CN114553402B - QKD system and method based on sagnac loop and irrelevant to reference system irrelevant measurement equipment - Google Patents
QKD system and method based on sagnac loop and irrelevant to reference system irrelevant measurement equipment Download PDFInfo
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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
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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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- 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
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Abstract
The invention discloses a system and a method for QKD irrelevant to reference system irrelevant measuring equipment based on a sagnac ring, wherein the system comprises a transmitting end Alice, a transmitting end Bob and a measuring end Charlie; the transmitting terminal Alice and the transmitting terminal Bob are connected with the measuring terminal Charlie through a free space channel; the transmitting end Alice comprises a Laser1 and a first sagnac loop modulator, wherein the first sagnac loop modulator comprises an intensity modulator IM1, a polarization controller PC1, an optical circulator Cir1, a first transmitting end sagnac loop, an optical attenuator ATT1 and an optical fiber collimator Col1; the transmitting end Bob comprises a Laser device Laser2 and a second sagnac loop modulator, wherein the second sagnac loop modulator comprises an intensity modulator IM2, a polarization controller PC2, an optical circulator Cir, a second transmitting end sagnac loop, an optical attenuator ATT2 and an optical fiber collimator Col2; the invention solves the problem of complex preparation in the prior art, has higher speed and better stability, achieves the purpose of eliminating the influence of the environment on the polarization state, does not need to align a reference system, simplifies the complexity of the system and improves the code rate.
Description
Technical Field
The invention belongs to the technical field of quantum information and optical communication, and particularly relates to a QKD system and a method which are irrelevant to reference system irrelevant measuring equipment and based on a sagnac ring.
Background
Quantum key distribution technology is based on the basic principle of quantum mechanics, and theoretically proves that unconditional secure key sharing can be realized. However, due to non-ideal characteristics of actual devices and equipment, a certain gap exists between the actual safety of the quantum key distribution system and theory, wherein the single photon detector in the detection end is the most vulnerable part, and the actual safety of the quantum key distribution system is seriously influenced.
The measurement device independent quantum key distribution protocol (Measurement Device Independent Quantum Key Distribution, MDI QKD) perfectly solves the security problem due to measurement end device non-idealities using Bell state (Bell state) projection measurement. In the measuring equipment independent quantum key distribution protocol, legal communication parties Alice and Bob are both senders, and send prepared quantum states to an untrusted third party Charlie for Bell state projection measurement to obtain projected Bell states, and the security of the Bell states is independent of the third party.
Prior art patent: (CN 108199768A) proposes to use a measurement device independent protocol in W state, which can completely eliminate the potential safety hazard of the detector. However, the adopted W-state preparation is complex, the technical requirement is high, and the W-state preparation is difficult to perfectly realize.
Prior art patent: (CN 108183793A) provides a measurement device independent protocol for modulating polarization state by using a polarization controller, and the adopted measurement device has the advantages of simple structure, less required detector and optical elements, low loss and low cost. But the polarization state modulation speed by using the polarization controller is slower and the stability is poorer.
Prior art patent: (CN 107332627A) provides a method for reducing the influence of environment on the polarization state by carrying out disturbance on the polarization state of an optical pulse signal or an optical quantum signal at a quantum state preparation transmitting end so that the polarization state of the optical pulse signal or the optical quantum signal is uniformly distributed on the surface of the Poincare sphere. But the method for utilizing the compound valve has complicated operation, complex structure and higher cost.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide a QKD system based on a reference system irrelevant measuring device of a Sagnac ring, and the invention provides a measurement device irrelevant protocol by generating a polarization state by using a Sagnac ring modulator, so that the method is simple to operate and easy to realize, and solves the problem of complex preparation in the prior art. In addition, the Sagnac loop modulator adopts the phase modulator to modulate polarization, so that the speed is higher and the stability is better; meanwhile, the invention better utilizes the relevant property of the Q-plate of the Q plate, thereby eliminating the influence of the environment on the polarization state, avoiding the need of reference system alignment and improving the code rate. And the operation is easy, and the structure is simple.
