441 research outputs found
Uncertainty Principle and Off-Diagonal Long Range Order in the Fractional Quantum Hall Effect
A natural generalization of the Heisenberg uncertainty principle inequality
holding for non hermitian operators is presented and applied to the fractional
quantum Hall effect (FQHE). This inequality was used in a previous paper to
prove the absence of long range order in the ground state of several 1D systems
with continuous group symmetries. In this letter we use it to rule out the
occurrence of Bose-Einstein condensation in the bosonic representation of the
FQHE wave function proposed by Girvin and MacDonald. We show that the absence
of off-diagonal long range order in this 2D problem is directly connected with
the behavior of the static structure function at small momenta.Comment: 10 pages, plain TeX, UTF-09-9
Quantum Hall Ferrimagnetism in lateral quantum dot molecules
We demonstrate the existance of ferrimagnetic and ferromagnetic phases in a
spin phase diagram of coupled lateral quantum dot molecules in the quantum Hall
regime. The spin phase diagram is determined from Hartree-Fock Configuration
Interaction method as a function of electron numbers N, magnetic field B,
Zeeman energy, and tunneling barrier height. The quantum Hall ferrimagnetic
phase corresponds to spatially imbalanced spin droplets resulting from strong
inter-dot coupling of identical dots. The quantum Hall ferromagnetic phases
correspond to ferromagnetic coupling of spin polarization at filling factors
between and .Comment: 4 pages, 4 figure
Incidence of the boundary shape in the effective theory of fractional quantum Hall edges
Starting from a microscopic description of a system of strongly interacting
electrons in a strong magnetic field in a finite geometry, we construct the
boundary low energy effective theory for a fractional quantum Hall droplet
taking into account the effects of a smooth edge. The effective theory obtained
is the standard chiral boson theory (chiral Luttinger theory) with an
additional self-interacting term which is induced by the boundary. As an
example of the consequences of this model, we show that such modification leads
to a non-universal reduction in the tunnelling exponent which is independent of
the filling fraction. This is in qualitative agreement with experiments, that
systematically found exponents smaller than those predicted by the ordinary
chiral Luttinger liquid theory.Comment: 12 pages, minor changes, replaced by published versio
Noise spectroscopy and interlayer phase-coherence in bilayer quantum Hall systems
Bilayer quantum Hall systems develop strong interlayer phase-coherence when
the distance between layers is comparable to the typical distance between
electrons within a layer. The phase-coherent state has until now been
investigated primarily via transport measurements. We argue here that
interlayer current and charge-imbalance noise studies in these systems will be
able to address some of the key experimental questions. We show that the
characteristic frequency of current-noise is that of the zero wavevector
collective mode, which is sensitive to the degree of order in the system. Local
electric potential noise measured in a plane above the bilayer system on the
other hand is sensitive to finite-wavevector collective modes and hence to the
soft-magnetoroton picture of the order-disorder phase transition.Comment: 5 pages, 2 figure
Observability of radiation pressure shot noise in optomechanical systems
We present a theoretical study of an experiment designed to detect radiation
pressure shot noise in an optomechanical system. Our model consists of a
coherently driven optical cavity mode that is coupled to a mechanical
oscillator. We examine the cross-correlation between two quadratures of the
output field from the cavity. We determine under which circumstances radiation
pressure shot noise can be detected by a measurement of this cross-correlation.
This is done in the general case of nonzero detuning between the frequency of
the drive and the cavity resonance frequency. We study the qualitative features
of the different contributions to the cross-correlator and provide quantitative
figures of merit for the relative importance of the radiation pressure shot
noise contribution to other contributions. We also propose a modified setup of
this experiment relevant to the "membrane-in-the-middle" geometry, which
potentially can avoid the problems of static bistability and classical noise in
the drive.Comment: 12 pages + 4 page appendix, 10 figure
Possible Quantum Spin Liquid States on the Triangular and Kagome Lattices
The frustrated spin-one-half Heisenberg model on triangualr and Kagome
Lattices is mapped onto a single specis of fermion carrying statistical flux.
The corresponding Chern-Simons gauge theory is analyzed at the Gaussian level
and found to be massive. This provides a new motivation for the spin-liquid
Kalmeyer-Laughlin wave function. Good overlap of this wave function with the
numerical ground state is found for small clusters.Comment: 13 pages, revtex. IUCM-920
Numerical evidences of spin-1/2 chain approaching spin-1 chain
In this article, we study the one dimensional Heisenberg spin-1/2 alternating
bond chain in which the nearest neighbor exchange couplings are ferromagnetic
(FM) and antiferromagnetic (AF) alternatively. By using exact diagonalization
and density matrix renormalization groups (DMRG) method, we discuss how the
system approaches to the AF uniform spin-1 chain under certain condition. When
the ratio of AF to FM coupling strength}
\textit{is very small, the physical quantities of the alternating bond chain
such as the spin-spin correlation, the string correlation function and the spin
density coincide with that of the AF uniform spin-1 chain. The edge state
problem is discussed in the present model with small}\textit{limit. In
addition, the Haldane gap of the AF uniform spin-1 chain is 4-times of the gap
of the system considered.Comment: 9pages,8page
State-dependent impedance of a strongly coupled oscillator-qubit system
We investigate the measurements of two-state quantum systems (qubits) at
finite temperatures using a resonant harmonic oscillator as a quantum probe.
The reduced density matrix and oscillator correlators are calculated by a
scheme combining numerical methods with an analytical perturbation theory.
Correlators provide us information about the system impedance, which depends on
the qubit state. We show in detail how this property can be exploited in the
qubit measurement.Comment: 8 pages, 16 image
- …