CN113572597A - Single-state half-quantum key distribution system and method - Google Patents
Single-state half-quantum key distribution system and method Download PDFInfo
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Abstract
The system comprises a sending end and a receiving end, wherein the sending end comprises a signal light unit, a light transmission unit, a phase modulator unit and a detector unit, the signal light unit, the light transmission unit and the phase modulator unit are sequentially connected, the detector unit is connected with the phase modulator unit and the light transmission unit, and the phase modulator unit is an unequal-arm interferometer; the receiving end comprises an intensity modulator unit, the intensity modulator unit is connected with the phase modulator unit, and the intensity modulator unit is an interference loop; the interference loop is used for loading voltage on the received optical pulse group sent by the unequal arm interferometer to obtain a processed optical pulse group and sending the processed optical pulse group to the unequal arm interferometer. The system and the method of the application realize the single-state half-quantum key distribution protocol by adopting a selective modulation mode, solve the problem of unreasonable design of the existing system, and have extremely high safety and feasibility of practical application.
Description
Technical Field
The application relates to the field of quantum secret communication, in particular to a system and a method for distributing a single-state half-quantum key.
Background
At present, with the use of computers and the internet in the field of communications, the encryption requirements for communication data are gradually increasing. Among data encryption means, certain encryption means depending on the complexity of calculation still have certain possibility of being decoded, and the quantum cryptography is based on the heisenberg inaccurate measurement principle and the unknown quantum state unclonable principle, so that the requirement of a one-time pad encryption system can be met theoretically, and the method has theoretical unconditional security.
In 1984, Bennett and Brassard proposed the first quantum key distribution protocol, and after that, both communication parties of the quantum key distribution protocol are often defined as an Alice terminal and a Bob terminal, and both communication parties have the capability of manipulating quanta, such as the preparation and measurement of qubits on any basis form. Until 2007, Boyer et al proposed the concept of a half-quantum key distribution protocol and a four-state protocol based on the previous quantum key distribution protocol, and reduced the requirements of the quantum key distribution protocol, and Bob only needs to have the capability of preparing quantum states in a Z-base form and directly transferring quantum bits.
In 2009, Zou et al proposed a singlet-state half-quantum key distribution protocol for half-quantum key distribution, which specifically includes the following steps: the method comprises the steps that an Alice end prepares a photon with a quantum state of | + >, the photon is sent to a Bob end, the Bob end randomly selects 'the photon is retransmitted after the photon is measured by using a Z base' or 'the photon is returned without any operation', the Alice end randomly selects the Z base or the X base to measure the photon sent back by the Bob end, finally, the Alice and the Bob simultaneously disclose operation selection of the Alice and the Bob, if the Bob end selects the Z base to measure and the Alice end also selects the Z base to measure, the quantum bit at the position can be used as a code, and if the Bob end selects the X base to measure and the Alice end does not return the photon without any operation, the quantum bit at the position can be used for detecting eavesdropping.
In the current implementation method, because the implementation method of the distribution of the singlet state half quantum key has certain defects in design, a receiving end needs to regenerate new photons according to the result obtained by measuring the photons and send the new photons to a sending end, the operation is complex, and the potential safety hazard of information leakage caused by the attack of a mark exists, so that the current implementation method is not safe enough and is difficult to have the feasibility of practical application.
Disclosure of Invention
The embodiment of the application aims to provide a system and a method for distributing a single-state half-quantum key, which realize a single-state half-quantum key distribution protocol by adopting a selective modulation mode, solve the problem of unreasonable design of a protocol system in the prior art, simplify the operation of a receiving end, realize a stable two-way experimental system for the single-state half-quantum key distribution protocol, and have extremely high safety and feasibility of practical application.
In a first aspect, an embodiment of the present application provides a singlet half quantum key distribution system, including a sending end and a receiving end, where the sending end includes a signal light unit, a light transmission unit, a phase modulator unit, and a detector unit, the signal light unit, the light transmission unit, and the phase modulator unit are connected in sequence, the detector unit is connected with the phase modulator unit and the light transmission unit, and the phase modulator unit is an unequal-arm interferometer;
the receiving end comprises an intensity modulator unit, the intensity modulator unit is connected with the unequal arm interferometer, and the intensity modulator unit is an interference loop;
the interference loop is used for loading voltage on the received optical pulse group sent by the unequal arm interferometer to obtain a processed optical pulse group, and sending the processed optical pulse group to the unequal arm interferometer.
