Probabilistic Teleportation of the Three—Particle Entangled State by the Partial Three—Particle Entangled State and the Three—Particle Entangled W State

We present a scheme to teleport an unknown three-particle entangled state from a sender to either one of two receivers. The partial three-particle entangled state and the three-particle entangled W state are considered as the quantum channels. An unknown three-particle entangled state can be perfectly teleported probabilistically by performing two generalized Bell measurements and the Hadamard operation at the sender‘s side and introducing an appropriate unitary transformation in each receiver‘s laboratory conditioned on the simple measurement outcome of the other. All kinds of unitary transformations are given in details. This scheme can be directly generalized to teleport an unknown three-particle entangled state from a sender to any one of N receivers by the partial three-particle entangled state and the (N 1)-particle entangled W state.     

Entanglement COncentration of Entangled Squeezed Vacuum States

By analysing the action of a beamsplitter on squeezed vacuum states(SVSs),it is found that,if the two input light beams of the beamsplitter have the same squeezing amplitude and phase,the output state is a two-mode SVS,If the two input light beams of the beamsplitter have the same squeezing amplitude but a phase difference of π,the output state is a direct porduct state of two single-mode SVS.Based on these results,we propose to distill a maximally entangled SVS from a partially entangled SVS by using a 50/50 beamsplitter and photodetectors.     

Many-Agent Controlled Teleportation of Multi-qubit Quantum Information via Quantum Entanglement Swapping

We present a method to teleport multi-qubit quantum information in an easy way from a sender to a receiver via the control of many agents in a network. Only when all the agents collaborate with the quantum information receiver can the unknown states in the sender＇s qubits be fully reconstructed in the receiver＇s qubits. In our method, agents＇s control parameters are obtained via quantum entanglement swapping. As the realization of the many-agent controlled teleportation is concerned, compared to the recent method [G.P. Yang, et al., Phys. Rev. A 70 （2004） 022329], our present method considerably reduces the preparation difficulty of initial states and the identification difficulty of entangled states, moreover, it does not need local Hadamard operations and it is more feasible in technology.     

Quantum Teleportation of a Three—Particle Entangled State

We present a scheme for teleporting a three-particle entangled state to three remote particles.In this scheme,three pairs of pure nonmaximally entangled states are considered as quantum channels.It is found that by means of optimal discrimination between two nonorthogonal quantum states,probabilistic teleportation of the three-particle entangled state can be achieved.     

Teleportation for an Ionic Entangled Internal State by Entanglement Swapping

We present an effective scheme to teleport an unknown ionic entangled internal state via trapped ions without joint Bell-state measurement. In the constructed quantum channel process, we adopt entanglement swapping to avoid decrease of entanglement during the distribution of particles. Thus our scheme provides new prospects for quantum teleportation over longer distance. The distinct advantages of our scheme are that our scheme is insensitive to heating of vibrational mode and can be generalized to teleport an N-ion electronic entangled GHZ class state. Furthermore, in our scheme the success probability can reach 1.     

Relative Entropy of Entanglement of a Kind of Two-Qubit Entangled States

We strictly prove that some block diagonalizable two-qubit entangled state with six non-zero elements reaches its quantum relative entropy entanglement by a separable state having the same matrix structure. The entangled state comprises local filtering result state as a special case.     

Squeezing Transformation of Three-Mode Entangled State

We introduce the three-mode entangled state and set up an experiment to generate it. Then we discuss the three-mode squeezing operator squeezed ｜p, X2, X3〉→μ^-3/2｜p/μ, X2/μ, X3/μ） and the optical implement to realize such a squeezed state. We also reveal that c-number .asymmetric shrink transform in the three-mode entangled state, i.e. ｜p, X2,X3）→μ^-1/2｜p/μ, X2,X3）, maps onto a kind of one-sided three-mode squeezing operator {iλ （∑i^3=1 Pi） （∑i^3=1 Qi） -λ/2}. Using the technique of integration within an ordered product （IWOP） of operators, we derive their normally ordered forms and construct the corresponding squeezed states.     

Quantum Remote Control of Unitary Operations on a Qubit of Pure Entangled States

We consider the remote implementation of an arbitrary unitary operation on one qubit of a pure two-qubit entangled state with 100% efficiency via entanglement swapping in detail, then directly generalize this protocol from two-qubit to N-qubit entangled states. The overall classical information and distributed entanglement cost required for this quantum remote control protocol is less than the bi-directional quantum state teleportation method.     

Entanglement Swapping and Disentanglement via an Entangled State of Atoms Interacting with a Cavity Field

We consider entanglement swapping and disentanglement schemes via an entangled state of three two-level atoms interacting with a coherent field.When a two-level atom C,entangled with two other two-level atoms A and B,is injected into a high-Q cavity and atoms A and B are far away from the cavity,the entanglement swapping or disentanglement can be realized by carrying out the measurement on the atom C and by selecting an appropriate interaction time of atom C with the coherent field.     

