence through a second phase modulator of an information sending end, and carrying out fixed-step continuous phase modulation on the received photon sequence in a set phase range to obtain a continuously-changed photon sequence and a corresponding continuously-changed second modulation voltage, wherein a second detector receives and counts the continuously-changed photon sequence, and the phase range is in a set range of pi phase; taking the count of a second detector of the communication information sending end as a vertical coordinate, and taking a second modulation voltage of the corresponding communication information sending end as a horizontal coordinate to construct a coordinate graph; and finding an extreme point of the coordinate graph, wherein an abscissa corresponding to the extreme point is the initial modulation voltage of the communication information sending end, the extreme point is a minimum value point or a maximum value point, and the second half-wave voltage of the communication information sending end is the difference value of the second modulation voltage corresponding to the adjacent maximum value point and the minimum value point in the coordinate graph.
Preferably, the method for obtaining the bit error rate includes:
a single photon is generated by a communication information receiving terminal and used as an information carrier, logic signals in different combination forms of a first working voltage and a first half-wave voltage are loaded on the single photon randomly for phase modulation, a first photon sequence is formed, receiving terminal logic information of the communication information receiving terminal is obtained, and the receiving terminal logic information comprises a basis vector and a classical bit of the first photon sequence;
the first photon sequence is sent to a communication information sending end through a quantum channel;
loading logic signals in different combination forms of initial modulation voltage and second half-wave voltage on the first photon sequence randomly through a second modulator of a communication information sending end to perform phase modulation to form a second photon sequence, receiving the second photon sequence by a second detector to obtain sending end logic information, wherein the sending end logic information comprises classical bits, basis vectors and sending time of the second photon sequence;
a communication information receiving end receives the logic information of the sending end and finds out the corresponding logic information of the receiving end according to the sending time of the logic information of the sending end;
screening out single photons of which the basis vectors of the communication information receiving end and the communication information sending end are the same, wherein the basis vectors correspond to the sending time;
screening out single photons with different classical bits of a communication information receiving end and classical bits of a communication information sending end from the single photons with the same basic vector;
and obtaining the error rate, wherein the proportion of the number of the single photons with different classical bits to the number of the single photons with the same basis vector is used as the error rate.
Further, preferably, the step of judging the drift direction of the initial modulation voltage and estimating the voltage drift amount includes:
screening out single photons with different base vectors from a communication information sending end and a communication information receiving end;
obtaining a first probability, wherein the proportion of the number of single photons with the same classical bits in the number of single photons with different basis vectors is used as the first probability;
when the first probability is 1, the voltage drift amount is
Figure GDA0002948421380000031
Wherein, Vhalf2The drift direction is a preset direction for the second half-wave voltage of the communication information sending end;
when the first probability is 0, the voltage drift amount is
Figure GDA0002948421380000032
The drifting direction is opposite to the preset direction;
when the first probability is 0.5, no drift exists;
when the first probability is larger than 0.5 and smaller than 1, the voltage drift amount and the first probability are in a sinusoidal relation, so that the voltage drift amount corresponding to the first probability is obtained, and the drift direction is a preset direction;
when the first probability is larger than 0 and smaller than 0.5, the voltage drift amount and the first probability are in a sinusoidal relation, so that the voltage drift amount corresponding to the first probability is obtained, and the drift direction is opposite to the preset direction.
Preferably, step S5 includes:
taking the initial modulation voltage of a communication information sending end as an end point of a modulation range;
taking the sum of the initial modulation voltage and the estimated voltage drift value as the other end point of the modulation range;
and scanning extreme points of the statistical number of the second detector by adopting a set step length in the modulation range, wherein the modulation voltage corresponding to the extreme points is used as a new modulation voltage.
According to another aspect of the present invention, there is provided a phase compensation system for a quantum secure direct communication system including a communication information receiving end, a communication information transmitting end, and a quantum channel and a classical channel between the two ends, the phase compensation system comprising:
the initialization module initializes the quantum secure direct communication system and obtains an initial modulation voltage of a communication information sending end;
the first judgment module generates a photon sequence through the initial modulation voltage phase modulation, obtains the bit error rate of the quantum channel according to the transmission of the photon sequence between the communication information receiving end and the communication information sending end, judges whether the bit error rate of the initialized quantum channel exceeds a threshold value or not, and continuously monitors the bit error rate of the initialized quantum channel if the bit error rate of the initialized quantum channel does not exceed the threshold value; if the threshold value is exceeded, sending a signal to a second judgment module;
the second judgment module is used for judging the drift direction of the initial modulation voltage and estimating the voltage drift amount by utilizing the photon sequence sent by the communication information receiving terminal and the basis vector and the classical bit of the photon sequence returned by the communication information receiving terminal;
and the updating module is used for scanning the fixed step length with a reduced range according to the drift direction of the initial modulation voltage of the second judging module and the estimated voltage drift amount, updating the initial modulation voltage of the communication information sending end, sending a signal to the first judging module, and judging whether the error rate of the quantum channel initialized by the updated initial modulation voltage of the communication information sending end exceeds a threshold value or not.
Preferably, the communication information receiving end includes:
the single photon source module is used for generating single photons as an information carrier;
the first phase modulator is used for carrying out phase modulation on the single photon generated by the single photon source module to form a photon sequence;
the communication information transmitting end includes:
the second phase modulator is used for carrying out phase modulation on the photon sequence of the communication information receiving end;
a second detector for counting the received photon sequence;
the initialization module comprises a setting unit, a first half-wave voltage obtaining unit, a second half-wave voltage obtaining unit, an initial modulation voltage obtaining unit and a coordinate graph obtaining unit, wherein:
the setting unit is used for setting a first working voltage and sending the first working voltage to a communication information receiving end, and setting a phase range to the communication information receiving end and a communication information sending end, wherein the phase range is within a set range of pi phase;
the first half-wave voltage obtaining unit sends a continuous phase modulation instruction to the first phase modulator and sends a receiving instruction to the second detector, so that the first phase modulator performs fixed-step continuous phase modulation on the single photon within a set phase range by adopting a first working voltage to form a continuously-changed photon sequence and a corresponding continuously-changed first modulation voltage; the second detector receives the photon sequence and counts, the coordinate graph obtaining unit takes the count of the second detector as a vertical coordinate, the corresponding first modulation voltage is a horizontal coordinate, a coordinate graph is constructed, the coordinate graph is returned to the first half-wave voltage obtaining unit, a maximum value point and a minimum value point of the coordinate graph are found, and the difference value of the first modulation voltage corresponding to the adjacent maximum value point and the adjacent minimum value point is the first half-wave voltage;