In order to achieve the aim of the invention, the invention adopts the following technical scheme: a QKD system based on a sagnac ring and irrelevant to reference system irrelevant to measurement equipment comprises a transmitting end Alice, a transmitting end Bob and a measuring end Charlie; the transmitting terminal Alice and the transmitting terminal Bob are connected with the measuring terminal Charlie through a free space channel;
the transmitting terminal Alice comprises a Laser1 and a first sagnac loop modulator which are connected with each other, wherein the first sagnac loop modulator comprises an intensity modulator IM1, a polarization controller PC1, an optical circulator Cir1, a first transmitting terminal sagnac loop, an optical attenuator ATT1, an optical fiber collimator Col1 and a Q plate Q-plate1;
the Laser1 is used for generating a first optical pulse, and the first optical pulse is used for system coding as a quantum signal to generate a secret key;
the intensity modulator IM1 is configured to intensity modulate the first light pulse;
the polarization controller PC1 is used for changing the quantum signal into 45-degree linearly polarized light;
the Q plate Q-plate1 is used for coupling spin angular momentum and orbital angular momentum;
the transmitting end Bob comprises a Laser2 and a second sagnac loop modulator which are connected with each other, wherein the second sagnac loop modulator comprises an intensity modulator IM2, a polarization controller PC2, an optical circulator Cir2, a second transmitting end sagnac loop, an optical attenuator ATT2, an optical fiber collimator Col2 and a Q plate Q-plate4;
the Laser2 is used for generating a second optical pulse, and the second optical pulse is used for system coding as a quantum signal to generate a secret key;
the intensity modulator IM2 is configured to perform single modulation on the second light pulse;
the polarization controller PC2 is used for changing the quantum light signal into 45-degree linearly polarized light;
the Q plate Q-plate4 is used for coupling spin angular momentum and orbital angular momentum;
the measuring end Charlie comprises reflecting mirrors Mirror 1-Mirror 4, a Q plate Q-plate2, a Q plate Q-plate3 and a BSM measuring instrument, and the BSM measuring instrument comprises a beam splitter BS, a polarization beam splitter PBS and a single photon detector D 1H Single photon detector D 1V Single photon detector D 2H And a single photon detector D 2V The method comprises the steps of carrying out a first treatment on the surface of the The beam splitter BS is coupled to the polarizing beam splitter PBS3 and the polarizing beam splitter PBS4, connection; the single photon detector D 1H And a single photon detector D 1V Is connected with the polarization beam splitter PBS 3; the single photon detector D 2H And a single photon detector D 2V Is connected with a polarization beam splitter PBS 4;
the first transmitting end sagnac loop is used for dividing 45-degree linearly polarized light into first horizontally polarized light and first vertically polarized light, converging the first horizontally polarized light and the first vertically polarized light, outputting the first horizontally polarized light to the optical attenuator ATT1 through the optical circulator Cir1, attenuating the first horizontally polarized light to set light intensity by the optical attenuator ATT1, converting the signal into a space light signal through the optical fiber collimator Col1, coupling the space light signal with the Q board, and transmitting the space light signal to the measuring end Charlie through a free space channel;
the second transmitting end sagnac ring is used for dividing 45-degree linearly polarized light into second horizontally polarized light and second vertically polarized light, converging the second horizontally polarized light and the second vertically polarized light, after converging through the PBS2, emitting the second horizontally polarized light to the optical attenuator ATT2 through the optical circulator Cir and attenuating the second horizontally polarized light to set light intensity by the optical attenuator ATT2, converting the signals into space light signals through the optical fiber collimator Col1, coupling the space light signals with the Q plate Q-plate1, and transmitting the space light signals to the measuring end Charlie through a free space channel;
after the first light pulse and the second light pulse reach the measuring end Charlie, the first light pulse and the second light pulse are reflected to the Q-plate2 and the Q-plate3 by the reflectors Mirror1 and Mirror3 respectively, demodulated by the Q-plate2 and the Q-plate3, reflected to the optical fiber collimators Col3 and Col4 by the reflectors Mirror2 and Mirror4 respectively, coupled into the optical fibers by the optical fiber collimators Col3 and Col4, and the two paths of signals are transmitted to the BSM to be measured in a Bell state.
Preferably, the first transmitting end sagnac loop includes a polarization beam splitter PBS1, a variable optical attenuator VOA1, a phase modulator PMA and an optical rotator1; the polarization beam splitter PBS1, the variable optical attenuator VOA1, the phase modulator PMA and the optical rotator1 are sequentially connected in series by adopting polarization maintaining fibers;
the polarization beam splitter PBS1 is used for dividing 45-degree linearly polarized light into first horizontally polarized light and first vertically polarized light;
the phase modulator PMA is configured to modulate the phase of polarized light in a clockwise or counter-clockwise direction;
the light rotator1 is used for rotating the horizontally polarized light propagating clockwise by 90 degrees to vertically polarized light and rotating the vertically polarized light propagating counterclockwise by 90 degrees to horizontally polarized light;
the first horizontally polarized light and the first vertically polarized light propagate in the polarization-preserving optical fiber clockwise and anticlockwise respectively; the first horizontal polarized light sequentially passes through the variable optical attenuator VOA1, the phase modulator PMA and the optical rotator rotor 1 to reach the polarization beam splitter PBS1, and the first vertical polarized light sequentially passes through the optical rotator rotor 1, the phase modulator PMA and the variable optical attenuator VOA1 to reach the polarization beam splitter PBS1 to be combined with the first horizontal polarized light reaching the polarization beam splitter PBS1.
Preferably, the phase modulator PMA is placed near the end of the polarizing beam splitter PBS1 where the vertically polarized light exits, so that the first horizontally polarized light and the second vertically polarized light reach the phase modulator PMA with a time difference for modulating the phase only in the clockwise or counter-clockwise direction for the clockwise and counter-clockwise propagating polarized light required for modulating the phase; when the phase modulator PMA loads the phase of 0 for the first vertically polarized light, at this time, |++ >, representing bit 1, is output from the polarization beam splitter PBS1; when the phase modulator PMA loads the first vertically polarized light with pi/2, it is, | -, which represents bit 0, that is output from the polarizing beam splitter PBS1 at this time.
