A practical two-way system of quantum key distribution with untrusted source

The most severe problem of a two-way ＂plug-and-play＂ （p ＆： p） quantum key distribution system is that the source can be controlled by the eavesdropper. This kind of source is defined as an ＂untrusted source＂. This paper discusses the effects of the fluctuation of internal transmittance on the final key generation rate and the transmission distance. The security of the standard BB84 protocol, one-decoy state protocol, and weak＋vacuum decoy state protocol, with untrusted sources and the fluctuation of internal transmittance are studied. It is shown that the one-decoy state is sensitive to the statistical fluctuation but weak＋vacuum decoy state is only slightly affected by the fluctuation. It is also shown that both the maximum secure transmission distance and final key generation rate are reduced when Alice＇s laboratory transmittance fluctuation is considered.

Quantum State Transfer between Charge and Flux Qubits in Circuit-QED

我们建议一个计划在混合电路量 electrodynamics (证完) 实现量状态转移由超导的费用 qubit，流动 qubit，和一根传播线组成的系统共鸣器(TLR ) 。量状态在费用 qubit 之间转，流动 qubit 能被把 TLR 用作数据总线认识到，这被显示出。

Quantum State Transfer in Trapped-Ion-Cavity Systems

我们在在洞领域(光子) 之中由三模式的 cross-Kerr-like 相互作用在洞由单个套住的离子组成的一个系统学习信息转移和纠纷转移， centre-of-mass 运动(声子) 和在羔羊 Dicke 和大 detuning 政体的套住的离子的内部状态。

Quantum Information Transfer from a Double Quantum Dot System to a Cavity Field

在这份报纸，我们建议一个计划从一个双量点(DQD ) 认识到量信息转移系统到一块使量子化的洞地。DQD 和洞地分别地被当作二状态的费用 qubit 和一个连续变量的系统。编码为二状态的 DQD 系统的量信息能关于 DQD 通过适当射影的大小与一个连续变量的基础被转移到洞地的量状态，这被显示出。

Symmetric Telecloning and Entanglement Distribution of Spin Quantum States

我们建议为旋转量状态克隆机器的对称的电视的一条物理认识。区域一般水准的概念。delity 被介绍描述克隆质量的电视。为某些输入状态，这数量可以来到足够的高水平满足量信息处理的需要，这被显示。我们也经由旋转链学习纠纷分发的性质因为任意的 two-qubit 作为输入纠缠了纯状态并且发现为输出状态的纠纷的腐烂比率被旋转链和等待的时间的参数仅仅决定，独立于起始的输入状态。

Properties on the distant distribution of entanglement for arbitrary two-qubit pure states via noisy quantum channels

This paper investigates the change of entanglement for transmitting an arbitrarily entangled two-qubit pure state via one of three typical kinds of noisy quantum channels： amplitude damping quantum channel, phase damping quantum channel and depolarizing quantum channel. It finds, in all these three cases, that the output distant entanglement （measured by concurrence） reduces proportionately with respect to its initial amount, and the decaying ratio is determined only by the noisy characteristics of quantum channels and independent of the form of initial input state.

Dark states and Aharonov-Bohm oscillations in multi-quantum-dot systems

We study the formation of dark states and the Aharonov-Bohm effect in symmetrically/asymmetrically coupled three- and four-quantum-dot systems. It is found that without a transverse magnetic field, destructive interference can trap an electron in a dark state. However, the introduction of a transverse magnetic field can disrupt the dark state, giving rise to oscillation in current. For symmetrically structured quantum-dot systems, the oscillation has a period of one flux quanta. But for asymmetrically structured dot systems, the period of oscillation is halved. In addition, the dephasing due to charge noise also blocks the formation of dark states, while it does not change the period of oscillation.

Distributed quantum information processing via quantum dot spins

We propose a scheme to engineer a non-local two-qubit phase gate between two remote quantum-dot spins. Along with one-qubit local operations, one can in principal perform various types of distributed quantum information processing. The scheme employs a photon with linearly polarisation interacting one after the other with two remote quantum-dot spins in cavities. Due to the optical spin selection rule, the photon obtains a Faraday rotation after the interaction process. By measuring the polarisation of the final output photon, a non-local two-qubit phase gate between the two remote quantum-dot spins is constituted. Our scheme may has very important applications in the distributed quantum information processing.

