C. J. Villas-Boas

Rabi model beyond the rotating-wave approximation: Generation of photons from vacuum through decoherence

We study numerically the dynamics of the Rabi Hamiltonian, which describes the interaction of a single cavity mode and a two-level atom without the rotating wave approximation. We analyze this system subjected to damping and dephasing reservoirs, included via the usual Lindblad superoperators in the master equation. We show that the combination of the antirotating term and the atomic dephasing leads to linear asymptotic photon generation from the vacuum. We reveal the origins of the phenomenon and estimate its importance in realistic situations.

Teleportation of a zero- and one-photon running-wave state by projection synthesis

We show how to teleport a running wave superposition of zero- and one-photon field state through the projection synthesis technique. The fidelity of the scheme is computed taking into account the noise introduced by dissipation and the efficiency of the detectors. These error sources have been introduced through a single general relationship between input and output operators.

One-cavity scheme for atomic-state teleportation through GHZ states

Abstract We present a one-cavity scheme for atomic-state teleportation employing the GHZ entangled state as the quantum channel. A scheme employing a single high- Q cavity turns out to be attractive to realize experimentally, while the GHZ state simplifies the procedure for the accomplishment of the required joint measurement.

Purity as a witness for initial system-environment correlations in open-system dynamics

We study the dynamics of a two-level atom interacting with a Lorentzian structured reservoir considering initial system-environment correlations. It is shown that under strong system-reservoir coupling the dynamics of purity can determine whether there are initial correlations between the system and the environment. Moreover, we investigate the interaction of two two-level atoms with the same reservoir. In this case, we show that, besides determining if there are initial system-environment correlations, the dynamics of the purity of the atomic system allows the identification of the distinct correlated initial states. In addition, the dynamics of quantum and classical correlations is analyzed.

Bilinear and quadratic Hamiltonians in two-mode cavity quantum electrodynamics

In this work we show how to engineer bilinear and quadratic Hamiltonians in cavity quantum electrodynamics through the interaction of a single driven two-level atom with cavity modes. The validity of the engineered Hamiltonians is numerically analyzed even when considering the effects of both dissipative mechanisms, the cavity field and the atom. The present scheme can be used, in both optical and microwave regimes, for quantum state preparation, the implementation of quantum logical operations, and fundamental tests of quantum theory.

Squeezing arbitrary cavity-field states through their interaction with a single driven atom

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.

Frequency up- and down-conversions in two-mode cavity quantum electrodynamics

In this Brief Report we present a scheme for the implementation of frequency up- and down-conversion operations in two-mode cavity quantum electrodynamics (QED). This protocol for engineering bilinear two-mode interactions could enlarge perspectives for quantum-information manipulation and also be employed for fundamental tests of quantum theory in cavity QED. As an application we show how to generate a two-mode squeezed state in cavity QED (the original entangled state of Einstein, Podolsky, and Rosen)

Nonadiabatic Coherent Evolution of Two-Level Systems under Spontaneous Decay

In this Letter we extend current perspectives in engineering reservoirs by producing a time-dependent master equation leading to a nonstationary superposition equilibrium state that can be nonadiabatically controlled by the system-reservoir parameters. Working with an ion trapped inside a nonideal cavity, we first engineer effective interactions, which allow us to achieve two classes of decoherence-free evolution of superpositions of the ground and excited ionic levels: those with a time-dependent azimuthal or polar angle. As an application, we generalize the purpose of an earlier study [Phys. Rev. Lett. 96, 150403 (2006)10.1103/PhysRevLett.96.150403], showing how to observe the geometric phases acquired by the protected nonstationary states even under nonadiabatic evolution.

Engineering squeezed states in high-Q cavities

While it has been possible to build fields in high-Q cavities with a high degree of squeezing for some years, the engineering of arbitrary squeezed states in these cavities has only recently been addressed [Phys. Rev. A 68, 061801(R) (2003)]. The present work examines the question of how to squeeze any given cavity-field state and, particularly, how to generate the squeezed displaced number state and the squeezed macroscopic quantum superposition in a a high-Q cavity.

Nonclassical behavior of an intense cavity field revealed by quantum discord.

We investigate the quantum-to-classical crossover of a dissipative cavity field by measuring the correlations between two noninteracting atoms coupled to the cavity mode. First, we note that there is a time window in which the mode shows a classical behavior, which depends on the cavity decay rate, the atom-field coupling strength, and the number of atoms. Then, considering the steady state of two atoms inside the cavity, we note that the entanglement between the atoms disappears while the mean number of photons of the cavity field (n) rises. However, the quantum discord reaches an asymptotic nonzero value even in the limit of n→∞, whether n is increased coherently or incoherently. Therefore, the cavity mode always preserves some quantum characteristics in the macroscopic limit, which is revealed by the quantum discord.