Preferably, the second transmitting end sagnac loop includes a polarization beam splitter PBS2, a variable optical attenuator VOA2, a phase modulator PMB, and an optical rotator2;
the polarization beam splitter PBS2, the variable optical attenuator VOA2, the phase modulator PMB and the optical rotator2 are sequentially connected in series by adopting polarization maintaining fibers;
the polarization beam splitter PBS2 divides 45-degree linearly polarized light into second horizontally polarized light and second vertically polarized light;
the phase modulator PMB is used for modulating the phase of polarized light in a clockwise or counterclockwise direction;
the light rotator2 is used for rotating the horizontally polarized light propagating clockwise by 90 degrees to vertically polarized light and rotating the vertically polarized light propagating counterclockwise by 90 degrees to horizontally polarized light;
the second horizontal polarized light and the second vertical polarized light respectively propagate in the polarization maintaining optical fiber clockwise and anticlockwise, the second horizontal polarized light sequentially passes through the variable optical attenuator VOA2, the phase modulator PMB and the optical rotator2 to reach the polarization beam splitter PBS2, and the second vertical polarized light sequentially passes through the optical rotator2, the phase modulator PMB and the variable optical attenuator VOA2 to reach the polarization beam splitter PBS2.
Preferably, the phase modulator PMB is disposed near an end of the polarizing beam splitter PBS2 near the vertical polarized light exit, so that the second horizontally polarized light and the second vertically polarized light reach the phase modulator PMB with a time difference that the clockwise and counterclockwise propagating polarized light required for modulating the phase modulates only the phase in the clockwise or counterclockwise direction; when the phase modulator PMB loads a phase of 0 for vertically polarized light, at this time, |++ >, representing bit 1, is output from the polarization beam splitter PBS 2; when the phase modulator PMB loads the vertically polarized light with pi/2, it is, | -, which represents bit 0, that is output from the polarization beam splitter PBS2 at this time.
Preferably, the light pulses of the clockwise propagating first and second horizontally polarized light have a polarization state of |H>By adjusting the phase modulator to become
The polarization states of the light pulses of the first and second vertically polarized light propagating counter-clockwise are |v >, which can be changed to +| by adjusting the phase modulator PMA and the phase modulator PMB>
The quantum state of the light pulse when the vertically polarized light and the horizontally polarized light are combined in the polarizing beam splitter PBS1 is
Preferably, the Q board QPlate1 and Q plate Q-plate4 will be polarized state |H>Becomes a quantum state
Changing polarization state |V > into quantum state +.>
To polarize status | ++ >. Conversion to the Quantum state->
Polarization state->Conversion to the Quantum state->
Wherein |R>Represents the right-hand circular polarization state, |L>Represents the left-hand circular polarization state, |l=1>Represents a state in which the orbital angular momentum topology charge value is 1, |l= -1>Representing a state where the orbital angular momentum topology charge value is-1.
Preferably, the Q-plates Q-plate2 and Q-plate3 will be quantum states
Convert back to polarization state |H>Will->
Convert back to polarization state |V>Quantum state->
Convert back to polarization state | +>Quantum state->
Returning to the polarization state->。
Preferably, the BSM measuring instrument can only measure the polarization state |ψ generated after the two signals are combined by the beam splitter BS + >And |psi - >When the polarization state of the light pulse is measured to be |ψ + >Single photon detector D 1H And D 1V Or D 2H And D 2V In simultaneous response, when the polarization state of the light pulse is measured to be |ψ - >Single photon detector D 1H And D 2V Or D 2H And D 1V While responding.
The invention also provides a QKD method based on the reference frame irrelevant measuring equipment of the sagnac loop, which is applied to the QKD system based on the reference frame irrelevant measuring equipment of the sagnac loop, and is characterized by comprising the following steps:
s1, a transmitting end Alice and a transmitting end Bob are used as communication parties to simultaneously transmit quantum signals, polarization information is loaded through loading phases by utilizing a sagnac loop, when a phase modulator does not modulate and a variable optical attenuator VOA blocks anticlockwise pulses, a polarization state |H >, when the phase modulator does not modulate and the VOA blocks clockwise pulses, a polarization state |V >, when the phase modulator modulates 0 degree on horizontal polarization and the variable optical attenuator VOA does not modulate, a polarization state|++ >, when the phase modulator modulates pi on horizontal polarization, a polarization state| > - >, and then the phase modulator is coupled through a Q plate and then transmitted to a measuring end Charlie through a free space channel;
s2, two paths of quantum signals reach a measuring end Charlie, polarization and orbital angular momentum are decoupled through two Q plates, then the two paths of quantum signals enter a BSM measuring instrument for measurement, and when the polarization state of a light pulse is measured to be |psi + >Single photon detector D 1H And D 1V Or D 2H And D 2V In simultaneous response, when the polarization state of the light pulse is measured to be |ψ - >Single photon detector D 1H And D 2V Or D 2H And D 1V Simultaneously responding;
s3, the measuring end Charlie publishes the measuring result of the BSM measuring instrument through a classical channel, and the two communication parties obtain a detection result from the measuring end Charlie;
s4, the transmitting terminal Alice publishes the condition of the base selection through a classical channel, and the transmitting terminal Bob discards detection results which are different from the base selection condition of the transmitting terminal Alice according to the condition of the base selection of the transmitting terminal Alice so as to obtain an original secret key;
s5, the transmitting terminal Bob selects part of the secret key to detect error codes; if the error rate exceeds the set threshold, proving that an eavesdropper exists, discarding the result and restarting; if the error rate does not exceed the set threshold value, continuing the next operation;
s6, post-processing is carried out on the original secret key to obtain a usable safety secret key.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention provides a device independent protocol for measuring by utilizing the polarization state generated by the Sagnac ring modulator, which is simple to operate and easy to realize, and solves the problem of complex preparation in the prior art.
