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arXiv:quant-ph/0307096 · Physical Review A

Preparation and control of a cavity-field state through an atom–driven-field interaction: Towards long-lived mesoscopic states

Celso J. Villas-Bôas, Fernando Rogério de Paula, Roberto M. Serra, M. H. Y. Moussa

Published Nov 20, 2003• 31 citations

Abstract

The preparation of mesoscopic states of radiation and matter fields through atom-field interactions has been achieved in recent years and employed for a range of striking applications in quantum optics. Here we present a technique for the preparation and control of a cavity mode which, in addition to interacting with a two-level atom, is simultaneously submitted to linear and parametric amplification processes. The role of the amplification-controlling fields in the achievement of real mesoscopic states is to produce highly squeezed field states and, consequently, to increase both (i) the distance in phase space between the components of the prepared superpositions and (ii) the mean photon number of such superpositions. When the squeezed superposition states are submitted to the action of similarly squeezed reservoirs, we demonstrate that under specific conditions the decoherence time of the states becomes independent of both the distance in phase space between their components and their mean photon number. An explanation is presented to support this remarkable result, together with a discussion of the experimental implementation of our proposal. We also show how to produce number states with fidelities higher than those derived as circular states.

DOI: 10.1103/physreva.68.053808

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We propose an implementation of the parametric amplification of an arbitrary radiation-field state previously prepared in a high-Q cavity. This nonlinear process is accomplished through the dispersive interactions of a single three-level atom (fundamental |g〉, intermediate |i〉, and excited |e〉 levels) simultaneously with (i) a classical driving field and (ii) a previously prepared cavity mode whose state we wish to squeeze. We show that, in the adiabatic approximantion, the preparation of the initial atomic state in the intermediate level |i〉 becomes crucial for obtaining the degenerated parametric amplification process.

We propose a scheme to generate superposition and entanglement between the mesoscopic squeezed vacuum states by considering the two-photon interaction of

N

two-level atoms in a cavity with high quality factor, assisted by a strong driving field. By virtue of specific choices of the cavity detuning, a number of multiparty entangled states can be prepared, including the entanglement between the atomic and the squeezed vacuum cavity states and between the squeezed vacuum states and the coherent states of the cavities. We also present how to prepare entangled states and ``Schr\"odinger cats'' states regarding the squeezed vacuum states of the cavity modes. The possible extension and application of our scheme are discussed. Our scheme is close to the reach with current cavity QED techniques.

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A single two-level atom can be used to prepare an arbitrary photon number state (Fock state) in a high Q cavity . The atom undergoes a controlled succession of interactions with two cavity modes. One of them contains a coherent field. The atom transfers photons one by one from this field to the initially empty second mode. The scheme can be extended to prepare a quantum superposition of the vacuum with a Fock state, a highly non-classical situation. We discuss the feasibility of the experiment with our present Rydberg-atom cavity QED set-up.