7,145 research outputs found
Lasing in circuit quantum electrodynamics with strong noise
We study a model which can describe a superconducting single electron
transistor (SSET) or a double quantum dot coupled to transmission-line
oscillator. In both cases the degree of freedom is given by a charged particle,
which couples strongly to the electromagnetic environment or phonons. We
consider the case where a lasing condition is established and study the
dependence of the average photon number in the resonator on the spectral
function of the electromagnetic environment. We focus on three important cases:
a strongly coupled environment with a small cut-off frequency, a structured
environment peaked at a specific frequency and 1/f-noise. We find that the
electromagnetic environment can have a substantial impact on the photon
creation. Resonance peaks are in general broadened and additional resonances
can appear
A Numerical Model Calculation of the Flow in DeSoto Canyon in Response to Northerly Wind Bursts in Winter
The continental shelf currents observed at the head of DeSoto Canyon offshore of Pensacola, FL, during Nov, 1997-Feb. 1998, are studied with the aid of a Bryan-Cox model of the entire Gulf of Mexico. The basic model circulation with no winds features a Loop Current and a weak flow in DeSoto Canyon. In contrast, the model response to northerly wind bursts produces strong canyon currents. Wind-driven southward currents on the West Florida Shelf (WFS) appear to pull a strong flow around DeSoto Canyon, giving rise to a strong up-canyon flow on the west flank The wind-enhanced flow in DeSoto Canyon is reproduced with a model run that incorporates wind stresses derived from the NCEP-NCAR reanalysis winds for March 1997-April 1998. The model flow for the winter period (Nov. 1997-Feb. 1998) is compared with observed currents at three canyon-head locations in 100 m of water available from a Science Applications International Corporation mooring experiment. Model and observed velocities in the general around-canyon direction track each other reasonably well, with peaks synchronized roughly with but lagging slightly northerly wind bursts. The lag time appears consistent with the generation at Key West of first-mode continental shelf waves responsible for wind-driven alongshore currents on the WFS. Pressure gradient slightly in excess of that necessary for a geostrophic balance with the (eastward) alongshore flow appears to generate onshore flows, giving rise to midshelf upwelling after northerly wind bursts
Dephasing at Low Temperatures
We discuss the significance and the calculation of dephasing at low
temperatures. The particle is moving diffusively due to a static disorder
configuration, while the interference between classical paths is suppressed due
to the interaction with a dynamical environment. At high temperatures we may
use the `white noise approximation' (WNA), while at low temperatures we
distinguish the contribution of `zero point fluctuations' (ZPF) from the
`thermal noise contribution' (TNC). We study the limitations of the above
semiclassical approach and suggest the required modifications. In particular we
find that the ZPF contribution becomes irrelevant for thermal motion.Comment: 4 pages, 1 figure, clearer presentatio
Quantal Brownian Motion - Dephasing and Dissipation
We analyze quantal Brownian motion in dimensions using the unified model
for diffusion localization and dissipation, and Feynman-Vernon formalism. At
high temperatures the propagator possess a Markovian property and we can write
down an equivalent Master equation. Unlike the case of the
Zwanzig-Caldeira-Leggett model, genuine quantum mechanical effects manifest
themselves due to the disordered nature of the environment. Using Wigner
picture of the dynamics we distinguish between two different mechanisms for
destruction of coherence. The analysis of dephasing is extended to the low
temperature regime by using a semiclassical strategy. Various results are
derived for ballistic, chaotic, diffusive, both ergodic and non-ergodic motion.
We also analyze loss of coherence at the limit of zero temperature and clarify
the limitations of the semiclassical approach. The condition for having
coherent effect due to scattering by low-frequency fluctuations is also pointed
out. It is interesting that the dephasing rate can be either larger or smaller
than the dissipation rate, depending on the physical circumstances.Comment: LaTex, 23 pages, 4 figures, published vesio
Electron transport through interacting quantum dots
We present a detailed theoretical investigation of the effect of Coulomb
interactions on electron transport through quantum dots and double barrier
structures connected to a voltage source via an arbitrary linear impedance.
Combining real time path integral techniques with the scattering matrix
approach we derive the effective action and evaluate the current-voltage
characteristics of quantum dots at sufficiently large conductances. Our
analysis reveals a reach variety of different regimes which we specify in
details for the case of chaotic quantum dots. At sufficiently low energies the
interaction correction to the current depends logarithmically on temperature
and voltage. We identify two different logarithmic regimes with the crossover
between them occurring at energies of order of the inverse dwell time of
electrons in the dot. We also analyze the frequency-dependent shot noise in
chaotic quantum dots and elucidate its direct relation to interaction effects
in mesoscopic electron transport.Comment: 21 pages, 4 figures. References added, discussion slightly extende
Broadband squeezed light from phase-locked single-mode sub-Poissonian lasers
We consider sub-Poissonian single-mode laser with external synchronization
and analyze its applicability to the problems of quantum information. Using
Heisenberg-Langevin theory we calculate the quadrature variances of the field
emitted by this laser. It is shown that such systems can demonstrate strong
quadrature squeezing. Taking into account that the emitted field is temporally
multi-mode the application of such sources to multichannel quantum
teleportation and dense coding protocols is discussed.Comment: 14 pages, 7 figure
Interaction-Induced Quantum Dephasing in Mesoscopic Rings
Combining nonperturbative techniques with Monte Carlo simulations we
demonstrate that quantum coherence effects for a particle on a ring are
suppressed beyond a finite length even at zero temperature if the
particle is coupled to a diffusive electron gas by means of long range Coulomb
interaction. This length is consistent with derived from
weak-localization-type of analysis.Comment: 4 revtex pages, 2 figure
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