Continuous variable quantum secure direct communication method

Abstract

The invention provides a continuous variable quantum secure direct communication method, and belongs to the technical field of quantum secure direct communication, and the method comprises the steps: a transmitting end prepares a dual-mode compression entangled light beam pair S, and transmits a light beam S1 to a receiving end; the transmitting end modulates the light beam S1 into a first Laguerre-Gaussian light beam S '1 and transmits the first Laguerre-Gaussian light beam S' 1 to the receiving end; selecting a subset by the transmitting end, measuring the orthogonal position and the orthogonal momentum of the light beam S2 in the subset, comparing the orthogonal position and the orthogonal momentum with the result of measuring the light beam S1 by the receiving end, and checking interference; and the receiving end modulates the S '1 into a second Laguerre-Gaussian beam S ''1 according to the secret information and sends the second Laguerre-Gaussian beam S'' 1 to the sending end, the sending end recombines the S2 and the S ''1 into a beam pair S' and performs imaging, and the secret information is obtained according to an imaging result. The problems that continuous variable quantum secure direct communication is prone to noise and loss in the transmission process, and implementation and management are complex are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantum secure direct communication, and in particular relates to a method for continuous variable quantum secure direct communication. Background Art

[0002] Quantum Secure Direct Communication (QSDC) is a technology that uses the principles of quantum mechanics to achieve secure communication. Unlike traditional quantum key distribution (QKD), QSDC allows communicating parties to directly transmit messages without having to establish and manage keys in advance. The quantum no-cloning theorem states that unknown quantum states cannot be accurately copied. This means that any attempt to copy or measure a quantum state will introduce a non-negligible disturbance that can be detected by both communicating parties; the Heisenberg uncertainty principle states that the position and momentum of a particle cannot be accurately measured at the same time, and any unauthorized measurement will introduce noise, thereby undermining the security of communication. Based on the quantum no-cloning theorem and the Heisenberg uncertainty principle, QSDC provides unconditional security and ensures the security of communication even under quantum computer attacks.

[0003] Continuous variable quantum secure direct communication (CV-QSDC) combines the advantages of continuous variable quantum systems and the security of QSDC, providing an efficient and secure communication method. CV-QSDC allows the communicating parties to directly transmit messages without the need to establish and manage keys in advance. It uses continuous variable quantum systems to achieve high-speed communication, and can achieve low-noise communication through highly sensitive detectors and advanced signal processing technology. Based on the quantum no-cloning theorem and Heisenberg's uncertainty principle, it provides unconditional security for communication.

[0004] However, continuous variable quantum secure direct communication is susceptible to noise and loss during transmission, and is relatively complex to implement and manage, which limits the application of quantum technology. Summary of the invention

[0005] The purpose of the present invention is to provide a method for continuous variable quantum secure direct communication to solve the problem that continuous variable quantum secure direct communication is susceptible to noise and loss during transmission and is complex to implement and manage.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is a method for continuous variable quantum secure direct communication, comprising the following steps:

[0007] S1, the transmitter uses two optical parametric oscillators to prepare momentum compression vacuum state and position compression vacuum state respectively, and then uses a beam splitter to prepare a dual-mode compressed entangled beam pair S, including beam S1 and beam S2. The transmitter directly sends beam S1 to the receiver and retains beam S2.

[0008] S2, the transmitting end modulates the light beam S1 into the first Laguerre-Gaussian beam S'1 through the liquid crystal spatial light modulator, and attenuates it to the quantum state through the attenuator, and sends it to the receiving end;

[0009] S3, the transmitter randomly selects a subset of the dual-mode compressed entangled beam pair, measures the orthogonal position and orthogonal momentum of the beam S2 in the subset, and publishes the position and measurement results of the subset through the classical channel. The receiver measures the orthogonal position and orthogonal momentum of the beam S1 according to the position of the subset;

[0010] S4, the receiving end modulates S'1 into a second Laguerre-Gaussian beam S"1 according to the secret information through a reflective liquid crystal spatial light modulator, and sends it to the transmitting end through a turbulent atmospheric channel;

[0011] S5. The transmitter recombines S2 and S”1 into a beam pair S’ through a beam splitter and images it on a charge-coupled camera. The transmitter determines the orbital angular momentum eigenstate of the beam pair S’ based on the imaging result and obtains the secret information.

