CN116599654A - System and method for quantum secure direct communication based on continuous variable - Google Patents
System and method for quantum secure direct communication based on continuous variable Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- 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
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- H—ELECTRICITY
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- 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
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- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
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Abstract
The invention relates to a quantum secure direct communication system and method based on continuous variable, which prepares entangled light beams with mutually orthogonal polarization states through a continuous variable entangled state light source and a polarizer, a transmitting end and a receiving end select continuous variable entangled quanta, and a data transmitting end respectively transmits the continuous variable quanta on different paths within a period of time by controlling an optical switch according to the bits required to be transmitted, so that the polarization states of the continuous variable quanta are rotated by 90 degrees or kept unchanged; the data receiving end divides the input continuous variable quantum into two beams through the polarization beam splitter, the continuous variable quantum with the polarization state rotated by 90 degrees or kept unchanged is detected by the optical power detector respectively, and the signal intensity detected by the optical power detector is compared to obtain a transmitted bit signal. The data receiver directly measures the polarization state of the light quantum to acquire the transmission bit, and the information transmission does not directly pass through the communication line, so that the attacker can be effectively prevented from intercepting the data on the communication line, and the safe transmission of the information is realized.
Description
Technical Field
The invention relates to the technical field of quantum communication, in particular to a system and a method for quantum safety direct communication based on continuous variables.
Background
Optical communication networks have become the most dominant communication network, and optical communication networks also face more and more serious network security problems when providing users with a high-capacity and high-bandwidth communication mode, wherein how to ensure that communication information is not eavesdropped, copied, and counterfeited, and realizing secure information communication becomes a great challenge. By utilizing the quantum mechanics principle and various quantum characteristics, the safety of communication information can be effectively ensured by realizing quantum communication.
Along with the maturation of quantum communication technology, a great deal of applications at present mainly focus on single photon-based measurement technology, realize the generation and the transmission of quantum secret key, and encrypt information with quantum secret key and transmit through classical information channel, realize secret communication. The scheme has high cost, technical realization difficulty and high requirements on the quantum transmission channel. The quantum communication method based on continuous variables has better compatibility with the existing optical communication technology, and related optical devices have universality, can realize the advantage of higher communication signal-to-noise ratio, and have better anti-interference capability; however, techniques and studies for achieving secure direct communication using a large number of photons, i.e., continuous variable techniques, are not yet common and have not yet been put into practical use. The quantum secure direct communication refers to a method for directly transmitting effective information, particularly confidential information, between two communication parties through a quantum channel by taking a quantum state as an information carrier and utilizing a quantum mechanics principle and various quantum characteristics. The quantum secure direct communication based on continuous variables does not need to generate a quantum key, and the secret information is transmitted safely and directly, so that the communication efficiency is improved, and the adaptability of an optical communication channel is also improved. Similar to quantum communication cryptography, the security of quantum secure direct communication is also ensured by uncertainty relation and irreproducibility in quantum mechanics, association and delocalization of entangled photons, and the like, and the security is reflected in that an eavesdropper cannot obtain any confidential information. Unlike quantum key distribution, which requires that an eavesdropper be detected and the communication process abandoned, quantum secure direct communication is performed with information, which requires that the information cannot be revealed, the quantum secure direct communication is higher than quantum key distribution. Thus, quantum secure direct communication methods can be used for the distribution of quantum keys and vice versa.
Quantum secure direct communication needs to meet two requirements: 1. after receiving the quantum state as the information carrier, the receiver can directly read out the confidential information sent by the sender without exchanging additional classical auxiliary information with the sender; 2. even if an eavesdropper eavesdrops on the quantum channel, no confidential information is obtained.
The quantum secure direct communication method based on continuous variables mainly comprises the following steps: ping-Pong quantum secure direct communication protocol, two-step quantum secure direct communication protocol, single photon based QSDC protocol, etc. However, the above communication methods all require measurement results of mutually interacted light quanta of the receiving and transmitting parties of the data, and transmission of the measurement results is accomplished through classical communication channels. By adopting the methods, the transmission process of the data can be completed by mutual negotiation between the sender and the receiver, and the negotiation process has the safety problem that the information is cracked and tampered, thereby influencing the safety of quantum secure direct communication.
Disclosure of Invention
The invention aims to provide a system and a method for quantum secure direct communication based on continuous variables, which effectively avoid the problem that data is intercepted on a communication line and realize the secure transmission of information.
