Security of quantum key distribution with virtual mutually unbiased bases

In a perfect quantum key distribution(QKD)protocol,quantum states should be prepared and measured with mutually unbiased bases(MUBs).However,in a practical QKD system,quantum states are generally prepared and measured with imperfect MUBs using imperfect devices,possibly reducing the secret key rate and transmission distance.To analyze the security of a QKD system with imperfect MUBs,we propose virtual MUBs to characterize the quantum channel against collective attack,and analyze the corresponding secret key rate under imperfect state preparation and measurement conditions.More generally,we apply the advantage distillation method for analyzing the security of QKD with imperfect MUBs,where the error tolerance and transmission distance can be sharply improved.Our analysis method can be applied to benchmark and standardize a practical QKD system,elucidating the security analysis of different QKD protocols with imperfect devices.

Delayed error verification in quantum key distribution

Quantum key distribution(QKD)provides an unconditional secure key generation method between two distant legitimate parties Alice and Bob based on the fundamental properties of quantum mechanics,in the presence of an eavesdropper Eve.Since key reconciliation cannot always assure that the reconciled keys between Alice and Bob are identical,error verification is an important step in QKD.In this paper,we propose a scheme of delayed error verification using extra keys gained by privacy amplification with an arbitrarily small failure probability.The proposed scheme simplifies the post-processing procedure in QKD,which can be applied in practical QKD systems.

Measurement-device-independent quantum key distribution for nonstandalone networks

Untrusted node networks initially implemented by measurement-device-independent quantum key distribution(MDI-QKD)protocol are a crucial step on the roadmap of the quantum Internet.Considering extensive QKD implementations of trusted node networks,a workable upgrading tactic of existing networks toward MDI networks needs to be explicit.Here,referring to the nonstandalone(NSA)network of 5G,we propose an NSA-MDI scheme as an evolutionary selection for existing phase-encoding BB84 networks.Our solution can upgrade the BB84 networks and terminals that employ various phase-encoding schemes to immediately support MDI without hardware changes.This cost-effective upgrade effectively promotes the deployment of MDI networks as a step of untrusted node networks while taking full advantage of existing networks.In addition,the diversified demands on security and bandwidth are satisfied,and network survivability is improved.

Polarization-insensitive interferometer based on a hybrid integrated planar light-wave circuit

Interferometers are essential elements in classical and quantum optical systems.The strictly required stability when extracting the phase of photons is vulnerable to polarization variation and phase shift induced by environment disturbance.Here,we implement polarization-insensitive interferometers by combining silica planar light-wave circuit chips and Faraday rotator mirrors.Two asymmetric interferometers with temperature controllers are connected in series to evaluate the single-photon interference.Average interference visibility over 12 h is above 99%,and the variations are less than 0.5%,even with active random polarization disturbance.The experiment results verify that the hybrid chip is available for high-demand applications like quantum key distribution and entanglement measurement.

Twin-field protocols:Towards intercity quantum key distribution without quantum repeaters

The main obstacle of realizing long-distance quantum key distribution(QKD)[1]is that the secret key rate(SKR)decreases with the loss of the quantum channel.Specifically,the transmittanceηof a quantum channel depends on its distance,namelyη=10^(−αl/10),whereα=0.2dB/km for a typical fiber channel,and l is the distance of the channel.For most single-photon-based QKD protocols,including the well-known BB84[1].