Energetics of an rf SQUID Coupled to Two Thermal Reservoirs.

We study energetics of a Josephson tunnel junction connecting a superconducting loop pierced by an external magnetic flux (an rf SQUID) and coupled to two independent thermal reservoirs of different temperature. In the framework of the theory of quantum dissipative systems, we analyze energy currents in stationary states. The stationary energy flow can be periodically modulated by the external magnetic flux exemplifying the rf SQUID as a quantum heat interferometer. We also consider the transient regime and identify three distinct regimes: monotonic decay, damped oscillations and pulse-type behavior of energy currents. The first two regimes can be controlled by the external magnetic flux while the last regime is robust against its variation.

Squeezing of magnetic flux in nanorings.

We study superconducting and non-superconducting nanorings and look for non-classical features of magnetic flux passing through nanorings. We show that the magnetic flux can exhibit purely quantum properties in some peculiar states with quadrature squeezing. We identify a subset of Gazeau-Klauder states in which the magnetic flux can be squeezed and, within tailored parameter regimes, quantum fluctuations of the magnetic flux can be maximally reduced.

Current in Hubbard rings manipulated via magnetic flux.

We study currents in a quantum ring threaded by a magnetic flux which is varied in an arbitrary way from an initial constant value φ(1) at time t(1) to a final constant value φ(2) at time t(2). We analyze how the induced currents for t > t(2) can be controlled by the rate of flux variation [Formula: see text]. The dynamics of electrons in the ring is described using the Hubbard and the extended Hubbard models. In the Hubbard model with infinite on-site repulsion the current for t > t(2) is shown to be independent of the flux variation before t(2) and is fully determined by a solution of the initial equilibrium problem and by the value φ(2) of the flux. For intermediate values of the interaction strength the current displays regular or irregular time oscillations and the amplitude of oscillations is sensitive to the rate of the flux changing [Formula: see text]: slow changes of the flux result in small amplitudes of the current oscillations and vice versa. We demonstrate that the time dependence of the induced current bears information on electronic correlations. Our results have important implications for not only mesoscopic rings but also the designing of quantum motors built out of ring-shaped optical lattices.

Entanglement of qubits via a nonlinear resonator.

Coherent coupling of two qubits mediated by a nonlinear resonator is studied. It is shown that the amount of entanglement accessible in the evolution depends on both the strength of nonlinearity in the Hamiltonian of the resonator and on the initial preparation of the system. The created entanglement survives in the presence of decoherence.

Entanglement of distant flux qubits mediated by non-classical electromagnetic field.

The mechanism for entanglement of two flux qubits each interacting with a single mode electromagnetic field is discussed. By performing a Bell state measurement (BSM) on photons we find the two qubits in an entangled state depending on the system parameters. We discuss the results for two initial states and take into consideration the influence of decoherence.

Dynamical bimodality in equilibrium monostable systems.

General features of the stochastic dynamics of classical systems approaching a thermodynamic equilibrium Gibbs state are studied via the numerical analysis of time-dependent solutions of the Fokker-Planck equation for an overdamped particle in various monostable potentials. A large class of initial states can dynamically bifurcate during its time evolution into bimodal transient states, which in turn wear off when approaching the long-time regime. Suitable quantifiers characterizing this transient dynamical bimodality, such as its lifetime, the positions of maxima, and the time-dependent well depth of the probability distribution, are analyzed. Some potential applications are pointed out that make use of this interesting principle which is based on an appropriately chosen initial preparation procedure.