In order to solve the technical problems, the technical scheme of the invention is as follows:
in a first aspect, a system for quantum secure direct communication based on continuous variables is provided, comprising:
continuous variable entangled state light source: for preparing entangled beams of mutually orthogonal polarization states;
polarizer: for obtaining linearly polarized light from the entangled beam;
and the data transmitting end: the device comprises a first circular polarization filter, a first polarization beam splitter, a first polarization controller, a controllable light switch and a second polarization controller which are sequentially connected; the second polarization controller is also connected with a data source;
the first polarization beam splitter outputs from the polarizer after the continuous variable entangled state light source, and selects one beam from the light beams passing through the first circular polarization filter and transmits the selected beam to the first polarization controller, the first polarization controller rotates the polarization state of the received light beam by 90 degrees and transmits the received light beam to the controllable optical switch, the controllable optical switch reads bits to be transmitted from the data source, and the controllable optical switch switching position is controlled according to the bits to be transmitted, so that the polarization state of the light beam passing through the controllable optical switch is kept unchanged or the polarization state of the light beam passing through the second polarization controller is rotated by 90 degrees;
and the data receiving end: the device comprises a second circular polarization filter, a second polarization beam splitter, a third polarization beam splitter and a fourth polarization beam splitter which are sequentially connected, wherein two output ends of the fourth polarization beam splitter are respectively connected with an optical power detector;
the second polarization beam splitter outputs from the continuous variable entangled state light source, and selects one beam from the light beams passing through the second circular polarization filter and transmits the selected beam to the third polarization beam splitter, the third polarization beam splitter selects one beam from the received light beams and transmits the selected beam to the fourth polarization beam splitter, the fourth polarization beam splitter divides the received photon beam into two beams and transmits the two beams to the two optical power detectors respectively, and then the output of the two optical power detectors is compared by the signal processor to determine bit signals sent by the data sending end;
wherein, the light beam received by the first polarization controller and the light beam received by the third polarization beam splitter are in an entangled state; the light beam received by the controllable light switch and the light beam received by the fourth polarization beam splitter are in an entangled state. Further, in the system, the continuous variable entangled-state light source transmits one beam of the entangled-beam pair to the data transmitting end through the polarizer and the first single-mode fiber channel;
in the system, a continuous variable entangled state light source transmits the other beam of the entangled beam pair to a data receiving end through a second single-mode optical fiber channel;
the second single mode fiber channel has a length greater than the length of the first single mode fiber channel.
Further, the first polarization beam splitter is connected with the first polarization controller, and the first polarization controller is connected with the controllable optical switch through polarization maintaining optical fibers.
Further, the data transmitting end further comprises a first laser terminator and a second laser terminator, and the first polarization beam splitter transmits the separated light beams which are not transmitted to the first polarization controller to the first laser terminator;
one output end of the controllable optical switch is connected to the second laser terminator through the polarization maintaining optical fiber, and the other output end of the controllable optical switch is connected to the second laser terminator through the second polarization controller.
Further, the data receiving end further comprises a third laser terminator, and the second polarization beam splitter transmits the separated light beams which are not transmitted to the third polarization beam splitter to the third laser terminator; and the third polarization beam splitter transmits the separated light beams which are not transmitted to the fourth polarization beam splitter to the third laser terminator.
Further, the signal processor at the receiving end, the controllable optical switch at the transmitting end and the data source are all calibrated and synchronized by the GPS clock.
In a second aspect, a method for quantum secure direct communication based on continuous variables is provided, using the above system, the method steps comprising:
step S100: preparing entangled light beams with mutually orthogonal polarization states through a continuous variable entangled state light source, obtaining linearly polarized light by one light beam through a polarizer, transmitting the linearly polarized light to a transmitting end through an optical fiber, and transmitting the other light beam to a receiving end through the optical fiber;
step S200: the transmitting end filters out circular polarization of the received light beam through a circular polarization filter, and the linear polarization light beam of the transmitting end is reserved; the method comprises the steps that a transmitting end linear polarized light beam passes through a first polarization beam splitter to select a light beam with a certain polarization direction, and then enters a first polarization controller;
step S300: the receiving end filters out circular polarization of the received light beam through a circular polarization filter, and the linear polarization light beam of the transmitting end is reserved; selecting a light beam which is in an entangled state with the light beam input into the first polarization controller by the transmitting end from the receiving end linear polarization light beam through the second polarization beam splitter;
step S400: the transmitting end rotates the polarization direction of the light beam by 90 degrees through the first polarization controller, and then inputs the light beam into the controllable optical switch;
step S500: the receiving end selects a light beam which is in an entangled state with the light beam input by the light switch of the transmitting end from the light beams transmitted by the second polarization beam splitter through the third polarization beam splitter;
step S600: the transmitting end controls the controllable optical switch according to the bit to be transmitted, so that the light beams are transmitted on different paths within a period of time respectively, and the polarization state is kept unchanged or rotated by 90 degrees through the second polarization controller;
step S700: the receiving end divides the light beam output from the third polarization beam splitter into two beams through the fourth polarization beam splitter, and respectively converts the two input light beams into voltage signals and then performs polarization state measurement so as to determine the bit signal sent by the data sending end.
