Chang-shui Yu

Remote preparation of a qudit using maximally entangled states of qubits

Known quantum pure states of a qudit can be remotely prepared onto a group of particles of qubits exactly or probabilistically with the aid of two-level Einstein-Podolsky-Rosen states. We present a protocol for such kind of remote state preparation. We are mainly focused on the remote preparation of the ensembles of equatorial states and those of states in real Hilbert space. In particular, a kind of states of qudits in real Hilbert space have been shown to be remotely prepared in faith without the limitation of the input space dimension.

Robust preparation of Greenberger-Horne-Zeilinger and w states of three distant atoms

Schemes to generate Greenberger-Horne-Zeilinger(GHZ) and W states of three distant atoms are proposed in this paper. The schemes use the effects of quantum statistics of indistinguishable photons emitted by the atoms inside optical cavities. The advantages of the schemes are their robustness against detection inefficiency and asynchronous emission of the photons. Moreover, in Lamb-Dicke limit, the schemes do not require simultaneous click of the detectors, this makes the schemes more realizable in experiments.

Direct scheme for measuring the geometric quantum discord

We propose a scheme to directly measure the exact value of the geometric quantum discord of an arbitrary two-qubit state. We need only to perform the projective measurement in all the anti-symmetric subspace and our scheme is parametrically efficient in contrast to the widely adopted quantum state tomography scheme in the sense of less parameter estimations and projectors. Moreover, the present scheme can be easily realized with the current experimental techniques.

Concurrence of superpositions

Bounds on the concurrence of the superposition state in terms of the concurrences of the states being superposed are found in this paper. The bounds on concurrence are quite different from those on the entanglement measured by von Neumann entropy [Linden et al., Phys. Rev. Lett. 97, 100502 (2006)]. In particular, a nonzero lower bound can be provided if the states being superposed are properly constrained.

Multipartite entanglement measure

In this paper, we generalize the residual entanglement to the case of multipartite states in arbitrary dimensions by making use of a different method. Through the introduction of a special entanglement measure, the residual entanglement of mixed states takes on a form that is more elegant than that used by Coffman et al. [Phys. Rev. A 61, 052306 (2000)]. The result obtained in this paper is different from the previous one given by Wong and Christensen [Phys. Rev. A 63, 044301 (2000)]. Several examples demonstrate that our present result is a good measurement of the multipartite entanglement. Furthermore, the original residual entanglement is a special case of our result.

Quantum discord induced by white noises

We discuss the creation of quantum discord between two two-level atoms trapped in an optical cavity in a noisy environment. It is shown that nonzero steady-state quantum discord between atoms can be obtained when the white-noise field is separately imposed on atoms or cavity mode, while the steady-state quantum discord reaches zero if both cavity mode and atoms are driven simultaneously by white-noise fields. In particular, we demonstrate that white-noise field in different cases can play a variously constructive role in the generation of quantum discord.

Entanglement Monogamy of Tripartite Quantum States

An interesting monogamy equation with the form of Pythagorean theorem is found for

Evolution of entanglement for quantum mixed states

2otimes 2otimes n

Measurable entanglement for tripartite quantum pure states of qubits

-dimensional pure states, which reveals the relation among bipartite concurrence, concurrence of assistance, and genuine tripartite entanglement. At the same time, a genuine tripartite entanglement monotone as a generalization of 3-tangle is naturally obtained for

Dual roles of quantum discord in a nondemolition probing task

(2otimes 2otimes n)