An Min Wang

Local implementation of nonlocal operations with block forms

We investigate the local implementation of nonlocal operations with the block matrix form, and propose a protocol for any diagonal or offdiagonal block operation. This method can be directly generalized to the two-party multiqubit case and the multiparty case. Especially, in the multiparty cases, any diagonal block operation can be locally implemented using the same resources as the multiparty control-U operation discussed in Ref. [Eisert et al., Phys. Rev. A 62, 052317(2000)]. Although in the bipartite case, this kind of operations can be transformed to control-U operation using local operations, these transformations are impossible in the multiparty cases. We also compare the local implementation of nonlocal block operations with the remote implementation of local operations, and point out a relation between them.

Hybrid protocol of remote implementations of quantum operations

We propose a protocol of remote implementations of quantum operations by hybridizing bidirectional quantum-state teleportation (BQST) [Huelga et al., Phys. Rev. A 63, 042303 (2001)] and the Wang protocol [Wang, Phys. Rev. A 74, 032317 (2006)]. The protocol is available for remote implementations of quantum operations in the restricted sets specified in the paper. We also give a proof of the protocol and point out its optimization. As an extension, this hybrid protocol can be reduced to the BQST and Wang protocols.

Relating tripartite quantum discord with multisite entanglement and their performance in the one-dimensional anisotropic XXZ model

In order to define quantum correlations, there are two important paradigms in quantum information theory, viz. the information-theoretic and the entanglement-separability ones. In this paper, we give an analytical relation between two measures of quantum correlations. One of them is related to the monogamy of squared bipartite quantum discord, which is a information-theoretic multipartite quantum correlation measure, while the other is the generalized geometric measure which lies in the entanglement-separability paradigm. We find a certain cone-like region on the two-dimensional spaces spanned by the two measures. Moreover, we have investigated the quantum phase transition with the two measures in the anisotropic spin XXZ model by exploiting the quantum renormalization group method.

Entanglement sudden death in a spin channel

We study the dynamic evolution of the entanglement in a spin channel with an XY-type interaction initially in an entangled state. We find that the phenomenon of entanglement sudden death (ESD) appears in the evolution of entanglement for some initial states. We calculate the entanglement and obtain the parameter regions of disentanglement for the chains with several numbers of sites. The influence of the presence of one common spin environment is also discussed.

Quantum simulation of pairing models on an NMR quantum computer

We give out a scheme of quantum simulation of pairing models on an NMR quantum computer. We show that it can obtain the spectrum of paring model in principle, and present a simple example. Similarly, it is possible to discuss the quantum simulation to obtain more differences of energy levels.

Entanglement dynamics and decoherence of three-qubit system in a fermionic environment

We study the entanglement dynamics of the three-qubit system in a symmetry-broken environment consisting of a fermionic bath. Decoherence induced by the bath is analysed. We find that the entanglement of states will decrease or remain unchanged under the system–bath interaction. The class of decoherence-free states of the three-qubit system of our model has been found out.

Quantum discord for a central two-qubit system coupled to an XY spin chain with Dzyaloshinsky–Moriya interaction

We investigated the quantum discord dynamics of a central two-qubit system coupled to an XY spin chain with the Dzyaloshinsky–Moriya (DM) interaction. We found that the DM interaction does not affect the behavior of the quantum phase transition induced by the external magnetic field. Moreover, the DM interaction enhances the decay of quantum discord in the weak-coupling regime, while it has no obvious effect on the quantum discord dynamics in the strong-coupling regime.

Multi-particle and high-dimension controlled order rearrangement encryption protocols

Abstract.Based on controlled order rearrange encryption (CORE) for quantum key distribution using EPR pairs [Fu.G. Deng, G.L. Long, Phys. Rev. A 68, 042315 (2003)], we propose generalized controlled order rearrangement encryption (GCORE) protocols of N qubits and N qutrits, and concretely display them in cases using 3-qubit, 2-qutrit maximally entangled basis states. We further show that our protocols will become safer with an increase in dimensions and number of particles. Moreover, we carry out the security analysis using quantum covariant cloning machine. Although the applications of the generalized scheme need to be further studied, GCORE has many distinct features such as large capacity and high efficiency.

Tripartite entanglement of a spin star model with Dzialoshinski---Moriya interaction

The effect of Dzialoshinski–Moriya (DM) interaction on the tripartite thermal entanglement of a spin-star model with four spins has been analyzed by an entanglement measure of the tripartite negativity. Our results imply that the tripartite thermal entanglement can be established among the three surrounding parties which do not interact with each other but interact with the central party independently. From the results, we find that the strong DM interaction can enhance the tripartite thermal entanglement while the high temperature can shrink it. The effect of the inhomogeneous coupling on the tripartite thermal entanglement is also discussed.

Interplay of Coulomb interaction and disorder in a two-dimensional semi-Dirac fermion system

It was recently found that Coulomb interaction can induce a series of nontrivial spectral and transport properties in a two-dimensional semi-Dirac fermion system. Different from graphene that is basically an ordinary Fermi liquid, the Coulomb interaction in this system invalidates the Fermi liquid description over a wide range of energy scales. We present a systematic renormalization group analysis of the interplay of Coulomb interaction and quenched disorder, and show that they have substantial mutual effects on each other, which leads to a variety of quantum phase transitions and non-Fermi liquid behaviors. The low-energy behaviors of the system depend sensitively on the effective strength of Coulomb interaction and disorder.