2. The Sagnac loop modulator provided by the invention adopts the phase modulator to modulate polarization, so that the speed is faster and the stability is better.
3. The invention better utilizes the relevant property of the Q-plate of the Q plate, eliminates the influence of the environment on the polarization state, does not need to align a reference system, simplifies the complexity of the system, improves the code rate, and has easy operation and simple structure.
4. The invention uses the idea of irrelevant measuring equipment, avoids all attacks to the measuring end, and has good stability and low cost.
Drawings
FIG. 1 is a schematic diagram of the structural principle of a system for measuring a device independent QKD based on a reference system of a sagnac loop of the present invention;
FIG. 2 is a schematic diagram of a BSM meter architecture for a frame independent measuring device independent QKD system based on a sagnac loop of the present invention;
FIG. 3 is a block diagram of a first sagnac loop modulator of a sagnac loop-based reference-system independent measurement device independent QKD system of the present invention;
FIG. 4 is a block diagram of a second sagnac loop modulator of a sagnac loop-based reference-system independent measurement device independent QKD system of the present invention;
FIG. 5 is a flow chart of a method of the invention for a frame independent measurement device independent QKD based on a sagnac loop;
Detailed Description
The present invention will be further described in detail with reference to the following examples, for the purpose of making the objects, technical solutions and advantages of the present invention more apparent, but the scope of the present invention is not limited to the following specific examples.
Example 1
As shown in fig. 1 to 4, the present invention provides a system QKD independent of reference frame independent measurement devices based on a sagnac loop, which includes a transmitting end Alice, a transmitting end Bob and a measuring end Charile; the transmitting end Alice and the transmitting end Bob are connected with the measuring end Chairle through a free space channel (the free space channel is air); the transmitting terminal Alice and the transmitting terminal Bob have the same structure, and the transmitting process of the signal of the present invention is described below by taking the transmitting terminal Alice as an example.
The transmitting terminal Alice comprises a Laser1 and a first sagnac loop modulator which are connected with each other, wherein the first sagnac loop modulator comprises an intensity modulator IM1, a polarization controller PC1, an optical circulator Cir1, a first transmitting terminal sagnac loop, an optical attenuator ATT1, an optical fiber collimator Col1 and a Q plate Q-plate1;
the transmitting end sagnac ring comprises a polarization beam splitter PBS1, a variable optical attenuator VOA1, a phase modulator PMA and an optical rotator1; the polarization beam splitter PBS1, the variable optical attenuator VOA1, the phase modulator PMA and the optical rotator1 are sequentially connected in series by adopting polarization maintaining fibers.
The Laser1 is used to generate light pulses that are used as quantum signals for system encoding to generate a key. The intensity modulator IM1 is configured to intensity modulate the first light pulse; the polarization controller PC1 is used for changing the quantum light signal into 45-degree linearly polarized light; the Q plate Q-plate1 is used for coupling spin angular momentum and orbital angular momentum;
the optical circulator Cir is an optical device that irreversibly polarizes an optical signal based on a faraday effect. The optical circulator is split into three ports and light can only propagate in one direction. Port 1 is the input port and port 2 is the output port, whereas the reflected signal reflected back to port 2 will be redirected to port 3 instead of port 1, the order of which is marked clockwise from bottom to top in the direction of the arrow in the figure.
The polarization beam splitter PBS1 divides 45 degrees of linearly polarized light into horizontally polarized light and vertically polarized light, and the polarization beam splitter PBS1 divides 45 degrees of linearly polarized light.
The light rotator1 is used for rotating the horizontally polarized light propagating clockwise by 90 degrees to vertically polarized light and rotating the vertically polarized light propagating counterclockwise by 90 degrees to horizontally polarized light;
the phase modulator PMA is configured to modulate the phase of polarized light in a clockwise or counter-clockwise direction; the phase modulator PMA is placed near the end of the polarization beam splitting PBS1 device where the vertically polarized light exits, so that the horizontally polarized light and the vertically polarized light reach the phase modulator PMA with a time difference, which is used for modulating the phase, the required clockwise and counter-clockwise propagating polarized light modulates only the phase in the clockwise or counter-clockwise direction, and may not modulate in the other direction.
The horizontally polarized light and the vertically polarized light respectively propagate in the clockwise and anticlockwise polarization-preserving fibers; the horizontal polarized light sequentially passes through a variable optical attenuator VOA1, a phase modulator PMA and an optical rotator1 to reach a polarization beam splitter PBS1; the vertically polarized light passes through the optical rotator1, the phase modulator PMA, and the variable optical attenuator VOA1 in this order to reach the polarization beam splitter PBS1.
When the horizontal polarized light and the vertical polarized light reach the adjustable variable optical attenuator VOA1, the adjustment can be carried out according to the requirements of the preparation base, and the specific adjustment modes and the results are shown in the following table 1;
TABLE 1
The horizontal polarized light and the vertical polarized light are converged by the PBS1, then are emitted to the optical attenuator ATT1 through the optical circulator Cir and attenuated to set light intensity by the optical attenuator ATT1, and then the signals are converted into space light signals through the optical collimator Col1 to be coupled with the Q plate Q-plate1 and transmitted to the measuring end Charlie through a free space channel.
