Minimax Strategy of Optimal Unambiguous State Discrimination

In this paper, we consider the minimax strategy to unambiguously discriminate two pure nonorthogonal quantum states without knowing a priori probability. By exploiting the positive-operator valued measure, we derive the upper bound of the minimax measurement of the optimal unambiguous state discrimination. Based on the linear optical devices, we propose an experimentally feasible scheme to implement a minimax measure of a general pair of two nonorthogonal quantum states.     

Unambiguous State Discrimination with Intrinsic Coherence

We investigate the discrimination of pure-mixed (quantum filtering) and mixed-mixed states and compare their optimal success probability with the one for discriminating other pairs of pure states superposed by the vectors included in the mixed states. We prove that under the equal-fidelity condition, the pure-pure state discrimination scheme is superior to the pure-mixed (mixed-mixed) one. With respect to quantum filtering, the coherence exists only in one pure state and is detrimental to the state discrimination for lower dimensional systems; while it is the opposite for the mixed-mixed case with symmetrically distributed coherence. Making an extension to infinite-dimensional systems, we find that the coherence which is detrimental to state discrimination may become helpful and vice versa.     

Understanding of Various Type of Unambiguous Discrimination in View of Coherence Distribution

Unambiguous quantum state discrimination is a strategy where the conclusive result can always be trusted. This strategy is very important, since it can be used for various quantum information protocols, including quantum key distribution. However, in the view of quantumness, it is not clear what is going on in performing unambiguous quantum state discrimination. To answer the question, we investigate coherence distribution when unambiguous discrimination is performed by generalized measurement. Specially, we study coherence distribution in three cases, which consist of unambiguous quantum state discrimination, sequential quantum state discrimination, and assisted optimal discrimination, which are considered to be a family of unambiguous quantum state discrimination. In this investigation, we show that the structure of generalized measurements performing various types of unambiguous quantum state discrimination can be understood in terms of coherence distribution. Our result is not limited to the discrimination of two pure quantum states, but it is extended to the discrimination of two mixed states.     

The Linear Optical Unambiguous Discrimination of Hyperentangled Bell States Assisted by Time Bin

A linear optical unambiguous discrimination of hyperentangled Bell states is proposed for two‐photon systems entangled in both the polarization and momentum degrees of freedom (DOFs) assisted by time bin. This unambiguous discrimination scheme can completely identify 16 orthogonal hyperentangled Bell states using only linear optical elements, where the function of the auxiliary entangled Bell state is replaced by time bin. Moreover, the possibility of extending this scheme for distinguishing hyperentangled Bell states in n DOFs is discussed, and it shows that $2^{n+k+1}$ hyperentangled Bell states in n ( $n\ge 2$) DOFs can be distinguished with k ( $k<n$) auxiliary entangled states of additional DOFs by introducing a time delay, which decreases the auxiliary entanglement resource required for unambiguous discrimination of hyperentangled Bell state. Therefore, this scheme provides a new way for distinguishing hyperentangled states with current technology, which will extend the application of discrimination of hyperentangled states via linear optics to other quantum information protocols besides hyperdense coding schemes in the future.     

Mutual Information and Quantum Discord in Quantum State Discrimination with a Fixed Rate of Inconclusive Outcomes

We studied the mutual information and quantum discord that Alice and Bob share when Bob implements a discrimination with a fixed rate of inconclusive outcomes (FRIO) onto two pure non-orthogonal quantum states, generated with arbitrary a priori probabilities. FRIO discrimination interpolates between minimum error (ME) and unambiguous state discrimination (UD). ME and UD are well known discrimination protocols with several applications in quantum information theory. FRIO discrimination provides a more general framework where the discrimination process together with its applications can be studied. In this setting, we compared the performance of optimum probability of discrimination, mutual information, and quantum discord. We found that the accessible information is obtained when Bob implements the ME strategy. The most (least) efficient discrimination scheme is ME (UD), from the point of view of correlations that are lost in the initial state and remain in the final state, after Bob’s measurement.     

Discrimination Among Quantum States

It has recently been shown that quantum measurement is not always useful for discrimination among quantum states (K. Hunter (2003). Physical Review A 68, 012306). This paper provides another proof of the necessary and sufficient condition for quantum measurement not to be useful and examines the condition by considering quantum measurement which discriminates between two spin-1/2 states in thermal equilibrium.     

From Quantum State Targeting to Bell Inequalities

Quantum state targeting is a quantum game which results from combining traditional quantum state estimation with additional classical information. We consider a particular version of the game and show how it can be played with maximally entangled states. The optimal solution of the game is used to derive a Bell inequality for two entangled qutrits. We argue that the nice properties of the inequality are direct consequences of the method of construction.     

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。     

最优实数态克隆作为标准BB84方案的最优个体窃听攻击

我们给出最优ARSC是对标准BB84方案的最优个体窃听分析.基于量子克隆的个体窃听,说明在由Csiszár和Korner定理的密钥产生率的两个充分条件中,其中一个可以作为最好的充分条件.     