In the implementation process, the singlet half-quantum key distribution system of the embodiment of the application adopts the interference loop as the intensity modulator unit of the receiving end and cooperates with the unequal-arm interferometer as the phase modulator unit, compared with the prior art, the system is a more reasonable receiving end design, can realize the singlet half-quantum key distribution protocol by adopting a selective modulation mode, solves the problem that the design of a protocol system in the prior art is unreasonable, and has extremely high safety and feasibility of practical application.
Furthermore, the interference loop comprises a polarization beam splitter and an intensity modulator, the polarization beam splitter is connected with the unequal-arm interferometer through a quantum channel, and two ends of the intensity modulator are respectively connected with the polarization beam splitter.
In the implementation process, the interference loop combining the polarization beam splitter and the intensity modulator is adopted, so that the operation of the receiving end on the sent optical pulse group in the singlet state half-quantum key distribution protocol can be effectively realized, the singlet state half-quantum key distribution protocol is realized in a selective modulation mode, the problem of unreasonable design of a protocol system in the prior art is solved, and the operation of the receiving end is simplified.
Further, the non-equal arm interferometer comprises a first beam splitter, a second beam splitter, a short arm subunit and a long arm subunit;
the first beam splitter is connected with the optical transmission unit, the first beam splitter is respectively connected with the long-arm subunit and the short-arm subunit, the long-arm subunit and the short-arm subunit are respectively connected with the second beam splitter, and the second beam splitter is connected with the interference loop through a quantum channel.
In the implementation process, the unequal-arm interferometer comprises a long-arm subunit and a short-arm subunit, and the unequal-arm interferometer comprises the two subunits with different lengths, and the optical paths of the two subunits are different, so that the optical pulse signals received by the unequal-arm interferometer from the optical transmission unit can be emitted into two optical pulses in a front-to-back manner under the cooperation of the first beam splitter, and the preparation operation required by a transmitting end in a singlet-state half-quantum key distribution protocol is realized.
Further, the long-arm subunit comprises a second polarizer and a fiber attenuator which are connected, the second polarizer is connected with the first beam splitter, and the fiber attenuator is connected with the second beam splitter;
the short-arm subunit comprises a phase modulator and a first polarizer which are connected, the phase modulator is connected with the first beam splitter, and the first polarizer is connected with the second beam splitter.
In the implementation process, one of the functions of the unequal-arm interferometer is to implement preparation of an optical pulse group by different optical path lengths of the long and short arm subunits, wherein the short arm subunit includes a phase modulator capable of loading a phase to an optical pulse incident to the short arm subunit, and the long arm subunit includes an optical fiber attenuator capable of adjusting intensity loss of the optical pulse of the long arm subunit, so that the optical pulse of the long arm subunit and the optical pulse of the short arm subunit have the same intensity, and a module of the long arm subunit and the short arm subunit constitutes a module to supplement and perfect the preparation problem of the optical pulse group.
Further, the signal light unit comprises a laser, an optical isolator and an optical attenuator which are connected in sequence, and the optical attenuator is connected with the light transmission unit.
In the implementation process, the combination of the laser, the optical isolator and the optical attenuator is adopted, the signal light unit can generate stable signal light, and the signal light is adjusted to be at proper intensity, so that a stable and proper signal light base is provided for the operation of a subsequent unit.
Further, the optical transmission unit comprises an optical circulator, and the optical circulator is connected with the signal optical unit and the unequal arm interferometer.
In the implementation process, the optical circulator in the optical transmission unit can effectively transmit the signal light between the signal light unit and the unequal-arm interferometer.
Furthermore, the detector unit comprises a first single-photon detector and a second single-photon detector, the first single-photon detector is connected with the unequal-arm interferometer, and the second single-photon detector is connected with the optical transmission unit.
In the implementation process, the detector unit is connected with the unequal-arm interferometer and the optical transmission unit, two different optical pulse interference signal results can be obtained, and therefore the content of the singlet state half quantum key distribution protocol is reliably implemented.
