15,384 research outputs found
Quantum charge pumping and electric polarization in Anderson insulators
We investigate adiabatic charge pumping in disordered system in one dimension
with open and closed boundary conditions. In contrast to the Thouless charge
pumping, the system has no gap even though all the states are localized, i.e.,
strong localization. Charge pumping can be achieved by making a loop
adiabatically in the two-dimensional parameter space of the Hamiltonian. It is
because there are many -function-like fluxes distributed over the
parameter space with random strength, in sharp contrast to the single
-function in the pure case. This provides a new and more efficient way
of charge pumping and polarization.Comment: 16 pages, 15 figure
Josephson-Majorana cycle in topological single-electron hybrid transistors
Charge transport through a small topological superconducting island in
contact with a normal and a superconducting electrode occurs through a cycle
that involves coherent oscillations of Cooper pairs and tunneling in/out the
normal electrode through a Majorana bound state, the Josephson-Majorana cycle.
We illustrate this mechanism by studying the current-voltage characteristics of
a superconductor-topological superconductor-normal metal single-electron
transistor. At low bias and temperature the Josephson-Majorana cycle is the
dominant mechanism for transport. We discuss a three-terminal configuration
where the non-local character of the Majorana bound states is emergent.Comment: 6 pages, 4 figure
Quantum Fluids and Classical Determinants
A "quasiclassical" approximation to the quantum spectrum of the Schroedinger
equation is obtained from the trace of a quasiclassical evolution operator for
the "hydrodynamical" version of the theory, in which the dynamical evolution
takes place in the extended phase space . The quasiclassical evolution operator is
multiplicative along the classical flow, the corresponding quasiclassical zeta
function is entire for nice hyperbolic flows, and its eigenvalue spectrum
contains the spectrum of the semiclassical zeta function. The advantage of the
quasiclassical zeta function is that it has a larger analyticity domain than
the original semiclassical zeta function; the disadvantage is that it contains
eigenvalues extraneous to the quantum problem. Numerical investigations
indicate that the presence of these extraneous eigenvalues renders the original
Gutzwiller-Voros semiclassical zeta function preferable in practice to the
quasiclassical zeta function presented here. The cumulant expansion of the
exact quantum mechanical scattering kernel and the cycle expansion of the
corresponding semiclassical zeta function part ways at a threshold given by the
topological entropy; beyond this threshold quantum mechanics cannot resolve
fine details of the classical chaotic dynamics.Comment: 33 pages, LaTeX with lamuphys.sty, epsf.sty, epsfig.sty macros,
available at http://www.nbi.dk/~predrag
Adiabatic perturbation theory and geometry of periodically-driven systems
We give a systematic review of the adiabatic theorem and the leading non-adiabatic corrections in periodically-driven (Floquet) systems. These corrections have a two-fold origin: (i) conventional ones originating from the gradually changing Floquet Hamiltonian and (ii) corrections originating from changing the micro-motion operator. These corrections conspire to give a Hall-type linear response for non-stroboscopic (time-averaged) observables allowing one to measure the Berry curvature and the Chern number related to the Floquet Hamiltonian, thus extending these concepts to periodically-driven many-body systems. The non-zero Floquet Chern number allows one to realize a Thouless energy pump, where one can adiabatically add energy to the system in discrete units of the driving frequency. We discuss the validity of Floquet Adiabatic Perturbation Theory (FAPT) using five different models covering linear and non-linear few and many-particle systems. We argue that in interacting systems, even in the stable high-frequency regimes, FAPT breaks down at ultra slow ramp rates due to avoided crossings of photon resonances, not captured by the inverse-frequency expansion, leading to a counter-intuitive stronger heating at slower ramp rates. Nevertheless, large windows in the ramp rate are shown to exist for which the physics of interacting driven systems is well captured by FAPT.The authors would like to thank M. Aidelsburger, M. Atala, E. Dalla Torre, N. Goldman, M. Heyl, D. Huse, G. Jotzu, C. Kennedy, M. Lohse, T. Mori, L. Pollet, M. Rudner, A. Russomanno, and C. Schweizer for fruitful discussions. This work was supported by AFOSR FA9550-16-1-0334, NSF DMR-1506340, ARO W911NF1410540, and the Hungarian research grant OTKA Nos. K101244, K105149. M. K. was supported by Laboratory Directed Research and Development (LDRD) funding from Berkeley Lab, provided by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The authors are pleased to acknowledge that the computational work reported in this paper was performed on the Shared Computing Cluster which is administered by Boston University's Research Computing Services. The authors also acknowledge the Research Computing Services group for providing consulting support which has contributed to the results reported within this paper. The study of the driven non-integrable transverse-field Ising model was carried out using QuSpin [185] - an open-source state-of-the-art Python package for dynamics and exact diagonalization of quantum many body systems, available to download here. (FA9550-16-1-0334 - AFOSR; DMR-1506340 - NSF; W911NF1410540 - ARO; K101244 - Hungarian research grant OTKA; K105149 - Hungarian research grant OTKA; DE-AC02-05CH11231 - Laboratory Directed Research and Development (LDRD) funding from Berkeley Lab)https://arxiv.org/pdf/1606.02229.pd
Optical Hall Effect in the Integer Quantum Hall Regime
Optical Hall conductivity is measured from the Faraday
rotation for a GaAs/AlGaAs heterojunction quantum Hall system in the terahertz
frequency regime. The Faraday rotation angle ( fine structure constant
mrad) is found to significantly deviate from the Drude-like behavior to
exhibit a plateau-like structure around the Landau-level filling . The
result, which fits with the behavior expected from the carrier localization
effect in the ac regime, indicates that the plateau structure, although not
quantized, still exists in the terahertz regime.Comment: 4 pages, 4 figure
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