Similarly, the transmitting end Bob transmits a space optical signal to the third-party measuring end Charlie through a free space channel;
the measuring end Charlie comprises reflecting mirrors Mirror 1-Mirror 4, a Q plate Q-plate2, a Q plate Q-plate3 and a BSM measuring instrument, and the BSM measuring instrument comprises a beam splitter BS, a polarization beam splitter PBS and a single photon detector D 1H The method comprises the steps of carrying out a first treatment on the surface of the Single photon detector D 1V Single photon detector D 2H And a single photon detector D 2V The method comprises the steps of carrying out a first treatment on the surface of the The beam splitter BS is connected with the polarizing beam splitter PBS3 and the polarizing beam splitter PBS 4; the single photon detector D 1H And a single photon detector D 1V Is connected with the polarization beam splitter PBS 3; the single photon detector D 2H And a single photon detector D 2V Is connected with a polarization beam splitter PBS 4;
after the light pulses of the transmitting end Alice and the transmitting end Bob reach the measuring end Charlie, the two light pulses are reflected to the Q-plate2 and the Q-plate3 by the reflectors Mirror1 and Mirror3 respectively, the two light pulses are demodulated by the Q-plate2 and the Q-plate3 and then reflected to the optical fiber collimators Col3 and Col4 by the reflectors Mirror2 and Mirror4 respectively, and are coupled into the optical fibers by the optical fiber collimators Col3 and Col 4. As shown in fig. 2, the two signals are transmitted to the BSM meter to perform Bell state measurement, and each single photon detector has different response according to the measurement result.
In the invention, the set light intensity is single photon light intensity, and the quantum state of the light pulse of the horizontal polarized light propagating clockwise is |H>By adjusting the phase modulator PMA post-quantum state becomes
The quantum state of the light pulse of the vertically polarized light propagating counterclockwise is |v>By adjusting the quantum state after the phase modulator PMA to +.>
The quantum state of the light pulse when the vertically polarized light and the horizontally polarized light are in the polarizing beam splitter PBS1 is +.>
In the invention, the phase modulator only modulates vertical polarized light to generate I++ > and I- >, and generates I H > and I V > by modulating the optical attenuator ATT1 to obtain X base and Z base.
As shown in fig. 1, two transmitting ends Alice and Bob have the same structure, taking the transmitting end Alice as an example, after the Laser1 generates pulse light, the pulse light is changed into 45 ° linearly polarized light through the action of the polarization controller PC1, the 45 ° linearly polarized light passes through the optical circulator Cir and is incident into the polarization beam splitter PBS1, at this time, the two light beams are separated into horizontal polarized light and vertical polarized light by the polarization beam splitter PBS1, the two light beams respectively propagate in the sagnac in the clockwise and counterclockwise directions, at this time, the purpose of loading the phase of only the vertical polarized light is achieved by calculating the time when the vertical polarized light and the horizontal polarized light reach the phase modulator PMA. When the phase modulator PMA loads the phase of 0 for vertically polarized light, at this time, |++ >, representing bit 1, is output from the polarization beam splitter; when the phase modulator PMA loads the vertically polarized light with pi/2, the output from the polarizing beam splitter is, | >, representing bit 0; when modulating the variable optical attenuator VOA without modulating the phase modulator PMA, the phase modulator PMA can generate H>And |V>Polarization state. Representing bit 1 and bit 0, respectively, all of the base information required for polarization BB84 is generated at this time. The Q-plate1 can realize polarization state |H>Becomes a quantum state
To the polarization state |V>Become quantum state->
Polarization state I+>Conversion to the Quantum state
Polarization state->Conversion to the Quantum state->
Wherein |R>Represents the right-hand circular polarization state, |L>Represents the left-hand circular polarization state, |l=1>Represents a state in which the orbital angular momentum topology charge value is 1, |l= -1>Representing a state where the orbital angular momentum topology charge value is-1.