In a second aspect, an embodiment of the present application provides a method for distributing a singlet half quantum key, including:
the signal light unit generates light pulses and transmits the light pulses to the unequal arm interferometer through the light transmission unit;
the unequal arm interferometer processes the received optical pulses to obtain a first pulse group and sends the first pulse group to the interference loop;
the interference loop processes the received first pulse group to obtain a second pulse group, and sends the second pulse group to the unequal-arm interferometer;
the unequal-arm interferometer processes the received second pulse group to obtain a third pulse group, and sends the third pulse group to the optical transmission unit and the detector unit;
the detector unit receives a third pulse group and detects the third pulse group to obtain a detection result;
and the singlet state half quantum key distribution system obtains a security key according to the detection result, the processing of the unequal-arm interferometer on the received optical pulse and the processing of the interference loop on the received first pulse group.
In the implementation process, the singlet state half-quantum key distribution method in the embodiment of the application adopts the interference loop as the intensity modulator unit of the receiving end, and is matched with the unequal-arm interferometer as the phase modulator unit.
Further, the processing, by the non-equal arm interferometer, the received optical pulses to obtain a first pulse group, including:
dividing the received signal pulse into a first optical pulse and a second optical pulse by the difference between the lengths of the long-arm subunit and the short-arm subunit in the unequal-arm interferometer, wherein the first optical pulse and the second optical pulse form the first pulse group.
In the implementation process, the process of preparing and sending the preset quantum state by the sending end in the singlet state half-quantum key distribution protocol can be better implemented by using the optical path difference value of the long-arm and short-arm subunits in the unequal-arm interferometer.
Further, the interference loop processes the received first pulse group to obtain a second pulse group, including:
the interference loop takes the received first set of pulses as the second set of pulses;
or, the interference loop performs voltage intervention operation on the first pulse of the first pulse group to obtain the second pulse group;
or the interference loop carries out voltage intervention operation on the second pulse of the first pulse group to obtain the second pulse group.
In the implementation process, the interference loop is used as the receiving end, the modulation operation of the receiving end on the optical pulse sent by the sending end is realized, the unimorph half-quantum key distribution protocol can be realized in a selective modulation mode, the problem that the design of a protocol system in the prior art is unreasonable is reasonably solved, the operation of the receiving end is simplified, and the stable unimorph half-quantum key distribution protocol double-path experimental system is realized.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments of the present application will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and that those skilled in the art can also obtain other related drawings based on the drawings without inventive efforts.
Fig. 1 is a schematic structural diagram of a singlet-state half-quantum key distribution system according to an embodiment of the present disclosure;
fig. 2 is a schematic structural diagram of a signal light unit according to an embodiment of the present disclosure;
fig. 3 is a schematic structural diagram of a phase modulator unit according to an embodiment of the present application;
fig. 4 is a schematic structural diagram of an intensity modulator unit according to an embodiment of the present application;
fig. 5 is a schematic flowchart of a singlet half-quantum key distribution method according to a second embodiment of the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. The components of the embodiments of the present application, generally described and illustrated in the figures herein, can be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present application, presented in the accompanying drawings, is not intended to limit the scope of the claimed application, but is merely representative of selected embodiments of the application. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present application without making any creative effort, shall fall within the protection scope of the present application.
In this application, the terms "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings. These terms are used primarily to better describe the present application and its embodiments, and are not used to limit the indicated devices, elements or components to a particular orientation or to be constructed and operated in a particular orientation.
Moreover, some of the above terms may be used to indicate other meanings besides the orientation or positional relationship, for example, the term "on" may also be used to indicate some kind of attachment or connection relationship in some cases. The specific meaning of these terms in this application will be understood by those of ordinary skill in the art as appropriate.
Furthermore, the terms "mounted," "disposed," "provided," "connected," and "connected" are to be construed broadly. For example, it may be a fixed connection, a removable connection, or a unitary construction; can be a mechanical connection, or a point connection; either directly or indirectly through intervening media, or may be an internal communication between two devices, elements or components. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as appropriate.
Furthermore, the terms "first," "second," and the like, are used primarily to distinguish one device, element, or component from another (the specific nature and configuration may be the same or different), and are not used to indicate or imply the relative importance or number of the indicated devices, elements, or components. "plurality" means two or more unless otherwise specified.
Example one
Referring to fig. 1, fig. 1 is a block diagram illustrating a structure of a singlet half-quantum key distribution system according to an embodiment of the present application.