the second half-wave voltage obtaining unit is used for sending a phase modulation command to the first phase modulator and sending a continuous phase modulation command to the second phase modulator, wherein the first phase modulator is used for carrying out phase modulation on the single photons by adopting a first working voltage to form a photon sequence and sending the photon sequence to the second phase modulator through a quantum channel; the second phase modulator carries out fixed-step continuous phase modulation on the received photon sequence within a set phase range to obtain a continuously-changed photon sequence and a corresponding continuously-changed second modulation voltage; a second detector receives the continuously varying photon sequence and counts; the coordinate graph obtaining unit takes the count of a second detector of the communication information sending end as a vertical coordinate, the corresponding second modulation voltage is a horizontal coordinate, a coordinate graph is constructed, and the coordinate graph is returned to the second half-wave voltage obtaining unit and the initial modulation voltage obtaining unit; the initial modulation voltage obtaining unit finds an extreme point of a coordinate graph, an abscissa corresponding to the extreme point is the initial modulation voltage of a communication information sending end, and the extreme point is a minimum value point or a maximum value point; the second half-wave voltage obtaining unit finds a maximum value point and a minimum value point of the coordinate graph, and takes a difference value of second modulation voltages corresponding to the adjacent maximum value point and the adjacent minimum value point as a second half-wave voltage.
Preferably, the first judging module includes:
the first photon sequence obtaining unit sends a modulation instruction to the first phase modulator, and loads logic signals in different combination forms of a first working voltage and a first half-wave voltage on the single photon randomly for phase modulation to form a first photon sequence and obtain receiving end logic information of a communication information receiving end, wherein the receiving end logic information comprises a basis vector and a classical bit of the first photon sequence;
the second photon sequence obtaining unit is used for sending a modulation instruction to the second phase modulator, the second phase modulator receives the first photon sequence through a quantum channel, logic signals in different combination forms of initial modulation voltage and second half-wave voltage are loaded on the first photon sequence randomly for phase modulation, a second photon sequence is formed, the second detector receives the second photon sequence, and sending end logic information is obtained, wherein the sending end logic information comprises classical bits, basis vectors and sending time of the second photon sequence;
the first judging unit is used for judging whether the basis vector of the communication information receiving end corresponding to the sending time is the same as the basis vector of the communication information sending end or not, sending a signal to the second judging unit if the basis vectors are the same, and sending a signal to the second judging module if the basis vectors are different;
the second judging unit judges whether the classical bit of the communication information receiving end is the same as the classical bit of the communication information sending end, and sends a signal to the first statistical unit;
the first statistic unit is used for counting the total number of single photons with the same basis vectors and the number of single photons with the same basis vectors and different classical bits;
the error rate obtaining unit is used for taking the ratio of the number of single photons with the same basis vector and different classical bits counted by the first statistic unit to the total number of single photons with the same basis vector as the error rate;
the third judgment unit judges whether the bit error rate of the initialized quantum channel exceeds a threshold value or not, and sends a signal to the second judgment module if the bit error rate of the initialized quantum channel exceeds the threshold value; and if the threshold value is not exceeded, sending a signal to the first photon sequence obtaining unit.
Preferably, the second determination module includes:
the second statistical unit is used for counting the total number of the single photons with different basis vectors and the number of the single photons with different basis vectors and same classical bits;
the first probability obtaining unit is used for taking the proportion of the number of single photons with the same classical bit in the number of single photons with different basis vectors as a first probability;
an estimating unit estimating a voltage drift amount and a drift direction of the initial modulation voltage according to the first probability of the first probability obtaining unit, wherein the voltage drift amount is 1 when the first probability is 1
Figure GDA0002948421380000051
Wherein, Vhalf2The drift direction is a preset direction for the second half-wave voltage; when the first probability is 0, the voltage drift amount is
Figure GDA0002948421380000052
The drifting direction is opposite to the preset direction; when the first probability is 0.5, no drift exists; when the first probability is larger than 0.5 and smaller than 1, the voltage drift amount and the first probability are in a sinusoidal relation, so that the voltage drift amount corresponding to the first probability is obtained, and the drift direction is a preset direction; when the first probability is larger than 0 and smaller than 0.5, the voltage drift amount and the first probability are in a sinusoidal relation, so that the voltage drift amount corresponding to the first probability is obtained, and the drift direction is opposite to the preset direction.
The phase compensation method and the system for the quantum secure direct communication system are low in error rate (high in reliability), compensation time is saved (high in efficiency), and the system can continuously and stably operate by adjusting the offset phase. When the error rate drifts out of the safe range, the correction can be carried out immediately; more accurate phase compensation results are obtained in the shortest possible compensation time. Finding out compensation voltage (new modulation voltage) by a scanning method in a half-wave voltage range, and only finding out the maximum value of counting statistical results of the detector in the period of time; the initialization process saves 50% of the compensation time again relative to scanning in a 2 pi phase period, where the scanning detector counts the minimum (or maximum) in the statistical time. For the amount of the phase modulation voltage that changes constantly with environmental changes, the shorter the scanning time, the more time-efficient the result obtained, and the lower the bit error rate. The measured data shows that the error rate can be strictly controlled below a set threshold value by adopting a feedback compensation method, and the reliability of the system is improved.
Drawings
FIG. 1 is a schematic diagram of a flow chart of a phase compensation method for a quantum secure direct communication system according to the present invention;
FIG. 2 is a schematic diagram of a block diagram of a phase compensation system for a quantum secure direct communication system according to the present invention;
fig. 3 is a schematic diagram of a block diagram of a phase compensation system for a quantum secure direct communication system according to a preferred embodiment of the present invention.
Detailed Description
In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident, however, that such embodiment(s) may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing one or more embodiments.
Various embodiments according to the present invention will be described in detail below with reference to the accompanying drawings.
Fig. 1 is a schematic diagram of a flow chart of a phase compensation method for a quantum secure direct communication system according to the present invention, as shown in fig. 1, where the quantum secure direct communication system includes a communication information receiving end, a communication information transmitting end, and a quantum channel and a classical channel between the two ends, and the phase compensation method includes:
step S1, initializing the quantum secure direct communication system, and obtaining the initial modulation voltage of the communication information sending end;
step S2, generating a photon sequence through the initial modulation voltage phase modulation, obtaining the error rate of a quantum channel according to the transmission of the photon sequence between a communication information receiving end and a communication information sending end, and judging whether the error rate exceeds a threshold value;
step S3, if not, returning to step S2;
step S4, if the threshold value is exceeded, the drift direction of the initial modulation voltage is judged by using the photon sequence sent by the communication information receiving terminal and the basis vector and the classical bit of the photon sequence returned by the communication information receiving terminal, and the voltage drift amount is estimated;
step S5, the communication information sending end carries out fixed step scanning with reduced range according to the drift direction of the initial modulation voltage and the estimated voltage drift amount to obtain a new modulation voltage of the communication information sending end (the initial modulation voltage sent by the communication information of step S1 is updated);
in step S6, a new modulation voltage (updated initial modulation voltage) is applied to the communication information transmitting end, and the process returns to step S2.