Quantum Entanglement of Two Atoms Inside an Optical Cavity

We investigate the system,which consists of two two-level atoms confined in a linear trap which has been surrounded by an optical cavity,with the Milburn model of intrinsic decoherence,and find an explicit analytical solution of the Milburn equation.the entanglement between the two atoms is then calculated by making use of concurrence.The influence of intrinsic decoherence on the entanglement is also discussed.     

Influence of Multi-Photon Process on Entanglement of Interacting System of the Qubit and Thermal Field

We study the system of a single qubit couples to a single mode thermal field according to a multi-photon Jaynes-Cummings-type interaction with phase decoherence. Both the time evolving entanglement and the stationary state entanglement are calculated by adopting the log-negativity as a measure. It is found that the multi-photonprocess can enhance the stationary state entanglement of this system and can enlarge the range of the parameter Δ/g and the mean photon number of initial thermal field in which the stationary state is distillable.     

Entanglement Swapping and Quantum Correlation Transferring

We report the experimentally realization of entanglement swapping and quantum correlation transferring for continuous variables. The initial entangled states are generated from two non-degenerate optical parametric amplifiers （OPA） operating at de-amplification pumped. Two beams from each OPAs are entangled through implementing the directly measurement of Bell state between other two beams. The quantum correlation degrees of 1.23 and 1. 12 dB below the shot noise limit for the amplitude and phase quadratures resulting from the entanglement swapping are measured straightly. The quantum correlation transferring is experimentally demonstrated with two quantum correlated twin beams. The initial correlated twin beams are generated from two separated non- degenerate OPO pumped by independent laser. The intensity quantum correlation degree of 1dB below SNL from the transferring is measured.     

Entanglement and Quantity in Quantum Space —— About Quantum Measurement （II）

As a continuation and extension of “quantity in phase space“ “quantity in quantum space“ is introduced. With that, the disappearing of quantum interference discussed in a previous paper [S. Du^err, et al., Nature 395 (1998) 33] is explained in the same spirit as our recent papers [Ren De-Ming, Commun. Theor. Phys. (Beijing, China) 41(2004) 685, 833].     

Efficient Quantum Cryptography Network without Entanglement and Quantum Memory

An efficient quantum cryptography network protocol is proposed with d-dimensional polarized photons, without resorting to entanglement and quantum memory. A server on the network, say Alice, provides the service for preparing and measuring single photons whose initial state are ｜0〉. The users code the information on the single photons with some unitary operations. To prevent the untrustworthy server Alice from eavesdropping the quantum lines, a nonorthogonal-coding technique is used in the process that the quantum signal is transmitted between the users. This protocol does not require the servers and the users to store the quantum states and almost all of the single photons can be used for carrying the information, which makes it more convenient for application than others with present technology. We also discuss the case with a faint laser pulse.     

Quantum Dense Coding in Multiparticle Entangled States via Local Measurements

We study quantum dense coding between two arbitrarily fixed particles in a (N 2)-particle maxlmally-entangled states through introducing an auxiliary qubit and carrying out local measurements. It is shown that the transmitted classical information amount through such an entangled quantum channel is usually less than two classical bits. However, the information amount may reach two classical bits of information, and the classical information capacity is independent of the number of the entangled particles under certain conditions. The results offer deeper insight into quantum dense coding via quantum channels of multi-particle entangled states.     

Teleportation of Quantum States through Mixed Entangled Pairs

We describe a protocol for quantum state teleportation via mixed entangled pairs. With the help of an ancilla, near-perfect teleportation might be achieved. For pure entangled pairs, perfect teleportation might be achieved with a certain probability without using an ancilla. The protocol is generalized to teleportation of multiparticle states and quantum secret sharing.     

Unidirectional Quantum Remote Control： Teleportation of Control－State

We investigate the problem of teleportation of unitary operations by unidirectional control-state telepor-ration and propose a scheme called unidirectional quantum remote control. The scheme is based on the isomorphism between operation and state. It allows us to store a unitary operation in a control state, thereby teleportatSon of the unitary operation can be implemented by unidirectional teleportation of the control-state. We find that the probability of success for implementing an arbitrary unitary operation on arbitrary A~-qubit state by unidirectional control-state teleportation is 4^-M, and 2M ebits and 4M cbits are consumed in each teleportation.     

Quantum Teleportation of One-to-Many Using （n ＋ 1）-Particle Entanglement

In this paper, quantum teleportatlon of one-to-many using （n ＋1）-particle entanglement is presented. If the sender （Alice） wants to transmit an unknown quantum state to a distant receiver （Bob）, similar to the previous schemes, Alice performs Bell-state measurement on particles belonging to herself and informs the receiver the results through the classical channel. After that, it needs to perform the Hadamard operation on the other （n - 1） particles and measure them as well. With the aid of the measurement results, Bob can operate a corresponding unitary transformation on his particle to reconstruct the original state. Of course, the reconstruction may realize at either location of n, but it cannot realize at all locations at the same time.     

Multiparty Simultaneous Quantum Identity Authentication Based on Entanglement Swapping

We present a multiparty simultaneous quantum identity authentication protocol based on entanglement swapping. In our protocol, the multi-user can be authenticated by a trusted third party simultaneously.