[0012] Further, in step S1, the preparation of light beam S1 and light beam S2 is expressed as:

[0013]

[0014] In the formula, is the orthogonal position of beam S1, is the orthogonal momentum of beam S1, is the orthogonal position of beam S2, is the orthogonal momentum of beam S2, is the orthogonal position of the momentum-compressed vacuum state, is the orthogonal position of the position-squeezed vacuum state, is the orthogonal momentum of the momentum-compressed vacuum state, is the orthogonal momentum of the position-compressed vacuum state, e is exp, i.e. the base of the natural logarithm, r is the compression coefficient, r>0, is the initial orthogonal position of the quantum state through the first optical parametric oscillator, is the initial orthogonal position of the quantum state through the second optical parametric oscillator, is the initial orthogonal momentum of the quantum state passing through the first optical parametric oscillator, is the initial orthogonal momentum of the quantum state passing through the second optical parametric oscillator.

[0015] Further, in step S2, the first Laguerre-Gaussian beam S'1 carries The orbital angular momentum of units, the orbital angular momentum eigenstate is expressed as |l1>, S'1 loading vortex phase exp(il1θ), where l1 is the topological charge of S'1, is the reduced Planck constant, exp is the base of the natural logarithm, i is the complex unit, and θ is the azimuth angle.

[0016] Furthermore, step S3 also includes a quantum state check. If the measurement results of the transmitter and the receiver in the subset meet the inseparable criterion, it means that the quantum state is not destroyed. The inseparable criterion is:

[0017]

[0018] In the formula, is the orthogonal position of beam S1 in this subset, is the orthogonal momentum of beam S1 in this subset, is the orthogonal position of beam S2 in this subset, is the orthogonal momentum of beam S2 in this subset.

[0019] Furthermore, in step S4, the second Laguerre-Gaussian beam S"1 is loaded with a vortex phase exp(il2θ), where l2 is the topological charge of S"1, i is a complex unit, θ is an azimuth angle, and if the secret information is 0, l2<0 is set; if the secret information is 1, l2>0 is set.

[0020] Furthermore, in step S5, if the imaging result on the charge coupled camera is a clockwise spiral, the transmitting end determines that the orbital angular momentum eigenstate l'2 of the light beam to S' is greater than 0, and the secret information is 1; if the imaging result is a counterclockwise spiral, the transmitting end determines that the orbital angular momentum eigenstate l'2 of the light beam to S' is less than 0, and the secret information is 0.

[0021] The beneficial effects of the present invention are:

[0022] (1) The present invention provides a method for continuous variable quantum secure direct communication, which uses continuous variable quantum technology to verify the security of communication by detecting the orthogonal position and orthogonal momentum of the quantum state, thereby ensuring the reliability of information transmission and being compatible with classical channels such as optical fiber, radio waves, and satellites;

[0023] (2) The present invention uses a liquid crystal spatial light modulator and a reflective liquid crystal spatial light modulator to modulate the orbital angular momentum of the Laguerre-Gaussian beam, and changes the orbital angular momentum eigenstate to carry secret information, which is easy to implement and manage. Any unauthorized measurement will introduce noise, destroy the orbital angular momentum eigenstate of the beam, and thus be detected by both parties of the communication, thereby achieving high-security, low-noise communication. The orbital angular momentum eigenstate of the Laguerre-Gaussian beam is judged by the imaging result of the charge-coupled camera and the secret information is obtained. Even if it is affected by channel noise and interferer attacks, it will not affect the imaging result, and has excellent security and robustness. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 It is a flowchart of a method for continuous variable quantum secure direct communication of the present invention;