In one embodiment, in step S1, the step of obtaining the initial modulation voltage of the communication information sending end includes:
setting a first working voltage of a communication information receiving end;
a single photon generated by a communication information receiving terminal is used as an information carrier;
obtaining a first half-wave voltage of a communication information receiving end, comprising: performing fixed-step continuous phase modulation on the single photon in a set phase range by adopting a first working voltage through a first phase modulator at a communication information receiving end to form a continuously-changed photon sequence and a corresponding continuously-changed first modulation voltage, wherein the phase range is in a set range of pi phase; the photon sequence is sent to a second detector of a communication information sending end through a quantum channel, and the second detector counts the received photon sequence; taking the count of the photon sequence received by the second detector as a vertical coordinate, and taking the first modulation voltage of the corresponding communication information receiving end as a horizontal coordinate to construct a coordinate graph; finding a maximum value point and a minimum value point of the coordinate graph, wherein the difference value of first modulation voltages corresponding to the adjacent maximum value point and minimum value point is a first half-wave voltage;
the method for obtaining the initial modulation voltage and the second half-wave voltage of the communication information sending terminal comprises the following steps: performing phase modulation on the single photon by adopting a first working voltage through a first phase modulator of a communication information receiving end to form a photon sequence, and sending the photon sequence to a communication information sending end through a quantum channel; receiving the photon sequence through a second phase modulator of an information sending end, and carrying out fixed-step continuous phase modulation on the received photon sequence in a set phase range to obtain a continuously-changed photon sequence and a corresponding continuously-changed second modulation voltage, wherein a second detector receives and counts the continuously-changed photon sequence, and the phase range is in a set range of pi phase; taking the count of a second detector of the communication information sending end as a vertical coordinate, and taking a second modulation voltage of the corresponding communication information sending end as a horizontal coordinate to construct a coordinate graph; and finding an extreme point of the coordinate graph, wherein an abscissa corresponding to the extreme point is the initial modulation voltage of the communication information sending end, the extreme point is a minimum value point or a maximum value point, and the second half-wave voltage of the communication information sending end is the difference value of the second modulation voltage corresponding to the adjacent maximum value point and the minimum value point in the coordinate graph.
In step S2, the method for obtaining the bit error rate includes:
a single photon is generated by a communication information receiving terminal and used as an information carrier, logic signals in different combination forms of a first working voltage and a first half-wave voltage are loaded on the single photon randomly for phase modulation, a first photon sequence is formed, receiving terminal logic information of the communication information receiving terminal is obtained, and the receiving terminal logic information comprises a basis vector and a classical bit of the first photon sequence;
the first photon sequence is sent to a communication information sending end through a quantum channel;
loading logic signals in different combination forms of initial modulation voltage and second half-wave voltage on the first photon sequence randomly through a second modulator of a communication information sending end to perform phase modulation to form a second photon sequence, receiving the second photon sequence by a second detector to obtain sending end logic information, wherein the sending end logic information comprises classical bits, basis vectors and sending time of the second photon sequence;
a communication information receiving end receives the logic information of the sending end and finds out the corresponding logic information of the receiving end according to the sending time of the logic information of the sending end;
screening out single photons of which the basis vectors of the communication information receiving end and the communication information sending end are the same, wherein the basis vectors correspond to the sending time;
screening out single photons with different classical bits of a communication information receiving end and classical bits of a communication information sending end from the single photons with the same basic vector;
and obtaining the error rate, wherein the proportion of the number of the single photons with different classical bits to the number of the single photons with the same basis vector is used as the error rate.
Preferably, the communication information receiving end randomly loads one of four logic signals for phase modulation, where the four logic signals include: a first operating voltage V1Second operating voltage
Figure GDA0002948421380000081
A third operating voltage V3＝V1+Vhalf1Fourth operating voltage
Figure GDA0002948421380000082
Wherein, Vhalf1For the first half-wave voltage, preferably, binary is used to represent the four logic signals, for example, the four operating voltages are 00, 10, 01 and 11 respectively, the basis vector in the logic information of the receiving end is the previous digit, i.e., 0, 1, 0 and 1 respectively, and the classical bits are 0, 1 and 1;
the communication information sending end is provided with two basis vector signals corresponding to two working voltages, which are respectively as follows: fifth operating voltage V5(initial modulation voltage obtained in step S1), sixth operating voltage
Figure GDA0002948421380000083
Fifth operating voltage V5For the phase compensation result, the fifth working voltage and the first working voltage and the third working voltage of the communication information receiving terminal are in a group, the sixth working voltage and the second working voltage and the fourth working voltage of the communication information receiving terminal are in a group, and two detectors are arranged at the communication information transmitting terminal, so that photons belonging to a group enter the same detector after detection, for example, the basis vector, V, of the second modulator5Is 0, V6And the classical bits received by the second detector are 00, 01, 10 and 11, the 00 of the classical bits obtained by the second detector is discarded, the 11 is randomly changed into 01 or 10, then the 01 is changed into 0, and the 10 is changed into 1, so that the classical bits of the second detector are changed into 1-bit number which is the same as the classical bit number of the logic information of the receiving end, and comparison in the process of obtaining the bit error rate is facilitated.
In step S4, the step of determining the drift direction of the initial modulation voltage and estimating the voltage drift amount includes:
screening out single photons with different base vectors from a communication information sending end and a communication information receiving end;
obtaining a first probability, wherein the proportion of the number of single photons with the same classical bits in the number of single photons with different basis vectors is used as the first probability;
when the first probability is 1, the voltage drift amount is
Figure GDA0002948421380000084
Wherein, Vhalf2The drift direction is a preset direction for the second half-wave voltage of the communication information sending end;
when the first probability is 0, the voltage drift amount is
Figure GDA0002948421380000085
The drifting direction is opposite to the preset direction;
when the first probability is 0.5, no drift exists;
when the first probability is larger than 0.5 and smaller than 1, the voltage drift amount and the first probability are in a sinusoidal relation, so that the voltage drift amount corresponding to the first probability is obtained, and the drift direction is a preset direction;
when the first probability is larger than 0 and smaller than 0.5, the voltage drift amount and the first probability are in a sinusoidal relation, so that the voltage drift amount corresponding to the first probability is obtained, and the drift direction is opposite to the preset direction.
In step S5, the step of performing the fixed-step scan for narrowing the range includes:
taking the initial modulation voltage of a communication information sending end as an end point of a modulation range;
taking the sum of the initial modulation voltage and the estimated voltage drift value as the other end point of the modulation range;
scanning out extreme points of the statistical number of the second detector in the modulation range by adopting a set step length, wherein the modulation voltage corresponding to the extreme points is used as a new modulation voltage, namely, the second phase modulator carries out fixed-step continuous phase modulation in the modulation range to form a changed photon sequence, the second detector receives and counts the photon sequence, and the modulation voltage in the modulation range corresponding to the counting extreme value is obtained as the new modulation voltage of the communication information sending end through a coordinate graph formed by the counting of the second detector and the modulation voltage in the modulation range.
