RU2798394C1 - Method and scheme for active reset synchronization and recovery of single photon detectors in a quantum key distribution system - Google Patents

Abstract

FIELD: quantum technologies.

SUBSTANCE: present technical solution is related in particular to a method and scheme for synchronizing the active reset and recovery of single photon detectors (SPD) in a quantum key distribution system (QKD). The claimed technical result is achieved due to the method of synchronizing two SPDs in the QKD system, in which each SPD contains an optical radiation receiver, a comparator connected to an output pulse shaping unit, connected to an active recovery pulse shaping unit, and in the event of one SPD being triggered, from said SPD a signal equal to the duration of the recovery pulse is transmitted to the second SPD, which, in response to receiving the said signal, blocks the comparator and generates a recovery pulse for its optical receiver.

EFFECT: increase of protection of the QKD system by reducing the probability of an attack on the dead time of single photon detectors.

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Description

FIELD OF TECHNOLOGY

[0001] This technical solution relates to the field of quantum technologies, in particular to a method and scheme for synchronizing the active reset and recovery of single photon detectors (SPDs) in a quantum key distribution (QKD) system.

BACKGROUND OF THE INVENTION

[0002] QKD systems use coding in an orthogonal basis of signals and to obtain the maximum key generation rate, two single photon detectors are always used - for each state in the basis. One of the vulnerabilities of such QKD systems is the possibility of an attack through the dead time of the detector [Weier H. et al. Quantum eavesdropping without interception: an attack exploiting the dead time of single-photon detectors // New Journal of Physics. - 2011. - T. 13. - no. 7. - C. 073024.]. The security of quantum key distribution can be easily compromised if an eavesdropper can exploit technical flaws in the actual implementation. Using the dead time effect of single-photon detectors, an eavesdropper can obtain (asymptotically) complete information about the generated keys without being detected by modern QKD protocols, which is a significant drawback of this approach to constructing QKD systems.

SUMMARY OF THE INVENTION

[0003] The claimed invention allows solving the technical problem in terms of increasing the security of operation in the QKD system of two or more DOPs.

[0004] A solution to avoid the above attack, the claimed solution proposes to use an output comparator off timing circuit. Such a measure disables the detector's digital output for the "dead" time of the triggered one, thus preventing a possible attacker from exploiting the vulnerability and seizing control of the non-triggered detector. At the same time, the non-operational detector is in working condition, that is, the single-photon avalanche photodiode (OPD) itself is in the Geiger mode; accordingly, a current can flow through it, which charges the traps in the APD structure, thus increasing the probability of an afterpulse at the end of the "dead" time of the triggered detector. The use of the DOP active reset synchronization scheme, in turn, makes it possible not only to protect against the above attack, but also to reduce the probability of a post-pulse for the non-operated detector, since during the entire “dead” time of the triggered detector, it will also be taken out of the Geiger mode.

[0005] The technical result is to increase the protection of the QKD system by reducing the probability of an attack on the dead time of single photon detectors.

[0006] The claimed technical result is achieved through a method for synchronizing two single photon detectors (SOPs) in a quantum key distribution (QKD) system, in which

each DOP contains an optical radiation receiver, a comparator connected to an output pulse shaping unit, connected to an active recovery pulse shaping unit, and

if one DOP is triggered, a signal equal to the duration of the recovery pulse is transmitted from the mentioned DOP to the second DOP, which, in response to receiving the mentioned signal, blocks the comparator and generates a recovery pulse of its optical receiver.

[0007] In one of the private embodiments of the method, the DOPs are connected via a synchronizing input-output.

[0008] In another particular embodiment of the method, the optical radiation receiver is an avalanche photodiode.

[0009] The claimed technical result is also achieved through a synchronization scheme for two single photon detectors (SOPs) in a quantum key distribution system (QKD) containing connected SOPs, in which

each DOP contains an optical radiation receiver, a comparator connected to an output pulse shaping unit, connected to an active recovery pulse shaping unit, and

if one DOP is triggered, a signal equal to the duration of the recovery pulse is transmitted from the mentioned DOP to the second DOP, which, in response to receiving the mentioned signal, blocks the comparator and generates a recovery pulse of its optical receiver.

DESCRIPTION OF THE DRAWINGS

[0010] In FIG. 1 shows the connection diagram of single photon detectors.

IMPLEMENTATION OF THE INVENTION

[0011] In FIG. 1 shows the claimed synchronization scheme (100) for the operation of two DOPs (10, 20). DOPs (10, 20) can be made in various configurations and connected either via a wired connection (for example, fiber optics) or placed on a single integrated circuit or board. Each DOP (10, 20) contains an optical receiver in the form of an avalanche photodiode (not shown in Fig. 1), which transmits signals to a comparator (101, 201). The comparator (101, 201) is connected to the output pulse generator (102, 202) connected to the active recovery pulse generator (104, 204) via an OR element (103, 203).

[0012] The claimed solution works as follows. When registering one DOP, for example, DOP (10) of the optical signal, an avalanche signal is sent to the input of the comparator (101), causing it to operate. The signal from the output of the comparator (101) goes to the output pulse shaper (102), from where it goes to the OR element (103), which blocks the output of the comparator (101) so that the electronic noise accompanying the avalanche signal does not provoke its repeated operation and, accordingly, unnecessary clicks on the terminal device of the CRC.

[0013] The same signal that came from the output of the output pulse shaper (102) to the OR element (103) starts the process of generating an active recovery pulse to the block (104), according to the duration corresponding to the dead time of the detector (10). This pulse, in turn, hits the APD and switches it to a linear regime, while preventing charge accumulation in the traps of the structure. This makes it possible to reduce the probability of an afterpulse.

[0014] At the same time, the pulse that triggered the above processes on the OR element (103) from the sync output SYNC OUT is fed to the sync input SYNC IN of the unworked DOP (20). From this input, a signal with a small delay relative to the triggered DOP (10) starts the processes of comparator blocking (201) and the formation of a recovery pulse on the block (204) on the DOP DOP (20), thus making it impossible to register DOP (20) photons or dark triggers in throughout the dead time. It should be noted that the dead time of both detectors need not be the same. When the dead time of the DOP (10) ends, respectively, the comparator (101) is unlocked, and the APD returns to the Geiger mode. The same happens on DOP (20).

[0015] In the event that the DOP (20) registers an operation, the DOP (10) will have its output turned off in accordance with the circuit algorithm and its DOP will be put into linear mode to prevent avalanche generation during the dead time of the DOP (20).

Claims (4)

1. A method for synchronizing two detectors of single photons (DOF) in a quantum key distribution system (QKD), in which each DOP contains an optical radiation receiver, a comparator connected to an output pulse shaping unit, connected to an active recovery pulse shaping unit, and in the event of operation of one DOP, from the said DOP, a signal equal to the duration of the recovery pulse is transmitted to the second DOP, which, in response to receiving the said signal, blocks the comparator and generates a recovery pulse of its optical receiver. 2. The method of claim 1, wherein the DOPs are connected via a clock input/output. 3. The method of claim 1, wherein the optical radiation receiver is an avalanche photodiode. Fig. 4. Synchronization circuit for two single photon detectors (SOPs) in a quantum key distribution system (QKD) containing connected first and second SOPs, in which each SOP contains an optical radiation receiver, a comparator connected to an output pulse shaping unit associated with a pulse shaping unit active recovery, and in case of operation of one DOP, a signal equal to the duration of the recovery pulse is transmitted from the mentioned DOP to the second DOP, which, in response to receiving the mentioned signal, blocks the comparator and generates a recovery pulse of its optical receiver.

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