[0026] Figure 2 is a schematic diagram of the encoding principle of orbital angular momentum in Embodiment 1 of the present invention;

[0027] Figure 3 is a schematic diagram of the intensity distribution of a Laguerre-Gaussian beam according to Example 2 of the present invention;

[0028] Figure 4 Schematic diagram of the phase distribution of the Laguerre-Gaussian beam in Example 2 of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] like Figure 1 As shown, the present invention provides a method for continuous variable quantum secure direct communication, comprising the following steps:

[0031] S1, the transmitter Bob prepares the momentum compression vacuum state through the first optical parametric oscillator OPO1, and prepares the position compression vacuum state through the second optical parametric oscillator OPO2, which is expressed as:

[0032]

[0033] In the formula, is the orthogonal position of the momentum-compressed vacuum state, is the orthogonal position of the position-compressed vacuum state, e is exp, i.e. the base of the natural logarithm, r is the compression coefficient, r>0, is the initial orthogonal position of the quantum state through OPO1, is the initial orthogonal position of the quantum state through OPO2, is the orthogonal momentum of the momentum-compressed vacuum state, is the orthogonal momentum of the position-squeezed vacuum state, is the initial orthogonal momentum of the quantum state passing through OPO1, is the initial orthogonal momentum of the quantum state passing through OPO2;

[0034] Bob performs balanced beam splitting of the momentum compressed vacuum state and the position compressed vacuum state through a beam splitter (BS) to prepare a dual-mode compressed entangled beam pair S, including beam S1 and beam S2, which can be expressed as:

[0035]

[0036] In the formula, is the orthogonal position of beam S1, is the orthogonal momentum of beam S1, is the orthogonal position of beam S2, is the orthogonal momentum of beam S2;

[0037] Bob sends beam S1 to the receiving end Alice and keeps beam S2.

[0038] S2, Bob modulates the beam S1 into the first Laguerre-Gaussian beam S'1 carrying orbital angular momentum through a liquid crystal spatial light modulator (LC-SLM). Its amplitude distribution presents a vortex phase structure, carrying The orbital angular momentum of units, the orbital angular momentum eigenstate is expressed as |l1>, S'1 loading vortex phase exp(il1θ), where exp is the base of the natural logarithm, l1 is the topological charge of the first Laguerre-Gaussian beam modulated by Bob, and S'1 is an arbitrary integer. is the reduced Planck constant, i is a complex unit, and θ is the azimuth angle;

[0039] Then Bob attenuates the first Laguerre-Gaussian beam S'1 into a quantum state through an attenuator (Att.) and sends it to Alice through a turbulent atmospheric channel (AT). The turbulent atmospheric channel has a transmittance of T and has excess noise ∈, which is introduced by possible interference.

[0040] S3, Bob randomly selects a subset of the dual-mode compressed entangled beam pair S, determines the position of the subset, and measures the orthogonal position of the beam S2 in the subset and orthogonal momentum Alice then measures the orthogonal position of beam S1 at the same subset position. and orthogonal momentum And perform quantum state check (CE). If the measurement result meets the non-separability criterion, that is:

[0041]

[0042] It means that the quantum state is not destroyed. Bob compares the measurement result with Alice's measurement result, calculates the key rate, and sets the threshold to 0. If the key rate is higher than the threshold, proceed to the next step. If the key rate is lower than the threshold, it means that the communication is eavesdropped and Bob gives up communicating.

[0043] S4. Alice sends the light beam S'1 into a reflective liquid crystal spatial light modulator (RLC-SLM) and modulates it into a second Laguerre-Gaussian beam S"1, loading the vortex phase exp(il2θ), where l2 is the topological charge of the light beam S"1 and is an arbitrary integer. Alice modulates the light beam S"1 according to the secret information. If the secret information is 0, l2<0 is set; if the secret information is 1, l2>0 is set.

