J. Plata

Classical-quantum correspondence for barrier crossing in a driven bistable potential

Both quantum and classical analyses are performed to study the barrier crossing dynamics in a driven quartic oscillator. The regions of phase space with regular classical motion are found to be smaller than the size of a quantum state. However, coherent tunnelling is still possible due to the existence of Floquet states localized on two small regular islands. The quantum evolution of localized wavepackets and the classical evolution of the corresponding distributions show similar coherence properties although the degree of coherence is quantally enhanced.

Periodic driving control of Raman-induced spin-orbit coupling in Bose-Einstein condensates: The heating mechanisms

We focus on a technique recently implemented for controlling the magnitude of synthetic spin-orbit coupling (SOC) in ultra-cold atoms in the Raman-coupling scenario. This technique uses a periodic modulation of the Raman-coupling amplitude to tune the SOC. Specifically, it has been shown that the effect of a high-frequency sinusoidal modulation of the Raman-laser intensity can be incorporated into the undriven Hamiltonian via effective parameters, whose adiabatic variation can then be used to steer the SOC. Here, we characterize the heating mechanisms that can be relevant to this method. We identify the main mechanism responsible for the heating observed in the experiments as basically rooted in driving-induced transfer of population to excited states. Characteristics of that process determined by the harmonic trapping, the decay of the excited states, and the technique used for preparing the system are discussed. Additional heating, rooted in departures from adiabaticity in the variation of the effective parameters, is also described. Our analytical study provides some clues that may be useful in the design of strategies for curbing the effects of heating on the efficiency of the control methods.

Stochastic dynamics of an electron in a Penning trap: Phase flips correlated with amplitude collapses and revivals

We study the effect of noise on the axial mode of an electron in a Penning trap under parametric-resonance conditions. Our approach, based on the application of averaging techniques to the description of the dynamics, provides an understanding of the random phase flips detected in recent experiments. The observed correlation between the phase jumps and the amplitude collapses is explained. Moreover, we discuss the actual relevance of noise color to the identified phase-switching mechanism. Our approach is then generalized to analyze the persistence of the stochastic phase flips in the dynamics of a cloud of N electrons. In particular, we characterize the detected scaling of the phase-jump rate with the number of electrons.