基于部分测量增强量子隐形传态过程的量子Fisher信息

量子Fisher信息(QFI)是量子度量学中的一个重要物理量,可给出预估参数精度的最优值.本文研究如何引入弱测量和测量反转操作,来提高有限温环境下以Greenberger-Horne-Zeilinger态作为量子通道的隐形传态过程中的QFI.依据隐形传态过程中量子比特的传输情形,考虑了三种不同方案相应的QFI.首先,通过构造每种量子隐形传态方案的量子线路图,分析了QFI与推广振幅衰减噪声参数的变化关系.随后对各种方案中的受噪声粒子施加弱测量和测量反转操作,并对相应的部分测量参数进行优化,着重探讨了施加最优部分测量操作后QFI的改进量.结果表明,经过优化后的部分测量操作能有效提高有限温环境下量子隐形传态过程输出态的QFI;而且量子系统所处的环境温度越低,QFI的提高效果可越显著.     

利用GHZ态实现多原子缠结态的量子隐形传态

提出一种利用GHZ态实现多原子缠结态的量子隐形传态方案.当作为量子通道的GHZ态含有一个单模高Q腔时,大大地简化了量子稳形传态中的联合测量过程.     

利用GHZ态实现多原子缠结态的量子隐形传态(英文)

提出一种利用 GHZ态实现多原子缠结态的量子隐形传态方案 .当作为量子通道的 GHZ态含有一个单模高 Q腔时 ,大大地简化了量子稳形传态中的联合测量过程     

利用单个三粒子最大GHZ态或两个EPR态隐形传送任意三粒子GHZ态

提出利用单个三粒子最大Greenberger-Horne-Zeilinger (GHZ)态或两个Einstein-Podolsky-Rosen (EPR)态作为量子信道确定性隐形传送任意三粒子GHZ态的两个方案，并将方案推广至隐形传送任意n(n≥4)粒子GHZ态的情况.讨论了量子信道受噪声影响时隐形传态的保真度.研究发现，当作为量子信道的单个三粒子最大GHZ态受到噪声影响时，隐形传态的保真度仅与量子信道的纠缠度有关，而当作为量子信道的两个EPR态受到噪声影响时，隐形传态的保真度不仅与量子信道的纠缠度有关，还与待传送态的纠缠度有关.所提出的方案具有节省量子信道纠缠资源的特点. 关键词： 隐形传态 三粒子Greenberger-Horne-Zeilinger态 量子逻辑门 保真度     

利用一个三粒子W态隐形传送N粒子GHZ态

杨洪钦等提出一个用两个三粒子W态作为量子信道将N粒子GHZ态从发送者传送给两个接收者中任意一个的量子隐形传送方案. 给出其理论分析,并提出了一个仅用一个三粒子W态作为量子信道将N粒子GHZ态传送给两个接收者之一的量子隐形传送的方案. 关键词： 隐形传态 GHZ态 W态量子信道     

二粒子纠缠态受控传递的最佳量子通道

本文研究了如何在二粒子纠缠态的量子受控传递中选择最佳量子通道的问题。分别利用四粒子GHZ态和四粒子特殊"反关联GHZ态"作为量子通道,本文提出了二粒子反关联纠缠态的量子受控传递的两个方案。通过对比两个方案下接受者最后采取的幺正操作的具体矩阵形式,分析了待传量子纠缠态与量子通道的关系,指出了四粒子GHZ态和四粒子特殊"反关联GHZ态"分别是二粒子正关联和反关联纠缠态各自隐形传递应该选择的最佳的量子通道。     

基于三粒子GHZ态的双向量子可控隐形传态

提出基于三粒子GHZ态的双向量子可控隐形传态方案.方案中,使用两个三粒子GHZ态作为量子通道.而根据在量子通道中发送者,接收者和控制者所拥有的粒子的不同以及所采用的测量基的不同,设计出了三方参与的双向可控量子隐形传态方案和四方参与的双向可控量子隐形传态方案.在方案中,Alice和Bob对所拥有的粒子做合适的投影测量,并将其测量结果通知对方和控制者.若控制者同意此次传态,则会对自己所拥有的粒子做投影测量,并将结果告知接收者.接收者根据发送者和控制者的测量信息,做出相对应的幺正操作来重建发送者的量子态.同时三方参与和四方参与的量子可控隐形传态方案提高了通信的安全性.     

耗散系统中实现原子态量子隐形传态的保真度

本文运用全量子理论并结合数值计算方法,研究了压缩真空库中利用原子纠缠态作为量子通道实现原子态量子隐形传态的保真度,讨论了被传送的原子初态形式以及压缩库的压缩参数r对保真度的影响.研究表明:当只有输入态受噪声影响,则被传送的初始态中基态概率越大的态,保真度越高;而当量子通道受影响时,则基态和激发态概率相等的原子叠加态传送的保真度最大. 关键词： 量子隐形传态 压缩真空库 保真度     

基于腔QED的多用户间的多原子量子信道的建立

提出基于腔QED技术的多用户间的多原子W态和GHZ态量子信道的建立方案.在量子网络的空闲时段,各个用户和量子交换机共享EPR对.量子交换机通过原子和腔场的相互作用将两个EPR对制备成W态,再与另一个EPR对进行纠缠交换,经过直接测量后为用户建立三原子W态量子信道;同时讨论了四用户间的W态量子信道的建立方案.量子交换机对三个EPR对进行纠缠交换,将三个原子同时与腔场作用,经过直接测量后为用户建立三原子GHZ态量子信道;并将此方法推广到N个用户间的GHZ态量子信道的建立. 关键词： 腔QED 量子信道 量子交换机 纠缠交换     

概率远程制备多粒子GHZ纠缠态

利用一个(N 1)粒子部分纠缠Greenberger-Home-Zeilinger(GHZ)态作为量子通道,提出了概率远程制备N粒子GHZ态的两个方案.我们考虑了怎样远程制备一个任意的GHZ态,即两个参数α和β都是复数的情况.此外,计算了远程制备总的成功概率和需要的经典信息量.     