The Q-plate2 can realize quantum state conversion
Convert back to polarization state |H>Will be
Convert back to polarization state |V>Quantum state->
Convert back to polarization state | +>Quantum state->
Returning to the polarization state->. At the measurement end Charlie, which is the conventional BB84 measurement equipment independent protocol, the satisfied relationship is shown in the table 1 above:
the BSM measuring instrument can only measure the polarization state |psi generated after the two paths of signals are combined by the beam splitter BS + >And |psi - >When the polarization state of the light pulse is measured to be |ψ + >Single photon detector D 1H And D 1V Or D 2H And D 2V In simultaneous response, when the polarization state of the light pulse is measured to be |ψ - >Single photon detector D 1H And D 2V Or D 2H And D 1V While responding. Wherein |H>And |V>Is Z base, | +>And->When the base selected by Alice and Bob is different, we consider that the base is not selected, in this case, the base is omitted when two communication parties pair the base, and when two communication parties simultaneously select one of the base X or the base Z, the measurement end Charlie is used for measuring the bellstate, and the code can be formed according to the response results of different single photon detectors. The corresponding relation between the detection result and the coding result is shown in the following table 2:
TABLE 2
As shown in fig. 5, the present invention further provides a method for QKD independent of a reference frame independent measuring device based on a sagnac loop, which is applied to a QKD system independent of a reference frame independent measuring device based on a sagnac loop as described in any one of the above, and is characterized in that: the method comprises the following steps:
s1, a transmitting end Alice and a transmitting end Bob are used as communication parties to simultaneously transmit quantum signals, polarization information is loaded through loading phases by utilizing a sagnac ring, when a phase modulator does not modulate and a variable optical attenuator VOA blocks anticlockwise pulses, a polarization state |H > is loaded, when the phase modulator does not modulate and the VOA blocks clockwise pulses, a polarization state |V > is loaded, when the phase modulator modulates 0 degree of horizontal polarization light and the variable optical attenuator VOA does not modulate, a polarization state|++ > is loaded, when the phase modulator modulates pi of horizontal polarization light, a polarization state|- >, and then the phase modulator is coupled through a Q plate and then transmitted to a measuring end Charlie through a free space channel;
s2, two paths of quantum signals reach a measuring end Charlie, polarization and orbital angular momentum are decoupled through two Q plates, then the two paths of quantum signals enter a BSM measuring instrument for measurement, and when the polarization state of a light pulse is measured to be |psi + >Single photon detector D 1H And D 1V Or D 2H And D 2V In simultaneous response, when the polarization state of the light pulse is measured to be |ψ - >Single photon detector D 1H And D 2V Or D 2H And D 1V Simultaneously responding;
s3, the measuring end Charlie publishes the measuring result of the BSM measuring instrument through a classical channel, namely, the single photon detector responds, and the two communication parties obtain the detecting result from the measuring end Charlie;
s4, the transmitting terminal Alice publishes the condition of the base selection through a classical channel, and the transmitting terminal Bob discards detection results which are different from the base selection condition of the transmitting terminal Alice according to the condition of the base selection of the transmitting terminal Alice so as to obtain an original secret key;
s5, the transmitting terminal Bob selects part of the secret key to detect error codes; if the error rate exceeds the set threshold, proving that an eavesdropper exists, discarding the result and restarting; if the error rate does not exceed the set threshold value, continuing the next operation;
s6, post-processing is carried out on the original secret key to obtain a usable safety secret key.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention provides a device independent protocol for measuring by utilizing the polarization state generated by the Sagnac ring modulator, which is simple to operate and easy to realize, and solves the problem of complex preparation in the prior art.
2. The Sagnac loop modulator provided by the invention adopts the phase modulator to modulate polarization, so that the speed is faster and the stability is better.
3. The invention better utilizes the relevant property of the Q-plate of the Q plate, eliminates the influence of the environment on the polarization state, does not need to align a reference system, simplifies the complexity of the system and improves the code rate. And the operation is easy, and the structure is simple.
4. The invention uses the idea of irrelevant measuring equipment, avoids all attacks to the measuring end, and has good stability and low cost.
Variations and modifications to the above would be obvious to persons skilled in the art to which the invention pertains from the foregoing description and teachings. Therefore, the invention is not limited to the specific embodiments disclosed and described above, but some modifications and changes of the invention should be also included in the scope of the claims of the invention. In addition, although specific terms are used in the present specification, these terms are for convenience of description only and do not constitute any limitation on the invention.
Claims (10)
1. A QKD system based on a sagnac ring and irrelevant to reference system irrelevant to measurement equipment comprises a transmitting end Alice, a transmitting end Bob and a measuring end Charlie; the transmitting terminal Alice and the transmitting terminal Bob are connected with the measuring terminal Charlie through a free space channel; the method is characterized in that:
the transmitting terminal Alice comprises a Laser1 and a first sagnac loop modulator which are connected with each other, wherein the first sagnac loop modulator comprises an intensity modulator IM1, a polarization controller PC1, an optical circulator Cir1, a first transmitting terminal sagnac loop, an optical attenuator ATT1, an optical fiber collimator Col1 and a Q plate Q-plate1;
the Laser1 is used for generating a first optical pulse, and the first optical pulse is used for system coding as a quantum signal to generate a secret key;
the intensity modulator IM1 is configured to intensity modulate the first light pulse;
the polarization controller PC1 is used for changing the quantum signal into 45-degree linearly polarized light;
the Q plate Q-plate1 is used for coupling spin angular momentum and orbital angular momentum;
the transmitting end Bob comprises a Laser2 and a second sagnac loop modulator which are connected with each other, wherein the second sagnac loop modulator comprises an intensity modulator IM2, a polarization controller PC2, an optical circulator Cir2, a second transmitting end sagnac loop, an optical attenuator ATT2, an optical fiber collimator Col2 and a Q plate Q-plate4;
the Laser2 is used for generating a second optical pulse, and the second optical pulse is used for system coding as a quantum signal to generate a secret key;