[0044] Because the vortex light has mirror characteristics, after n reflections, the eigenstate of orbital angular momentum changes to:

[0045] |l>→|(-1) n l>

[0046] Where n is the number of reflections, l is the topological charge, which is an arbitrary integer.

[0047] The orbital angular momentum eigenstate changes after passing through the reflective liquid crystal spatial light modulator are:

[0048]

[0049] After the modulation is completed, Alice sends the beam S”1 to Bob through the turbulent atmospheric channel;

[0050] S5. Bob recombines the light beam S2 and the light beam S”1 into a light beam pair S’ through a beam splitter, and images them on a charge coupled camera (CCD). Bob determines the orbital angular momentum eigenstate |l’2> of the light beam pair S’ based on the imaging result. If the imaging result on the charge coupled camera is a clockwise spiral, Bob determines that the orbital angular momentum eigenstate l’2>0 of the light beam pair S’, and obtains the secret information as 1. If the imaging result is a counterclockwise spiral, Bob determines that the orbital angular momentum eigenstate l’2<0 of the light beam pair S’, and obtains the secret information as 0.

[0051] Example 1

[0052] The continuous variable quantum secure direct communication method of the present invention is used for communication, and l1=2, l2=5 are set.

[0053] like Figure 2 As shown in the figure, it is a schematic diagram of orbital angular momentum encoding principle of Example 1 of the present invention. Bob uses a liquid crystal spatial light modulator to encode the orbital angular momentum of a Gaussian beam to generate vortex light. The vortex light carries The orbital angular momentum of units, the orbital angular momentum eigenstate is |2>, after being sent through the atmospheric turbulence channel, it is modulated by the reflective liquid crystal spatial light modulator. At this time, the vortex light increases The orbital angular momentum unit is |3>. After the mirror reflection, the orbital angular momentum of the vortex light becomes the original negative number. Therefore, the final orbital angular momentum eigenstate returning to Bob's position is recorded as |-(l1+l2)>, which is |-5>.

[0054] Example 2

[0055] The method for continuous variable quantum secure direct communication of the present invention is used for communication, and l2=1, -1, 3, -3 is set.

[0056] like Figure 3 As shown, it is the intensity distribution of the second Laguerre-Gaussian beam S"1 in Example 2 of the present invention. The first row represents the intensity distribution of the beam S"1 generated by Alice, the second row represents the intensity distribution of S"1 after passing through the turbulent atmospheric channel, and the third row represents the intensity distribution of S"1 after being interfered by the interferer Eve. It can be seen from the second row that due to the influence of atmospheric turbulence, the intensity distribution of the beam will have some random fluctuations, but most of the intensity is still retained overall; it can be seen from the third row that the interference of the interferer Eve further increases the randomness of the beam intensity distribution, but the core intensity of the beam still exists, which shows that the present invention has excellent security.

[0057] like Figure 4 As shown, it is the phase distribution of the second Laguerre-Gaussian beam S"1 in Example 2 of the present invention. The first row represents the phase distribution of the beam S"1 generated by Alice, the second row represents the phase distribution of S"1 after passing through the turbulent atmospheric channel, and the third row represents the phase distribution of S"1 after being interfered by the interferer Eve. It can be seen from the second row that due to the influence of atmospheric turbulence, the phase distribution of the light beam fluctuates randomly. It can be seen from the third row that the interference of the interferer Eve further increases the fluctuation of the phase distribution of the light beam, but obvious spiral features can still be observed. It can be seen that external influences will not interfere with the present invention in obtaining secret information according to the spiral direction, and it has excellent robustness.

