6,896 research outputs found
Quantized Adiabatic Charge Transport in a Carbon Nanotube
The coupling of a metallic Carbon nanotube to a surface acoustic wave (SAW)
is proposed as a vehicle to realize quantized adiabatic charge transport in a
Luttinger liquid system. We demonstrate that electron backscattering by a
periodic SAW potential, which results in miniband formation, can be achieved at
energies near the Fermi level. Electron interaction, treated in a Luttinger
liquid framework, is shown to enhance minigaps and thereby improve current
quantization. Quantized SAW induced current, as a function of electron density,
changes sign at half-filling.Comment: 5 pages, 2 figure
Weak Field Phase Diagram for an Integer Quantum Hall Liquid
We study the localization properties in the transition from a two-dimensional
electron gas at zero magnetic field into an integer quantum Hall (QH) liquid.
By carrying out a direct calculation of the localization length for a finite
size sample using a transfer matrix technique, we systematically investigate
the field and disorder dependences of the metal-insulator transition in the
weak field QH regime. We obtain a different phase diagram from the one
conjectured in previous theoretical studies. In particular, we find that: (1)
the extended state energy for each Landau level (LL) is {\it always}
linear in magnetic field; (2) for a given Landau level and disorder
configuration there exists a critical magnetic field below which the
extended state disappears; (3) the lower LLs are more robust to the
metal-insulator transition with smaller . We attribute the above results
to strong LL coupling effect. Experimental implications of our work are
discussed.Comment: 4 pages, ReVTeX 3.0, 4 figures (available upon request
Scattering of first and second sound waves by quantum vorticity in superfluid Helium
We study the scattering of first and second sound waves by quantum vorticity
in superfluid Helium using two-fluid hydrodynamics. The vorticity of the
superfluid component and the sound interact because of the nonlinear character
of these equations. Explicit expressions for the scattered pressure and
temperature are worked out in a first Born approximation, and care is exercised
in delimiting the range of validity of the assumptions needed for this
approximation to hold. An incident second sound wave will partly convert into
first sound, and an incident first sound wave will partly convert into second
sound. General considerations show that most incident first sound converts into
second sound, but not the other way around. These considerations are validated
using a vortex dipole as an explicitely worked out example.Comment: 24 pages, Latex, to appear in Journal of Low Temperature Physic
Spin dynamics with non-abelian Berry gauge fields as a semiclassical constrained hamiltonian system
The dynamics of observables which are matrices depending on \hbar and taking
values in classical phase space is defined retaining the terms up to the first
order in \hbar of the Moyal bracket. Within this semiclassical approach a first
order lagrangian involving gauge fields is studied as a constrained hamiltonian
system. This provides a systematic study of spin dynamics in the presence of
non-abelian Berry gauge fields. We applied the method to various types of
dynamical spin systems and clarified some persisting discussions. In particular
employing the Berry gauge field which generates the Thomas precession, we
calculated the force exerted on an electron in the external electric and
magnetic fields. Moreover, a simple semiclassical formulation of the spin Hall
effect is accomplished.Comment: References and some clarification added. Published versio
Non-uniform Black Strings with Schwarzschild-(Anti-)de Sitter Foliation
We present some exact non-uniform black string solutions of 5-dimensional
pure Einstein gravity as well as Einstein-Maxwell-dilaton theory at arbitrary
dilaton coupling. The solutions share the common property that their
4-dimensional slices are Schwarzchild-(anti-)de Sitter spacetimes. The pure
gravity solution is also generalized to spacetimes of dimensions higher than 5
to get non-uniform black branes.Comment: LaTeX 14 pages, 3 eps figures. V2: version appeared in CQ
Quantum Key Distribution between N partners: optimal eavesdropping and Bell's inequalities
Quantum secret-sharing protocols involving N partners (NQSS) are key
distribution protocols in which Alice encodes her key into qubits, in
such a way that all the other partners must cooperate in order to retrieve the
key. On these protocols, several eavesdropping scenarios are possible: some
partners may want to reconstruct the key without the help of the other ones,
and consequently collaborate with an Eve that eavesdrops on the other partners'
channels. For each of these scenarios, we give the optimal individual attack
that the Eve can perform. In case of such an optimal attack, the authorized
partners have a higher information on the key than the unauthorized ones if and
only if they can violate a Bell's inequality.Comment: 14 pages, 1 figur
Pumping in an interacting quantum wire
We study charge and spin pumping in an interacting one-dimensional wire. We
show that a spatially periodic potential modulated in space and time acts as a
quantum pump inducing a dc-current component at zero bias. The current
generated by the pump is strongly affected by the interactions. It has a power
law dependence on the frequency or temperature with the exponent determined by
the interaction in the wire, while the coupling to the pump affects the
amplitudes only. We also show that pure spin-pumping can be achieved, without
the presence of a magnetic field.Comment: 13 pages,2 figure
Quantum Communication between N partners and Bell's inequalities
We consider a family of quantum communication protocols involving
partners. We demonstrate the existence of a link between the security of these
protocols against individual attacks by the eavesdropper, and the violation of
some Bell's inequalities, generalizing the link that was noticed some years ago
for two-partners quantum cryptography. The arguments are independent of the
local hidden variable debate.Comment: 4 pages, 2 figure
Wave-packet dynamics in slowly perturbed crystals: Gradient corrections and Berry-phase effects
We present a unified theory for wave-packet dynamics of electrons in crystals
subject to perturbations varying slowly in space and time. We derive the
wave-packet energy up to the first order gradient correction and obtain all
kinds of Berry-phase terms for the semiclassical dynamics and the quantization
rule. For electromagnetic perturbations, we recover the orbital magnetization
energy and the anomalous velocity purely within a single-band picture without
invoking inter-band couplings. For deformations in crystals, besides a
deformation potential, we obtain a Berry-phase term in the Lagrangian due to
lattice tracking, which gives rise to new terms in the expressions for the
wave-packet velocity and the semiclassical force. For multiple-valued
displacement fields surrounding dislocations, this term manifests as a Berry
phase, which we show to be proportional to the Burgers vector around each
dislocation.Comment: 12 pages, RevTe
Integer Quantum Hall Effect with Realistic Boundary Condition : Exact Quantization and Breakdown
A theory of integer quantum Hall effect(QHE) in realistic systems based on
von Neumann lattice is presented. We show that the momentum representation is
quite useful and that the quantum Hall regime(QHR), which is defined by the
propagator in the momentum representation, is realized. In QHR, the Hall
conductance is given by a topological invariant of the momentum space and is
quantized exactly. The edge states do not modify the value and topological
property of in QHR. We next compute distribution of current based
on effective action and find a finite amount of current in the bulk and the
edge, generally. Due to the Hall electric field in the bulk, breakdown of the
QHE occurs. The critical electric field of the breakdown is proportional to
and the proportional constant has no dependence on Landau levels in
our theory, in agreement with the recent experiments.Comment: 48 pages, figures not included, some additions and revision
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