the intensity modulator IM2 is configured to perform single modulation on the second light pulse;
the polarization controller PC2 is used for changing the quantum light signal into 45-degree linearly polarized light;
the Q plate Q-plate4 is used for coupling spin angular momentum and orbital angular momentum;
the measuring end Charlie comprises reflecting mirrors Mirror 1-Mirror 4, a Q plate Q-plate2, a Q plate Q-plate3 and a BSM measuring instrument, and the BSM measuring instrument comprises a beam splitter BS, a polarization beam splitter PBS and a single photon detector D 1H Single photon detector D 1V Single photon detector D 2H And a single photon detector D 2V The method comprises the steps of carrying out a first treatment on the surface of the The beam splitter BS is connected with the polarizing beam splitter PBS3 and the polarizing beam splitter PBS 4; the single photon detector D 1H And a single photon detector D 1V Is connected with the polarization beam splitter PBS 3; the single photon detector D 2H And a single photon detector D 2V Is connected with a polarization beam splitter PBS 4;
the first transmitting end sagnac loop is used for dividing 45-degree linearly polarized light into first horizontally polarized light and first vertically polarized light, converging the first horizontally polarized light and the first vertically polarized light, outputting the first horizontally polarized light to the optical attenuator ATT1 through the optical circulator Cir1, attenuating the first horizontally polarized light to set light intensity by the optical attenuator ATT1, converting the signal into a space light signal through the optical fiber collimator Col1, coupling the space light signal with the Q board, and transmitting the space light signal to the measuring end Charlie through a free space channel;
the second transmitting end sagnac loop is used for dividing 45-degree linearly polarized light into second horizontally polarized light and second vertically polarized light, converging the second horizontally polarized light and the second vertically polarized light, outputting the converged second horizontally polarized light and the converged second vertically polarized light to an optical attenuator ATT2 through an optical circulator Cir after PBS2 is converged and attenuating the converged second horizontally polarized light and the converged second vertically polarized light to set light intensity by the optical attenuator ATT2, converting the signals into space light signals through an optical fiber collimator Col1, coupling the space light signals with a Q plate Q-plate1, and transmitting the space light signals to a measuring end Charlie through a free space channel;
after the first light pulse and the second light pulse reach the measuring end Charlie, the first light pulse and the second light pulse are reflected to the Q-plate2 and the Q-plate3 by the reflectors Mirror1 and Mirror3 respectively, demodulated by the Q-plate2 and the Q-plate4, reflected to the optical fiber collimators Col3 and Col4 by the reflectors Mirror2 and Mirror4 respectively, coupled into the optical fibers by the optical fiber collimators Col3 and Col4, and the two paths of signals are transmitted to the BSM to be measured in a Bell state.
2. The sagnac loop-based reference-frame independent measurement device independent QKD system of claim 1, wherein: the first transmitting end sagnac loop comprises a polarization beam splitter PBS1, a variable optical attenuator VOA1, a phase modulator PMA and an optical rotator1; the polarization beam splitter PBS1, the variable optical attenuator VOA1, the phase modulator PMA and the optical rotator1 are sequentially connected in series by adopting polarization maintaining fibers;
the polarization beam splitter PBS1 is used for dividing 45-degree linearly polarized light into first horizontally polarized light and first vertically polarized light;
the phase modulator PMA is configured to modulate the phase of polarized light in a clockwise or counter-clockwise direction;
the light rotator1 is used for rotating the horizontally polarized light propagating clockwise by 90 degrees to vertically polarized light and rotating the vertically polarized light propagating counterclockwise by 90 degrees to horizontally polarized light;
the first horizontally polarized light and the first vertically polarized light propagate in the polarization-preserving optical fiber clockwise and anticlockwise respectively; the first horizontal polarized light sequentially passes through the variable optical attenuator VOA1, the phase modulator PMA and the optical rotator rotor 1 to reach the polarization beam splitter PBS1, and the first vertical polarized light sequentially passes through the optical rotator rotor 1, the phase modulator PMA and the variable optical attenuator VOA1 to reach the polarization beam splitter PBS1 to be combined with the first horizontal polarized light reaching the polarization beam splitter PBS1.
3. The sagnac loop-based reference-frame independent measurement device independent QKD system of claim 2, wherein: the phase modulator PMA is disposed at one end near the vertical polarized light outlet of the polarizing beam splitter PBS1, so that the first horizontal polarized light and the second vertical polarized light reach the phase modulator PMA with a time difference, and the time difference is used for modulating the phase of the clockwise and counterclockwise polarized light only in the clockwise or counterclockwise direction; when the phase modulator PMA loads the phase of 0 for the first vertically polarized light, at this time, |++ >, representing bit 1, is output from the polarization beam splitter PBS1; when the phase modulator PMA loads the first vertically polarized light with pi/2, it is, | -, which represents bit 0, that is output from the polarizing beam splitter PBS1 at this time.
4. A sagnac loop-based reference-frame independent measurement device independent QKD system according to claim 3, wherein: the second transmitting end sagnac loop comprises a polarization beam splitter PBS2, a variable optical attenuator VOA2, a phase modulator PMB and an optical rotator2;
the polarization beam splitter PBS2, the variable optical attenuator VOA2, the phase modulator PMB and the optical rotator2 are sequentially connected in series by adopting polarization maintaining fibers;
the polarization beam splitter PBS2 divides 45-degree linearly polarized light into second horizontally polarized light and second vertically polarized light;
the phase modulator PMB is used for modulating the phase of polarized light in a clockwise or counterclockwise direction;
the light rotator2 is used for rotating the horizontally polarized light propagating clockwise by 90 degrees to vertically polarized light and rotating the vertically polarized light propagating counterclockwise by 90 degrees to horizontally polarized light;
the second horizontal polarized light and the second vertical polarized light respectively propagate in the polarization maintaining optical fiber clockwise and anticlockwise, the second horizontal polarized light sequentially passes through the variable optical attenuator VOA2, the phase modulator PMB and the optical rotator2 to reach the polarization beam splitter PBS2, and the second vertical polarized light sequentially passes through the optical rotator2, the phase modulator PMB and the variable optical attenuator VOA2 to reach the polarization beam splitter PBS2.