The phase compensation method has the characteristics of low bit error rate (high reliability) and compensation time saving (high efficiency), thereby solving the problem that the influence of environment change and system noise on single photons in quantum secure direct communication is large, and the phase drift is easily caused. By using a method of error rate feedback, if the error rate exceeds a threshold value, the system information transmission is suspended, phase compensation is carried out, and the reliability of the system is improved; by utilizing a method for counting the probability of relevant data, the voltage drift direction can be found and the voltage drift amount can be estimated, so that the scanning range is further shortened to save the compensation time; the shorter the time is, the more accurate the result is and the error rate is lower; the compensation voltage is found by utilizing a method of scanning in a half-wave voltage range, and meanwhile, the compensation time is further saved relative to the scanning in a 2 pi phase period.
Fig. 2 is a schematic diagram of a block diagram of a phase compensation system for a quantum secure direct communication system according to the present invention, and as shown in fig. 2, the quantum secure direct communication system 10 includes a communication information receiving end 1, a communication information transmitting end 2, and a quantum channel 3 and a classical channel 4 between the two ends, and the phase compensation system 100 includes:
the initialization module 110 is used for initializing the quantum secure direct communication system and obtaining an initial modulation voltage of a communication information sending end;
the first judging module 120 generates a photon sequence through the initial modulation voltage phase modulation, obtains the bit error rate of the quantum channel according to the transmission of the photon sequence between the communication information receiving end and the communication information transmitting end, judges whether the bit error rate of the initialized quantum channel exceeds a threshold value, and continuously monitors the bit error rate of the initialized quantum channel if the bit error rate of the initialized quantum channel does not exceed the threshold value; if the threshold value is exceeded, sending a signal to a second judgment module;
the second judging module 130 judges the drift direction of the initial modulation voltage and estimates the voltage drift amount by using the photon sequence sent by the communication information receiving terminal and the basis vector and the classical bit of the photon sequence returned by the communication information receiving terminal;
the updating module 140 performs a fixed-step scanning with a reduced range according to the drift direction of the initial modulation voltage and the estimated voltage drift amount of the second determining module 130, updates the initial modulation voltage of the communication information sending end, sends a signal to the first determining module, and determines whether the bit error rate of the quantum channel initialized by using the updated initial modulation voltage of the communication information sending end exceeds a threshold.
In one embodiment, the communication information receiving end 1 includes:
the single photon source module 11 is used for generating single photons as an information carrier;
the first phase modulator 12 is used for performing phase modulation on the single photon generated by the single photon source module 11 to form a photon sequence;
the communication information transmitting end 2 includes:
the second phase modulator 21 is configured to perform phase modulation on the photon sequence of the communication information receiving end 1;
a second detector 22 for counting the received photon sequence;
in the compensation system 100, the initialization module 110 includes a setting unit 111, a first half-wave voltage obtaining unit 112, a second half-wave voltage obtaining unit 113, an initial modulation voltage obtaining unit 114, and a coordinate graph obtaining unit 115, wherein:
the setting unit 111 sets a first working voltage, sends the first working voltage to the communication information receiving terminal 1, sets a phase range, and sends the phase range to the communication information receiving terminal and the communication information sending terminal 2, wherein the phase range is within a set range of pi phase;
the first half-wave voltage obtaining unit 112 sends a continuous phase modulation command to the first phase modulator 12, and sends a receiving command to the second detector 22, so that the first phase modulator 12 performs fixed-step continuous phase modulation on the single photon within a set phase range by using the first working voltage to form a continuously-changing photon sequence and a corresponding continuously-changing first modulation voltage; the second detector 22 receives the photon sequence and counts the number, the coordinate graph obtaining unit 115 takes the count of the second detector 22 as a vertical coordinate, the corresponding first modulation voltage is a horizontal coordinate, a coordinate graph is constructed, the coordinate graph is returned to the first half-wave voltage obtaining unit 112, a maximum value point and a minimum value point of the coordinate graph are found, and the difference value of the first modulation voltages corresponding to the adjacent maximum value point and the adjacent minimum value point is the first half-wave voltage;
the second half-wave voltage obtaining unit 113 sends a phase modulation instruction to the first phase modulator 12, and sends a continuous phase modulation instruction to the second phase modulator 21, wherein the first phase modulator 12 performs phase modulation on the single photon by using the first working voltage to form a photon sequence, and sends the photon sequence to the second phase modulator 21 through a quantum channel; the second phase modulator 21 performs fixed-step continuous phase modulation on the received photon sequence within a set phase range to obtain a continuously-changed photon sequence and a corresponding continuously-changed second modulation voltage; the second detector 22 receives the continuously varying sequence of photons and counts; the coordinate graph obtaining unit 115 takes the count of the second detector 22 of the communication information transmitting terminal 2 as a vertical coordinate, and the corresponding second modulation voltage as a horizontal coordinate, constructs a coordinate graph, and returns the coordinate graph to the second half-wave voltage obtaining unit 113 and the initial modulation voltage obtaining unit 114; the initial modulation voltage obtaining unit 114 finds an extreme point of the coordinate graph, an abscissa corresponding to the extreme point is the initial modulation voltage of the communication information transmitting terminal 2, the extreme point is a minimum value point or a maximum value point, the second half-wave voltage obtaining unit 113 finds the maximum value point and the minimum value point of the coordinate graph, and a difference value of second modulation voltages corresponding to adjacent maximum value points and minimum value points is used as the second half-wave voltage.
In one embodiment, the first determining module 120 includes:
the first photon sequence obtaining unit 121 sends a modulation instruction to the first phase modulator 12, and loads a logic signal in different combination forms of a first working voltage and a first half-wave voltage randomly on a single photon to perform phase modulation, so as to form a first photon sequence and obtain receiving end logic information of the communication information receiving end 1, where the receiving end logic information includes a basis vector and a classical bit of the first photon sequence;
the second photon sequence obtaining unit 122 sends a modulation instruction to the second phase modulator 21, the second phase modulator 21 receives the first photon sequence through a quantum channel, and randomly loads a logic signal in different combination forms of an initial modulation voltage and a second half-wave voltage on the first photon sequence for phase modulation to form a second photon sequence, the second detector 22 receives the second photon sequence to obtain sending end logic information, and the sending end logic information includes a classical bit, a basis vector and sending time of the second photon sequence;
the first determining unit 123 determines whether the basis vector of the communication information receiving terminal 1 corresponding to the sending time is the same as the basis vector of the communication information sending terminal 2, sends a signal to the second determining unit 124 if the basis vectors are the same, and sends a signal to the second determining module if the basis vectors are not the same;
the second judging unit 124 judges whether the classical bit of the communication information receiving terminal 1 is the same as the classical bit of the communication information transmitting terminal 2, and transmits a signal to the first statistical unit;
the first statistic unit 125 is configured to count the total number of single photons with the same basis vectors and the number of single photons with the same basis vectors and different classical bits;
the error rate obtaining unit 126 is configured to use a ratio of the number of single photons with the same basis vector and different classical bits counted by the first statistical unit to the total number of single photons with the same basis vector as an error rate;