The singlet-state half-quantum key distribution system comprises a sending end and a receiving end, wherein the sending end comprises a signal light unit 1, a light transmission unit 2, a phase modulator unit 3 and a detector unit 4, the signal light unit 1, the light transmission unit 2 and the phase modulator unit 3 are sequentially connected, the phase modulator unit 3 is connected with the receiving end, the detector unit 4 is connected with the phase modulator unit 3 and the light transmission unit 2, and the phase modulator unit 4 is an unequal-arm interferometer;
the receiving end comprises an intensity modulator unit 5, the intensity modulator unit 5 is connected with the unequal arm interferometer, and the intensity modulator unit 5 is an interference loop;
the interference loop is used for loading voltage on the received optical pulse group sent by the unequal arm interferometer to obtain a processed optical pulse group, and sending the processed optical pulse group to the unequal arm interferometer.
In the present embodiment, the signal light unit 1 can provide a stable signal light output; the optical transmission unit 2 is used for effectively transmitting signal light between the signal light unit and the unequal arm interferometer; the non-equal arm interferometer can realize the encoding process of time phase in a single-state half-quantum key distribution protocol; the detector unit 4 can detect the interference result of the signal light pulse; the interference loop is used for realizing a single-state half-quantum key distribution protocol and selecting and operating the optical pulse.
The sending end can also be called an Alice sending end or an Alice end, and the receiving end can also be called a Bob receiving end or a Bob end; the single-state half-quantum key distribution system has a bidirectional channel, and the channel along the signal light unit 1, the light transmission unit 2, the unequal-arm interferometer and the interference loop is a channel sent by a sending end to a receiving end and is a forward channel; the channels along the interference loop, the unequal-arm interferometer, the optical transmission unit 2 and the detector unit 4 are channels sent from the receiving end to the sending end, and are reverse channels.
The interference loop processing the loading voltage of the received optical pulse group is divided into two options, wherein one option is that the voltage is not loaded on the optical pulse group and is directly sent to the unequal arm interferometer through the interference loop, and the option can be defined as CTRL operation of a receiving end; another option is to apply a voltage to the optical pulse train and send the voltage-applied optical pulse train to the non-equal arm interferometer, which can be defined as SIFT operation at the receiving end.
Because SIFT operation of the receiving end is realized through an interference loop, new optical pulses are not needed to be manufactured and sent to the sending end again by the receiving end, the original optical pulses subjected to voltage loading processing are sent to the sending end, operation is simplified, meanwhile, the safety problem that information is leaked due to marking attack in the process of manufacturing the new optical pulses can be avoided, and safety of a system and feasibility of practical application are improved.
Alternatively, the non-equal arm interferometer may be an non-equal arm Mach-Zehnder interferometer, and the interferometric loop may be a Sagnac interferometric loop.
Compared with the prior art, the unimorph half-quantum key distribution system adopts the interference loop as the intensity modulator unit of the receiving end and is matched with the unequal-arm interferometer as the phase modulator unit, is a more reasonable receiving end design, can adopt a selective modulation mode to realize a unimorph half-quantum key distribution protocol, solves the problem that the design of a protocol system in the prior art is unreasonable, and has extremely high safety and feasibility of practical application.
Referring to fig. 1 and 2, fig. 2 is a schematic structural diagram of a signal light unit according to the present application, where the signal light unit 1 includes a laser 101, an optical isolator 102, and an optical attenuator 103, and the laser 101, the optical isolator 102, and the optical attenuator 103 are connected in sequence.
Wherein, the laser 101 is used for generating stable signal light; the optical isolator 102 is used for preventing backward transmission light generated in an optical path from generating adverse effects on a light source and an optical path system, namely isolating the backward transmission light and avoiding the backward transmission light from generating interference; the optical attenuator 103 is used to adjust the output signal light to reach a proper intensity, which means that the light intensity is within the threshold of the detector when the signal light finally reaches the detector of the detector unit.
Referring to fig. 1, the optical transmission unit 2 includes an optical circulator, where the optical circulator has three ports, where a first port of the optical circulator is connected to the optical attenuator 103, a second port of the optical circulator is connected to the phase modulator unit 3, and a third port of the optical circulator is connected to the detector unit 4;
the optical circulator functions to transmit signal light as optical pulses to the phase modulator unit 3 connected to the second port and to transmit optical pulses returned from the phase modulator unit 3 to the detector unit 4 connected to the third port, upon receiving the signal light generated by the signal light unit 1.
