512 research outputs found
The spatial statistical properties of wave functions in a disordered finite one-dimensional sample
For a given wave function one can define a quantity having a meaning
of its inverse spatial size. The Laplace transform of the distribution function
is calculated analytically for a 1D disordered sample with a finite
length .Comment: LaTEX, 7 pages, Preprint IFUM-456/FT, Milano, Jan.199
Theory of 4e versus 2e supercurrent in frustrated Josepshon-junction rhombi chain
We consider a chain of Josepshon-junction rhombi (proposed originally in
\cite{Doucot}) in quantum regime, and in the realistic case when charging
effects are determined by junction capacitances. In the maximally frustrated
case when magnetic flux through each rhombi is equal to one half of
superconductive flux quantum , Josepshon current is due to correlated
transport of {\em pairs of Cooper pairs}, i.e. charge is quantized in units of
. Sufficiently strong deviation from the maximally frustrated point brings the system back to
usual -quantized supercurrent. We present detailed analysis of Josepshon
current in the fluctuation-dominated regime (sufficiently long chains) as
function of the chain length, ratio and flux deviation .
We provide estimates for the set of parameters optimized for the observation of
-supercurrent.Comment: 23 pages, 9 figure
Vortex Plasma in a Superconducting Film with Magnetic Dots
We consider a superconducting film, placed upon a magnetic dot array.
Magnetic moments of the dots are normal to the film and randomly oriented. We
determine how the concentration of the vortices in the film depends on the
magnetic moment of a dot at low temperatures. The concentration of the
vortices, bound to the dots, is proportional to the density of the dots and
depends on the magnetization of a dot in a step-like way. The concentration of
the unbound vortices oscillates about a value, proportional to the magnetic
moment of the dots. The period of the oscillations is equal to the width of a
step in the concentration of the bound vortices.Comment: RevTeX, 4 page
Electronic structure of unidirectional superlattices in crossed electric and magnetic fields and related terahertz oscillations
We have studied Bloch electrons in a perfect unidirectional superlattice
subject to crossed electric and magnetic fields, where the magnetic field is
oriented ``in-plane'', i.e. in parallel to the sample plane. Two orientation of
the electric field are considered. It is shown that the magnetic field
suppresses the intersubband tunneling of the Zener type, but does not change
the frequency of Bloch oscillations, if the electric field is oriented
perpendicularly to both the sample plane and the magnetic field. The electric
field applied in-plane (but perpendicularly to the magnetic field) yields the
step-like electron energy spectrum, corresponding to the magnetic-field-tunable
oscillations alternative to the Bloch ones.Comment: 7 pages, 1 figure, accepted for publication in Phys. Rev.
Decoherence of number states in phase-sensitive reservoirs
The non-unitary evolution of initial number states in general Gaussian
environments is solved analytically. Decoherence in the channels is quantified
by determining explicitly the purity of the state at any time. The influence of
the squeezing of the bath on decoherence is discussed. The behavior of coherent
superpositions of number states is addressed as well.Comment: 5 pages, 2 figures, minor changes, references adde
Shape of Deconstruction
We construct a six-dimensional Maxwell theory using a latticized extra space,
the continuum limit of which is a shifted torus recently discussed by Dienes.
This toy model exhibits the correspondence between continuum theory and
discrete theory, and give a geometrical insight to theory-space model building.Comment: 10 pages, 2 figures, RevTeX4. a citation adde
Exact Solution for Bulk-Edge Coupling in the Non-Abelian Quantum Hall Interferometer
It has been predicted that the phase sensitive part of the current through a
non-abelian quantum Hall Fabry-Perot interferometer will depend on
the number of localized charged quasiparticles (QPs) inside the
interferometer cell. In the limit where all QPs are far from the edge, the
leading contribution to the interference current is predicted to be absent if
the number of enclosed QPs is odd and present otherwise, as a consequence of
the non-abelian QP statistics. The situation is more complicated, however, if a
localized QP is close enough to the boundary so that it can exchange a Majorana
fermion with the edge via a tunneling process. Here, we derive an exact
solution for the dependence of the interference current on the coupling
strength for this tunneling process, and confirm a previous prediction that for
sufficiently strong coupling, the localized QP is effectively incorporated in
the edge and no longer affects the interference pattern. We confirm that the
dimensionless coupling strength can be tuned by the source-drain voltage, and
we find that not only does the magnitude of the even-odd effect change with the
strength of bulk-edge coupling, but in addition, there is a universal shift in
the interference phase as a function of coupling strength. Some implications
for experiments are discussed at the end.Comment: 12 pages, 3 figure
Local density approximation for a perturbative equation of state
The knowledge of a series expansion of the equation of state provides a deep
insight into the physical nature of a quantum system. Starting from a generic
``perturbative'' equation of state of a homogeneous ultracold gas we make
predictions for the properties of the gas in the presence of harmonic
confinement. The local density approximation is used to obtain the chemical
potential, total and release energies, Thomas-Fermi size and density profile of
a trapped system in three-, two-, and one- dimensional geometries. The
frequencies of the lowest breathing modes are calculated using scaling and
sum-rule approaches and could be used in an experiment as a high precision tool
for obtaining the expansion terms of the equation of state. The derived
formalism is applied to dilute Bose and Fermi gases in different dimensions and
to integrable one-dimensional models. Physical meaning of expansion terms in a
number of systems is discussed.Comment: 3 Figure
Interaction of Kelvin waves and nonlocality of energy transfer in superfluids
We argue that the physics of interacting Kelvin Waves (KWs) is highly nontrivial and cannot be understood on the basis of pure dimensional reasoning. A consistent theory of KW turbulence in superfluids should be based upon explicit knowledge of their interactions. To achieve this, we present a detailed calculation and comprehensive analysis of the interaction coefficients for KW turbuelence, thereby, resolving previous mistakes stemming from unaccounted contributions. As a first application of this analysis, we derive a local nonlinear (partial differential) equation. This equation is much simpler for analysis and numerical simulations of KWs than the Biot-Savart equation, and in contrast to the completely integrable local induction approximation (in which the energy exchange between KWs is absent), describes the nonlinear dynamics of KWs. Second, we show that the previously suggested Kozik-Svistunov energy spectrum for KWs, which has often been used in the analysis of experimental and numerical data in superfluid turbulence, is irrelevant, because it is based upon an erroneous assumption of the locality of the energy transfer through scales. Moreover, we demonstrate the weak nonlocality of the inverse cascade spectrum with a constant particle-number flux and find resulting logarithmic corrections to this spectrum
Characterization of tomographically faithful states in terms of their Wigner function
A bipartite quantum state is tomographically faithful when it can be used as
an input of a quantum operation acting on one of the two quantum systems, such
that the joint output state carries a complete information about the operation
itself. Tomographically faithful states are a necessary ingredient for
tomography of quantum operations and for complete quantum calibration of
measuring apparatuses. In this paper we provide a complete classification of
such states for continuous variables in terms of the Wigner function of the
state. For two-mode Gaussian states faithfulness simply resorts to correlation
between the modes.Comment: 9 pages. IOPAMS style. Some improvement
- ā¦