3,611 research outputs found
Leggett-Garg inequalities for the statistics of electron transport
We derive a set of Leggett-Garg inequalities (temporal Bell's inequalities)
for the moment generating function of charge transferred through a conductor.
Violation of these inequalities demonstrates the absence of a macroscopic-real
description of the transport process. We show how these inequalities can be
violated by quantum-mechanical systems and consider transport through normal
and superconducting single-electron transistors as examples.Comment: 5 pages; 3 figure
Entanglement and the Phase Transition in Single Mode Superradiance
We consider the entanglement properties of the quantum phase transition in
the single-mode superradiance model, involving the interaction of a boson mode
and an ensemble of atoms. For infinite system size, the atom-field entanglement
of formation diverges logarithmically with the correlation length exponent.
Using a continuous variable representation, we compare this to the divergence
of the entropy in conformal field theories, and derive an exact expression for
the scaled concurrence and the cusp-like non-analyticity of the momentum
squeezing.Comment: 4 pages, 2 figue
Three-level mixing and dark states in transport through quantum dots
We consider theoretically the transport through the double quantum dot
structure of the recent experiment of C. Payette {\it et al.} [Phys. Rev. Lett.
{\bf 102}, 026808 (2009)] and calculate stationary current and shotnoise.
Three-level mixing gives rise to a pronounced current suppression effect, the
character of which charges markedly with bias direction. We discuss these
results in connexion with the dark states of coherent population trapping in
quantum dots.Comment: 6 pages, 5 fig
Modelling the spinning dust emission from LDN 1780
We study the anomalous microwave emission (AME) in the Lynds Dark Nebula
(LDN) 1780 on two angular scales. Using available ancillary data at an angular
resolution of 1 degree, we construct an SED between 0.408 GHz to 2997 GHz. We
show that there is a significant amount of AME at these angular scales and the
excess is compatible with a physical spinning dust model. We find that LDN 1780
is one of the clearest examples of AME on 1 degree scales. We detected AME with
a significance > 20. We also find at these angular scales that the
location of the peak of the emission at frequencies between 23-70 GHz differs
from the one on the 90-3000 GHz map. In order to investigate the origin of the
AME in this cloud, we use data obtained with the Combined Array for Research in
Millimeter-wave Astronomy (CARMA) that provides 2 arcmin resolution at 30 GHz.
We study the connection between the radio and IR emissions using morphological
correlations. The best correlation is found to be with MIPS 70m, which
traces warm dust (T50K). Finally, we study the difference in radio
emissivity between two locations within the cloud. We measured a factor
of difference in 30 GHz emissivity. We show that this variation can
be explained, using the spinning dust model, by a variation on the dust grain
size distribution across the cloud, particularly changing the carbon fraction
and hence the amount of PAHs.Comment: 14 pages, 11 figures, submitted to MNRA
Confirming the existence of π-allyl-palladium intermediates during the reaction of meta photocycloadducts with palladium(ii) compounds
The transient existence of π-allyl-palladium intermediates formed by the reaction of Pd(OAc)2 and anisole-derived meta photocycloadducts has been demonstrated using NMR techniques. The intermediates tended to be short-lived and underwent rapid reductive elimination of palladium metal to form allylic acetates, however this degradation process could be delayed by changing the reaction solvent from acetonitrile to chloroform
Spin entangled two-particle dark state in quantum transport through coupled quantum dots
We present a transport setup of coupled quantum dots that enables the
creation of spatially separated spin-entangled two-electron dark states. We
prove the existence of an entangled transport dark state by investigating the
system Hamiltonian without coupling to the electronic reservoirs. In the
transport regime the entangled dark state which corresponds to a singlet has a
strongly enhanced Fano factor compared to the dark state which corresponds to a
mixture of the triplet states. Furthermore we calculate the concurrence of the
occupying electrons to show the degree of entanglement in the transport regime.Comment: 9 pages and 3 figure
Opinion Shopping and Audit Committees
This paper tests whether companies engage in opinion shopping and examines the role of audit committees when auditors are dismissed (1996-98). There are three findings. First, US companies strategically dismiss when incumbent auditors are more likely to issue unfavorable audit opinions compared to newly appointed auditors. I estimate opinion shopping motivates 17% of auditor dismissals, and I find opinion shopping dismissals occur significantly later in the reporting period than other dismissals. Second, audit committees are more likely to disapprove of auditor dismissals that are motivated by opinion shopping. This is consistent with the argument that audit committees help maintain the integrity of the audit reporting process. Third, independent audit committee members are more likely to leave committees that disapprove of opinion shopping. This suggests either senior management dismiss audit committee members who oppose opinion shopping, or committee members resign because they do not wish to be associated with opinion shopping.
Quantum versus classical counting in nonMarkovian master equations
We discuss the description of full counting statistics in quantum transport
with a nonMarkovian master equation. We focus on differences arising from
whether charge is considered as a classical or a quantum degree of freedom.
These differences manifest themselves in the inhomogeneous term of the master
equation which describes initial correlations. We describe the influence on
current and in particular, the finite-frequency shotnoise. We illustrate these
ideas by studying transport through a quantum dot and give results that include
both sequential and cotunneling processes. Importantly, the noise spectra
derived from the classical description are essentially frequency-independent
and all quantum noise effects are absent. These effects are fully recovered
when charge is considered as a quantum degree of freedom.Comment: 12 pages; 3 figure
- …