Referring to fig. 1 and 3, where fig. 3 is a schematic structural diagram of a phase modulator unit of the present application, the phase modulator unit 3 is an unequal arm interferometer, the unequal arm interferometer includes a first beam splitter 105, a second beam splitter 110, a long arm subunit and a short arm subunit, the first beam splitter 105 has four ports, a first port of the first beam splitter 105 is connected to a second port of the optical circulator, a second port of the first beam splitter 105 is connected to one end of the long arm subunit, a third port of the first beam splitter 105 is connected to one end of the short arm subunit, and a fourth port of the first beam splitter 105 is connected to the detector unit 4; the second beam splitter 110 has three ports, the other end of the long-arm subunit is connected to the first port of the second beam splitter 110, the other end of the short-arm subunit is connected to the second port of the second beam splitter 110, and the third port of the second beam splitter 110 is connected to the interference loop of the receiving end through a quantum channel.
The first beam splitter 105 is configured to split the received optical pulse into a first optical pulse and a second optical pulse, and to emit the first optical pulse and the second optical pulse to the long-arm subunit and the short-arm subunit from the second port and the third port of the first beam splitter 105.
In this embodiment, the short-arm subunit includes a phase modulator 106 and a first polarizer 107 connected to each other, where the phase modulator 106 is connected to the third port of the first beam splitter 105, the first polarizer 107 is connected to the second port of the second beam splitter 110, and the phase modulator 106 is configured to apply a phase to the received optical pulse; the first polarizer 107 functions to adjust the polarization mode of the returned optical pulse in the backward channel when the short arm subunit receives the optical pulse returned from the second beam splitter 110, so that the optical pulse reaches the maximum output power when being incident on the phase modulator 106.
In this embodiment, the long-arm subunit includes a second polarizer 108 and a fiber attenuator 109 connected to each other, where the second polarizer 108 is connected to the second port of the first beam splitter 105, the fiber attenuator 109 is connected to the first port of the second beam splitter 110, the second polarizer 108 functions in a reverse channel, and when the long-arm subunit receives an optical pulse returned from the fiber attenuator 109, a polarization mode of the returned optical pulse is adjusted, so that when the optical pulse is incident on the first beam splitter 105, a preset interference contrast may be achieved; the function of the fiber attenuator 109 is to adjust the loss of the optical pulse in the long-arm subunit so that the optical pulse in the long-arm subunit has the same intensity as the optical pulse in the short-arm subunit.
The second beam splitter can emit the first optical pulse and the second optical pulse from the third port and send the first optical pulse and the second optical pulse to the interference loop through the quantum channel, the first optical pulse and the second optical pulse can be emitted from the ports in tandem due to the arm length difference between the long-arm subunit and the short-arm subunit, and the first optical pulse and the second optical pulse can be considered to be combined to obtain a first pulse group.
In this embodiment, when the phase modulator 106 does not apply a phase voltage to the optical pulse, it corresponds to the Z-basis vector in the time phase encoding, and when the phase modulator selects to apply two voltages, i.e. 0 or V pi, to the optical pulse, it corresponds to the X-basis vector in the time phase encoding; wherein, V pi is half-wave voltage of the phase modulator.
Alternatively, the phase of the optical pulse loaded by the phase modulator 106 may be 0 or π.
Optionally, first beam splitter 105 and second beam splitter 110 each have a splitting ratio of 1: 1.
Referring to fig. 1, the detector unit 4 includes a first single-photon detector 111 and a second single-photon detector 112, the first single-photon detector 111 is connected to the third port of the optical circulator, and the second single-photon detector 112 is connected to the fourth port of the first beam splitter 105.
Referring to fig. 1 and 4, fig. 4 is a schematic structural diagram of an intensity modulator unit of the present application, and the intensity modulator unit 5 is an interference loop and includes a polarization beam splitter 201 and an intensity modulator 202, where the polarization beam splitter 201 is connected to a second beam splitter 202 through a quantum channel, and two ends of the intensity modulator 202 are respectively connected to the polarization beam splitter 201.
The intensity modulator 202 is used to generate a selection of equal probability, select whether to modulate the voltage applied to the received first pulse group, if not, the intensity modulator 202 does not operate, and send the first pulse group back to the second beam splitter 110 through the polarization beam splitter 201 in the original order, and if modulation is selected, generate a new equal probability selection, select to reduce the intensity of the first optical pulse or the second optical pulse to 0, that is, randomly reserve one optical pulse of the first pulse group, and finally send the reserved optical pulse as the second pulse group to the second beam splitter 110 through the polarization beam splitter 201.
