1,620 research outputs found
Nonequilibrium Transport in Quantum Impurity Models (Bethe-Ansatz for open systems)
We develop an exact non-perturbative framework to compute steady-state
properties of quantum-impurities subject to a finite bias. We show that the
steady-state physics of these systems is captured by nonequilibrium scattering
eigenstates which satisfy an appropriate Lippman-Schwinger equation.
Introducing a generalization of the equilibrium Bethe-Ansatz - the
Nonequilibrium Bethe-Ansatz (NEBA), we explicitly construct the scattering
eigenstates for the Interacting Resonance Level model and derive exact,
nonperturbative results for the steady-state properties of the system.Comment: 4 pages, 1 figur
Frequency dependent effective conductivity of two-dimensional metal-dielectric composites
We analyze a random resistor-inductor-capacitor lattice model of
2-dimensional metal-insulator composites. The results are compared with
Bruggeman's and Landauer's Effective Medium Approximations where a discrepancy
was observed for some frequency zones. Such a discrepancy is mainly caused by
the strong conductivity fluctuations. Indeed, a two-branches distribution is
observed for low frequencies. We show also by increasing the system size that
at the so-called Drude peak vanishes; it increases for vanishing losses.Comment: 7 pages including all figures, accepted in Int. J. Mod. Phys.
Landauer Conductance of Luttinger Liquids with Leads
We show that the dc conductance of a quantum wire containing a Luttinger
liquid and attached to non-interacting leads is given by per spin
orientation, regardless of the interactions in the wire. This explains the
recent observations of the absence of conductance renormalization in long
high-mobility wires by Tarucha, Honda and Saku (Solid State
Communications {\bf 94}, 413 (1995)).Comment: 4 two-column pages, RevTeX + 1 uuencoded figure
Exact Master Equation and Quantum Decoherence of Two Coupled Harmonic Oscillators in a General Environment
In this paper we derive an exact master equation for two coupled quantum
harmonic oscillators interacting via bilinear coupling with a common
environment at arbitrary temperature made up of many harmonic oscillators with
a general spectral density function. We first show a simple derivation based on
the observation that the two-harmonic oscillator model can be effectively
mapped into that of a single harmonic oscillator in a general environment plus
a free harmonic oscillator. Since the exact one harmonic oscillator master
equation is available [Hu, Paz and Zhang, Phys. Rev. D \textbf{45}, 2843
(1992)], the exact master equation with all its coefficients for this two
harmonic oscillator model can be easily deduced from the known results of the
single harmonic oscillator case. In the second part we give an influence
functional treatment of this model and provide explicit expressions for the
evolutionary operator of the reduced density matrix which are useful for the
study of decoherence and disentanglement issues. We show three applications of
this master equation: on the decoherence and disentanglement of two harmonic
oscillators due to their interaction with a common environment under Markovian
approximation, and a derivation of the uncertainty principle at finite
temperature for a composite object, modeled by two interacting harmonic
oscillators. The exact master equation for two, and its generalization to ,
harmonic oscillators interacting with a general environment are expected to be
useful for the analysis of quantum coherence, entanglement, fluctuations and
dissipation of mesoscopic objects towards the construction of a theoretical
framework for macroscopic quantum phenomena.Comment: 35 pages, revtex, no figures, 2nd version, references added, to
appear in PR
Intensity distribution of scalar waves propagating in random media
Transmission of the scalar field through the random medium, represented by
the system of randomly distributed dielectric cylinders is calculated
numerically. System is mapped to the problem of electronic transport in
disordered two-dimensional systems. Universality of the statistical
distribution of transmission parameters is analyzed in the metallic and in the
localized regimes.In the metallic regime the universality of the transmission
statistics in all transparent channels is observed. In the band gaps, we
distinguish the disorder induced (Anderson) localization from the tunneling
through the system due to the gap in the density of states. We show also that
absorption causes rapid decrease of the mean conductance, but, contrary to the
localized regime, the conductance is self-averaged with a
Gaussian distribution
Quantum heat transfer through an atomic wire
We studied the phononic heat transfer through an atomic dielectric wire with
both infinite and finite lengths by using a model Hamiltonian approach. At low
temperature under ballistic transport, the thermal conductance contributed by
each phonon branch of a uniform and harmonic chain cannot exceed the well-known
value which depends linearly on temperature but is material independent. We
predict that this ballistic thermal conductance will exhibit stepwise behavior
as a function of temperature. By performing numerical calculations on a more
realistic system, where a small atomic chain is placed between two reservoirs,
we also found resonance modes, which should also lead to the stepwise behavior
in the thermal conductance.Comment: 14 pages, 2 separate figure
Experimental Verification of the Quantized Conductance of Photonic Crystal Waveguides
We report experiments that demonstrate the quantization of the conductance of
photonic crystal waveguides. To obtain a diffusive wave, we have added all the
transmitted channels for all the incident angles. The conductance steps have
equal height and a width of one half the wavelength used. Detailed numerical
results agree very well with the novel experimental results.Comment: Phys. Rev. B (submitted
Rashba effect induced localization in quantum networks
We study a quantum network extending in one-dimension (chain of square loops
connected at one vertex) made up of quantum wires with Rashba spin-orbit
coupling. We show that the Rashba effect may give rise to an electron
localization phenomenon similar to the one induced by magnetic field. This
localization effect can be attributed to the spin precession due to the Rashba
effect. We present results both for the spectral properties of the infinite
chain, and for linear transport through a finite-size chain connected to leads.
Furthermore, we study the effect of disorder on the transport properties of
this network.Comment: To appear in Phys. Rev. Let
Quantum Ballistic Evolution in Quantum Mechanics: Application to Quantum Computers
Quantum computers are important examples of processes whose evolution can be
described in terms of iterations of single step operators or their adjoints.
Based on this, Hamiltonian evolution of processes with associated step
operators is investigated here. The main limitation of this paper is to
processes which evolve quantum ballistically, i.e. motion restricted to a
collection of nonintersecting or distinct paths on an arbitrary basis. The main
goal of this paper is proof of a theorem which gives necessary and sufficient
conditions that T must satisfy so that there exists a Hamiltonian description
of quantum ballistic evolution for the process, namely, that T is a partial
isometry and is orthogonality preserving and stable on some basis. Simple
examples of quantum ballistic evolution for quantum Turing machines with one
and with more than one type of elementary step are discussed. It is seen that
for nondeterministic machines the basis set can be quite complex with much
entanglement present. It is also proved that, given a step operator T for an
arbitrary deterministic quantum Turing machine, it is decidable if T is stable
and orthogonality preserving, and if quantum ballistic evolution is possible.
The proof fails if T is a step operator for a nondeterministic machine. It is
an open question if such a decision procedure exists for nondeterministic
machines. This problem does not occur in classical mechanics.Comment: 37 pages Latexwith 2 postscript figures tar+gzip+uuencoded, to be
published in Phys. Rev.
Electron-vibration interaction in single-molecule junctions: from contact to tunneling regime
Point contact spectroscopy on a H2O molecule bridging Pt electrodes reveals a
clear crossover between enhancement and reduction of the conductance due to
electron-vibration interaction. As single channel models predict such a
crossover at transmission probability of t=0.5, we used shot noise measurements
to analyze the transmission and observed at least two channels across the
junction where the dominant channel has t=0.51+/-0.01 transmission probability
at the crossover conductance, which is consistent with the predictions for
single-channel models.Comment: 4 pages, 1 table, 4 figure
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