Phase drift is an inherent problem in phase-encoded quantum key distribution(QKD) systems.The current active phase trackingand compensation solutions cannot satisfy the requirements of a system with nonlinearity in phase modulation.This paper presents a four-phase scanning method,which is based on the quantitative analysis of the quantum bit error rate(QBER) from phasedrift and the performance requirements of phase compensation.By obtaining the four interference fringes and adjusting the codingmatrix of the system,this method automatically calculates the accurate driving voltages for the phase modulator.The implementation and experimental tests show that the proposed method can compensate phase drift caused by environmental changes and thesystem's nonlinearity,and is applicable to large-scale QKD networks.
We review some recent progresses on the study of ultracold Fermi gases with synthetic spin-orbit coupling.In particular,we focus on the pairing superfluidity in these systems at zero temperature.Recent studies have shown that different forms of spin-orbit coupling in various spatial dimensions can lead to a wealth of novel pairing superfluidity.A common theme of these variations is the emergence of new pairing mechanisms which are direct results of spin-orbit-coupling-modified single-particle dispersion spectra.As different configurations can give rise to single-particle dispersion spectra with drastic differences in symmetry,spin dependence and low-energy density of states,spin-orbit coupling is potentially a powerful tool of quantum control,which,when combined with other available control schemes in ultracold atomic gases,will enable us to engineer novel states of matter.
The decoy state protocol was proposed to overcome the primitive photon number splitting attack.When using a better strategy,the attacker can ensure that the ratio of the overall gain of the signal state pulse against the decoy state pulse changes very little,even to keep the overall gain of the signal state pulses equal to that obtained without attacker.In this paper we first give a model of the partial photon number splitting attack which contains the original one,and then find that the decoy state protocol still works effectively under the partial photon number splitting attack.
LIU DongWANG ShuangYIN ZhenQiangCHEN WeiHAN ZhengFu