Optionally, the intensity modulator 202 and the polarization beam splitter 201 are connected by polarization maintaining fiber, and the lengths of the connected polarization maintaining fibers should be the same.
Optionally, in the singlet-state half-quantum-key distribution system according to the embodiment of the present application, the connection mode adopted by each unit may be an optical fiber connection, where the optical fiber may be a single-mode optical fiber.
In the singlet half-quantum key distribution system in the embodiment of the present application, the process of determining the key refers to the following relevant content of the singlet half-quantum key distribution method, and is not described herein again.
Example two
Referring to fig. 1 and fig. 5, where fig. 5 is a schematic flowchart of a method for distributing a singlet half quantum key according to an embodiment of the present application, the method for distributing a singlet half quantum key according to an embodiment of the present application includes:
step S110, generating a light pulse by the signal light unit 1, and transmitting the light pulse to the unequal arm interferometer through the light transmission unit 2;
step S120, the unequal arm interferometer processes the received light pulse to obtain a first pulse group and sends the first pulse group to the interference loop;
step S130, the interference loop processes the received first pulse group to obtain a second pulse group, and sends the second pulse group to the unequal-arm interferometer;
step S140, the unequal-arm interferometer processes the received second pulse group to obtain a third pulse group, and sends the third pulse group to the optical transmission unit 2 and the detector unit 4;
step S150, the detector unit 4 receives the third pulse group and detects the third pulse group to obtain a detection result;
and step S160, the singlet state half quantum key distribution system obtains a security key according to the detection result, the processing of the unequal-arm interferometer on the received optical pulse and the processing of the interference loop on the received first pulse group.
Compared with the prior art, the unimorph half-quantum key distribution protocol is realized by adopting a selective modulation mode, the operation of the receiving end is simplified, and the method is a reliable unimorph half-quantum key distribution method.
As an alternative implementation, step S120, the interference loop processing the received first pulse group to obtain a second pulse group, may include:
the received signal pulse is divided into a first optical pulse and a second optical pulse through the length difference of a long-arm subunit and a short-arm subunit in the unequal-arm interferometer, and the first optical pulse and the second optical pulse form a first pulse group.
When the first pulse group exits from the third port of the second beam splitter 110 of the non-equal-arm interferometer, no phase difference exists, and the first pulse group may correspond to a | + > state of a time phase encoding X basis vector and also to a | + > state that Alice needs to prepare in a singlet-state half-quantum key distribution protocol.
As an alternative implementation, in step S130, the interference loop processes the received first pulse group to obtain a second pulse group, which may include:
step S131, the interference loop takes the received first pulse group as a second pulse group;
or, step S132, the interference loop performs voltage intervention operation on the first pulse of the first pulse group to obtain a second pulse group;
or, in step S133, the interference loop performs a voltage intervention operation on the second pulse of the first pulse group to obtain a second pulse group.
Wherein, step S131 may be defined as CTRL operation of interference loop selection, and step S132 and step S133 may be defined as SIFT operation of interference loop selection, in which voltage intervention operation would reduce the intensity of the selected light pulse in the first pulse group to 0, and the obtained second pulse group has different definitions according to the different selected light pulses, if the operation performed by the interference loop is CTRL operation, the returned second pulse group corresponds to | + state of time phase encoding, and if the operation performed by the interference loop is SIFT operation, the second pulse group corresponds to |0> state or |1> state of time phase encoding according to a preset specification, for example, the definitions may be performed: the second pulse group obtained in the SIFT operation corresponding to the operation of step S132 corresponds to the |0> state of the time phase code; the second pulse group obtained in the SIFT operation corresponding to the operation of step S133 corresponds to the time-phase encoded |1> state.
When the unequal-arm interferometer receives the second pulse group, the second pulse group input into the second beam splitter 110 can split the second pulse group first, the second pulse group beam entering the short-arm subunit through beam splitting can receive a random selection of the phase modulator, whether voltage is loaded to perform 0 or pi phase modulation on the second pulse group beam splitting is selected, and the second pulse group beam entering the long-arm subunit through beam splitting is adjusted in intensity.