5. The sagnac loop-based reference-frame independent measurement device independent QKD system of claim 4, wherein: the phase modulator PMB is disposed at one end near the vertical polarized light outlet of the polarizing beam splitter PBS2, so that the second horizontal polarized light and the second vertical polarized light reach the phase modulator PMB with a time difference, and the time difference is that the clockwise and counterclockwise polarized light required for modulating the phase modulates only the phase in the clockwise or counterclockwise direction; when the phase modulator PMB loads a phase of 0 for vertically polarized light, at this time, |++ >, representing bit 1, is output from the polarization beam splitter PBS 2; when the phase modulator PMB loads the vertically polarized light with pi/2, it is, | -, which represents bit 0, that is output from the polarization beam splitter PBS2 at this time.
6. The sagnac loop-based reference-frame independent measurement device independent QKD system of claim 5, wherein: the polarization state of the light pulse of the first horizontal polarized light and the second horizontal polarized light propagating clockwise is |H>By adjusting the phase modulator to become
The polarization state of the light pulses of the first and second vertically polarized light propagating counterclockwise is |V>By adjusting the phase modulator PMA and the phase modulator PMB, it becomes +.>
The quantum state of the light pulse when the vertically polarized light and the horizontally polarized light are combined in the polarizing beam splitter PBS1 is
7. The sagnac loop-based reference-frame independent measurement device independent QKD system of claim 6, wherein: the Q-plates Q-plate1 and Q-plate4 will have polarization state |H>Becomes a quantum state
To the polarization state |V>Become quantum state->
Polarization state I+>Conversion to the Quantum state->
Polarization state->Conversion to the Quantum state->
Wherein |R>Represents the right-hand circular polarization state, |L>Represents the left-hand circular polarization state, |l=1>Represents a state in which the orbital angular momentum topology charge value is 1, |l= -1>Representing a state where the orbital angular momentum topology charge value is-1.
8. The sagnac loop-based reference-frame independent measurement device independent QKD system of claim 7, wherein: the Q-board 2 and the Q-board 3 are used for quantum state
Convert back to polarization state |H>Will be
Convert back to polarization state |V>Quantum state->
Convert back to polarization state | +>Quantum state->
Returning to the polarization state->。
9. The sagnac loop-based reference-frame independent measurement device independent QKD system of claim 1, wherein: the BSM measuring instrument can only measure the polarization state |psi generated after the two paths of signals are combined by the beam splitter BS + > and |psi - When the polarization state of the light pulse is measured to be |psi + At > time, single photon detector D 1H And D 1V Or D 2H And D 2V In simultaneous response, when the polarization state of the light pulse is measured to be |ψ - >Single photon detector D 1H And D 2V Or D 2H And D 1V While responding.
10. A sagnac loop-based reference-independent measurement device independent QKD method for use in a sagnac loop-based reference-independent QKD system as claimed in any one of claims 1-9, comprising the steps of:
s1, a transmitting end Alice and a transmitting end Bob are used as communication parties to simultaneously transmit quantum signals, polarization information is loaded through loading phases by utilizing a sagnac loop, when a phase modulator does not modulate and a variable optical attenuator VOA blocks anticlockwise pulses, a polarization state |H >, when the phase modulator does not modulate and the VOA blocks clockwise pulses, a polarization state |V >, when the phase modulator modulates 0 DEG on horizontal polarization and the variable optical attenuator VOA does not modulate, a polarization state|++ >, when the phase modulator modulates pi on horizontal polarization, a polarization state|- >, and then the phase modulator is coupled through a Q plate and then transmitted to a measuring end Charlie through a free space channel;
s2, two paths of quantum signals reach a measuring end Charlie, polarization and orbital angular momentum are decoupled through two Q plates, then the two paths of quantum signals enter a BSM measuring instrument for measurement, and when the polarization state of a light pulse is measured to be |psi + >Single photon detector D 1H And D 1 Or D 2H And D 2V In simultaneous response, when the polarization state of the light pulse is measured to be |ψ - At > time, single photon detector D 1H And D 2V Or D 2H And D 1V Simultaneously responding;
s3, the measuring end Charlie publishes the measuring result of the BSM measuring instrument through a classical channel, and the two communication parties obtain a detection result from the measuring end Charlie;
s4, the transmitting terminal Alice publishes the condition of the base selection through a classical channel, and the transmitting terminal Bob discards detection results which are different from the base selection condition of the transmitting terminal Alice according to the condition of the base selection of the transmitting terminal Alice so as to obtain an original secret key;
s5, the transmitting terminal Bob selects part of the secret key to detect error codes; if the error rate exceeds the set threshold, proving that an eavesdropper exists, discarding the result and restarting; if the error rate does not exceed the set threshold value, continuing the next operation;
s6, post-processing is carried out on the original secret key to obtain a usable safety secret key.
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