Quantum Ratchet Accelerator without a Bichromatic Lattice Potential

In a quantum ratchet accelerator system, a linearly increasing directed current can be dynamically generated without using a biased field. Generic quantum ratchet acceleration with full classical chaos [Gong and Brumer, Phys. Rev. Lett. 97, 240602 (2006)] constitutes a new element of quantum chaos and an interesting violation of a sum rule of classical ratchet transport. Here we propose a simple quantum ratchet accelerator model that can also generate linearly increasing quantum current with full classical chaos. This new model does not require a bichromatic lattice potential. It is based on a variant of an on-resonance kicked-rotor system, periodically kicked by two optical lattice potentials of the same lattice constant, but with unequal amplitudes and a fixed phase shift between them. The dependence of the ratchet current acceleration rate on the system parameters is studied in detail. The cold-atom version of our new quantum ratchet accelerator model should be realizable by introducing slight modifications to current cold-atom experiments.Comment: 9 pages, 6 figures, submitted to Phys. Rev.

Conservation Laws and Thermodynamic Efficiencies

We show that generic systems with a single relevant conserved quantity reach the Carnot efficiency in the thermodynamic limit. Such a general result is illustrated by means of a diatomic chain of hard-point elastically colliding particles where the total momentum is the only relevant conserved quantity.Comment: 5 pages, 4 figure

Heat conductivity in linear mixing systems

We present analytical and numerical results on the heat conduction in a linear mixing system. In particular we consider a quasi one dimensional channel with triangular scatterers with internal angles irrational multiples of pi and we show that the system obeys Fourier law of heat conduction. Therefore deterministic diffusion and normal heat transport which are usually associated to full hyperbolicity, actually take place in systems without exponential instability.Comment: Revtex, 4 pages, 6 EPS figure

Non-ergodicity and localization of invariant measure for two colliding masses

We show evidence, based on extensive and carefully performed numerical experiments, that the system of two elastic hard-point masses in one-dimension is not ergodic for a generic mass ratio and consequently does not follow the principle of energy equipartition. This system is equivalent to a right triangular billiard. Remarkably, following the time-dependent probability distribution in a suitably chosen velocity direction space, we find evidence of exponential localization of invariant measure. For non-generic mass ratios which correspond to billiard angles which are rational, or weak irrational multiples of pi, the system is ergodic, in consistence with existing rigorous results.Comment: 4+ pages in RevTex with 5 figure

Self-duality triggered dynamical transition

A basic result about the dynamics of spinless quantum systems is that the Maryland model exhibits dynamical localization in any dimension. Here we implement mathematical spectral theory and numerical experiments to show that this result does not hold, when the 2-dimensional Maryland model is endowed with spin 1/2 -- hereafter dubbed spin-Maryland (SM) model. Instead, in a family of SM models, tuning the (effective) Planck constant drives dynamical localization{delocalization transitions of topological nature. These transitions are triggered by the self-duality, a symmetry generated by some transformation in the parameter -- the inverse Planck constant -- space. This provides significant insights to new dynamical phenomena such as what occur in the spinful quantum kicked rotor.Comment: 18 pages, 6 figure