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Guangdian gongcheng

Solution for synchronization of signal in free-space quantum key distribution

Changqiang Wang

Published Jan 1, 2006• 0 citations
OpenAlex

Abstract

Aiming at the difficulty in synchronization of signal in the system of Quantum Key Distribution (QKD) in free space, we proposed a method that deals with this problem with outer light signal, named light-synchronization method. In transmitter, continuous signal of an external laser is modulated into a light pulse sequence by using an acousto-optic modulator. And the light pulse sequence is sent to the receiver. The receiver incepts the light pulse signal by using a multiplier phototube, and generates synchronal signal as time base, then take count of single photon. The inner clock signal of high frequency is used for monitoring the generated synchronizing signal for enhancing precision. The scheme has the advantage of long-distance, wireless and low-complexity, and it has been applied in a Free-Space QKD system which is based on B92 protocol.

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Aiming at the difficulty in synchronization of signal in the system of Quantum Key Distribution (QKD) in free space, we proposed a method that deals with this problem with outer light signal, named light-synchronization method. In transmitter, continuous signal of an external laser is modulated into a light pulse sequence by using an acousto-optic modulator. And the light pulse sequence is sent to the receiver. The receiver incepts the light pulse signal by using a multiplier phototube, and generates synchronal signal as time base, then take count of single photon. The inner clock signal of high frequency is used for monitoring the generated synchronizing signal for enhancing precision. The scheme has the advantage of long-distance, wireless and low-complexity, and it has been applied in a Free-Space QKD system which is based on B92 protocol.
A light synchronization scheme to solve the key problem of signal synchronization in quantum key distribution(QKD)system is proposed.At side of the transmitter,the field-programmable gate array (FPGA)chip produces a synchronization pulse sequence of certain pattern.The pulse sequence drives laser to transmit sync light through one fiber along with signal light to the receiver.The sync light reverts to sync pulse sequence through fast discrimination at side of the receiver,and the pulses are provided to the single-photon detector as gate after high-precision delay adjustment.Simultaneously,the receiver uses a high-frequency clock to sample the sync pulse sequence in FPGA for encoding,synchronizing the transmitter and receiver.The scheme has a high-precision,low-cost,high fault tolerance feature,and was successfully applied to metro quantum communication network.
We propose a novel synchronization scheme using a periodic light pulse for free-space quantum key distribution (QKD) system. For our 10MHz system, the repetition rate of timing pulse in the novel synchronization scheme can be reduced to 100 KHz or even lower. It allows employing a KHz repetition rate ultrashort pulse laser as timing synchronization source to implement high precision time synchronization. In this paper, short term time drift induced by atmospheric turbulence is analyzed, and how the time deviation impacts on the final secure key generation rate in our QKD system is calculated. In addition, we carried out the QKD experiments over the distance of 1.38 km. The results of the experiments indicate that our scheme is feasible.
We propose a novel synchronization scheme using a periodic light pulse for free-space quantum key distribution (QKD) system. For our 10MHz system, the repetition rate of timing pulse in the novel synchronization scheme can be reduced to 100 KHz or even lower. It allows employing a KHz repetition rate ultrashort pulse laser as timing synchronization source to implement high precision time synchronization. In this paper, short term time drift induced by atmospheric turbulence is analyzed, and how the time deviation impacts on the final secure key generation rate in our QKD system is calculated. In addition, we carried out the QKD experiments over the distance of 1.38 km. The results of the experiments indicate that our scheme is feasible.
High-resolution time synchronization is the crucial technology of quantum key distribution experiment from ground to satellite.A new scheme of time synchronization was presented.In this scheme,a synchronous pulse which has the same wavelength with the quantum signal was adopted and single photo detector was used to detect the synchronous pulse.High-resolution time measurement module was used to measure the instance of synchronous pulse and signal pulse.This scheme overcomes the problem that the the synchronization laser requires much more resources of satellite and the isolation between the synchronization pulse and quantum single pulse.This system was successfully applied to the 16 km quantum key distribution in free space channel.Synchronous resolution of the system is 1.023 ns and bit rate of the raw key for the quantum key distribution is 8.27 kHz.
Time synchronization is a crucial requirement in quantum key distribution (QKD)8 protocols, ensuring accurate key generation via the correct assignment of bits of raw key and9 enabling eavesdropping detection via the precise recording of photon statistics. State-of-the-art10 experiments typically use an extra channel to synchronize the clocks of the transmitter and receiver11 via classical signals. In this work, we study the possibility of performing clock synchronization12 via the signals used for the key generation, which are already present in decoy-state-based BB8413 protocols.14 Without altering the protocol in any way, we use the different mean photon numbers of the15 signal and decoy states for time synchronization without a dedicated physical channel capable of16 clock synchronization. The proposed method relies only on the photons sent and received for17 key generation and does not require any change to the QKD protocol. The only change in the18 experiment is on the software level, thus making it very simple to implement.19 We demonstrate clock synchronization method in a simulation of a specific fiber-based QKD20 experiment. Like other decoy-state-based BB84 protocols, it is based on weak coherent pulses.21 In this simulation, we investigate the parameter space to find limits and optimal choices of our22 proposed method.23 In addition to the non-protocol-altering clock synchronization method, we also discuss an24 approach that significantly improves performance in lossy channels by introducing an additional25 decoy state with a very high mean photon number.26 By eliminating the need for an extra channel capable of clock synchronization, both methods27 proposed potentially reduce the complexity and cost of QKD systems and improve their agility
Precise synchronization between a transmitter and receiver is crucial for quantum communications protocols such as quantum key distribution (QKD) to efficiently correlate the transmitted and received signals and increase the signal-to-noise ratio. In this work, we introduce a synchronization technique that exploits a co-propagating classical optical communications link and tests its performance in a free-space QKD system. Previously, existing techniques required additional laser beams or relied on the capability to retrieve the synchronization from the quantum signal itself; this approach, however, is not applicable in high channel loss scenarios. On the contrary, our method exploits classical and quantum signals locked to the same master clock, allowing the receiver to synchronize both the classical and quantum communications links by performing a clock-data-recovery routine on the classical signal. In this way, by exploiting the same classical communications already required for post-processing and key generation, no additional hardware is required, and the synchronization can be reconstructed from a high-power signal. Our approach is suitable for both satellite and fiber infrastructures, where a classical and quantum channel can be transmitted through the same link.