Further, in step S200 and step S300, continuous variable entanglement quanta for loading transmission data are preliminarily selected through the first polarizing beam splitter at the transmitting end and the second polarizing beam splitter at the receiving end; in step S400 and step S500, photons in an un-entangled state are filtered by a first polarization controller at the transmitting end and a third polarization beam splitter at the receiving end.
Further, the step S600 specifically includes:
the controllable optical switch reads the bits to be transmitted;
if the read bit is 1, the position of the controllable optical switch is changed over to enable the light beam output by the first polarization controller to be transmitted to the second polarization controller, so that the polarization state of the light beam is rotated by 90 degrees;
if the read bit is 0, the position of the controllable optical switch is changed to enable the light beam output by the first polarization controller to be transmitted to the polarization maintaining optical fiber, so that the polarization state of the light beam is kept unchanged.
Further, the step S700 specifically includes:
the fourth polarization beam splitter splits the received light beam into two beams, one beam is consistent with the polarization direction of the light beam transmitted by the third polarization beam splitter, and the two beams are converted into a voltage signal V through the optical power detector 1 The other beam is rotated by 90 DEG in polarization direction and converted into a voltage signal V by an optical power detector 2 ；
Comparing the output power of the optical power detectors at the same moment;
if V is detected 1 Greater than V 2 The light beam input into the second laser terminator in the data transmitting end is determined to be unchanged in polarization state, and the bit transmitted by the data transmitting end is determined to be 0;
if V is detected 2 Greater than V 1 The polarization state of the light beam input into the second laser terminator in the data transmitting end is determined to be rotated by 90 degrees, and the bit transmitted by the data transmitting end is determined to be 1;
if V is detected 2 Equal to V 1 And determining invalid data and discarding the detection result.
The invention has the following beneficial effects:
1. based on the quantum entanglement principle, the invention realizes quantum secure direct communication through a continuous variable quantum entanglement technology, and realizes transmission bit acquisition by directly measuring the state (polarization state) of light quanta by a data receiver, thereby acquiring data information transmitted by a transmitting end; meanwhile, the measurement result of the receiver does not need to be told to the sender through other communication modes; because the information is transmitted not directly through the communication line, the invention can effectively avoid the attacker from intercepting the data on the communication line, and realize the safe transmission of the information;
the invention can realize the transmission of the optical signal through the common optical fiber by utilizing the uncertainty relation and the irreproducibility of the quantum mechanics and the relevance and the delocalization equivalent sub-characteristics of entangled photons, and the optical signal does not contain any valuable information in the transmission process, and any eavesdropping action can not cause information leakage; the invention can realize direct secret communication on a conventional optical fiber communication link, can also be used for transmission of encryption keys, and provides a good platform for safe communication of data;
2. according to the invention, through a quantum technology based on continuous variables, the signal strength of a received signal is improved, and the signal to noise ratio of communication is improved, so that the recognition capability of the signal is improved, and meanwhile, the influence of interference on quantum measurement is reduced; in addition, according to the characteristics of continuous variables, the invention adopts a polarizer and a circular polarization filter, so that signal interference is avoided;
3. the invention can select different light quanta to load information by changing the internal structure of the sending end device and the receiving end device, thus increasing the difficulty of an attacker to attack the transmitted information.
