Time-Correlated Vortex Tunneling in Layered Superconductors

The nucleation and dynamics of Josephson and Abrikosov vortices determine the critical currents of layered high-Tc superconducting (HTS) thin films, grain boundaries, and coated conductors, so understanding their mechanisms is of crucial importance. Here we treat pair creation of Josephson and Abrikosov vortices in layered superconductors as a secondary Josephson effect, in which each full vortex is viewed as a composite fluid of micro-vortices, such as pancake vortices, which tunnel coherently via a tunneling matrix element. We introduce a two-terminal magnetic (Weber) blockade effect that blocks tunneling below a threshold current, and simulate time-correlated vortex tunneling above threshold. The model shows nearly precise agreement with voltage-current (V-I) characteristics of HTS cuprate grain boundary junctions, which becomes more concave rounded as temperature decreases, and also explains the piecewise linear V-I behavior observed in iron-pnictide bicrystal junctions and other HTS devices. When applied to either Abrikosov or Josephson pair creation, the model explains a plateau seen in plots of critical current vs. thickness of HTS coated conductors. The observed correlation between theory and experiment strongly supports the proposed quantum picture of vortex nucleation and dynamics in layered superconductors.

Quantum evolution of a qubit state with decoherence and LFC

We study the Rabi oscillation of two-level system in double quantum dots, and found that the Rabi oscillation considering decoherence rate is a cycle attenuated oscillation when the qubit energy asymmetry [Formula: see text] ([Formula: see text] is the qubit energy asymmetry). The peak of Rabi oscillation alternatively changes in the case of the qubit energy asymmetry [Formula: see text] ([Formula: see text] is the qubit tunneling matrix element). Moreover, the local field correction (LFC) greatly affects the frequency of Rabi oscillation, in which the Rabi frequency changes fast with LFC increasing.

QUANTUM CONTROL IN STRONGLY DRIVEN OPTICAL LATTICES

Matter waves can be coherently and adiabatically loaded and controlled in strongly driven optical lattices. This coherent control is used in order to modify the modulus and the sign of the tunneling matrix element in the tunneling Hamiltonian. Our findings pave the way for studies of driven quantum systems and new methods for engineering Hamiltonians that are impossible to realize with static techniques.

EXACTLY SOLVABLE MODEL FOR THE DECAY OF SUPERDEFORMED NUCLEI

The history and importance of superdeformation in nuclei is briefly discussed. A simple two-level model is then employed to obtain an elegant expression for the branching ratio for the decay via the E1 process in the normal-deformed band of superdeformed nuclei. From this expression, the spreading width Γ↓ for superdeformed decay is found to be determined completely by experimentally known quantities. The accuracy of the two-level approximation is verified by considering the effects of other normal-deformed states. Furthermore, by using a statistical model of the energy levels in the normal-deformed well, we can obtain a probabilistic expression for the tunneling matrix element V.

CROSSOVER FROM RABI TO JOSEPHSON DYNAMICS IN TWO-COUPLED BOSE–EINSTEIN CONDENSATES AS A PHASE TRANSITION PROCESS

Crossover from individual Rabi dynamics to collective Josephson dynamics in two-coupled Bose–Einstein condensates is studied as a phase transition process. We obtain the critical value of the parameter Λ (ratio of the mean field energy to the tunneling matrix element) for the π-phase oscillations from the non-linear perturbation expansion of small oscillations around the saddle point of the first-order Euclidean (imaginary time) differential equations for polar and azimuthal angles θ and ϕ without approximation.