3,048 research outputs found
Current-voltage correlations in interferometers
We investigate correlations of current at contacts and voltage fluctuations
at voltage probes coupled to interferometers. The results are compared with
correlations of current and occupation number fluctuations at dephasing probes.
We use a quantum Langevin approach for the average quantities and their
fluctuations. For higher order correlations we develop a stochastic path
integral approach and find the generating functions of voltage or occupation
number fluctuations. We also derive a generating function for the joint
distribution of voltage or occupation number at the probe and current
fluctuations at a terminal of a conductor. For energy independent scattering we
found earlier that the generating function of current cumulants in
interferometers with a one-channel dephasing or voltage probe are identical.
Nevertheless, the distribution function for voltage and the distribution
function for occupation number fluctuations differ, the latter being broader
than that of former in all examples considered here.Comment: 23 pages, 10 figures, minor changes, additional appendix, added
reference
Nonmonotonic energy harvesting efficiency in biased exciton chains
We theoretically study the efficiency of energy harvesting in linear exciton
chains with an energy bias, where the initial excitation is taking place at the
high-energy end of the chain and the energy is harvested (trapped) at the other
end. The efficiency is characterized by means of the average time for the
exciton to be trapped after the initial excitation. The exciton transport is
treated as the intraband energy relaxation over the states obtained by
numerically diagonalizing the Frenkel Hamiltonian that corresponds to the
biased chain. The relevant intraband scattering rates are obtained from a
linear exciton-phonon interaction. Numerical solution of the Pauli master
equation that describes the relaxation and trapping processes, reveals a
complicated interplay of factors that determine the overall harvesting
efficiency. Specifically, if the trapping step is slower than or comparable to
the intraband relaxation, this efficiency shows a nonmonotonic dependence on
the bias: it first increases when introducing a bias, reaches a maximum at an
optimal bias value, and then decreases again because of dynamic (Bloch)
localization of the exciton states. Effects of on-site (diagonal) disorder,
leading to Anderson localization, are addressed as well.Comment: 9 pages, 6 figures, to appear in Journal of Chemical Physic
Parity detection and entanglement with a Mach-Zehnder interferometer
A parity meter projects the state of two qubits onto two subspaces with
different parities, the states in each parity class being indistinguishable. It
has application in quantum information for its entanglement properties. In our
work we consider the electronic Mach-Zehnder interferometer (MZI) coupled
capacitively to two double quantum dots (DQDs), one on each arm of the MZI.
These charge qubits couple linearly to the charge in the arms of the MZI. A key
advantage of an MZI is that the qubits are well separated in distance so that
mutual interaction between them is avoided. Assuming equal coupling between
both DQDs and the arms and the same bias for each DQD, this setup usually
detects three different currents, one for the odd states and two for each even
state. Controlling the magnetic flux of the MZI, we can operate the MZI as a
parity meter: only two currents are measured at the output, one for each parity
class. In this configuration, the MZI acts as an ideal detector, its Heisenberg
efficiency being maximal. For a class of initial states, the initially
unentangled DQDs become entangled through the parity measurement process with
probability one.Comment: 9 pages, 2 figure
A Population of Teraelectronvolt Pulsar Wind Nebulae in the H.E.S.S. Galactic Plane Survey
The most numerous source class that emerged from the H.E.S.S. Galactic Plane
Survey are Pulsar Wind Nebulae (PWNe). The 2013 reanalysis of this survey,
undertaken after almost 10 years of observations, provides us with the most
sensitive and most complete census of gamma-ray PWNe to date. In addition to a
uniform analysis of spectral and morphological parameters, for the first time
also flux upper limits for energetic young pulsars were extracted from the
data. We present a discussion of the correlation between energetic pulsars and
TeV objects, and their respective properties. We will put the results in
context with the current theoretical understanding of PWNe and evaluate the
plausibility of previously non-established PWN candidates.Comment: 4 pages, 5 figures. In Proceedings of the 33rd International Cosmic
Ray Conference (ICRC2013), Rio de Janeiro (Brazil
Simultaneous measurements from the Millstone Hill radar and the Active satellite during the SAID/SAR arc event of the March 1990 CEDAR storm
Exactly soluble model of resonant energy transfer between molecules
F\"orster's theory of resonant energy transfer (FRET) predicts the strength
and range of exciton transport between separated molecules. We introduce an
exactly soluble model for FRET which reproduces F\"orster's results as well as
incorporating quantum coherence effects. As an application the model is used to
analyze a system composed of quantum dots and the protein bacteriorhodopsin.Comment: 10 pages, 2 figure
Strong field ionization to multiple electronic states in water
High harmonic spectra show that laser-induced strong field ionization of
water has a significant contribution from an inner-valence orbital. Our
experiment uses the ratio of H2O and D2O high harmonic yields to isolate the
characteristic nuclear motion of the molecular ionic states. The nuclear motion
initiated via ionization of the highest occupied molecular orbital (HOMO) is
small and is expected to lead to similar harmonic yields for the two isotopes.
In contrast, ionization of the second least bound orbital (HOMO-1) exhibits
itself via a strong bending motion which creates a significant isotope effect.
We elaborate on this interpretation by simulating strong field ionization and
high harmonic generation from the water isotopes using the time-dependent
Schr\"odinger equation. We expect that this isotope marking scheme for probing
excited ionic states in strong field processes can be generalized to other
molecules
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