Drawings
FIG. 1 illustrates a block diagram of a system for continuous variable based quantum secure direct communication in an embodiment of the present disclosure;
fig. 2 illustrates a flow chart of a method of quantum secure direct communication based on continuous variables in an embodiment of the present disclosure.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Referring to fig. 1, the present invention is a system for quantum secure direct communication based on continuous variables, comprising: a continuous variable entangled state light source, a polarizer, a data transmitting end and a data receiving end;
continuous variable entangled state light source: for preparing entangled beams of mutually orthogonal polarization states;
a polarizer for obtaining linearly polarized light from the light beam;
in the embodiment of the disclosure, a continuous variable entangled-state light source transmits a beam of entangled-state light beams to a data transmitting end through a polarizer and a first single-mode fiber channel; transmitting the other beam of the entangled-state light beam to the data receiving end by the continuous variable entangled-state light source through the second single-mode fiber channel; the second single mode fiber channel has a length greater than the length of the first single mode fiber channel.
In the embodiment of the disclosure, since the entangled-state light source based on continuous variable is adopted, the two output light beams are entangled, so that after the light beam input by the transmitting end obtains linear polarized light by adopting the polarizer, the light beam at the receiving end is also converted into linear polarized light, and therefore, only one end adopts the polarizer.
And the data transmitting end: the device comprises a first circular polarization filter, a first polarization beam splitter, a first polarization controller, a controllable light switch and a second polarization controller which are sequentially connected; the second polarization controller is also connected with a data source; the first circular polarization filter is used for filtering circular polarization generated in transmission, and after linear polarized light is transmitted through the optical fiber, certain possibility is changed into circular polarization, and the reasons include non-uniformity in the optical fiber, influence of external environment and the like, so that the linear polarized light is filtered by the circular polarization filter;
the first polarization beam splitter outputs from a continuous variable entangled state light source, selects one beam from the light beams passing through the polarizer and the first circular polarization filter, transmits the light beams to the first polarization controller, rotates the polarization state of the received light beams by 90 degrees, and transmits the light beams to the controllable optical switch, the controllable optical switch reads bits to be transmitted from a data source, and controls the switching position of the controllable optical switch according to the bits to be transmitted, so that the polarization state of the light beams passing through the controllable optical switch is kept unchanged or the polarization state of the light beams passing through the second polarization controller is rotated by 90 degrees;
in the embodiment of the disclosure, the first polarization beam splitter is connected with the first polarization controller through a first polarization maintaining fiber, and the first polarization controller is connected with the controllable optical switch through a second polarization maintaining fiber.
In the embodiment of the disclosure, the data transmitting end further comprises a first laser terminator and a second laser terminator, and the first polarization beam splitter transmits the separated light beams which are not transmitted to the first polarization controller to the first laser terminator; one output end of the controllable optical switch is connected to the second laser terminator through a third polarization maintaining fiber, and the other output end of the controllable optical switch is connected to the second laser terminator through a second polarization controller.
And the data receiving end: the device comprises a second circular polarization filter, a second polarization beam splitter, a third polarization beam splitter and a fourth polarization beam splitter which are sequentially connected, wherein two output ends of the fourth polarization beam splitter are respectively connected with an optical power detector; wherein the second circular polarization filter is used for filtering circular polarization generated in transmission;
the second polarization beam splitter outputs from the continuous variable entangled state light source, and selects one beam from the light beams passing through the second circular polarization filter and transmits the selected beam to the third polarization beam splitter, the third polarization beam splitter selects one beam from the received light beams and transmits the selected beam to the fourth polarization beam splitter, the fourth polarization beam splitter divides the received photon beam into two beams and transmits the two beams to the two optical power detectors respectively, and then the output of the two optical power detectors is compared by the signal processor to determine bit signals sent by the data sending end;
wherein, the light beam received by the first polarization controller and the light beam received by the third polarization beam splitter are in an entangled state; the light beam received by the controllable light switch and the light beam received by the fourth polarization beam splitter are in an entangled state.
In the embodiment of the disclosure, the data receiving end further includes a differential amplifier, and the output of the optical power detector is connected to the differential amplifier to amplify the signal and output to the signal processor.
In an embodiment of the disclosure, the data receiving end further includes a third laser terminator, and the second polarization beam splitter transmits the split light beam which is not transmitted to the third polarization beam splitter to the third laser terminator; and the third polarization beam splitter transmits the separated light beams which are not transmitted to the fourth polarization beam splitter to the third laser terminator.