Protecting Quantum Fisher Information in Correlated Quantum Channels

Quantum Fisher information (QFI) has potential applications in quantum metrology tasks. QFI is investigated when the consecutive actions of a quantum channel on the sequence of qubits have partial classical correlations. The results showed that while the decoherence effect is detrimental to QFI, effects of such classical correlations on QFI are channel-dependent. For the Bell-type probe states, the classical correlations on consecutive actions of the depolarizing and phase flip channels can be harnessed to improve QFI, while the classical correlations in the bit flip and bit-phase flip channels induce a slight decrease of QFI. For a more general parameterization form of the probe states, the advantage of using the initial correlated system on improving QFI can also remain in a wide regime of the correlated quantum channels.     

Phase damping destroys quantum Fisher information of W states

We study the quantum Fisher information (QFI) of W states in the basic decoherence channels. We show that, as decoherence starts and increases, under i) depolarizing, QFI smoothly decays; ii) amplitude damping, QFI first exhibits a sudden drop to the shot noise level, then decreases to zero and finally increases back to the shot noise level; iii) phase damping, QFI is zero for all non-zero decoherence. We also find that on the contrary to GHZ states, QFI of W states in x and y directions are equal to each other and zero in z direction.     

Quantum State Preparation and Protection by Measurement-Based Feedback Control Against Decoherence

We consider an open quantum system subjected to a noise channel under measurement-based feedback control and two prototypical classes of decoherence channels are considered: phase damping and generalized amplitude damping. Based on quantum trajectory theory, we obtain an extended master equation for the dynamics of the reduced system in the presence of feedback control. For a qubit system we analytically solve this master equation and obtain the solution of the state vector dynamics. Then we propose an effective feedback control scheme for preparing an arbitrary quantum pure state. We also study how to protect two nonorthogonal states effectively, and find that projective measurement with unbiased basis is not optimal for this task, while weak measurement with biased basis could realize the best protection of two nonorthogonal states. Furthermore, the inefficiencies in the feedback process are also discussed.     

Quantum Fisher Information of Decohered W and GHZ Superposition States with Arbitrary Relative Phase

Quantum Fisher Information (QFI) is a very useful concept for analyzing situations that require phase sensitivity. It become a popular topic especially in Quantum Metrology domain. In this work, we study the changes in quantum Fisher information (QFI) values for one relative arbitrary phased quantum system consisting of a superposition of N Qubits W and GHZ states. In a recent work (Ozaydin et al. Int. J. Theor. Phys. 52, 2977, 2013), QFI values of this mentioned system for N qubits were studied. In this work, we extend this problem for the changes of QFI values in some noisy channels for the studied system. We show the changes in QFI depending on noise parameters. We report interesting results for different type of decoherence channels. We show the general case results for this problem.     

Preserving entanglement and the fidelity of three-qubit quantum states undergoing decoherence using weak measurement

We demonstrate a method to preserve entanglement and improve fidelity of three-qubit quantum states undergoing amplitude-damping decoherence using weak measurement and quantum measurement reversal. It is shown that we are able to enhance entanglement to the greatest extent, and to circumvent entanglement sudden death by increasing the weak measurement strength both for the GHZ state and the W state. The weak measurement technique can also enhance the fidelity to the quantum region and even close to 1 for the whole range of the decoherence parameter in both of the two cases. In addition, the W state can maintain more fidelity than the GHZ state in the protection protocol. However, the GHZ state has a higher success probability than the W state.     

Improving Quantum Metrology via Purifying and Distilling Noisy Probe States

In quantum metrology, the precision of unknown parameter estimation is studied in the quantum regime, and the choice of the probe state plays an important role in determining the precision of the parameter to be estimated. The quality of quantum metrology will be reduced in the presence of quantum noise during the memory time of probe states after preparation. Meanwhile the noisy probe state can be manipulated by different protocols such as single‐qubit purification, entanglement purification, and entanglement distillation etc. In this paper, the effects of these manipulations on the usefulness, that is, quantum Fisher information (QFI), of the noisy probe state in quantum metrology are studied. The results show that joint operations in single‐qubit purification and entanglement purification processes play positive roles in enhancing the QFI of the probe states, and local measurements in entanglement purification and entanglement distillation processes play both positive and negative roles in enhancing the QFI of the probe states. In this sense, single‐qubit purification will always be helpful in parameter estimation by using single qubits as probe, and entanglement purification process maybe more suitable for improving the estimation precision when entangled‐state probe is adopted.     

Quantum Fisher Information of Several Qubitsin the Superposition of A GHZ and two W Stateswith Arbitrary Relative Phase

We study the quantum Fisher information (QFI) of a system of several particles which is in a superposition of a GHZ and two W states with arbitrary relative phase. We show that as the number of particles increases from 3 to 4, the behavior of QFI drastically changes. We also show how the dependence of QFI on the relative phase weakens as the number of particles increases. We also analyze the QFI for the state for several instances of N due to the change of the relative phases.