If the operation performed by the interference loop is CTRL operation, the second pulse group here has first and second light pulses before and after, and since the difference between the first two pulses is generated based on the arm length difference between the short arm subunit and the long arm subunit, when the second pulse group passes through the short arm subunit and the long arm subunit and is combined by the first beam splitter 105, the second light pulse split by the short arm subunit and the first light pulse split by the long arm subunit interfere with each other, and three light pulses in three equidistant time slots are obtained, that is, the third pulse group.
If the operation performed by the interference loop is the SIFT operation, the second pulse group only has the first light pulse or the second light pulse, and the first beam splitter 105 combines the first light pulse or the second light pulse to obtain three light pulses on three equidistant time slots, namely a third pulse group, wherein the three light pulses comprise a null pulse. If SIFT operation carried out by the interference loop reduces the light intensity of the first previous light pulse to 0, namely a null pulse, the first pulse in the third pulse group is a null pulse, and if SIFT operation carried out by the receiving end of the interference loop reduces the light intensity of the second next pulse to 0, namely a null pulse, the third pulse in the third pulse group is a null pulse.
If the interference loop performs CTRL operation, the result detected by the detector unit may be different according to the phase modulation of the second pulse group by the phase modulator; for example, in the case that the loading phase of the phase modulator is 0, when the third pulse group reaches the first single-photon detector 111, the first single-photon detector 111 may obtain a single-photon count corresponding to the interference constructive pattern at the preset time slot position, and when the third pulse group reaches the second single-photon detector 112, the second single-photon detector 112 may obtain a single-photon count corresponding to the interference destructive pattern at the preset time slot position; and if the loading phase of the phase modulator is pi, the result is opposite, the first single-photon detector 111 can obtain the single-photon count corresponding to the interference cancellation pattern at the preset time slot position, the second single-photon detector 112 can obtain the single-photon count corresponding to the interference cancellation pattern at the preset time slot position, and the single-photon counts at the two positions are the detection results obtained by the detector unit.
The 3 equidistant time slots from front to back are set as t00, t01 and t02, if the operation of the interference loop is CTRL operation, the single photon counting corresponding to interference can be obtained at the position of t01 as the preset time slot, and if the operation of the interference loop is SIFT operation, only one light pulse is in the position of t01, and no interference occurs.
After obtaining the detection result, the sending end can judge the selection of the receiving end, namely the interference loop, on the intensity modulation through the counting on different time slots, and transmit the selection of the loading phase voltage corresponding to the sending end to the receiving end through the public channel.
The singlet state half quantum key distribution system judges the acquired detection result, the processing of the unequal-arm interferometer on the received optical pulse and the processing of the interference loop on the received first pulse group according to a singlet state half quantum key distribution protocol, and specifically comprises the following steps:
when the interference loop processes the received first pulse group as a SIFT operation, if the transmitting end adopts Z-basis vector measurement, that is, detects a null pulse at a time slot t00 or a time slot t02 through the first single-photon detector and the second single-photon detector, then it can form a code according to the measurement result, where: if SIFT operation and measurement result of the interference loop are |0> state, the code can be 0; if SIFT operation and measurement of the interferometric loop are in state |1>, code 1 can be formed.
When the interference loop processes the received first pulse group as a SIFT operation, if the sending end adopts X-base vector measurement, the bit code is discarded no matter whether the measurement result is in a | + > state or a | - > state.
When the interference loop processes the received first pulse group as CTRL operation, if the sending end adopts X-base vector measurement, namely the first single-photon detector and the second single-photon detector detect the phenomena of interference growth and cancellation at the preset position of a time slot, the sending end can monitor whether the system is intercepted according to the measurement result, and if the sending end adopts Z-base vector measurement, the bit code is discarded.
The rest of the content of the singlet half-quantum key distribution system in the embodiment of the present application may refer to the specific content of the first embodiment, and is not described herein again.
In all the above embodiments, the terms "large" and "small" are relative terms, and the terms "more" and "less" are relative terms, and the terms "upper" and "lower" are relative terms, so that the description of these relative terms is not repeated herein.
It should be appreciated that reference throughout this specification to "in this embodiment," "in an embodiment of the present application," or "as an alternative implementation" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present application. Thus, the appearances of the phrases "in this embodiment," "in the examples of the present application," or "as an alternative embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Those skilled in the art should also appreciate that the embodiments described in this specification are all alternative embodiments and that the acts and modules involved are not necessarily required for this application.
