One-step quantum dialogue

Quantum dialogue(QD)enables two communication parties to directly exchange secret messages simultaneously.In conventional QD protocols,photons need to transmit in the quantum channel for two rounds.In this paper,we propose a one-step QD protocol based on the hyperentanglement.With the help of the non-local hyperentanglement-assisted Bell state measurement(BSM),the photons only need to transmit in the quantum channel once.We prove that our one-step QD protocol is secure in theory and numerically simulate its secret message capacity under practical experimental condition.Compared with previous QD protocols,the one-step QD protocol can effectively simplify the experiment operations and reduce the message loss caused by the photon transmission loss.Meanwhile,the non-local hyperentanglement-assisted BSM has a success probability of 100%and is feasible with linear optical elements.Moreover,combined with the hyperentanglement heralded amplification and purification,our protocol is possible to realize long-distance one-step QD.

Visualizing and witnessing first-order coherence,Bell nonlocality and purity by using a quantum steering ellipsoid in the non-inertial frame

A quantum steering ellipsoid(QSE)is a visual characterization for bipartite qubit systems,and it is also a novel avenue for describing and detecting quantum correlations.Herein,by using a QSE,we visualize and witness the first-order coherence(FOC),Bell nonlocality(BN)and purity under non-inertial frames.Also,the collective influences of the depolarizing channel and the non-coherence-generating channel(NCGC)on the FOC,BN and purity are investigated in the QSE formalism.The results reveal that the distance from the center of the QSE to the center of the Bloch sphere visualizes the FOC of a bipartite system,the lengths of the QSE semiaxis visualize the BN,and the QSE's shape and position dominate the purity of the system.One can capture the FOC,BN and purity via the shape and position of the QSE in the non-inertial frame.The depolarizing channel(the NCGC)gives rise to the shrinking and degradation(the periodical oscillation)of the QSE.One can use these traits to visually characterize and detect the FOC,BN and purity under the influence of external noise.Of particular note is that the condition for the QSE to achieve the center of the Bloch sphere cannot be influenced by the depolarizing channel and the NCGC.The characterization shows that the conditions for the disappearance of the FOC are invariant under the additional influences of the depolarizing channel and NCGC.

单光子空间W态的高效无噪线性放大方案

光子传输损耗是长距离量子通信实用化的重要障碍.单光子空间W态是量子通信的重要资源.为保护单光子空间W态抵御其在远距离纠缠分发过程中的光子传输损耗,本文提出了一种基于具有局域压缩操作的高效量子剪刀的单光子空间W态无噪线性放大方案.本方案中,各个远距离用户需要同时运行带有局域压缩操作的高效量子剪刀方案.只有当所有用户的量子剪刀方案都运行成功时,单光子空间W态的无噪线性放大方案才运行成功.通过在量子剪刀中加入局域压缩操作,本方案可有效提升对单光子空间W态的放大因子.本方案在未来基于单光子空间W态的长距离量子通信领域具有潜在的应用.

Correlation-induced coherence and its use in detecting quantum phase transitions

The past two decades have witnessed a surge of interest in exploring correlation and coherence measures to investigate quantum phase transitions(QPTs). Here, motivated by the continued push along this direction, we propose a measure which is built upon the so-called degree of coherence, and advocate using the susceptibility of our measure to detect QPTs. We show that our measure can capture both the notions of coherence and correlations exhibited in bipartite states and therefore represents a hybrid of these two notions. Through examining the XXZ model and the Kitaev honeycomb model, we demonstrate that our measure is favorable for detecting QPTs in comparison to many previous proposals.

Generation of hyperentangled state encoded in three degrees of freedom

Hyperentanglement, the simultaneous entanglement in more than one degree of freedom(DOF), plays an important role in quantum communication and quantum information processing for it can effectively increase the channel capacity. Existing hyperentanglement sources mainly focus on the generation of the hyperentanglement in two DOFs. In this paper, we design the generation protocols for three kinds of hyperentanglement encoded in three DOFs with the practical coherent pulses sources, including the polarization-frequency-space hyperentanglement, the polarization-frequency-time-bin hyperentanglement, and the polarizationspace-time-bin hyperentanglement. These protocols exploit the spontaneous parametric down-conversion(SPDC) process and the Sagnac interferometer. The three protocols are all based on feasible experimental condition and may have potential applications in future hyperentanglement-based quantum communication and quantum information processing protocols.