In the embodiment of the disclosure, a receiving end signal processor, a transmitting end controllable optical switch and a data source are all calibrated and synchronized by a GPS clock; the GPS in the working state sends the timing information to the signal processor of the receiving end, the controllable optical switch of the sending end and the data source, so that all the systems operate in the same physical time, and the synchronization of data sending and data receiving processing is ensured.
Referring to fig. 2, the invention further provides a method for quantum secure direct communication based on continuous variables, and the method comprises the following steps:
step S100: preparing entangled light beams with mutually orthogonal polarization states through a continuous variable entangled state light source, obtaining linearly polarized light by one light beam through a polarizer, transmitting the linearly polarized light to a transmitting end through an optical fiber, and transmitting the other light beam to a receiving end through the optical fiber;
step S200: the transmitting end filters out circular polarization of the received light beam through a first circular polarization filter, and the linear polarization light beam of the transmitting end is reserved; the method comprises the steps that a transmitting end linear polarized light beam passes through a first polarization beam splitter to select a light beam with a certain polarization direction, and then enters a first polarization controller;
step S300: the receiving end filters out circular polarization of the received light beam through a circular polarization filter, and the linear polarization light beam of the transmitting end is reserved; selecting a light beam which is in an entangled state with the light beam input into the first polarization controller by the transmitting end from the receiving end linear polarization light beam through the second polarization beam splitter;
step S400: the transmitting end rotates the polarization direction of the light beam by 90 degrees through the first polarization controller, and then inputs the light beam into the controllable optical switch;
step S500: the receiving end selects a light beam which is in an entangled state with the light beam input by the light switch of the transmitting end from the light beams transmitted by the second polarization beam splitter through the third polarization beam splitter;
step S600: the transmitting end controls the controllable optical switch according to the bit to be transmitted, so that the light beams are transmitted on different paths within a period of time respectively, and the polarization state is kept unchanged or rotated by 90 degrees through the second polarization controller;
step S700: the receiving end divides the light beam output from the third polarization beam splitter into two beams through the fourth polarization beam splitter, and respectively converts the two input light beams into voltage signals and then performs polarization state measurement so as to determine the bit signal sent by the data sending end.
In the embodiment of the disclosure, in step S200 and step S300, continuous variable entanglement quanta for loading transmission data are preliminarily selected through a first polarization beam splitter at a transmitting end and a second polarization beam splitter at a receiving end;
in step S400 and step S500, photons in an un-entangled state are filtered by a first polarization controller at a transmitting end and a third polarization beam splitter at a receiving end;
in step S600 and step S700, the data transmitting end respectively transmits continuous variable quanta on different paths within a period of time or rotates the polarization state of the continuous variable quanta by 90 degrees or keeps unchanged by controlling the optical switch according to the bits to be transmitted; the data receiving end divides the input continuous variable quantum into two beams through the polarization beam splitter, detects the continuous variable quantum with the polarization state rotated by 90 degrees and the continuous variable quantum with the polarization state kept unchanged by using 2 optical power detectors respectively, and obtains a transmitting bit signal by comparing the signal intensities detected by the optical power detectors.
The respective steps in fig. 2 are specifically described below.
In step S100, a pair of entangled beams b having polarization states orthogonal to each other are generated by a continuously variable entangled-state light source Hair brush And b Collecting and recovering Subscript is the beam number; b of entangled beam pair Hair brush B in entangled beam pair distributed to data transmitting end by polarizer and first single-mode fiber channel Collecting and recovering Distributing the data to a data receiving end through a second single mode fiber channel; the first single-mode optical fiber channel and the second single-mode optical fiber channel are conventional optical fiber channels, and the optical fiber of the second single-mode optical fiber channel is slightly longer than that of the first single-mode optical fiber channel;
in step S200, the transmitting end filters out the circular polarization of the received light beam by using a first circular polarization filter, retains the linear polarization portion, and the retained linear polarization light beam passes through a first polarization beam splitter PBS 1 Split into two bundles, one bundle entering the first polarization maintaining fiber b Hair 1 The other beam enters the first laser terminator after passing through a section of optical fiber;
in the disclosed embodiment, the PBS is used by the first polarizing beam splitter 1 Selected b Hair 1 The first polarization maintaining fiber maintains the polarization direction of the light beam in the vertical direction, and transmits the light beam in the vertical direction.
