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arXiv:quant-ph/0409164 · Physical Review Letters

Entangled and Disentangled Evolution for a Single Atom in a Driven Cavity

Julio R. Gea-Banacloche, T. C. Burt, Perry R. Rice, Luis A. Orozco

Published Feb 10, 2005• 30 citations
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Abstract

For an atom in an externally driven cavity, we show that special initial states lead to near-disentangled atom-field evolution, and superpositions of these can lead to near maximally entangled states. Somewhat counterintutively, we find that (moderate) spontaneous emission in this system actually leads to a transient increase in entanglement beyond the steady-state value. We also show that a particular field correlation function could be used, in an experimental setting, to track the time evolution of this entanglement.

DOI
10.1103/physrevlett.94.053603

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For an atom in an externally driven cavity, we show that special initial states lead to near-disentangled atom-field evolution, and superpositions of these can lead to near maximally entangled states. Somewhat counterintutively, we find that (moderate) spontaneous emission in this system actually leads to a transient increase in entanglement beyond the steady-state value. We also show that a particular field correlation function could be used, in an experimental setting, to track the time evolution of this entanglement.
We explore the entanglement between a single atom and a single, resonant field mode of a driven optical cavity, focusing on the strong driving regime. We show that, in the absence of spontaneous emission, there are special initial conditions that lead to approximately disentangled trajectories, whereas spontaneous emission results in coherent superpositions of such trajectories that may lead to (transient) near-maximally entangled atom-field states. We also discuss the possibility of using a special "asymmetric" field correlation function to track the time evolution of this entanglement.
We investigate steady state entanglement in an open quantum system, specifically a single atom in a driven optical cavity with cavity loss and spontaneous emission. The system reaches a steady pure state when driven very weakly. Under these conditions, there is an optimal value for atom-field coupling to maximize entanglement, as larger coupling favors a loss port due to the cavity enhanced spontaneous emission. We address ways to implement measurements of the entanglement and find that normalized cross-correlation functions are indicators of the entanglement in the system. The equal time intensity-field cross correlation between the transmitted field of the cavity and the fluorescence intensity is proportional to the entanglement of formation for weak driving fields.
The effect of spontaneously generated coherence on evolution of the entanglement between a driven four-level Y-type atom and its spontaneous emission field is studied. We have shown that the atom will be entangled to its spontaneous emission field due to spontaneously generated coherence and coherent population trapping at the steady state. It is found that the degree of entanglement strongly depends on the initial atomic state. So, it can be controlled by the pumping laser pulses used for preparing an initial atomic system. More interestingly, the atom–field system can be found in a permanently disentangled state for a properly prepared atom.
We investigate the degree of entanglement between an atom and a driven cavity mode in the presence of dissipation. Previous work has shown that in the limit of weak driving fields, the steady-state entanglement is proportional to the square of the driving intensity. This quadratic dependence is due to the generation of entanglement by the creation of pairs of photons or excitations. In this work we investigate the entanglement between an atom and a cavity in the presence of multiple photons. Nonlinearity of the atomic response is needed to generate entanglement, but as that nonlinearity saturates the entanglement vanishes. We posit that this is due to spontaneous emission, which puts the atom in the ground state and the atom-field state into a direct product state. An intermediate value of the driving field, near the field that saturates the atomic response, optimizes the atom-field entanglement. In a parameter regime for which multiphoton resonances occur, we find that entanglement recurs at those resonances. In this regime, we find that the entanglement decreases with increasing photon number. We also investigate, in the bimodal regime, the entanglement as a function of atom and/or cavity detuning. Here we find that there is evidence of a phase transition in the entanglement, which occurs at $2\ensuremath{\epsilon}/g\ensuremath{\ge}1$.