Coexistence of absolute negative mobility and anomalous diffusion

Using extensive numerical studies we demonstrate that absolute negative mobility of a Brownian particle (i.e. the net motion into the direction opposite to a constant biasing force acting around zero bias) does coexist with anomalous diffusion. The latter is characterized in terms of a nonlinear scaling with time of the mean-square deviation of the particle position. Such anomalous diffusion covers "coherent" motion (i.e. the position dynamics x(t) approaches in evolving time a constant dispersion), ballistic diffusion, subdiffusion, superdiffusion and hyperdiffusion. In providing evidence for this coexistence we consider a paradigmatic model of an inertial Brownian particle moving in a one-dimensional symmetric periodic potential being driven by both an unbiased time-periodic force and a constant bias. This very setup allows for various sorts of different physical realizations

Energy of a free Brownian particle coupled to thermal vacuum

Experimentalists have come to temperatures very close to absolute zero at which physics that was once ordinary becomes extraordinary. In such a regime quantum effects and fluctuations start to play a dominant role. In this context we study the simplest open quantum system, namely, a free quantum Brownian particle coupled to thermal vacuum, i.e. thermostat in the limiting case of absolute zero temperature. We analyze the average energy $E=E(c)$ of the particle from a weak to strong interaction strength $c$ between the particle and thermal vacuum. The impact of various dissipation mechanisms is considered. In the weak coupling regime the energy tends to zero as $E(c) \sim c\, \ln{(1/c)}$ while in the strong coupling regime it diverges to infinity as $E(c) \sim \sqrt{c}$. We demonstrate it for selected examples of the dissipation mechanisms defined by the memory kernel $\gamma(t)$ of the Generalized Langevin Equation. We reveal how at a fixed value of $c$ the energy $E(c)$ depends on the dissipation model: one has to compare values of the derivative $\gamma'(t)$ of the dissipation function $\gamma(t)$ at time $t=0$ or at the memory time $t=\tau_c$ which characterizes the degree of non-Markovianity of the Brownian particle dynamics. The impact of low temperature is also presented.Comment: In press in Scientific Reports (2021

Anomalous transport in biased ac-driven Josephson junctions: Negative conductances

We investigate classical anomalous electrical transport in a driven, resistively and capacitively shunted Josephson junction device. Novel transport phenomena are identified in chaotic regimes when the junction is subjected to both, a time periodic (ac) and a constant, biasing (dc) current. The dependence of the voltage across the junction on the dc-current exhibits a rich diversity of anomalous transport characteristics: In particular, depending on the chosen parameter regime we can identify so termed absolute negative conductance around zero dc-bias, the occurrence of negative differential conductance and, after crossing a zero conductance, the emergence of a negative nonlinear conductance in the non-equilibrium response regime remote from zero dc-bias.Comment: 7 pages, 5 figure

Many faces of nonequilibrium: anomalous transport phenomena in driven periodic systems

We consider a generic system operating under non-equilibrium conditions. Explicitly, we consider an inertial classical Brownian particle dwelling a periodic structure with a spatially broken reflection symmetry. The particle is coupled to a bath at the temperature $T$ and is driven by an unbiased time-periodic force. In the asymptotic long time regime the particle operates as a Brownian motor exhibiting finite directed transport although no net biasing force acts on the system. Here we review and interpret in further detail recent own research on the peculiar transport behaviour for this setup. The main focus is put on those different emerging Brownian diffusion anomalies. Particularly, within the transient, time-dependent domain the particle is able to exhibit anomalous diffusive motion which eventually crosses over into normal diffusion only in the asymptotic long-time limit. In the latter limit this normal diffusion coefficient may even show a non-monotonic temperature dependence, meaning that it is not monotonically increasing with increasing temperature, but may exhibit instead an extended, intermediate minimum before growing again with increasing temperature.Comment: in press in the special issue of Acta Physica Polonica

Dephasing of qubits by the Schr\"odinger cat

We study the dephasing of a single qubit coupled to a bosonic bath. In particular, we investigate the case when the bath is initially prepared in a pure state known as the Schr\"odinger cat. In clear contradistinction to the time-evolution of an initial coherent state, the time evolutions of the purity and the coherence factor now depend on the particular choice of the Schr\"odinger cat state. We also demonstrate that the evolution of the entanglement of a two--qubit system depends on the initial conditions in a similar way.Comment: Physica E (accepted

Current-flux characteristics in mesoscopic nonsuperconducting rings

We propose four different mechanisms responsible for paramagnetic or diamagnetic persistent currents in normal metal rings and determine the circumstances for change of the current from paramagnetic to diamagnetic ones and {\it vice versa}. It might qualitatively reproduce the experimental results of Bluhm et al. (Phys. Rev. Lett. 102, 136802 (2009)).Comment: 8 pages, 1 figur