In various embodiments of the present application, it should be understood that the size of the serial number of each process described above does not mean that the execution sequence is necessarily sequential, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.
The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present application, and shall be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (10)
1. A single-state semi-quantum key distribution system is characterized in that the system comprises a sending end and a receiving end,
the sending end comprises a signal light unit, a light transmission unit, a phase modulator unit and a detector unit, the signal light unit, the light transmission unit and the phase modulator unit are sequentially connected, the detector unit is connected with the phase modulator unit and the light transmission unit, and the phase modulator unit is an unequal-arm interferometer;
the receiving end comprises an intensity modulator unit, the intensity modulator unit is connected with the unequal arm interferometer, and the intensity modulator unit is an interference loop;
the interference loop is used for loading voltage on the received optical pulse group sent by the unequal arm interferometer to obtain a processed optical pulse group, and sending the processed optical pulse group to the unequal arm interferometer.
2. The singlet half quantum key distribution system of claim 1,
the interference loop comprises a polarization beam splitter and an intensity modulator, the polarization beam splitter is connected with the unequal-arm interferometer through a quantum channel, and two ends of the intensity modulator are respectively connected with the polarization beam splitter.
3. The singlet half quantum key distribution system of claim 1,
the non-equal arm interferometer comprises a first beam splitter, a second beam splitter, a short arm subunit and a long arm subunit,
the first beam splitter is connected with the optical transmission unit, the first beam splitter is respectively connected with the long-arm subunit and the short-arm subunit, the long-arm subunit and the short-arm subunit are respectively connected with the second beam splitter, and the second beam splitter is connected with the interference loop through a quantum channel.
4. The singlet half quantum key distribution system of claim 3,
the long-arm subunit comprises a second polarizer and an optical fiber attenuator which are connected, the second polarizer is connected with the first beam splitter, and the optical fiber attenuator is connected with the second beam splitter;
the short-arm subunit comprises a phase modulator and a first polarizer which are connected, the phase modulator is connected with the first beam splitter, and the first polarizer is connected with the second beam splitter.
5. The singlet half quantum key distribution system of claim 1,
the signal light unit comprises a laser, an optical isolator and an optical attenuator which are connected in sequence, and the optical attenuator is connected with the optical transmission unit.
6. The singlet half quantum key distribution system of claim 1,
the optical transmission unit comprises an optical circulator, and the optical circulator is connected with the signal optical unit and the unequal-arm interferometer.
7. The singlet half quantum key distribution system of claim 1,
the detector unit comprises a first single-photon detector and a second single-photon detector, the first single-photon detector is connected with the unequal-arm interferometer, and the second single-photon detector is connected with the optical transmission unit.
8. A method for distributing a singlet-state half-quantum key, based on the singlet-state half-quantum key distribution system of any one of claims 1 to 7, the method comprising:
the signal light unit generates light pulses and transmits the light pulses to the unequal arm interferometer through the light transmission unit;
the unequal arm interferometer processes the received optical pulses to obtain a first pulse group and sends the first pulse group to the interference loop;
the interference loop processes the received first pulse group to obtain a second pulse group, and sends the second pulse group to the unequal-arm interferometer;
the unequal-arm interferometer processes the received second pulse group to obtain a third pulse group, and sends the third pulse group to the optical transmission unit and the detector unit;
the detector unit receives a third pulse group and detects the third pulse group to obtain a detection result;
and the singlet state half quantum key distribution system obtains a security key according to the detection result, the processing of the unequal-arm interferometer on the received optical pulse and the processing of the interference loop on the received first pulse group.
9. The method of claim 8, wherein the processing the received optical pulses by the non-equiarm interferometer to obtain a first set of pulses comprises:
dividing the received signal pulse into a first optical pulse and a second optical pulse by the difference between the lengths of the long-arm subunit and the short-arm subunit in the unequal-arm interferometer, wherein the first optical pulse and the second optical pulse form the first pulse group.
10. The method of claim 8, wherein the interferometric loop processes the received first set of pulses to obtain a second set of pulses, comprising:
the interference loop takes the received first set of pulses as the second set of pulses;
or, the interference loop performs voltage intervention operation on the first pulse of the first pulse group to obtain the second pulse group;
or the interference loop carries out voltage intervention operation on the second pulse of the first pulse group to obtain the second pulse group.
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