[0058] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A method for continuous variable quantum secure direct communication, characterized in that: The following steps are involved: S1, the transmitter uses two optical parametric oscillators to prepare momentum compression vacuum state and position compression vacuum state respectively, and then uses a beam splitter to prepare a dual-mode compressed entangled beam pair S, including beam S1 and beam S2. The transmitter directly sends beam S1 to the receiver and retains beam S2. S2, the transmitting end modulates the light beam S1 into the first Laguerre-Gaussian beam S'1 through the liquid crystal spatial light modulator, and attenuates it to the quantum state through the attenuator, and sends it to the receiving end; S3, the transmitter randomly selects a subset of the dual-mode compressed entangled beam pair, measures the orthogonal position and orthogonal momentum of the beam S2 in the subset, and publishes the position and measurement results of the subset through the classical channel. The receiver measures the orthogonal position and orthogonal momentum of the beam S1 according to the position of the subset; S4, the receiving end modulates S'1 into a second Laguerre-Gaussian beam S'1' according to the secret information through a reflective liquid crystal spatial light modulator, and sends it to the transmitting end through a turbulent atmospheric channel; S5. The transmitter recombines S2 and S'1' into a beam pair S' through a beam splitter and images it on a charge-coupled camera. The transmitter determines the orbital angular momentum eigenstate of the beam pair S' based on the imaging results and obtains the secret information.

2. A method for continuous variable quantum secure direct communication according to claim 1, characterized in that: In step S1, the preparation of light beam S1 and light beam S2 is expressed as: In the formula, is the orthogonal position of beam S1, is the orthogonal momentum of beam S1, is the orthogonal position of beam S2, is the orthogonal momentum of beam S2, is the orthogonal position of the momentum-compressed vacuum state, is the orthogonal position of the position-compressed vacuum state, is the orthogonal momentum of the momentum-compressed vacuum state, is the orthogonal momentum of the position-compressed vacuum state, e is exp, i.e. the base of the natural logarithm, r is the compression coefficient, r>0, is the initial orthogonal position of the quantum state through the first optical parametric oscillator, is the initial orthogonal position of the quantum state through the second optical parametric oscillator, is the initial orthogonal momentum of the quantum state passing through the first optical parametric oscillator, is the initial orthogonal momentum of the quantum state passing through the second optical parametric oscillator.

3. The method of continuous variable quantum secure direct communication according to claim 1, characterized in that: In step S2, the first Laguerre-Gaussian beam S'1 carries The orbital angular momentum of units, the orbital angular momentum eigenstate is expressed as |l1>, S'1 loading vortex phase exp(il1θ), where l1 is the topological charge of S'1, is the reduced Planck constant, exp is the base of the natural logarithm, i is the complex unit, and θ is the azimuth angle.

4. The method of continuous variable quantum secure direct communication according to claim 1, characterized in that: Step S3 also includes a quantum state check. If the measurement results of the transmitter and the receiver in the subset meet the inseparable criterion, it means that the quantum state is not destroyed. The inseparable criterion is: In the formula, is the orthogonal position of beam S1 in this subset, is the orthogonal momentum of beam S1 in this subset, is the orthogonal position of beam S2 in this subset, is the orthogonal momentum of beam S2 in this subset.

5. The method of continuous variable quantum secure direct communication according to claim 1, characterized in that: In step S4, the second Laguerre-Gaussian beam S″1 is loaded with a vortex phase exp(il2θ), where l2 is the topological charge of S″1, i is a complex unit, θ is the azimuth angle, and if the secret information is 0, l2<0 is set; if the secret information is 1, l2>0 is set.

6. The method of continuous variable quantum secure direct communication according to claim 1, characterized in that: In step S5, if the imaging result on the charge coupled camera is a clockwise spiral, the transmitting end determines that the orbital angular momentum eigenstate l'2 of the light beam to S' is greater than 0, and the secret information is 1. If the imaging result is a counterclockwise spiral, the transmitting end determines that the orbital angular momentum eigenstate l'2 of the light beam to S' is less than 0, and the secret information is 0.

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