3,440 research outputs found
Interference, Coulomb blockade, and the identification of non-abelian quantum Hall states
We examine the relation between different electronic transport phenomena in a
Fabry-Perot interferometer in the fractional quantum Hall regime. In
particular, we study the way these phenomena reflect the statistics of quantum
Hall quasi-particles. For two series of states we examine, one abelian and one
non-abelian, we show that the information that may be obtained from
measurements of the lowest order interference pattern in an open Fabry-Perot
interferometer is identical to the one that may be obtained from the
temperature dependence of Coulomb blockade peaks in a closed interferometer. We
argue that despite the similarity between the experimental signatures of the
two series of states, interference and Coulomb blockade measurements are likely
to be able to distinguish between abelian and non-abelian states, due to the
sensitivity of the abelian states to local perturbations, to which the
non-abelian states are insensitive.Comment: 10 pages. Published versio
Signatures of neutral quantum Hall modes in transport through low-density constrictions
Constrictions in fractional quantum Hall (FQH) systems not only facilitate
backscattering between counter-propagating edge modes, but also may reduce the
constriction filling fraction with respect to the bulk filling fraction
. If both and correspond to incompressible FQH states,
at least part of the constriction region is surrounded by composite edges,
whose low energy dynamics is characterized by a charge mode and one or several
neutral modes. In the incoherent regime, decay of neutral modes describes the
equilibration of composite FQH edges, while in the limit of coherent transport,
the presence of neutral modes gives rise to universal conductance fluctuations.
In addition, neutral modes renormalize the strength of scattering across the
constriction, and thus can determine the relative strength of forward and
backwards scattering.Comment: corrected description of the results of Ref. [10], Ref. [17] adde
The Physical Significance of Singularities in the Chern--Simons Fermi Liquid Description of a Partially Filled Landau Level
We analyze the linear response of a half filled Landau level to long
wavelength and low frequency driving forces, using Fermi liquid theory for
composite fermions. This response is determined by the composite fermions
quasi--particle effective mass, , and quasi--particle Landau interaction
function . Analyzing infra--red divergences of perturbation
theory, we get an exact expression for , and conjecture the form of the
. We then conclude that in the limit of infinite cyclotron
frequency, and small , the composite fermion excitation
spectrum is continuous for , with
an unknown number. For fractional quantum Hall states near a half
filled Landau level, we derive an exact expression for the energy gap.Comment: 4 pages, RevTeX. This paper, being short and non-technical, could
serve as a useful starting point for reading our manuscript cond-mat/9502032.
The present paper does, however, include results not published in the forme
Understanding the dynamics of fractional edge states with composite fermions
Fractional edge states can be viewed as integer edge states of composite
fermions. We exploit this to discuss the conductance of the fractional
quantized Hall states and the velocity of edge magnetoplasmons.Comment: 3 pages, revte
Driven nonlinear dynamics of two coupled exchange-only qubits
Inspired by creation of a fast exchange-only qubit (Medford et al., Phys.
Rev. Lett., 111, 050501 (2013)), we develop a theory describing the nonlinear
dynamics of two such qubits that are capacitively coupled, when one of them is
driven resonantly at a frequency equal to its level splitting. We include
conditions of strong driving, where the Rabi frequency is a significant
fraction of the level splitting, and we consider situations where the splitting
for the second qubit may be the same or different than the first. We
demonstrate that coupling between qubits can be detected by reading the
response of the second qubit, even when the coupling between them is only of
about of their level splittings, and calculate entanglement between
qubits. Patterns of nonlinear dynamics of coupled qubits and their entanglement
are strongly dependent on the geometry of the system, and the specific
mechanism of inter-qubit coupling deeply influences dynamics of both qubits. In
particular, we describe the development of irregular dynamics in a two-qubit
system, explore approaches for inhibiting it, and demonstrate existence of an
optimal range of coupling strength maintaining stability during the operational
time.Comment: 11 pages, 6 figures; One additional figure with changes to the text
about the results. Additional references include
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