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arXiv:1005.2114

Generating maximal entanglement between non-interacting atoms by collective decay and symmetry breaking

Xiaoting Wang, S. G. Schirmer

Published May 12, 2010• 12 citations

Abstract

A simple scheme is presented for achieving effectively maximal pure-state entanglement between non-interacting atoms through purely collective decay and controlled symmetry breaking. The scheme requires no measurements or feedback or even knowledge of the initial states of the atoms. It relies on breaking the symmetry of the system Hamiltonian to ensure the existence of a unique attractive steady state and minimal control to achieve almost perfect overlap of this steady state with the maximally entangled singlet state. We demonstrate how our scheme can be implemented for two qubits encoded in hyperfine levels of atoms such as Rubidium in a lossy microwave cavity using only small magnetic field gradient. Error analysis suggests considerable robustness with regard to many imperfections including atomic decay, asymmetric atom-cavity coupling and frequency offsets.

DOI: 10.48550/arxiv.1005.2114

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A simple scheme is presented for achieving effectively maximal pure-state entanglement between non-interacting atoms through purely collective decay and controlled symmetry breaking. The scheme requires no measurements or feedback or even knowledge of the initial states of the atoms. It relies on breaking the symmetry of the system Hamiltonian to ensure the existence of a unique attractive steady state and minimal control to achieve almost perfect overlap of this steady state with the maximally entangled singlet state. We demonstrate how our scheme can be implemented for two qubits encoded in hyperfine levels of atoms such as Rubidium in a lossy microwave cavity using only small magnetic field gradient. Error analysis suggests considerable robustness with regard to many imperfections including atomic decay, asymmetric atom-cavity coupling and frequency offsets.

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A scheme for generating the maximally entangled mixed state of two atoms on-resonance asymmetrically coupled to a single mode optical cavity field is presented. The part frontier of both maximally entangled mixed states and maximal Bell violating mixed states can be approximately reached by the evolving reduced density matrix of two atoms if the ratio of coupling strengths of two atoms is appropriately controlled. It is also shown that exchange symmetry of global maximal concurrence is broken if and only if coupling strength ratio lies between

\frac{\sqrt{3}}{3}

and

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for the case of one-particle excitation and asymmetric coupling, while this partial symmetry breaking cannot be verified by detecting maximal Bell violation.

We present a scheme for realizing a steady entanglement state between two trapped atoms, without requiring the initialization of atom-cavity system nor fine time-controlling of evolution dynamics. We show that high-fidelity entanglement of atomic state can be obtained in a period of time equal to a few times the inverse of atomic's spontaneous decay rate. The robustness against cavity decay $\ensuremath{\kappa}$ and cavity thermal field

{n}_{T}

has also been examined.

Abstract We present a scheme for the dissipative preparation of an entangled steady state between two atomic qubits separately trapped in the coupled cavities. The combination of coherent driving fields and dissipative processes will drive the system into a steady state. By choosing different frequency of classical laser field, the target steady state can be generated in different ways. In our scheme, the atomic spontaneous emission and the cavity decay can be used as a prerequisite. The numerical simulation shows that the maximally entangled state with high fidelity and purity can be produced regardless of the initial state. The fidelity is insensitive to the fluctuation of the system parameters.

We propose a scheme for generating an entangled state for two atoms trapped in two separate cavities coupled to each other. The scheme is based on the competition between the unitary dynamics induced by the classical fields and the collective decays induced by the dissipation of two non-local bosonic modes. In this scheme, only one qubit is driven by external classical fields, whereas the other need not be manipulated via classical driving. This is meaningful for experimental implementation between separate nodes of a quantum network. The steady entanglement can be obtained regardless of the initial state, and the robustness of the scheme against parameter fluctuations is numerically demonstrated. We also give an analytical derivation of the stationary fidelity to enable a discussion of the validity of this regime. Furthermore, based on the dissipative entanglement preparation scheme, we construct a quantum state transfer setup with multiple nodes as a practical application.