Véronique Zehnlé

Behavior of a CO2 laser under loss modulation : critical analysis of different theoretical models

Abstract Various theoretical rate equation models describing the dynamics of the CO 2 laser are developed and analysed. In the frame-work of these models, the response of a CO 2 laser subjected to cavity loss modulation is investigated. A critical analysis of these descriptions is performed by comparison with experimental data. It is shown that both the so-called two- and three-level models are inadequate to reproduce, even qualitatively, the experimental data. On the other hand, the four-level model which includes the rovibrational level manifolds fits the experiments correctly.

Theoretical analysis of quantum dynamics in one-dimensional lattices: Wannier-Stark description

This paper presents a formalism describing the dynamics of a quantum particle in a one-dimensional, tilted, time-dependent lattice. The description uses the Wannier-Stark states, which are localized in each site of the lattice, and provides a simple framework leading to fully analytical developments. Particular attention is devoted to the case of a time-dependent potential, which results in a rich variety of quantum coherent dynamics.

Kicked rotor quantum resonances in position space

We present an approach of the kicked rotor quantum resonances in position-space, based on its analogy with the optical Talbot effect. This approach leads to a very simple picture of the physical mechanism underlying the dynamics and to analytical expressions for relevant physical quantities, such as mean momentum or kinetic energy. The ballistic behavior, which is closely associated to quantum resonances, is analyzed and shown to emerge from a coherent adding of successive kicks applied to the rotor thanks to a periodic reconstruction of the spatial wavepacket.

Atomic motion in tilted optical lattices: an analytical approach

This paper presents general results concerning the quantum dynamics in a tilted, time-modulated, one-dimensional, optical lattice. A dynamic equation describing the atomic motion is analytically solved, and the solution used to characterize the corresponding dynamics through the spatial mean position and dispersion of the wavepacket. The analysis of such quantities gives a quite complete picture of the quantum dynamics, and provides evidence for the central role of the quantum coherence.

Quantum motor: Directed wave-packet motion in an optical lattice

We propose a method for arbitrary manipulations of a quantum wave packet in an optical lattice by a suitable modulation of the lattice amplitude. A theoretical model allows us to determine the modulation needed to generate an arbitrary atomic trajectory; wave-packet rotations can also be implemented. The method is immediately usable in state-of-the-art experiments.

Wave-packet reconstruction via local dynamics in a parabolic lattice

We study the dynamics of a wave packet in a potential formed by the sum of a periodic lattice and a parabolic potential. The dynamics of the wave packet is essentially a superposition of oscillations with frequencies proportional to the local slope of the parabolic potential. The amplitude and the phase of the Fourier transform of a signal characterizing this dynamics then contain information about the amplitude and the phase of the wave packet at a given lattice site. Hence, complete reconstruction of the wave packet in real space can be performed from a study of the dynamics of the system.

Simulating Dirac models with ultracold atoms in optical lattices

We present a general model allowing quantum simulation of one-dimensional Dirac models with two- and four-component spinors using ultracold atoms in driven one-dimensional tilted optical latices. The resulting Dirac physics is illustrated by one of its well-known manifestations, zitterbewegung. This general model can be extended and applied with great flexibility to more complex situations.

Quantum interference in a driven washboard potential

The dynamics of a quantum particle in a one-dimensional, tilted (“washboard”) and time-dependent lattice is studied. The approach uses quantum mechanics at the undergraduate level and leads to analytical results that show a rich variety of dynamical behavior and illustrate the fundamental role of interference in quantum systems.

Suppression of decoherence-induced diffusion in the quantum kicked rotor

We describe a method that allows transient suppression of spontaneous emission-induced diffusion in the atom-optics realization of the kicked rotor. The system is prepared in an initial state with a momentum distribution concentrated in an interval much sharper than the Brillouin zone; the measure of the momentum distribution is restricted to this interval of quasimomenta. Because most of the atoms undergoing decoherence processes fall outside this detection range and thus are not detected, the measured signal is effectively free of decoherence-induced diffusion effects.

Tracking quasiclassical chaos in ultracold boson gases.

We study the dynamics of an ultracold boson gas in a lattice submitted to a constant force. We track the route of the system towards chaos created by the many-body-induced nonlinearity and show that relevant information can be extracted from an experimentally accessible quantity, the gas mean position. The threshold nonlinearity for the appearance of chaotic behavior is deduced from Kolmogorov-Arnold-Moser arguments and agrees with the value obtained by calculating the associated Lyapunov exponent.