8,212 research outputs found
Superfluid Optomechanics: Coupling of a Superfluid to a Superconducting Condensate
We investigate the low loss acoustic motion of superfluid He
parametrically coupled to a very low loss, superconducting Nb, TE
microwave resonator, forming a gram-scale, sideband resolved, optomechanical
system. We demonstrate the detection of a series of acoustic modes with quality
factors as high as . At higher temperatures, the lowest
dissipation modes are limited by an intrinsic three phonon process. Acoustic
quality factors approaching may be possible in isotopically purified
samples at temperatures below 10 mK. A system of this type may be utilized to
study macroscopic quantized motion and as an ultra-sensitive sensor of
extremely weak displacements and forces, such as continuous gravity wave
sources
Ultra-high Q Acoustic Resonance in Superfluid 4He
We report the measurement of the acoustic quality factor of a gram-scale,
kilo-hertz frequency superfluid resonator, detected through the parametric
coupling to a superconducting niobium microwave cavity. For temperature between
400mK and 50mK, we observe a temperature dependence of the quality
factor, consistent with a 3-phonon dissipation mechanism. We observe Q factors
up to , consistent with the dissipation due to dilute He
impurities, and expect that significant further improvements are possible.
These experiments are relevant to exploring quantum behavior and decoherence of
massive macroscopic objects, the laboratory detection of continuous wave
gravitational waves from pulsars, and the probing of possible limits to
physical length scales.Comment: 5 pages, 2 figure
Observation and interpretation of motional sideband asymmetry in a quantum electro-mechanical device
Quantum electro-mechanical systems offer a unique opportunity to probe
quantum noise properties in macroscopic devices, properties which ultimately
stem from the Heisenberg Uncertainty Principle. A simple example of this is
expected to occur in a microwave parametric transducer, where mechanical motion
generates motional sidebands corresponding to the up and down
frequency-conversion of microwave photons. Due to quantum vacuum noise, the
rates of these processes are expected to be unequal. We measure this
fundamental imbalance in a microwave transducer coupled to a radio-frequency
mechanical mode, cooled near the ground state of motion. We also discuss the
subtle origin of this imbalance: depending on the measurement scheme, the
imbalance is most naturally attributed to the quantum fluctuations of either
the mechanical mode or of the electromagnetic field
Sparse Deterministic Approximation of Bayesian Inverse Problems
We present a parametric deterministic formulation of Bayesian inverse
problems with input parameter from infinite dimensional, separable Banach
spaces. In this formulation, the forward problems are parametric, deterministic
elliptic partial differential equations, and the inverse problem is to
determine the unknown, parametric deterministic coefficients from noisy
observations comprising linear functionals of the solution.
We prove a generalized polynomial chaos representation of the posterior
density with respect to the prior measure, given noisy observational data. We
analyze the sparsity of the posterior density in terms of the summability of
the input data's coefficient sequence. To this end, we estimate the
fluctuations in the prior. We exhibit sufficient conditions on the prior model
in order for approximations of the posterior density to converge at a given
algebraic rate, in terms of the number of unknowns appearing in the
parameteric representation of the prior measure. Similar sparsity and
approximation results are also exhibited for the solution and covariance of the
elliptic partial differential equation under the posterior. These results then
form the basis for efficient uncertainty quantification, in the presence of
data with noise
Quantum squeezing of motion in a mechanical resonator
As a result of the quantum, wave-like nature of the physical world, a
harmonic oscillator can never be completely at rest. Even in the quantum ground
state, its position will always have fluctuations, called the zero-point
motion. Although the zero-point fluctuations are unavoidable, they can be
manipulated. In this work, using microwave frequency radiation pressure, we
both prepare a micron-scale mechanical system in a state near the quantum
ground state and then manipulate its thermal fluctuations to produce a
stationary, quadrature-squeezed state. We deduce that the variance of one
motional quadrature is 0.80 times the zero-point level, or 1 dB of
sub-zero-point squeezing. This work is relevant to the quantum engineering of
states of matter at large length scales, the study of decoherence of large
quantum systems, and for the realization of ultra-sensitive sensing of force
and motion
Spin polarizations and spin Hall currents in a two-dimensional electron gas with magnetic impurities
We consider a two-dimensional electron gas in the presence of Rashba
spin-orbit coupling, and study the effects of magnetic s-wave impurities and
long-range non-magnetic disorder on the spin-charge dynamics of the system. We
focus on voltage induced spin polarizations and their relation to spin Hall
currents. Our results are obtained using the quasiclassical Green function
technique, and hold in the full range of the disorder parameter .Comment: 5 pages, 2 figures. References added, minor stylistic modification
Retention of Administrators in Nursing Homes: What Can Management Do?