Quantum thermal discord in a two-spin-1/2 XXZ model

We study the quantum discord in a two-spin-1/2 XXZ model in thermal equilibrium at temperature T in the presence of an external magnetic field B. Special attention is paid to the dependence of quantum discord on the temperature T and magnetic field B. It is found that quantum thermal discord is more robust than concurrence against temperature, in the sense that quantum thermal discord does not vanish at finite temperatures, but concurrence vanishes completely at a critical temperature.

Distributed quantum computation with superconducting qubit via LC circuit using dressed states

A scheme is proposed where two superconducting qubits driven by a classical field interacting separately with two distant LC circuits connected by another LO circuit through mutual inductance, are used for implementing quantum gates. By using dressed states, quantum state transfer and quantum entangling gate can be implemented. With the help of the time-dependent electromagnetic field, any two dressed qubits can be selectively coupled to the data bus （the last LC circuit）, then quantum state can be transferred from one dressed qubit to another and multi-mode entangled state can also be formed. As a result, the promising perspectives for quantum information processing of mesoscopic superconducting qubits are obtained and the distributed and scalable quantum computation can be implemented in this scheme.

Dynamics of quantum Fisher information in a two-level system coupled to multiple bosonic reservoirs

We consider the optimal parameter estimation for a two-level system coupled to multiple bosonic reservoirs. By using quantum Fisher information （QFI）, we investigate the effect of the Markovian reservoirs＇ number N on QFI in both weak and strong coupling regimes for a two-level system surrounded by N zero-temperature reservoirs of field modes initially in the vacua. The results show that the dynamics of QFI non-monotonically decays to zero with revival oscillations at some time in the weak coupling regime depending on the reservoirs＇ parameters. Furthermore, we also present the relations between the QFI flow, the flows of energy and information, and the sign of the decay rate to gain insight into the physical processes characterizing the dynamics.

Preparation of N-Qubit GHZ State with a Hybrid Quantum System Based on Nitrogen-Vacancy Centers

We propose a novel scheme for generating N-qubit GHZ entangled state with a hybrid quantum system,which consists of N nitrogen-vacancy centers,N transmission line resonators,a current-biased Josephson junction superconducting qubit,and three kinds of interaction Hamiltonians.The proposal requires no adjustment of the qubit level spacings during the entire operation.Moreover,it is shown that the operation time is independent of the number of qubits.The present proposal is quite useful,and is a promising step to realize the large-sized quantum networks for quantum information processing and quantum computation.

Dynamical control of population and entanglement for open Λ-type atoms by engineering the environment

The exactly analytical solution for the dynamics of the dissipative Λ-type atom in the zero-temperature Lorentzian environment is presented. On this basis, we study the evolution of the population and entanglement. We find that the stable populations on the two lower levels of the Λ-type atom can be effectively adjusted by the combination of the relative decay rate and the environmental spectral frequency. However, for the initial Werner-like state, the stable entanglement between the two Λ-type atoms has very little tunability. Furthermore, the stable entanglement for the bilateral environment case is larger than that of the unilateral environmental case. A nonintuitive relation between the stable entanglement and stable population is found.

Reduction of entropic uncertainty in entangled qubits system by local PT-symmetric operation

We investigate the quantum-memory-assisted entropic uncertainty for an entangled two-qubit system in a local quantum noise channel with PT-symmetric operation performing on one of the two particles. Our results show that the quantum-memory-assisted entropic uncertainty in the qubits system can be reduced effectively by the local PT-symmetric operation. Physical explanations for the behavior of the quantum-memory-assisted entropic uncertainty are given based on the property of entanglement of the qubits system and the non-locality induced by the re-normalization procedure for the non-Hermitian PT-symmetric operation.

