3,472 research outputs found
Balanced homodyne detectors in QFT
Within the dipole approximation we describe the interaction of a photodiode
with the quantum electric field. The diode is modelled by an electron in a
bound state which upon interaction, treated perturbatively in the paper, can
get excited to one of the scattering states. We furthermore analyze a balanced
homodyne detector (BHD) with a local oscillator (LO) consisting of two
photodiodes illuminated by a monochromatic coherent state. We show, that to the
leading order the BHD's output measures the expectation value of the quantum
electric field, in the state without the LO, restricted to the frequency of the
LO. The square of the output measures the two-point function of the quantum
field. This shows that the BHDs provide tools for measurements of sub-vacuum
(negative) expectation values of the squares quantum fields and thus for test
of Quantum Energy Inequality - like bounds, or other QFT effects under the
influence of external conditions.Comment: Revised version with minor mistakes remove
Quantum theory of a vortex line in an optical lattice
We investigate the quantum theory of a vortex line in a stack of
weakly-coupled two-dimensional Bose-Einstein condensates, that is created by a
one-dimensional optical lattice. We derive the dispersion relation of the
Kelvin modes of the vortex line and also study the coupling between the Kelvin
modes and the quadrupole modes. We solve the coupled dynamics of the vortex
line and the quadrupole modes, both classically as well as quantum
mechanically. The quantum mechanical solution reveals the possibility of
generating nonequilibrium squeezed vortex states by strongly driving the
quadrupole modes.Comment: Minor changes in response to a referee repor
Entanglement conditions for two-mode states: Applications
We examine the implications of several recently derived conditions [Hillery
and Zubairy, Phys. Rev. Lett. 96, 050503 (2006)] for determining when a
two-mode state is entangled. We first find examples of non-Gaussian states that
satisfy these conditions. We then apply the entanglement conditions to the
study of several linear devices, the beam splitter, the parametric amplifier,
and the linear phase-insensitive amplifier. For the first two, we find
conditions on the input states that guarantee that the output states are
entangled. For the linear amplifier, we determine in the limit of high and no
gain, when an entangled input leads to an entangled output. Finally, we show
how application of two two-mode entanglement conditions to a three-mode state
can serve as a test of genuine three-mode entanglement.Comment: 7 pages, no figures, replaced with published versio
Polarization entanglement visibility of photon pairs emitted by a quantum dot embedded in a microcavity
We study the photon emission from a quantum dot embedded in a microcavity.
Incoherent pumping of its excitons and biexciton provokes the emission of leaky
and cavity modes. By solving a master equation we obtain the correlation
functions required to compute the spectrum and the relative efficiency among
the emission of pairs and single photons. A quantum regime appears for low
pumping and large rate of emission. By means of a post-selection process, a two
beams experiment with different linear polarizations could be performed
producing a large polarization entanglement visibility precisely in the quantum
regime.Comment: 13 pages and 6 figure
Correlations in atomic systems: Diagnosing coherent superpositions
While investigating quantum correlations in atomic systems, we note that
single measurements contain information about these correlations. Using a
simple model of measurement -- analogous to the one used in quantum optics --
we show how to extract higher order correlation functions from individual
"phtotographs" of the atomic sample. As a possible application we apply the
method to detect a subtle phase coherence in mesoscopic superpostitions.Comment: 4 pages, 2 figures, provisionally accepted to Physical Review Letter
Spatial Correlation Functions of one-dimensional Bose gases at Equilibrium
The dependence of the three lowest order spatial correlation functions of a
harmonically confined Bose gas on temperature and interaction strength is
presented at equilibrium. Our analysis is based on a stochastic Langevin
equation for the order parameter of a weakly-interacting gas. Comparison of the
predicted first order correlation functions to those of appropriate mean field
theories demonstrates the potentially crucial role of density fluctuations on
the equilibrium coherence length. Furthermore,the change in both coherence
length and shape of the correlation function, from gaussian to exponential,
with increasing temperature is quantified. Moreover, the presented results for
higher order correlation functions are shown to be in agreeement with existing
predictions. Appropriate consideration of density-density correlations is shown
to facilitate a precise determination of quasi-condensate density profiles,
providing an alternative approach to the bimodal density fits typically used
experimentally
Quantum Trajectory Analysis of the Two-Mode Three-Level Atom Microlaser
We consider a single atom laser (microlaser) operating on three-level atoms
interacting with a two-mode cavity. The quantum statistical properties of the
cavity field at steady state are investigated by the quantum trajectory method
which is a Monte Carlo simulation applied to open quantum systems. It is found
that a steady state solution exists even when the detailed balance condition is
not guaranteed. The differences between a single mode microlaser and a two-mode
microlaser are highlighted. The second-order correlation function g^2(T) of a
single mode is studied and special attention is paid to the one-photon trapping
state, for which a simple formula is derived for its correlation function. We
show the effects of the velocity spread of the atoms used to pump the
microlaser cavity on the second-order correlation function, trapping states,
and phase transitions of the cavity field
Heat Capacity Mapping Mission
The Tasman Front was delineated by airborne expendable bathythermograph survey; and an Heat Capacity Mapping Mission (HCMM) IR image on the same day shows the same principal features as determined from ground-truth. It is clear that digital enhancement of HCMM images is necessary to map ocean surface temperatures and when done, the Tasman Front and other oceanographic features can be mapped by this method, even through considerable scattered cloud cover
Shale Investment Dashboard in Ohio
This report presents findings from an investigation into shale-related investment in Ohio from researchers at Cleveland State and Youngstown State Universities. The investment estimates are cumulative from 2011 through the summer of 2016. Subsequent reports will estimate additional investment since the date of this report.
The investigation was made into upstream, midstream and downstream investments. The downturn in oil and gas prices in late 2014 that continued through 2016 has constrained upstream investment in Ohio, as drilling slowed. However low hydrocarbon prices have increased a nationwide appetite for natural gas and natural gas liquids. This has led to a continuation of midstream and downstream investment.
Since operating companies do not generally make investments publicly available, upstream investments were estimated by using approximations for typical expenditures on wells that are drilled in the Utica. Information for typical investments were obtained through a combination of industry interviews and publicly available data
Theory of single-photon transport in a single-mode waveguide coupled to a cavity containing a two-level atom
The single-photon transport in a single-mode waveguide, coupled to a cavity
embedded with a two-leval atom is analyzed. The single-photon transmission and
reflection amplitudes, as well as the cavity and the atom excitation
amplitudes, are solved exactly via a real-space approach. It is shown that the
dissipation of the cavity and of the atom respectively affects distinctively on
the transport properties of the photons, and on the relative phase between the
excitation amplitudes of the cavity mode and the atom.Comment: 28 pages, 6 figures. Accepted by Physical Review A (2009
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