the third judging unit 127 judges whether the bit error rate of the initialized quantum channel exceeds a threshold value, and if the bit error rate exceeds the threshold value, sends a signal to the second judging module; if the threshold value is not exceeded, a signal is sent to the first photon sequence obtaining unit 121.
In one embodiment, the second determining module 130 includes:
a second counting unit 131 for counting the total number of the single photons with different basis vectors and the number of the single photons with different basis vectors and same classical bits;
the first probability obtaining unit 132 is configured to use, as the first probability, a ratio of the number of single photons with the same classical bit to the number of single photons with different basis vectors among the single photons with different basis vectors;
an estimating unit 133 for estimating a voltage drift amount and a drift direction of the initial modulation voltage based on the first probability of the first probability obtaining unit, wherein the voltage drift amount is 1 when the first probability is 1
Figure GDA0002948421380000111
Wherein, Vhalf2The drift direction is a preset direction for the second half-wave voltage; when the first probability is 0, the voltage drift amount is
Figure GDA0002948421380000112
The drifting direction is opposite to the preset direction; when the first probability is 0.5, no drift exists; when the first probability is larger than 0.5 and smaller than 1, the voltage drift amount and the first probability are in a sinusoidal relation, so that the voltage drift amount corresponding to the first probability is obtained, and the drift direction is presetThe determined direction; when the first probability is larger than 0 and smaller than 0.5, the voltage drift amount and the first probability are in a sinusoidal relation, so that the voltage drift amount corresponding to the first probability is obtained, and the drift direction is opposite to the preset direction.
In one embodiment, the update module 140 includes:
a first updating unit 141, which uses the initial modulation voltage of the communication information sending end 2 as one end point of the modulation range according to the signal sent by the estimating unit, uses the sum of the initial modulation voltage and the estimated voltage drift amount as the other end point of the modulation range, and sends the sum to the second phase modulator 21 to perform fixed-step continuous phase modulation in the modulation range, wherein the positive and negative of the voltage drift amount are determined according to the drift direction, the drift direction is the same as the preset direction, and is positive, otherwise, the drift direction is negative;
the second updating unit 142 finds the modulation voltage corresponding to the new extreme point as a new modulation voltage through the second detector 22, the coordinate graph obtaining unit 115, and the initial modulation voltage obtaining unit 114 in the process that the second phase modulator 21 performs continuous phase modulation using the modulation voltage range of the first updating unit 141, and updates the initial modulation voltage.
In a preferred embodiment of the present invention, each constituent module of the compensation system of each of the above embodiments may be integrated into a quantum secure direct communication system, and may use the same divided functional module, or may use different divided functional modules, as shown in fig. 3, the compensation system includes a detection module 23 and a signal processing module 13, where:
the detection module 23 is arranged at the communication information sending end 2, and randomly selects a part of photons in the photon sequence of the received communication information receiving end 1 to perform security detection (eavesdropping detection);
the signal processing module 13, the quantum state decoding, and the signal post-processing, includes the initialization module 110, the first judgment module 120, the second judgment module 130, and the update module 140 in the above embodiments.
In addition, the communication information receiving terminal 1 is a light source generating terminal, and further includes:
single photon source module 11: a carrier (single photon) for generating information;
first phase modulator 12: preparing a series of phase single photon states and sending the photons to a communication information sending end 2;
a signal processing module 13;
the photon detection module 14: an avalanche photodiode single photon detector;
the first detector 15, which is used for the detection of the information sequence, does not function during the phase compensation process.
And the classical channel is used for classical information interaction such as interception detection and protocol execution condition confirmation.
The communication information transmitting end 2 further includes: the encoding module 24: sequentially encoding information for the rest photons in the received photon sequence of the communication information receiving end 1 except for a part of photons screened by the detection module to form an information sequence: and selecting unitary operation to act on the single photon state according to the fact that the classical information needing to be coded is 0 or 1.
Preferably, the communication information receiving end 1 further includes a first control circuit module 16, an electric control system matched with the optical path system of the communication information receiving end 1, a control timing sequence, an optical device, a result feedback, and the like; the communication information sending end 2 further includes a second control circuit module 25, an electric control system matched with the optical path system of the communication information sending end 2, a control timing sequence, an optical device, result feedback, and the like.
In one embodiment, a method is to adopt the phase compensation method of the present application, set the threshold of the bit error rate to 3%, when the bit error rate exceeds the set threshold, find the voltage drift direction and estimate the voltage drift amount, carry on the feedback compensation; in the other method, a fixed time interval is set for compensation in the prior art, the compensation process is 2 pi full-period scanning, the phase compensation and the error rate of the two methods within 17 minutes are shown in the following table 1,
TABLE 1
Figure GDA0002948421380000121
As can be seen from the above table, the bit error rate of the present application is much smaller than that of the prior art, and the compensation time is much shorter than that of the prior art, specifically:
first, the bit error rate (reliability) is the maximum bit error rate of the quantum secure direct communication system, and when the bit error rate exceeds a threshold, the security guarantee is lost when the system sends information. Therefore, the smaller the maximum value of the error rate of the system is, the higher the reliability is, and when the environment is changed violently for a certain period of time, the error rate exceeds the safety range before the next compensation is carried out by adopting a timing compensation method, so that the reliability of the system is reduced. If the backoff interval is shortened, the information transfer time is overwhelmed, the system efficiency is reduced, and the system error rate cannot be guaranteed to be below the threshold. It can be seen that the maximum value of the system error rate can be firmly controlled below the set threshold value by adopting the feedback mode of the invention, and the reliability is highest.
Secondly, in terms of compensation time (efficiency), each compensation process is a full-period scan at 2 pi phase, using existing methods. The method for counting the probability of the related data is utilized, the voltage drift direction can be found, the voltage drift amount can be estimated, and the scanning range can be obviously shortened to save the compensation time. The bit error rate threshold set in this embodiment is 3%, and the scanning time can be shortened to 5% or less of the original compensation time. And the quantum secure direct communication system can not transmit information in the compensation process, so the shorter the compensation time is, the higher the transmission efficiency of the system is. The transmission efficiency can be improved by shortening the compensation time.
Thirdly, in the engineering of the initialization of the whole system, the compensation voltage is found by utilizing a scanning method in a half-wave voltage range, and only the maximum value of the counting statistical result of the detector in the period of time needs to be found; compared with the scanning in the 2 pi phase period, the scanning detector counts the minimum value in the statistical time, and the initialization process saves 50% of the compensation time. For the amount of the phase modulation voltage that changes constantly with environmental changes, the shorter the scanning time, the more time-efficient the result obtained, and the lower the bit error rate. The measured data shows that the error rate can be strictly controlled below a set threshold value by adopting a feedback compensation method, and the reliability of the system is improved.
While the foregoing disclosure shows illustrative embodiments of the invention, it should be noted that various changes and modifications could be made herein without departing from the scope of the invention as defined by the appended claims. The methods, functions, steps and/or actions of the embodiments of the invention described herein, claimed herein need not be performed in any particular order. Furthermore, although elements of the invention may be described or claimed in the singular, the plural is contemplated unless limitation to a single element is explicitly stated.

