607 research outputs found
Local Fields without Restrictions on the Spectrum of 4-Momentum Operator and Relativistic Lindblad Equation
Quantum theory of Lorentz invariant local scalar fields without restrictions
on 4-momentum spectrum is considered. The mass spectrum may be both discrete
and continues and the square of mass as well as the energy may be positive or
negative. Such fields can exist as part of a hidden matter in the Universe if
they interact with ordinary fields very weakly. Generalization of
Kallen-Lehmann representation for propagators of these fields is found. The
considered generalized fields may violate CPT- invariance. Restrictions on
mass-spectrum of CPT-violating fields are found. Local fields that annihilate
vacuum state and violate CPT- invariance are constructed in this scope. Correct
local relativistic generalization of Lindblad equation for density matrix is
written for such fields. This generalization is particulary needed to describe
the evolution of quantum system and measurement process in a unique way.
Difficulties arising when the field annihilating the vacuum interacts with
ordinary fields are discussed.Comment: Latex 23 pages, sent to "Foundations of Physics
Correlated sequential tunneling through a double barrier for interacting one-dimensional electrons
The problem of resonant tunneling through a quantum dot weakly coupled to
spinless Tomonaga-Luttinger liquids has been studied. We compute the linear
conductance due to sequential tunneling processes upon employing a master
equation approach. Besides the previously used lowest-order golden rule rates
describing uncorrelated sequential tunneling (UST) processes, we systematically
include higher-order correlated sequential tunneling (CST) diagrams within the
standard Weisskopf-Wigner approximation. We provide estimates for the parameter
regions where CST effects can be important. Focusing mainly on the temperature
dependence of the peak conductance, we discuss the relation of these findings
to previous theoretical and experimental results.Comment: replaced with the published versio
Signatures of Strong Correlations in One-Dimensional Ultra-Cold Atomic Fermi Gases
Recent success in manipulating ultra-cold atomic systems allows to probe
different strongly correlated regimes in one-dimension. Regimes such as the
(spin-coherent) Luttinger liquid and the spin-incoherent Luttinger liquid can
be realized by tuning the inter-atomic interaction strength and trap
parameters. We identify the noise correlations of density fluctuations as a
robust observable (uniquely suitable in the context of trapped atomic gases) to
discriminate between these two regimes. Finally, we address the prospects to
realize and probe these phenomena experimentally using optical lattices.Comment: 4 pages, 2 figure
Transport in the Laughlin quasiparticle interferometer: Evidence for topological protection in an anyonic qubit
We report experiments on temperature and Hall voltage bias dependence of the
superperiodic conductance oscillations in the novel Laughlin quasiparticle
interferometer, where quasiparticles of the 1/3 fractional quantum Hall fluid
execute a closed path around an island of the 2/5 fluid. The amplitude of the
oscillations fits well the quantum-coherent thermal dephasing dependence
predicted for a two point-contact chiral edge channel interferometer in the
full experimental temperature range 10.2<T<141 mK. The temperature dependence
observed in the interferometer is clearly distinct from the behavior in
single-particle resonant tunneling and Coulomb blockade devices. The 5h/e flux
superperiod, originating in the anyonic statistical interaction of Laughlin
quasiparticles, persists to a relatively high T~140 mK. This temperature is
only an order of magnitude less than the 2/5 quantum Hall gap. Such protection
of quantum logic by the topological order of fractional quantum Hall fluids is
expected to facilitate fault-tolerant quantum computation with anyons.Comment: 13 pages, 10 figure
Non-equilibrium Plasmons in a Quantum Wire Single Electron Transistor
We analyze a single electron transistor composed of two semi-infinite one
dimensional quantum wires and a relatively short segment between them. We
describe each wire section by a Luttinger model, and treat tunneling events in
the sequential approximation when the system's dynamics can be described by a
master equation. We show that the steady state occupation probabilities in the
strongly interacting regime depend only on the energies of the states and
follow a universal form that depends on the source-drain voltage and the
interaction strength.Comment: 4 pages, 3 figures. To appear in the Phys. Rev. Let
Broken symmetry, hyper-fermions, and universal conductance in transport through a fractional quantum Hall edge
We have found solution to a model of tunneling between a multi-channel Fermi
liquid reservoir and an edge of the principal fractional quantum Hall liquid
(FQHL) in the strong coupling limit. The solution explains how the absence of
the time-reversal symmetry at high energies due to chiral edge propagation
makes the universal two-terminal conductance of the FQHL fractionally quantized
and different from that of a 1D Tomonaga-Luttinger liquid wire, where a similar
model but preserving the time-reversal symmetry predicts unsuppressed
free-electron conductance.Comment: 5 twocolumn pages in RevTex, no figures, more explanations added, a
short version was published in JETP Letters, vol.74, 87 (2001
Spin effects in transport through non-Fermi liquid quantum dots
The current-voltage characteristic of a one dimensional quantum dot connected
via tunnel barriers to interacting leads is calculated in the region of
sequential tunneling. The spin of the electrons is taken into account.