Annual turnover among nursing home administrators may be 40% or higher. To investigate the factors that could lead to greater administrator retention, responses to a survey (53% response rate) were analyzed using factor analysis and multiple regression models. Results show that higher retention is observed when administrators are allowed to function independently, are involved in decision making, are treated fairly, and are given reasonable goals to achieve. Organizations must hire administrators whose values match theirs. Multifacility chain organizations and for-profit facilities appear to have a greater need to embrace organizational principles that lead to greater job satisfaction
Mechanically Detecting and Avoiding the Quantum Fluctuations of a Microwave Field
During the theoretical investigation of the ultimate sensitivity of
gravitational wave detectors through the 1970's and '80's, it was debated
whether quantum fluctuations of the light field used for detection, also known
as photon shot noise, would ultimately produce a force noise which would
disturb the detector and limit the sensitivity. Carlton Caves famously answered
this question with "They do." With this understanding came ideas how to avoid
this limitation by giving up complete knowledge of the detector's motion. In
these back-action evading (BAE) or quantum non-demolition (QND) schemes, one
manipulates the required quantum measurement back-action by placing it into a
component of the motion which is unobserved and dynamically isolated. Using a
superconducting, electro-mechanical device, we realize a sensitive measurement
of a single motional quadrature with imprecision below the zero-point
fluctuations of motion, detect both the classical and quantum measurement
back-action, and demonstrate BAE avoiding the quantum back-action from the
microwave photons by 9 dB. Further improvements of these techniques are
expected to provide a practical route to manipulate and prepare a squeezed
state of motion with mechanical fluctuations below the quantum zero-point
level, which is of interest both fundamentally and for the detection of very
weak forces
Predicting Turnover and Retention in Nursing Home Administrators: Management and Policy Implications
Administrator turnover and its impact on the quality of patient care are important concerns in the nursing home industry. This study evaluates a model to determine which factors, attitudes, and personal characteristics can predict tenure. Responses to a survey from 290 nursing home administrators (NHAs) who furnished data on their previous positions were analyzed using logistic regression methods. The extracted model correlates tenure with the administrator\u27s past patterns of stability, community attachment, organizational commitment, and facility performance. The model is particularly effective (85% accuracy) in flagging NHAs who are likely to depart within their first 3 years of employment. Implications of these findings for recruitment, retention, and licensure policy are discussed
Inverse Spin Hall Effect and Anomalous Hall Effect in a Two-Dimensional Electron Gas
We study the coupled dynamics of spin and charge currents in a
two-dimensional electron gas in the transport diffusive regime. For systems
with inversion symmetry there are established relations between the spin Hall
effect, the anomalous Hall effect and the inverse spin Hall effect. However, in
two-dimensional electron gases of semiconductors like GaAs, inversion symmetry
is broken so that the standard arguments do not apply. We demonstrate that in
the presence of a Rashba type of spin-orbit coupling (broken structural
inversion symmetry) the anomalous Hall effect, the spin Hall and inverse spin
Hall effect are substantially different effects. Furthermore we discuss the
inverse spin Hall effect for a two-dimensional electron gas with Rashba and
Dresselhaus spin-orbit coupling; our results agree with a recent experiment.Comment: 5 page
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