No alternatives to entanglement

David E. Steinberg

Min Cao, Shiqun Zhu

The concurrence of two alternate qubits in a four-qubit Heisenberg $XX$ chain is investigated when a uniform magnetic field $B$ is included. It is found that there is no thermal entanglement between alternate qubits if $B$ is close to zero. A magnetic field can induce entanglement in a certain range both for the antiferromagnetic and ferromagnetic cases. Near zero temperature, the entanglement undergoes two sudden changes with increasing value of the magnetic field $B$. This is due to the changes in the ground state. This novel property may be used as a quantum entanglement switch. The anisotropy in the system can also induce the entanglement between two alternate qubits.

Juan M. Romero, Emiliano Montoya-González, Oscar Velazquez-Alvarado

Bell's states are among the most useful in quantum computing. These state are an orthonormal base of entagled states with two qubits. We propose alternative bases of entangled states. Some of these states depend on a continuous parameter. We present the quantum circuit and code of these alternative bases. In addition, we study quantum teleportation with these entangled states and present their quantum circuits and codes associated.

Eva Haifa Giraud

Eva Haifa Giraud

Timothy C. Ralph, Gerard J Milburn, T. G. Downes

We discuss an alternative formulation of the problem of quantum optical fields in a curved space-time using localized operators. We contrast this formulation with the standard approach and find observable differences for entangled states. We propose an experiment in which an entangled pair of optical pulses are propagated through nonuniform gravitational fields and find that the alternative formulation predicts decorrelation of the optical entanglement under experimentally realistic conditions.