Distillability sudden death in a two qutrit systems under a thermal reservoir

The dynamics of distillability entanglement between qutrit-qutrit systems interacting with a thermal reservoir is investigated in this paper. We discovered an interesting phenomenon that under a thermal reservoir certain initially prepared free=entangled states become bound-entangled states in a finite time, which is called distillability sudden death （DSD）. We use a realignment criterion to measure the nine-dimensional density matrix of the entanglement. Moreover, we analyze some other parameters to investigate the effects to the systems. Explanations are then given.

The population and decay evolution of a qubit under the time-convolutionless master equation

We consider the population and decay of a qubit under the electromagnetic environment. Employing the time- convolutionless master equation, we investigate the Markovian and non-Markovian behaviour of the corresponding perturbation expansion. The Jaynes-Cummings model on resonance is investigated. Some figures clearly show the different evolution behaviours. The reasons are interpreted in the paper.

Super-sensitive phase estimation with coherent boosted light using parity measurements

We consider a passive and active hybrid interferometer for phase estimation, which can reach the sub-shot-noise limit in phase sensitivity with only the cheapest coherent sources. This scheme is formed by adding an optical parametric amplifier before a Mach-Zehnder interferometer. It is shown that our hybrid protocol can obtain a better quantum Cramer- Rao bound than the pure active （e.g., SU（1, I）） interferometer, and this precision can be reached by implementing the parity measurements. Furthermore, we also draw a detailed comparison between our scheme and the scheme suggested by Caves [Phys. Rev. D 23 1693 （1981）], and it is found that the optimal phase sensitivity gain obtained in our scheme is always larger than that in Caves＇ scheme.

Enhanced Deflection of Light Ray by Atomic Ensemble on Coherent Population Oscillation

在最近的实验[例如，自然物理 2 (2006 ) 332 ] ，在一个原子整体的提高的轻偏转被电镀物品有磁力地由于不同类的地表明导致的透明性(EIT ) 基于机制。在这篇论文，我们为提高的轻偏转的类似的现象探索不同机制。这机制基于协调人口摆动，它导致在吸收光谱烧的洞。引起探查光的偏转的媒介是在二光子回声上由一块强壮的控制的地操作的二水平的原子的一个整体。处于大 detuning 条件，到泵地和信号地的媒介的反应与稳定的州的近似被获得。并且在越过媒介的探查域旅行以后，信号光线由于控制横梁的空间依赖者的侧面弯曲，这被发现。

Quantum Dynamics of Entanglement and Single Excitation Transfer in LH1-RC-Type Trimer

In this paper,we study quantum dynamics of entanglement and single excitation transfer(SET) in an LH1-RC-type trimer which can describe a basic unit cell in the LH1-RC complex in the photosynthetic process.It is shown that there exists a sudden change of entanglement at the critic point of quantum phase transition(QPT) of the system at low temperatures,the entanglement sudden change caused by the QPT is suppressed at higher temperatures.We investigate the influence of environment on entanglement and SET.We show the generation of the dephasing-assisted entanglement between a donor and an acceptor and the existence of the steady-state entanglement,and demonstrate the entanglement transfer from donor-donor entanglement to donor-acceptor entanglement in the dynamic evolution.We reveal the close relation between the SET probability and donor-acceptor entanglement.Especially,we find that the SET probability is proportional to the amount of donor-acceptor entanglement under certain conditions.

Entanglement and non-Markovianity of a spin-S system in a dephasing environment

We study the entanglement （measured by negativity） evolution and the non-Markovianity for the dynamical process of a spin-S system embedded in dephasing environments. The exact analytical solution is presented, which shows that the decoherence function governs the evolutions of coherence, entanglement, and the non-Markovianity of the correspond- ing dynamical processes. For Ohmic and sub-Ohmic reservoirs, the negativity decreases monotonically in time and the corresponding dynamics is Markovian. While for super-Ohmic reservoirs with non-monotonic decoherence function, the negativity appears as the phenomenon of revival and the corresponding dynamics is non-Markovian. The relation between non-Markovianity and the system dimension is studied.