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arXiv:1908.06594 · Physical Review A

Deterministic generation of maximally discordant mixed states by dissipation

X. X. Li, Hao-Hao Yin, Dongxiao Li, Xiao‐Qiang Shao

Published Jan 17, 2020• 13 citations

Abstract

Entanglement can be considered as a special quantum correlation, but not the only kind. Even for a separable quantum system, nonclassical correlations are allowed to exist. Here we propose two dissipative schemes for generating a maximally correlated state of two qubits in the absence of quantum entanglement, which was proposed by Galve et al. [F. Galve, G. L. Giorgi, and R. Zambrini, Phys. Rev. A 83, 012102 (2011)]. These protocols take full advantage of the interaction between four-level atoms and strongly lossy optical cavities. In the first scenario, we alternatively change the phases of two classical driving fields, while the second proposal introduces a strongly lossy coupled-cavity system. Both schemes can realize all Lindblad terms required by the dissipative dynamics, guaranteeing the maximally quantum dissonant state to be the unique steady state for a certain subspace of the system. Moreover, since the target state is a mixed state, the performance of our method is evaluated by the definition of superfidelity $G({\ensuremath{\rho}}_{1},{\ensuremath{\rho}}_{2})$, and the strictly numerical simulations indicate that fidelity outstripping $99%$ of the quantum dissonant state is achievable with the current cavity quantum electrodynamics parameters.

DOI: 10.1103/physreva.101.012329

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Entanglement can be considered as a special quantum correlation, but not the only kind. Even for a separable quantum system, nonclassical correlations are allowed to exist. Here we propose two dissipative schemes for generating a maximally correlated state of two qubits in the absence of quantum entanglement, which was proposed by Galve et al. [F. Galve, G. L. Giorgi, and R. Zambrini, Phys. Rev. A 83, 012102 (2011)]. These protocols take full advantage of the interaction between four-level atoms and strongly lossy optical cavities. In the first scenario, we alternatively change the phases of two classical driving fields, while the second proposal introduces a strongly lossy coupled-cavity system. Both schemes can realize all Lindblad terms required by the dissipative dynamics, guaranteeing the maximally quantum dissonant state to be the unique steady state for a certain subspace of the system. Moreover, since the target state is a mixed state, the performance of our method is evaluated by the definition of superfidelity

G({\ensuremath{\rho}}_{1},{\ensuremath{\rho}}_{2})

, and the strictly numerical simulations indicate that fidelity outstripping

99%

of the quantum dissonant state is achievable with the current cavity quantum electrodynamics parameters.

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.

A new mechanism is proposed for dissipatively preparing maximal Bell entangled state of two atoms in an optical cavity. This scheme integrates the spontaneous emission, the light shift of atoms in the presence of dispersive microwave field, and the quantum Zeno dynamics induced by continuous coupling, to obtain a unique steady state irrespective of initial state. Even for a large cavity decay, a high-fidelity entangled state is achievable at a short convergence time, since the occupation of the cavity mode is inhibited by the Zeno requirement. Therefore, a low single-atom cooperativity C=g2/(κγ) is good enough for realizing a high fidelity of entanglement in a wide range of decoherence parameters. As a straightforward extension, the feasibility for preparation of two-atom Knill–Laflamme–Milburn state with the same mechanism is also discussed.

The dynamics of entanglement and quantum discord between two identical qubits strongly interacting with a common single mode leaky cavity field have been investigated beyond the rotating wave approximation (RWA) by using a recently derived Lindblad type quantum optical master equation [F. Beaudoin, J. M. Gambetta, and A. Blais, Phys. Rev. A 84, 043832 (2011)] that can describe the losses of the cavity field in a strong atom-field coupling regime. Contrary to previous investigations of the same model in the dissipative regime by using the standard Lindblad quantum optical master equation in a strong-coupling regime, the atom-field steady states are found to be cavity decay rate independent and have a very simple structure determined solely by the overlap of initial atomic state with the subradiant state which is valid for all coupling regimes. Non-RWA dynamics are found to have remarkable effects on the steady state quantum discord and entanglement that cannot be achieved under RWA conditions, for instance, they can induce steady state entanglement even for the initial states that have no overlap with the subradiant state. Moreover, the non-RWA dynamics are found to reverse the initial state dependence of steady state entanglement and quantum discord contrary to the RWA case.

We propose a scheme for generating steady-state entanglement between two distant atomic qubits in the coupled-cavity system via laser cooling. With suitable choice of the laser frequencies, the target entangled state is the only ground state that is not excited by the lasers due to large detunings. The laser excitations of other ground states, together with dissipative processes, drive the system to the target state which is the unique steady state of the system. Numerical simulation shows that the maximally entangled state with high fidelity can be produced with presently available cooperativity.

We propose a scheme for generating steady entanglement between two distant atomic qubits in the coupled-cavity system via laser cooling. With suitable choice of the laser frequencies, the target entangled state is the only ground state that is not excited by the lasers due to large detunings. The laser excitations of other ground states, together with dissipative processes, drive the system to the target state which is the unique steady state of the system. Numerical simulation shows that the maximally entangled state with high fidelity can be produced with presently available cooperativity.

We propose a scheme for the generation of entangled states for two atoms trapped in 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 delocalized field modes. Under certain conditions, the symmetric or asymmetric entangled state is produced in the steady state. The analytical result shows that the distributed steady entanglement can be achieved with high fidelity independent of the initial state and is robust against parameter fluctuations. We also find out that the linear scaling of entanglement fidelity has a quadratic improvement compared to distributed entangled state preparation protocols based on unitary dynamics.