5,572 research outputs found
Quantum-Classical Transition of Photon-Carnot Engine Induced by Quantum Decoherence
We study the physical implementation of the Photon Carnot engine (PCE) based
on the cavity QED system [M. Scully et al, Science, \textbf{299}, 862 (2003)].
Here, we analyze two decoherence mechanisms for the more practical systems of
PCE, the dissipation of photon field and the pure dephasing of the input atoms.
As a result we find that (I) the PCE can work well to some extent even in the
existence of the cavity loss (photon dissipation); and (II) the short-time
atomic dephasing, which can destroy the PCE, is a fatal problem to be overcome.Comment: 6 pages, 3 figure
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
Dynamics of Entanglement Transfer Through Multipartite Dissipative Systems
We study the dynamics of entanglement transfer in a system composed of two
initially correlated three-level atoms, each located in a cavity interacting
with its own reservoir. Instead of tracing out reservoir modes to describe the
dynamics using the master equation approach, we consider explicitly the
dynamics of the reservoirs. In this situation, we show that the entanglement is
completely transferred from atoms to reservoirs. Although the cavities mediate
this entanglement transfer, we show that under certain conditions, no
entanglement is found in cavities throughout the dynamics. Considering the
entanglement dynamics of interacting and non-interacting bipartite subsystems,
we found time windows where the entanglement can only flow through interacting
subsystems, depending on the system parameters.Comment: 8 pages, 11 figures, publishe in Physical Review
Precision quantum metrology and nonclassicality in linear and nonlinear detection schemes
We examine whether metrological resolution beyond coherent states is a
nonclassical effect. We show that this is true for linear detection schemes but
false for nonlinear schemes, and propose a very simple experimental setup to
test it. We find a nonclassicality criterion derived from quantum Fisher
information.Comment: 4 pages, 1 figur
Universal Dephasing Control During Quantum Computation
Dephasing is a ubiquitous phenomenon that leads to the loss of coherence in
quantum systems and the corruption of quantum information. We present a
universal dynamical control approach to combat dephasing during all stages of
quantum computation, namely, storage, single- and two-qubit operators. We show
that (a) tailoring multi-frequency gate pulses to the dephasing dynamics can
increase fidelity; (b) cross-dephasing, introduced by entanglement, can be
eliminated by appropriate control fields; (c) counter-intuitively and contrary
to previous schemes, one can increase the gate duration, while simultaneously
increasing the total gate fidelity.Comment: 4 pages,3 figure
Efficient excitation of a two level atom by a single photon in a propagating mode
State mapping between atoms and photons, and photon-photon interactions play
an important role in scalable quantum information processing. We consider the
interaction of a two-level atom with a quantized \textit{propagating} pulse in
free space and study the probability of finding the atom in the
excited state at any time . This probability is expected to depend on (i)
the quantum state of the pulse field and (ii) the overlap between the pulse and
the dipole pattern of the atomic spontaneous emission. We show that the second
effect is captured by a single parameter , obtained by
weighting the dipole pattern with the numerical aperture. Then can be
obtained by solving time-dependent Heisenberg-Langevin equations. We provide
detailed solutions for both single photon Fock state and coherent states and
for various temporal shapes of the pulses.Comment: 6 pages, 5 figures, 2 table
Entanglement of formation for a class of -dimensional systems
Currently the entanglement of formation can be calculated analytically for
mixed states in a -dimensional Hilbert space. For states in higher
dimensional Hilbert space a closed formula for quantifying entanglement does
not exist. In this regard only entanglement bounds has been found for
estimating it. In this work, we find an analytical expression for evaluating
the entanglement of formation for bipartite ()-dimensional mixed
states.Comment: 5 pages, 4 figures. Submitted for publicatio
Witnessing Entanglement with Second-Order Interference
Second-order interference and Hanbury-Brown and Twiss type experiments can
provide an operational framework for the construction of witness operators that
can test classical and nonclassical properties of a Gaussian squeezed state
(GSS), and provide entanglement witness operators to study the separability
properties of correlated Gaussian squeezed sates.Comment: 10 pages, 12 figure
Crew Quarters (CQ) and Electromagnetic Interference (EMI) Measurement Facility Combined Impedance Study
This report documents an investigation into observed failures associated with conducted susceptibility testing of Crew Quarters (CQ) hardware in the Johnson Space Center (JSC) Electromagnetic Interference (EMI) Measurement Facility, and the work accomplished to identify the source of the observed behavior. Investigation led to the conclusion that the hardware power input impedance was interacting with the facility power impedance leading to instability at the observed frequencies of susceptibility. Testing performed in other facilities did not show this same behavior, pointing back to the EMI Measurement Facility power as the potential root cause. A LISN emulating the Station power bus impedance was inserted into the power circuit, and the susceptibility was eliminated from the measurements
US 31W Jefferson County Pavement Surface Treatment Evaluation
Reflective cracking inevitably occurs when asphaltic concrete (AC) is placed over an existing unfractured Portland cement concrete (PCC) pavement. However, manufacturers state their products will mitigate reflective cracking, therefore extending the pavement life cycle.
To evaluate the performance of each manufacturer’s product, an experimental test section consisting of a southbound and northbound segment was established on US 31W in Louisville, Kentucky. The funding for this project will help track the performance of each product from the construction phase through the long-term monitoring phase. Hall Construction performed all work
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