Noise-Enhanced Directed Transport of Cold Atoms
Thesis
The possibility of enhancing directed transport for a driven quantum particle in the presence of noise is investigated. Specifically, we deal with cold atoms trapped in an asymmetric optical lattice potential (ratchet potential), with amplitude noise, which is periodically switched on/off. Such potential in the absence of noise is the recently engineered optical lattice of ratchet type. The dynamics of this system are governed by the Time-Dependent Schrodinger Equation (TDSE) with noise or so-called Stochastic TDSE. Much like in the case of the TDSE, the Stochastic TDSE is solved utilizing the FFT Split Operator Method subject to a certain number of realization of the noise. Our observables of interest here are the current, the energy, and the momentum distribution wave function of the particle. In the absence of noise, we have been able to retrieve existing results in the literature demonstrating interesting directed transport properties within the quantum resonance regime (QR). We also checked that the counter-intuitive current reversal that occurs here goes hand in hand with the full classical chaos observed by solving the associated classical map of the system. Switching on the noise and still within QR and for weak potential strengths, optimal currents emerged for given noise intensities. At the limit of the very high noise intensity, the current saturates. On the other hand, for a strong potential strength, the noise suppresses the current and in some cases even leads to current reversal. The effect should be readily observable in experiments