Quantum Discord and Entanglement of Quasi-Werner States Based on Bipartite Entangled Coherent States

Present work is an attempt to compare quantum discord and quantum entanglement of quasi-Werner states formed with the four bipartite entangled coherent states (ECS) used recently for quantum teleportation of a qubit encoded in superposed coherent state. Out of these, the quasi-Werner states based on maximally ECS due to its invariant nature under local operation is independent of measurement basis and mean photon numbers, while for quasi-Werner states based on non-maximally ECS, it depends upon measurement basis as well as on mean photon number. However, for large mean photon numbers since non-maximally ECS becomes almost maximally entangled therefore dependence of quantum discord for non-maximally ECS based quasi-Werner states on the measurement basis disappears.     

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     

Teleportations of Mixed States and Multipartite Quantum States

In this paper, we propose a protocol to deterministically teleport an unknown mixed state of qubit by utilizing a maximally bipartite entangled state of qubits as quantum channel. Ira non-maximally entangled bipartite pure state is employed as quantum channel, the unknown mixed quantum state of qubit can be teleported with 1 -√ 1- C^2 probability, where C is the concurrence of the quantum channel. The protocol can also be generalized to teleport a mixed state of qudit or a multipartite mixed state. More important purpose is that, on the basis of the protocol, the teleportation of an arbitrary multipartite （pure or mixed） quantum state can be decomposed into the teleportation of each subsystem by employing separate entangled states as quantum channels. In the case of deterministic teleportation, Bob only needs to perform unitary transformations on his single particles in order to recover the initial teleported multipartite quantum state.     

Teleportation of tripartite entangled coherent states

This paper proposes a feasible scheme for the quantum teleportation of tripartite entangled coherent states by using linear optical devices such as beam splitters, phase shifters and photo detectors. The scheme is based on the bipartite maximally entangled coherent state and the tripartite entangled coherent state with bipartite maximal entanglement as quantum channels. It shows that when the mean number of photons is equal to 2, the total minimum of the average fidelity for an arbitrary tripartite entangled state is 1-0.67×10 ^-3.     

通过cluster态实现两粒子纠缠态的量子几率隐形传态

提出通过一个四粒子cluster非最大纠缠态作为量子信道来实现一未知两粒子纠缠态的量子几率隐形传态方案。在此方案中,纠缠态可以实现一定的几率传输,此几率由cluster态中绝对值较小的两个系数决定。如果我们用cluster最大纠缠态作为量子信道,此时几率隐形传态就成了一般的隐形传态,即成功传输的几率为100%。     

Cooperative Communications via Dual-Teleportation with Non-maximally Entanglement Measurements

We investigate a framework of the cooperative quantum teleportation (CQT) based on non-maximally entangled state basis (NB) measurements, instead of maximally entangled state basis (MB) measurements. It is implemented with two consecutive conventional (or direct) quantum telportations (DQT), where unknown quantum states can be transmitted in a point-to-point fashion. The security is based on the quantum-mechanical impossibility of local unitary transformations between non-maximally entangled states. It shows that the CQT can enhance the successful transmissions by self-correcting the errors introduced in the dual-teleportations.     

Teleportation of an arbitrary three—particle state

We propose two schemes for teleporting an arbitrary three-particle state.In the first scheme,a two-particle state and a three-particle entangled state (both non-maximally entangled states)are used as quantum channels,while in the second scheme,three non-mnaximally entangled particle pairs are employed as quantum channels.We show that teleportation can be successfully realized with certain probability if a receiver adopts some appropriate unitary transformations.Their success probabilities and the classical communication costs are different.     

Scheme for Implementing Assisted Cloning of an Unknown d-Dimension Equatorial Quantum State by Remote State Preparation

In this paper, we propose a protocol that can produce perfect copy of an unknown d-dimensional equatorial quantum state with assistance from a state preparer. In this protocol, the maximally and non-maximally entangled bipartite d-dimensional of states are used as the quantum channels, respectively. The first stage of the protocol requires usual teleportation. In the second stage of the protocol, with the assistance of the preparer, the perfect copy of an original unknown state can be produced.     