Scheme for Implementation of Optimal Cloning of Arbitrary Single Particle Atomic State into Two Photonic States

We present a feasible scheme to implement the 1→2 optimal cloning of arbitrary single particle atomic state into two photonic states, which is important for applications in long distance quantum communication. Our scheme also realizes the tele-NOT gate of one atom to the distant atom trapped in another cavity. The scheme is based on the adiabatic passage and the polarization measurement. It is robust against a number of practical noises such as the violation of the Lamb Dicke condition, spontaneous emission, and detection inefficiency.     

Linear optical implementation of optimal unambiguous discrimination among quantum states

In this paper, we present a linear optical scheme for optimal unambiguous discrimination among nonorthogonal quantum states in terms of the multiple-rail and polarization representation of a single photon. In our scheme, discriminated quantum states are expressed by using the spatial degree of freedom of a single photon while the polarization degree of freedom of the single photon is used to act as an auxiliary qubit. The optical components used in our scheme are only passive linear optical elements such as polarizing beam splitters, wave plates, polarizers, single photon detectors, and single photon source.     

线性光学实现量子普适确切态识别

给出一种量子普适确切态识别的线性光学实现方案.此方案只用到双光子的干涉和符合测量,在实验上是简单可行的.同时提出一种改进方案,通过一定量的辅助光子,使得上述方案成功概率得以提高.这一方案将可应用于量子密钥分配等安全信息交流中. 关键词： 确切态识别 线性光学     

Ambiguous Discrimination of General Quantum Operations

We consider the problem of discriminating general quantum operations. Using the definition of mapping operator to vector, and by some calculating skills, we derive an explicit formulation as a new bound on the minimum-error probability for ambiguous discrimination between arbitrary m quantum operations. This formulation consists only of Kraus-operators, the dimension, and the priori probabilities of the discriminated quantum operations, and is independent of input states. To some extent, we further generalize the bounds on the minimum-error probability for discriminating mixed states to quantum operations.     

Optimal Conclusive Teleportation of an Arbitrary d-Dimensional N-Particle Unknown State via a Partially Entangled Quantum Channel

In the paper we generalize the standard teleportation to the conclusive teleportation case which can teleportan arbitrary d-dimensional N-particle unknown state via the partially entangled quantum channel. We show that onlyif the quantum channel satisfies a constraint condition can the most general d-dimensional N-particle unknown state beperfect conclusively teleported. We also present a method for optimal conclusively teleportation of the N-particle statesand for constructing the joint POVM which can discern the quantum states on the sender's (Alice's) side. Two typicalexamples are given so that one can see how our method works.     

A Theoretical Scheme for Multiparty Multi-particle State Sharing

A theoretical scheme for multiparty multi-particle state sharing is proposed. After she introduces auxiliary particles and Einstein-Podolsky-Rosen （EPIC） pairs, the sender （Alice） performs Hadamard （14） gate operations and Controlled-NOT （CNOT） gate operations on them. Subsequently, the sender leaves one particle sequence and distributes the rest particles to the other participants. And then, the sender makes Bell-state measurements on her particles and publishes the measurement outcomes via the classical channel to realize the quantum state sharing among the others. Only the simple operations are used to realize quantum state sharing. The sender may increase or decrease the number of the participants by changing the number of the auxiliary particles.     

Teleportation of Two-Particle Entangled State via Cluster State

In this paper,two schemes for teleporting an unknown two-particle entangled state from the sender (Alice)to the receiver (Bob) via a four-particle entangled cluster state are proposed.In these two schemes,the unknown twoparticle entangled state can be teleported perfectly.The successful probabilities and fidelities of the schemes can reach unity.     

A Scheme of Controlled Quantum State Swapping

A scheme for controlled quantum state swapping is presented using maximally entangled five-qubit state,i.e.,Alice wants to transmit an entangled state of particle a to Bob and at the same time Bob wants to transmit an entangled state of particle b to Alice via the control of the supervisor Charlie.The operations used in this swapping process including C-not operation and a series of single-qubit measurements performed by Alice,Bob,and Charlie.     

Controlled Teleportation of an Unknown N-qubit Entangled GHZ State

A scheme for controlled teleportation of an unknown N-qubit entangled GHZ state from the sender Alice to the distant receiver Bob is proposed. And m-qubit GHZ state is sufficient for the task of control by m spatially- separated supervisors. Conditioned on the local operations executed by all participants, Bob can faithfully restore the original state by performing relevant unitary transformations with the aid of some classical message about measurement results. Anyone＇s absence will absolutely lead to the failure of teleportation.     

Quantum Secret Sharing Using GHZ-Like State

This paper presents a simple and novel quantum secret sharing scheme using GHZ-like state. The characteristics of the GHZ-like state are used to develop the quantum secret sharing scheme. In contrast with the other GHZ-based QSS protocols with the same assumptions, the proposed protocol provides the best quantum bit efficiency.     

A Scheme of Controlled Quantum State Swapping

A scheme for controlled quantum state swapping is presented using maximally entangled five-qubit state, i.e., Alice wants to transmit an entangled state of particle a to Bob and at the same time Bob wants to transmit an entangled state of particle b to Alice via the control of the supervisor Charlie. The operations used in this swapping process including C-not operation and a series of single-qubit measurements performed by Alice, Bob, and Charlie.