Claims (4)

1. A phase compensation method for a quantum secure direct communication system, the quantum secure direct communication system including a communication information receiving end, a communication information transmitting end, and a quantum channel and a classical channel between the two ends, the phase compensation method comprising:
step S1, initializing the quantum secure direct communication system, and obtaining an initial modulation voltage of a communication information sending end, including:
setting a first working voltage of a communication information receiving end;
a single photon generated by a communication information receiving terminal is used as an information carrier;
obtaining a first half-wave voltage of a communication information receiving end, comprising: performing fixed-step continuous phase modulation on the single photon in a set phase range by adopting a first working voltage through a first phase modulator at a communication information receiving end to form a continuously-changed photon sequence and a corresponding continuously-changed first modulation voltage, wherein the phase range is in a set range of pi phase; the photon sequence is sent to a second detector of a communication information sending end through a quantum channel, and the second detector counts the received photon sequence; taking the count of the photon sequence received by the second detector as a vertical coordinate, and taking the first modulation voltage of the corresponding communication information receiving end as a horizontal coordinate to construct a coordinate graph; finding a maximum value point and a minimum value point of the coordinate graph, wherein the difference value of first modulation voltages corresponding to the adjacent maximum value point and minimum value point is a first half-wave voltage;
the method for obtaining the initial modulation voltage and the second half-wave voltage of the communication information sending terminal comprises the following steps: performing phase modulation on the single photon by adopting a first working voltage through a first phase modulator of a communication information receiving end to form a photon sequence, and sending the photon sequence to a communication information sending end through a quantum channel; receiving the photon sequence through a second phase modulator of an information sending end, and carrying out fixed-step continuous phase modulation on the received photon sequence in a set phase range to obtain a continuously-changed photon sequence and a corresponding continuously-changed second modulation voltage, wherein a second detector receives and counts the continuously-changed photon sequence, and the phase range is in a set range of pi phase; taking the count of a second detector of the communication information sending end as a vertical coordinate, and taking a second modulation voltage of the corresponding communication information sending end as a horizontal coordinate to construct a coordinate graph; finding an extreme point of a coordinate graph, wherein an abscissa corresponding to the extreme point is an initial modulation voltage of a communication information sending end, the extreme point is a minimum value point or a maximum value point, and a second half-wave voltage of the communication information sending end is a difference value of second modulation voltages corresponding to an adjacent maximum value point and the minimum value point in the coordinate graph;
step S2, generating a photon sequence through the initial modulation voltage phase modulation, obtaining the error rate of a quantum channel according to the transmission of the photon sequence between a communication information receiving end and a communication information sending end, and judging whether the error rate exceeds a threshold value;
step S3, if not, returning to step S2;
step S4, if the threshold is exceeded, determining the drift direction of the initial modulation voltage and estimating the voltage drift amount by using the photon sequence sent by the communication information receiving terminal and the basis vector and the classical bit of the photon sequence returned by the communication information receiving terminal, including:
screening out single photons with different base vectors from a communication information sending end and a communication information receiving end;
obtaining a first probability, wherein the proportion of the number of single photons with the same classical bits in the number of single photons with different basis vectors is used as the first probability;
when the first probability is 1, the voltage drift amount is
Figure FDA0002948421370000021
Wherein, Vhalf2The drift direction is a preset direction for the second half-wave voltage of the communication information sending end;
when the first probability is 0, the voltage drift amount is
Figure FDA0002948421370000022
The drifting direction is opposite to the preset direction;
when the first probability is 0.5, no drift exists;
when the first probability is larger than 0.5 and smaller than 1, the voltage drift amount and the first probability are in a sinusoidal relation, so that the voltage drift amount corresponding to the first probability is obtained, and the drift direction is a preset direction;
when the first probability is larger than 0 and smaller than 0.5, the voltage drift amount and the first probability are in a sinusoidal relation, so that the voltage drift amount corresponding to the first probability is obtained, and the drift direction is opposite to the preset direction;
step S5, the communication information sending end performs a fixed step scan to reduce the range according to the drift direction of the initial modulation voltage and the estimated voltage drift amount, to obtain a new modulation voltage of the communication information sending end, including:
taking the initial modulation voltage of a communication information sending end as an end point of a modulation range;
taking the sum of the initial modulation voltage and the estimated voltage drift value as the other end point of the modulation range;
scanning extreme points of the statistical number of the second detector by adopting a set step length in the modulation range, wherein the modulation voltage corresponding to the extreme points is used as a new modulation voltage;
in step S6, a new modulation voltage is applied to the transmission end of the communication information, and the process returns to step S2.
2. The phase compensation method according to claim 1, wherein the bit error rate obtaining method comprises:
a single photon is generated by a communication information receiving terminal and used as an information carrier, logic signals in different combination forms of a first working voltage and a first half-wave voltage are loaded on the single photon randomly for phase modulation, a first photon sequence is formed, receiving terminal logic information of the communication information receiving terminal is obtained, and the receiving terminal logic information comprises a basis vector and a classical bit of the first photon sequence;
the first photon sequence is sent to a communication information sending end through a quantum channel;
loading logic signals in different combination forms of initial modulation voltage and second half-wave voltage on the first photon sequence randomly through a second modulator of a communication information sending end to perform phase modulation to form a second photon sequence, receiving the second photon sequence by a second detector to obtain sending end logic information, wherein the sending end logic information comprises classical bits, basis vectors and sending time of the second photon sequence;
a communication information receiving end receives the logic information of the sending end and finds out the corresponding logic information of the receiving end according to the sending time of the logic information of the sending end;
screening out single photons of which the basis vectors of the communication information receiving end and the communication information sending end are the same, wherein the basis vectors correspond to the sending time;
screening out single photons with different classical bits of a communication information receiving end and classical bits of a communication information sending end from the single photons with the same basic vector;
and obtaining the error rate, wherein the proportion of the number of the single photons with different classical bits to the number of the single photons with the same basis vector is used as the error rate.
3. A phase compensation system for a quantum secure direct communication system, the quantum secure direct communication system comprising a communication information receiving end, a communication information transmitting end, and a quantum channel and a classical channel between the two ends, the phase compensation system comprising:
the initialization module initializes the quantum secure direct communication system and obtains an initial modulation voltage of a communication information sending end;
the first judgment module generates a photon sequence through the initial modulation voltage phase modulation, obtains the bit error rate of the quantum channel according to the transmission of the photon sequence between the communication information receiving end and the communication information sending end, judges whether the bit error rate of the initialized quantum channel exceeds a threshold value or not, and continuously monitors the bit error rate of the initialized quantum channel if the bit error rate of the initialized quantum channel does not exceed the threshold value; if the threshold value is exceeded, sending a signal to a second judgment module;
the second judgment module is used for judging the drift direction of the initial modulation voltage and estimating the voltage drift amount by utilizing the photon sequence sent by the communication information receiving terminal and the basis vector and the classical bit of the photon sequence returned by the communication information receiving terminal;