三粒子纠缠Ｗ态的隐形传态

提出利用三个二粒子纠缠态作为量子信道，实现三粒子纠缠Ｗ态的隐形传态的方案.首先考察量子信道是最大纠缠态的情形，然后进一步考察量子信道是非最大纠缠态的情形.发现在量子信道为非最大纠缠态时，通过引进一个辅助粒子，并构造一个幺正变换矩阵，即可以一定的概率完成三粒子纠缠Ｗ态的隐形传态. 关键词： 隐形传态 三粒子纠缠 纠缠Ｗ态 非最大纠缠量子信道     

A new representation and probabilistic teleportation of an arbitrary and unknown N-particle state

A new representation of an arbitrary and unknown N-particle state is presented at first. As an application, a scheme for teleporting an arbitrary and unknown N-particle state is proposed when N pairs of two-particle non- maximally entangled states are utilized as quantum channels. After Alice （sender） makes Bell-state measurement on her particles, Bob （recipient） introduces an auxiliary particle and carries out appropriate unitary transformation on his particle and the auxiliary particle depending on classical information from Alice. Then, von Neumann measurement that confirms whether the teleportation succeeds or not is performed by Bob on the auxiliary particle. In order to complete the teleportation, another N-1 times operations need to be performed which are similar to the above ones. It can be successfully realized with a certain probability which is determined by the product of the smaller coefficients of non-maximally entangled pairs. All possible unitary transformations are given in detail.     

Scheme for cloning an unknown single qutrit state with assistance

We propose a scheme for cloning an unknown single qutrit state with assistance. The scheme includes a qutrit-state teleportation at the cloner's site. During this process different states (i.e., the maximally entangled or non-maximally entangled two-qutrit states) as quantum channel are taken into account. After the teleportation, to help the cloner Alice to reestablish the unknown state, the state preparer Victor should perform a single-qutrit measurement and tell her the outcome. In this scheme, the success probability of cloning the original state is determined by the used quantum channel.     

Schemes for Probabilistic Teleportation of an Unknown Three-Particle Three-Level Entangled State

In this paper, two schemes for teleporting an unknown three-particle three-level entangled state are proposed. In the first scheme, two partial three-particle three-level entangled states are used as the quantum channels, while in the second scheme, three two-particle three-level non-maximally entangled states are employed as quantum channels. It is shown that the teleportation can be successfully realized with certain probability, for both two schemes, if a receiver adopts some appropriate unitary transformations. It is shown also that the successful probabilities of these two schemes are different.     

Probabilistic Teleportation of a Four-Particle Entangled W State

In this paper, two schemes for teleporting an unknown four-particle entangled W state is proposed. In the first scheme, two partial entangled four-particle states are used as quantum channels, while in the second scheme, four non-maximally entangled particle pairs are considered as quantum channels. It is shown that the teleportation can be successfully realized with certain probability, for both schemes, if a receiver adopts some appropriate unitary transformations. It is also shown that the successful probabilities of these two schemes are different.     

Probabilistic Teleportation of Three-Atom State via Five-Atom Cluster State

A scheme for probabilistic teleportation of an unknown three-atom entangled state via a five-atom non-maximally entangled cluster state as quantum channel is proposed. In this scheme, the sender performs two Bell state and a single-atom measurements on the atoms, the receiver can reconstruct the original state with a certain probability by introducing an auxiliary atom and operating appropriate unitary transformations and controlled-not (C-not) operations according to the sender Alice's measurement results. As a result, the probability of successful teleportation is determined by the smallest two of the coefficients'absolute values of the cluster state. The considerable advantage of our scheme is that we employ a non-maximally entangled cluster state as quantum channel in the scheme, which can greatly reduce the amount of entanglement resources and need less classical bits. If we employ a maximally entangled cluster state as quantum channel, the probabilistic teleportation scheme becomes usual teleportation, the successful probability being 100%.     