In step S300, the receiving end slightly lags behind the receiving end receiving b Collecting and recovering The received light beam is filtered by a second circular polarization filter to remove circular polarization, the linear polarization part is reserved, and the reserved linear polarization light beam passes through a second polarization beam splitter PBS 2 Is divided into two beams, wherein one beam is set as b in entangled state with the light beam input into the polarization-maintaining optical fiber at the transmitting end Receive 1 The other beam is input into a third laser terminator through an optical fiber;
in the implementation of the present disclosure, the receiving end passes through the second polarizing beam splitter PBS 2 Selected beam b Receive 1 Orthogonal to the beam selected by the data transmitting end,i.e. the receiving end passes through the second polarization beam splitter PBS 2 Selected beam b Receive 1 Is a horizontally polarized light beam.
In step S400, the transmitting end inputs the light beam b of the first polarization maintaining fiber Hair 1 Through the first polarization controller PC 1 The polarization direction is rotated by 90 degrees and then is input into a second polarization maintaining optical fiber, and the polarization direction of the light beam is kept unchanged through the second polarization maintaining optical fiber, and b is set as Hair 2 ；
In the embodiment of the disclosure, the transmitting end passes through the first polarization controller PC 1 To vertically polarized light beam b Hair 1 Rotated by 90 degrees to obtain a polarized light beam b in the horizontal direction Hair 2 。
In step S500, the data receiving end again selects entangled photons through the polarizing beam splitter, so as to ensure that the photon beam for loading data is entangled; specifically, the receiving end passes through the third polarization beam splitter PBS 3 Again b Receive 1 Split into two beams, pass through a third polarization beam splitter PBS 3 Transmitted beam and second polarizing beam splitter PBS 2 The transmitted beam is rotated by 90 ° in polarization direction, wherein the third polarizing beam splitter PBS 3 Transmitted beam b Receive 2 Beam b input into polarization maintaining fiber at transmitting end Hair 2 In the entangled state, the other reflected beam is input into a third laser terminator through an optical fiber;
in embodiments of the present disclosure, b Receive 1 A third polarization beam splitter PBS for horizontally polarized light beam 3 Transmitted beam b Receive 2 For vertically polarized light beam, b is as above Hair 2 Is a polarized light beam in the horizontal direction, namely a third polarization beam splitter PBS 3 Transmitted beam b Receive 2 Beam b input into polarization maintaining fiber at transmitting end Hair 2 In an entangled state.
In step S600, the transmitting-end controllable optical switch switches the switch position of the controllable optical switch at intervals according to the bit to be transmitted, i.e., binary data, so that the photon beam b Hair 2 Transmitting on different paths, so that the polarization direction of the photon beam is deflected by 90 degrees or kept unchanged;
in the embodiment of the disclosure, a controllable optical switch reads bits to be transmitted in a data source;
if the read bit is 1, the position of the controllable optical switch is changed to enable the light beam b output by the first polarization controller Hair 2 Transmitted to a second polarization controller PC 2 Rotating the polarization state of the light beam by 90 degrees, and then enabling the light beam to enter a second laser terminator;
if the read bit is 0, the position of the controllable optical switch is changed to enable the light beam b output by the first polarization controller Hair 2 Transmitting to a third polarization maintaining optical fiber to keep the polarization state of the light beam unchanged, and then enabling the light beam to enter a second laser terminator.
Step S700, the receiving end passes through a fourth polarization beam splitter PBS 4 Input beam b Receive 2 Split into two beams, one beam and a third polarization beam splitter PBS 3 The polarization direction of the transmitted beam is kept consistent, and the polarization direction of the other beam is rotated by 90 DEG and is respectively set as b 1 Receive 2 And b 2 Receive 2 The method comprises the steps of carrying out a first treatment on the surface of the Two input beams b 1 Receive 2 And b 2 Receive 2 Respectively transmitting to corresponding optical power detectors and converting two photon beams into voltage signals, wherein the output of the optical power detectors is connected to a differential amplifier, the signals are amplified and output through the differential amplifier, and finally the output power of the optical power detectors at the same moment is compared through a signal processor, so that the output power of the optical power detectors is input into a fourth polarization beam splitter PBS (polarization beam splitter) 4 Is set in (a) beam b Receive 2 The polarization direction of the continuous variable entangled light beam is judged to be deflected by 90 degrees or kept unchanged by the transmitting end, so that the switching position of the controllable optical switch is obtained, and the bit transmitted by the data transmitting end is further determined.