the updating module is used for scanning the fixed step length with a reduced range according to the drift direction of the initial modulation voltage of the second judging module and the estimated voltage drift amount, updating the initial modulation voltage of the communication information sending end, sending a signal to the first judging module, and judging whether the error rate of the quantum channel initialized by the updated initial modulation voltage of the communication information sending end exceeds a threshold value or not;
wherein, the communication information receiving end includes:
the single photon source module is used for generating single photons as an information carrier;
the first phase modulator is used for carrying out phase modulation on the single photon generated by the single photon source module to form a photon sequence;
the communication information transmitting end includes:
the second phase modulator is used for carrying out phase modulation on the photon sequence of the communication information receiving end;
a second detector for counting the received photon sequence;
the initialization module comprises a setting unit, a first half-wave voltage obtaining unit, a second half-wave voltage obtaining unit, an initial modulation voltage obtaining unit and a coordinate graph obtaining unit, wherein:
the setting unit is used for setting a first working voltage and sending the first working voltage to a communication information receiving end, and setting a phase range to the communication information receiving end and a communication information sending end, wherein the phase range is within a set range of pi phase;
the first half-wave voltage obtaining unit sends a continuous phase modulation instruction to the first phase modulator and sends a receiving instruction to the second detector, so that the first phase modulator performs fixed-step continuous phase modulation on the single photon within a set phase range by adopting a first working voltage to form a continuously-changed photon sequence and a corresponding continuously-changed first modulation voltage; the second detector receives the photon sequence and counts, the coordinate graph obtaining unit takes the count of the second detector as a vertical coordinate, the corresponding first modulation voltage is a horizontal coordinate, a coordinate graph is constructed, the coordinate graph is returned to the first half-wave voltage obtaining unit, a maximum value point and a minimum value point of the coordinate graph are found, and the difference value of the first modulation voltage corresponding to the adjacent maximum value point and the adjacent minimum value point is the first half-wave voltage;
the second half-wave voltage obtaining unit is used for sending a phase modulation command to the first phase modulator and sending a continuous phase modulation command to the second phase modulator, wherein the first phase modulator is used for carrying out phase modulation on the single photons by adopting a first working voltage to form a photon sequence and sending the photon sequence to the second phase modulator through a quantum channel; the second phase modulator carries out fixed-step continuous phase modulation on the received photon sequence within a set phase range to obtain a continuously-changed photon sequence and a corresponding continuously-changed second modulation voltage; a second detector receives the continuously varying photon sequence and counts; the coordinate graph obtaining unit takes the count of a second detector of the communication information sending end as a vertical coordinate, the corresponding second modulation voltage is a horizontal coordinate, a coordinate graph is constructed, and the coordinate graph is returned to the second half-wave voltage obtaining unit and the initial modulation voltage obtaining unit; the initial modulation voltage obtaining unit finds an extreme point of a coordinate graph, an abscissa corresponding to the extreme point is the initial modulation voltage of a communication information sending end, and the extreme point is a minimum value point or a maximum value point; the second half-wave voltage obtaining unit finds a maximum value point and a minimum value point of the coordinate graph, and takes the difference value of second modulation voltages corresponding to the adjacent maximum value point and minimum value point as a second half-wave voltage;
wherein the second judging module comprises:
the second statistical unit is used for counting the total number of the single photons with different basis vectors and the number of the single photons with different basis vectors and same classical bits;
the first probability obtaining unit is used for taking the proportion of the number of single photons with the same classical bit in the number of single photons with different basis vectors as a first probability;
an estimating unit estimating a voltage drift amount and a drift direction of the initial modulation voltage according to the first probability of the first probability obtaining unit, wherein the voltage drift amount is 1 when the first probability is 1
Figure FDA0002948421370000041
Wherein, Vhalf2The drift direction is a preset direction for the second half-wave voltage; when the first probability is 0, the voltage drift amount is
Figure FDA0002948421370000042
The drifting direction is opposite to the preset direction; when the first probability is 0.5, no drift exists; when the first probability is larger than 0.5 and smaller than 1, the voltage drift amount and the first probability are in a sinusoidal relation, so that the voltage drift amount corresponding to the first probability is obtained, and the drift direction is a preset direction; when the first probability is larger than 0 and smaller than 0.5, the voltage drift amount and the first probability are in a sinusoidal relation, so that the voltage drift amount corresponding to the first probability is obtained, and the drift direction is opposite to the preset direction;
wherein the update module comprises:
the first updating unit is used for taking the initial modulation voltage of the communication information sending end as one end point of a modulation range according to the signal sent by the estimating unit, taking the sum of the initial modulation voltage and the estimated voltage drift amount as the other end point of the modulation range, and sending the sum to the second phase modulator to perform fixed-step continuous phase modulation in the modulation range, wherein the positive and negative of the value of the voltage drift amount are determined according to the drift direction, and the drift direction is positive when the drift direction is the same as the preset direction, otherwise, the drift direction is negative;
and the second updating unit finds the modulation voltage corresponding to the new extreme value point as a new modulation voltage through the second detector, the coordinate graph obtaining unit and the initial modulation voltage obtaining unit in the process that the second phase modulator adopts the modulation voltage range of the first updating unit to perform continuous phase modulation, and updates the initial modulation voltage.
4. The phase compensation system of claim 3, wherein the first determining module comprises:
the first photon sequence obtaining unit sends a modulation instruction to the first phase modulator, and loads logic signals in different combination forms of a first working voltage and a first half-wave voltage on the single photon randomly for phase modulation to form a first photon sequence and obtain receiving end logic information of a communication information receiving end, wherein the receiving end logic information comprises a basis vector and a classical bit of the first photon sequence;
the second photon sequence obtaining unit is used for sending a modulation instruction to the second phase modulator, the second phase modulator receives the first photon sequence through a quantum channel, logic signals in different combination forms of initial modulation voltage and second half-wave voltage are loaded on the first photon sequence randomly for phase modulation, a second photon sequence is formed, the second detector receives the second photon sequence, and sending end logic information is obtained, wherein the sending end logic information comprises classical bits, basis vectors and sending time of the second photon sequence;
the first judging unit is used for judging whether the basis vector of the communication information receiving end corresponding to the sending time is the same as the basis vector of the communication information sending end or not, sending a signal to the second judging unit if the basis vectors are the same, and sending a signal to the second judging module if the basis vectors are different;
the second judging unit judges whether the classical bit of the communication information receiving end is the same as the classical bit of the communication information sending end, and sends a signal to the first statistical unit;
the first statistic unit is used for counting the total number of single photons with the same basis vectors and the number of single photons with the same basis vectors and different classical bits;
the error rate obtaining unit is used for taking the ratio of the number of single photons with the same basis vector and different classical bits counted by the first statistic unit to the total number of single photons with the same basis vector as the error rate;
the third judgment unit judges whether the bit error rate of the initialized quantum channel exceeds a threshold value or not, and sends a signal to the second judgment module if the bit error rate of the initialized quantum channel exceeds the threshold value; and if the threshold value is not exceeded, sending a signal to the first photon sequence obtaining unit.
CN202010151097.1A 2020-03-06 2020-03-06 Phase compensation method and system for quantum secure direct communication system Active CN111200494B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202010151097.1A CN111200494B (en) 2020-03-06 2020-03-06 Phase compensation method and system for quantum secure direct communication system

