Abstract adiabatic charge pumping

This paper is devoted to the analysis of an abstract formula describing quantum adiabatic charge pumping in a general context. We consider closed systems characterized by a slowly varying time-dependent Hamiltonian depending on an external parameter $\alpha$. The current operator, defined as the derivative of the Hamiltonian with respect to $\alpha$, once integrated over some time interval, gives rise to a charge pumped through the system over that time span. We determine the first two leading terms in the adiabatic parameter of this pumped charge under the usual gap hypothesis. In particular, in case the Hamiltonian is time periodic and has discrete non-degenerate spectrum, the charge pumped over a period is given to leading order by the derivative with respect to $\alpha$ of the corresponding dynamical and geometric phases

Disordered Josephson junction chains: Anderson localization of normal modes and impedance fluctuations

We study the properties of the normal modes of a chain of Josephson junctions in the simultaneous presence of disorder and absorption. We consider the superconducting regime of small phase fluctuations and focus on the case where the effects of disorder and absorption can be treated additively. We analyze the frequency shift and the localization length of the modes. We also calculate the distribution of the frequency-dependent impedance of the chain. The distribution is Gaussian if the localization length is long compared to the absorption length; it has a power law tail in the opposite limit.Comment: 16 pages, 8 figure

Nonadiabatic creation of macroscopic superpositions with strongly correlated 1D bosons on a ring trap

We consider a strongly interacting quasi-one dimensional Bose gas on a tight ring trap subjected to a localized barrier potential. We explore the possibility to form a macroscopic superposition of a rotating and a nonrotating state under nonequilibrium conditions, achieved by a sudden quench of the barrier velocity. Using an exact solution for the dynamical evolution in the impenetrable-boson (Tonks-Girardeau) limit, we find an expression for the many-body wavefunction corresponding to a superposition state. The superposition is formed when the barrier velocity is tuned close to multiples of integer or half-integer number of Coriolis flux quanta. As a consequence of the strong interactions, we find that (i) the state of the system can be mapped onto a macroscopic superposition of two Fermi spheres, rather than two macroscopically occupied single-particle states as in a weakly interacting gas, and (ii) the barrier velocity should be larger than the sound velocity to better discriminate the two components of the superposition.Comment: 5 pages, 3 figures, revised introduction and new Fig3, final version to appear in PR

Correlated tunneling into a superconductor in a multiprobe hybrid structure

We consider tunneling in a hybrid system consisting of a superconductor with two or more probe electrodes which can be either normal metals or polarized ferromagnets. In particular we study transport at subgap voltages and temperatures. Besides Andreev pair tunneling at each contact, in multi-probe structures subgap transport involves additional channels, which are due to coherent propagation of two particles (electrons or holes), each originating from a different probe electrode. The relevant processes are electron cotunneling through the superconductor and conversion of two electrons stemming from different probes in a Cooper pair. These processes are non-local and decay when the distance between the pair of involved contacts is larger than the superconducting coherence length. The conductance matrix of a the three terminal hybrid structure is calculated. The multi-probe processes enhance the conductance of each contact. If the contacts are magnetically polarized the contribution of the various conduction channels may be separately detected.Comment: 7 pages, 1 figure, accepted in Europhysics Letters, minor changes, 3 references adde