Non-Fermi liquid correlations implying spin-charge separation are assumed to be
present in the dot and in the leads. It is found that the energetic distance of
the peaks in the linear conductance shows a spin-induced parity effect at zero
temperature T. The temperature dependence of the positions of the peaks depends
on the non-Fermi liquid nature of the system. For non-symmetric tunnel barriers
negative differential conductances are predicted, which are related to the
participation in the transport of collective states in the quantum dot with
larger spins. Without spin-charge separation the negative differential
conductances do not occur. Taking into account spin relaxation destroys the
spin-induced conductance features. The possibility of observing in experiment
the predicted effects are briefly discussed.Comment: 15 pages, 16 figures, accepted for publication on Physical Review
First-principles study of the atomic and electronic structure of the Si(111)-(5x2-Au surface reconstruction
We present a systematic study of the atomic and electronic structure of the
Si(111)-(5x2)-Au reconstruction using first-principles electronic structure
calculations based on the density functional theory. We analyze the structural
models proposed by Marks and Plass [Phys. Rev. Lett.75, 2172 (1995)], those
proposed recently by Erwin [Phys. Rev. Lett.91, 206101 (2003)], and a
completely new structure that was found during our structural optimizations. We
study in detail the energetics and the structural and electronic properties of
the different models. For the two most stable models, we also calculate the
change in the surface energy as a function of the content of silicon adatoms
for a realistic range of concentrations. Our new model is the energetically
most favorable in the range of low adatom concentrations, while Erwin's "5x2"
model becomes favorable for larger adatom concentrations. The crossing between
the surface energies of both structures is found close to 1/2 adatoms per 5x2
unit cell, i.e. near the maximum adatom coverage observed in the experiments.
Both models, the new structure and Erwin's "5x2" model, seem to provide a good
description of many of the available experimental data, particularly of the
angle-resolved photoemission measurements
Spin-excitations of the quantum Hall ferromagnet of composite fermions
The spin-excitations of a fractional quantum Hall system are evaluated within
a bosonization approach. In a first step, we generalize Murthy and Shankar's
Hamiltonian theory of the fractional quantum Hall effect to the case of
composite fermions with an extra discrete degree of freedom. Here, we mainly
investigate the spin degrees of freedom, but the proposed formalism may be
useful also in the study of bilayer quantum-Hall systems, where the layer index
may formally be treated as an isospin. In a second step, we apply a
bosonization scheme, recently developed for the study of the two-dimensional
electron gas, to the interacting composite-fermion Hamiltonian. The dispersion
of the bosons, which represent quasiparticle-quasihole excitations, is
analytically evaluated for fractional quantum Hall systems at \nu = 1/3 and \nu
= 1/5. The finite width of the two-dimensional electron gas is also taken into
account explicitly. In addition, we consider the interacting bosonic model and
calculate the lowest-energy state for two bosons. Besides a continuum
describing scattering states, we find a bound-state of two bosons. This state
is interpreted as a pair excitation, which consists of a skyrmion of composite
fermions and an antiskyrmion of composite fermions. The dispersion relation of
the two-boson state is evaluated for \nu = 1/3 and \nu = 1/5. Finally, we show
that our theory provides the microscopic basis for a phenomenological
non-linear sigma-model for studying the skyrmion of composite fermions.Comment: Revised version, 14 pages, 4 figures, accepted to Phys. Rev.
Infrared catastrophe and tunneling into strongly correlated electron systems: Perturbative x-ray edge limit
The tunneling density of states exhibits anomalies (cusps, algebraic
suppressions, and pseudogaps) at the Fermi energy in a wide variety of
low-dimensional and strongly correlated electron systems. We argue that in many
cases these spectral anomalies are caused by an infrared catastrophe in the
screening response to the sudden introduction of a new electron into the system
during a tunneling event. A nonperturbative functional-integral method is
introduced to account for this effect, making use of methods developed for the
x-ray edge singularity problem. The formalism is applicable to lattice or
continuum models of any dimensionality, with or without translational
invariance. An approximate version of the technique is applied to the 1D
electron gas and the 2D Hall fluid, yielding qualitatively correct results.Comment: 6 page
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