In an embodiment of the disclosure, the fourth polarizing beam splitter PBS 4 Dividing the received light beam into two beams, wherein one beam is consistent with the polarization direction of the light beam transmitted by the third polarization beam splitter, and the two beams are converted into a voltage signal V by an optical power detector 1 The other beam is rotated by 90 DEG in polarization direction and converted into a voltage signal V by an optical power detector 2 ；
Comparing the output power of the optical power detectors at the same moment;
if V is detected 1 Greater than V 2 The light beam input into the second laser terminator in the data transmitting end is determined to be unchanged in polarization state, and the bit transmitted by the data transmitting end is determined to be 0;
if V is detected 2 Greater than V 1 The polarization state of the light beam input into the second laser terminator in the data transmitting end is determined to be rotated by 90 degrees, and the bit transmitted by the data transmitting end is determined to be 1;
if V is detected 2 Equal to V 1 And determining invalid data and discarding the detection result.
The principle of step S700 is: the input optical signal is converted into an electric signal through the optical power detector, and the polarization state is determined by amplifying and comparing the outputs of different optical power detectors, so that the bit signal is determined.
The invention is not related in part to the same or implemented in part by the prior art.
The foregoing is a further detailed description of the invention in connection with specific embodiments, and it is not intended that the invention be limited to such description. It will be apparent to those skilled in the art that several simple deductions or substitutions may be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.
Claims (10)
1. A system for quantum secure direct communication based on continuous variables, characterized by: comprising
Continuous variable entangled state light source: for preparing entangled beams of mutually orthogonal polarization states;
polarizer: for obtaining linearly polarized light from the entangled beam;
and the data transmitting end: the device comprises a first circular polarization filter, a first polarization beam splitter, a first polarization controller, a controllable light switch and a second polarization controller which are sequentially connected; the second polarization controller is also connected with a data source;
the first polarization beam splitter outputs from the polarizer after the continuous variable entangled state light source, and selects one beam from the light beams passing through the first circular polarization filter and transmits the selected beam to the first polarization controller, the first polarization controller rotates the polarization state of the received light beam by 90 degrees and transmits the received light beam to the controllable optical switch, the controllable optical switch reads bits to be transmitted from the data source, and the controllable optical switch switching position is controlled according to the bits to be transmitted, so that the polarization state of the light beam passing through the controllable optical switch is kept unchanged or the polarization state of the light beam passing through the second polarization controller is rotated by 90 degrees;
and the data receiving end: the device comprises a second circular polarization filter, a second polarization beam splitter, a third polarization beam splitter and a fourth polarization beam splitter which are sequentially connected, wherein two output ends of the fourth polarization beam splitter are respectively connected with an optical power detector;
the second polarization beam splitter outputs from the continuous variable entangled state light source, and selects one beam from the light beams passing through the second circular polarization filter and transmits the selected beam to the third polarization beam splitter, the third polarization beam splitter selects one beam from the received light beams and transmits the selected beam to the fourth polarization beam splitter, the fourth polarization beam splitter divides the received photon beam into two beams and transmits the two beams to the two optical power detectors respectively, and then the output of the two optical power detectors is compared by the signal processor to determine bit signals sent by the data sending end;
wherein, the light beam received by the first polarization controller and the light beam received by the third polarization beam splitter are in an entangled state; the light beam received by the controllable light switch and the light beam received by the fourth polarization beam splitter are in an entangled state.
2. The continuous variable based quantum secure direct communication system of claim 1, wherein: in the system, a continuous variable entangled state light source transmits one beam of entangled beam pairs to a data transmitting end through a polarizer and a first single-mode fiber channel;
in the system, a continuous variable entangled state light source transmits the other beam of the entangled beam pair to a data receiving end through a second single-mode optical fiber channel;
the second single mode fiber channel has a length greater than the length of the first single mode fiber channel.
3. The continuous variable based quantum secure direct communication system of claim 1, wherein: the first polarization beam splitter is connected with the first polarization controller, and the first polarization controller is connected with the controllable optical switch through polarization maintaining optical fibers.
4. The continuous variable based quantum secure direct communication system of claim 1, wherein: the data transmitting end further comprises a first laser terminator and a second laser terminator, and the first polarization beam splitter transmits the separated light beams which are not transmitted to the first polarization controller to the first laser terminator;
one output end of the controllable optical switch is connected to the second laser terminator through the polarization maintaining optical fiber, and the other output end of the controllable optical switch is connected to the second laser terminator through the second polarization controller.