Probabilistic Teleportation of an Arbitrary Two-Particle State and Its Quantum Circuits

Two simple schemes for probabilistic teleportation of an arbitrary unknown two-particle state using a non-maximally entangled EPR pair and a non-maximally entangled GHZ state as quantum channels are proposed. After receiving Alice's Bell state measurement results, Bob performs a collective unitary transformation on his inherent particles without introducing the auxiliary qubit. The original state can be probabilistically teleported. Meanwhile, quantum circuits for realization of successful teleportation are also presented.     

通过四个纠缠态粒子来实现未知的三个纠缠态粒子的量子几率隐形传输

提出一种分别利用四个三态粒子的最大纠缠态和非最大纠缠态作为量子通道来传输一未知的三个三态粒子纠缠态的方案.首先考察量子通道是最大纠缠态的情况,然后进一步考察量子通道是非最大纠缠态的情况,同时发现在后者情况时,通过引进一个辅助粒子,并构造一幺正变换矩阵,即可以一定的几率完成该三态粒子纠缠态的隐形传输.     

Quantum logic networks for probabilistic teleportation

By eans of the primitive operations consisting of single-qubit gates.two-qubit controlled-not gates,Von Neuman measurement and classically controlled operations.,we construct efficient quantum logic networks for implementing probabilistic teleportation of a single qubit,a two-particle entangled state,and an N-particle entanglement.Based on the quantum networks,we show that after the partially entangled states are concentrated into maximal entanglement,the above three kinds of probabilistic teleportation are the same as the standard teleportation using the corresponding maximally entangled states as the quantum channels.     

Quantum multicast schemes of different quantum states via non-maximally entangled channels with multiparty involvement

Due to the unavoidable interaction between the quantum channel and its ambient environment, it is difficult to generate and maintain the maximally entanglement. Thus, the research on multiparty information transmission via non-maximally entangled channels is of academic value and general application. Here, we utilize the non-maximally entangled channels to implement two multiparty remote state preparation schemes for transmitting different quantum information from one sender to two receivers synchronously. The first scheme is adopted to transmit two different four-qubit cluster-type entangled states to two receivers with a certain probability. In order to improve success probabilities of such multicast remote state preparation using non-maximally entangled channels, we put forward the second scheme, which deals with the situation that is a synchronous transfer of an arbitrary single-qubit state and an arbitrary two-qubit state from one sender to two receivers. In particular, its success probability can reach 100% in principle, and independent of the entanglement degree of the shared non-maximally entangled channel. Notably, in the second scheme, the auxiliary particle is not required.     

Continuous-Variable Quantum Teleportation of Entangled Coherent States

We propose a quantum teleportation scheme for tripartite entangled coherent state （ECS） with continuous variable. Our scheme is feasible and economical in the sense that we need only linear optical devices such as beam splitters, phase shifters and photon detectors and employ three bipartite maximally ECSs as quantum channels. We also generalize the tripartite scheme into multipartite ease and calculate the minimum average fidelity for the schemes in tripartite and multipartite cases.     

Continuous variable quantum teleportation with sculptured and noisy non-Gaussian resources

We investigate continuous variable (CV) quantum teleportation using relevant classes of non-Gaussian states of the radiation field as entangled resources. First, we introduce the class two-mode squeezed symmetric superposition of Fock states, including finite truncations of twin-beam Gaussian states as special realizations. These states depend on a set of free independent parameters that can be adjusted for the optimization of teleportation protocols, with an enhancement of the success probability of teleportation both for coherent and Fock input states. We show that the optimization procedure reduces the entangled resources to truncated twin beam states, which thus represents an optimal class of non-Gaussian resources for quantum teleportation. We then introduce a further class of two-mode non-Gaussian entangled resources, in the form of squeezed cat-like states. We analyze the performance and the properties of such states when optimized for (CV) teleportation, and compare them to the optimized squeezed Bell-like states introduced in a previous work [12]. We discuss how optimal resources for teleportation are characterized by a suitable balance of entanglement content and squeezed vacuum affinity. We finally investigate the effects of thermal noise on the efficiency of quantum teleportation. To this aim, a convenient framework is to describe noisy entangled resources as linear superpositions of non-Gaussian state and thermal states. Although the presence of the thermal component strongly reduces the teleportation fidelity, noisy non-Gaussian states remain preferred resources when compared to noisy twin-beam Gaussian states.