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202010151097.1A CN111200494B (en) 2020-03-06 2020-03-06 Phase compensation method and system for quantum secure direct communication system

Publications (2)

Publication Number Publication Date
CN111200494A CN111200494A (en) 2020-05-26
CN111200494B true CN111200494B (en) 2021-07-09

Family

ID=70746658

Family Applications (1)

Application Number Title Priority Date Filing Date
CN202010151097.1A Active CN111200494B (en) 2020-03-06 2020-03-06 Phase compensation method and system for quantum secure direct communication system

Country Status (1)

Country Link
CN (1) CN111200494B (en)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113676322B (en) * 2021-10-22 2022-01-07 国开启科量子技术(北京)有限公司 Method and device for reducing QKD system error rate

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108988953A (en) * 2017-06-02 2018-12-11 科大国盾量子技术股份有限公司 A kind of phase feedback approach and controller
CN109039592A (en) * 2017-06-12 2018-12-18 科大国盾量子技术股份有限公司 Fast polarization feedback control method and device
WO2020030847A1 (en) * 2018-08-10 2020-02-13 Nokia Technologies Oy Fibre-based communication

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4888630B2 (en) * 2005-07-08 2012-02-29 日本電気株式会社 Communication system and supervisory control method thereof
CN101630975A (en) * 2008-07-16 2010-01-20 华为技术有限公司 Method and device for controlling bias voltage of photomodulator
CN102868520B (en) * 2012-08-28 2015-10-14 上海交通大学 Continuous variable quantum key distribution system and phase compensating method thereof
CN103178954B (en) * 2013-03-12 2016-01-06 华南师范大学 A kind of method measuring confidence level for improving half-wave voltage of phase modulator
CN106254071B (en) * 2016-09-27 2019-05-14 四川航天机电工程研究所 A kind of real-time phase compensation system and method for quantum key distribution
KR102409883B1 (en) * 2017-12-07 2022-06-22 칸도우 랩스 에스에이 Decision feedback equalization correction of eye scope measurements
CN108768637B (en) * 2018-06-01 2021-03-19 华南师范大学 Quantum key distribution interference ring intermittent phase compensation control method and system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108988953A (en) * 2017-06-02 2018-12-11 科大国盾量子技术股份有限公司 A kind of phase feedback approach and controller
CN109039592A (en) * 2017-06-12 2018-12-18 科大国盾量子技术股份有限公司 Fast polarization feedback control method and device
WO2020030847A1 (en) * 2018-08-10 2020-02-13 Nokia Technologies Oy Fibre-based communication

Also Published As

Publication number Publication date
CN111200494A (en) 2020-05-26

Similar Documents

Publication Publication Date Title
CN106712940B (en) Quantum key distribution system and method irrelevant to measurement and equipment
CN107733640B (en) Continuous variable quantum key distribution method based on continuous random measurement basis
US10879932B2 (en) Encoding method and device, and apparatus
CN111200494B (en) Phase compensation method and system for quantum secure direct communication system
CN111082938B (en) Method and device for improving quantum key distribution system code rate
Wu et al. On joint communication and channel discrimination
EP3656079B1 (en) Quantum key distribution communication devices, methods and systems
CN112996099B (en) Method for transmitting and receiving polarized time slot ALOHA resisting time slot deletion
Abdallah et al. Adaptive discrete rate and power transmission for spectrum sharing systems
Song et al. Efficient direct detection of M-PAM sequences with implicit CSI acquisition for the FSO system
Shevchuk et al. Efficient encoding and transmission of monitoring data in information-efficient wireless networks
CN115834046A (en) Reference system independent quantum key distribution method with light source monitoring function
WO2023057366A1 (en) A method for a transmitter to transmit a signal to a receiver in a communication system, and corresponding receiving method, transmitter, receiver and computer program.
Jin et al. Insights into the stable recovery of sparse solutions in overcomplete representations using network information theory
CN113132093B (en) Quantum key distribution method and node
US10567088B2 (en) Optical noise removal circuit, optical receiver, and optical chip
CN109660320B (en) Network end-to-end error control transmission method and device and electronic equipment
Winter et al. A lattice-reduction aided vector perturbation precoder relying on quantum annealing
Wang et al. Blind recognition of (n, k, m) convolutional code based on local decision in a noisy environment
KR102178275B1 (en) Apparatus and method for estimating interleaving period
JP4509530B2 (en) Quantum cryptography communication method
Wang et al. Role of feedback in modulo-sum computation over K-user erasure multiple-access channels
Lim et al. Nonuniform encoding and hybrid decoding schemes for equal error protection of rateless codes
KR20090095413A (en) Low density parity check encoding apparatus and method thereof
Annafianto et al. Experimental shot-by-shot estimation of quantum measurement accuracy

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination
GR01 Patent grant
GR01 Patent grant