5. The continuous variable based quantum secure direct communication system of claim 1, wherein: the data receiving end further comprises a third laser terminator, and the second polarization beam splitter transmits the separated light beams which are not transmitted to the third polarization beam splitter to the third laser terminator; and the third polarization beam splitter transmits the separated light beams which are not transmitted to the fourth polarization beam splitter to the third laser terminator.
6. The continuous variable based quantum secure direct communication system of claim 1, wherein: the signal processor at the receiving end, the controllable optical switch at the transmitting end and the data source are all calibrated and synchronized by a GPS clock.
7. A method for quantum secure direct communication based on continuous variables, characterized by: the method steps using the system of any one of claims 1-6, comprising:
step S100: preparing entangled light beams with mutually orthogonal polarization states through a continuous variable entangled state light source, obtaining linearly polarized light by one light beam through a polarizer, transmitting the linearly polarized light to a transmitting end through an optical fiber, and transmitting the other light beam to a receiving end through the optical fiber;
step S200: the transmitting end filters out circular polarization of the received light beam through a circular polarization filter, and the linear polarization light beam of the transmitting end is reserved; the method comprises the steps that a transmitting end linear polarized light beam passes through a first polarization beam splitter to select a light beam with a certain polarization direction, and then enters a first polarization controller;
step S300: the receiving end filters out circular polarization of the received light beam through a circular polarization filter, and the linear polarization light beam of the transmitting end is reserved; selecting a light beam which is in an entangled state with the light beam input into the first polarization controller by the transmitting end from the receiving end linear polarization light beam through the second polarization beam splitter;
step S400: the transmitting end rotates the polarization direction of the light beam by 90 degrees through the first polarization controller, and then inputs the light beam into the controllable optical switch; step S500: the receiving end selects a light beam which is in an entangled state with the light beam input by the light switch of the transmitting end from the light beams transmitted by the second polarization beam splitter through the third polarization beam splitter;
step S600: the transmitting end controls the controllable optical switch according to the bit to be transmitted, so that the light beams are transmitted on different paths within a period of time respectively, and the polarization state is kept unchanged or rotated by 90 degrees through the second polarization controller;
step S700: the receiving end divides the light beam output from the third polarization beam splitter into two beams through the fourth polarization beam splitter, and respectively converts the two input light beams into voltage signals and then performs polarization state measurement so as to determine the bit signal sent by the data sending end.
8. The method of continuous variable based quantum secure direct communication of claim 7, wherein: in the method, in step S200 and step S300, continuous variable entanglement quanta for loading transmission data are preliminarily selected through a first polarization beam splitter at a transmitting end and a second polarization beam splitter at a receiving end; in step S400 and step S500, photons in an un-entangled state are filtered by a first polarization controller at the transmitting end and a third polarization beam splitter at the receiving end.
9. The method of continuous variable based quantum secure direct communication of claim 7, wherein: the step S600 specifically includes:
the controllable optical switch reads the bits to be transmitted;
if the read bit is 1, the position of the controllable optical switch is changed over to enable the light beam output by the first polarization controller to be transmitted to the second polarization controller, so that the polarization state of the light beam is rotated by 90 degrees;
if the read bit is 0, the position of the controllable optical switch is changed to enable the light beam output by the first polarization controller to be transmitted to the polarization maintaining optical fiber, so that the polarization state of the light beam is kept unchanged.
10. The method of continuous variable based quantum secure direct communication of claim 9, wherein: the step S700 specifically includes:
the fourth polarization beam splitter splits the received light beam into two beams, one beam is consistent with the polarization direction of the light beam transmitted by the third polarization beam splitter, and the two beams are converted into a voltage signal V through the optical power detector 1 The other beam is rotated by 90 DEG in polarization direction and converted into a voltage signal V by an optical power detector 2 ；
Comparing the output power of the optical power detectors at the same moment;
if V is detected 1 Greater than V 2 The light beam input into the second laser terminator in the data transmitting end is determined to be unchanged in polarization state, and the bit transmitted by the data transmitting end is determined to be 0;
if V is detected 2 Greater than V 1 The polarization state of the light beam input into the second laser terminator in the data transmitting end is determined to be rotated by 90 degrees, and the bit transmitted by the data transmitting end is determined to be 1;
if V is detected 2 Equal to V 1 And determining invalid data and discarding the detection result.
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