234 research outputs found
Emergence of atom-light-mirror entanglement inside an optical cavity
We propose a scheme for the realization of a hybrid, strongly
quantum-correlated system formed of an atomic ensemble surrounded by a
high-finesse optical cavity with a vibrating mirror. We show that the steady
state of the system shows tripartite and bipartite continuous variable
entanglement in experimentally accessible parameter regimes, which is robust
against temperature
Self-cooling of a movable mirror to the ground state using radiation pressure
We show that one can cool a micro-mechanical oscillator to its quantum ground
state using radiation pressure in an appropriately detuned cavity
(self-cooling). From a simple theory based on Heisenberg-Langevin equations we
find that optimal self-cooling occurs in the good cavity regime, when the
cavity bandwidth is smaller than the mechanical frequency, but still larger
than the effective mechanical damping. In this case the intracavity field and
the vibrational mechanical mode coherently exchange their fluctuations. We also
present dynamical calculations which show how to access the mirror final
temperature from the fluctuations of the field reflected by the cavity.Comment: 4 pages, 3 figure
Recovery of missing data in correlated smart grid datasets
We study the recovery of missing data from multiple smart grid datasets within a matrix completion framework. The datasets contain the electrical magnitudes required for monitoring and control of the electricity distribution system. Each dataset is described by a low rank matrix. Different datasets are correlated as a result of containing measurements of different physical magnitudes generated by the same distribution system. To assess the validity of matrix completion techniques in the recovery of missing data, we characterize the fundamental limits when two correlated datasets are jointly recovered. We then proceed to evaluate the performance of Singular Value Thresholding (SVT) and Bayesian SVT (BSVT) in this setting. We show that BSVT outperforms SVT by simulating the recovery for different correlated datasets. The performance of BSVT displays the tradeoff behaviour described by the fundamental limit, which suggests that BSVT exploits the correlation between the datasets in an efficient manner
Quantum entanglement and teleportation in pulsed cavity-optomechanics
Entangling a mechanical oscillator with an optical mode is an enticing and
yet a very challenging goal in cavity optomechanics. Here we consider a pulsed
scheme to create Einstein-Podolsky-Rosen-type entanglement between a
traveling-wave light pulse and a mechanical oscillator. The entanglement can be
verified unambiguously by a pump-probe sequence of pulses. In contrast to
schemes that work in a steady-state regime under a continuous-wave drive, this
protocol is not subject to stability requirements that normally limit the
strength of achievable entanglement. We investigate the protocol's performance
under realistic conditions, including mechanical decoherence, in full detail.
We discuss the relevance of a high mechanical Qf product for entanglement
creation and provide a quantitative statement on which magnitude of the Qf
product is necessary for a successful realization of the scheme. We determine
the optimal parameter regime for its operation and show it to work in current
state-of-the-art systems.Comment: 10 pages, 2 figure
Robust recovery of missing data in electricity distribution systems
The advanced operation of future electricity distribution systems is likely to require significant observability of the different parameters of interest (e.g., demand, voltages, currents, etc.). Ensuring completeness of data is, therefore, paramount. In this context, an algorithm for recovering missing state variable observations in electricity distribution systems is presented. The proposed method exploits the low rank structure of the state variables via a matrix completion approach while incorporating prior knowledge in the form of second order statistics. Specifically, the recovery method combines nuclear norm minimization with Bayesian estimation. The performance of the new algorithm is compared to the information-theoretic limits and tested trough simulations using real data of an urban low voltage distribution system. The impact of the prior knowledge is analyzed when a mismatched covariance is used and for a Markovian sampling that introduces structure in the observation pattern. Numerical results demonstrate that the proposed algorithm is robust and outperforms existing state of the art algorithms
Recovering Missing Data via Matrix Completion in Electricity Distribution Systems
The performance of matrix completion based recovery of missing data in electricity distribution systems is analyzed. Under the assumption that the state variables follow a multivariate Gaussian distribution the matrix completion recovery is compared to estimation and information theoretic limits. The assumption about the distribution of the state variables is validated by the data shared by Electricity North West Limited. That being the case, the achievable distortion using minimum mean square error (MMSE) estimation is assessed for both random sampling and optimal linear encoding acquisition schemes. Within this setting, the impact of imperfect second order source statistics is numerically evaluated. The fundamental limit of the recovery process is characterized using Rate-Distortion theory to obtain the optimal performance theoretically attainable. Interestingly, numerical results show that matrix completion based recovery outperforms MMSE estimator when the number of available observations is low and access to perfect source statistics is not availabl
Micro-mechanical oscillator ground state cooling via intracavity optical atomic excitations
We predict ground state cooling of a micro-mechanical oscillator, i.e. a
vibrating end-mirror of an optical cavity, by resonant coupling of mirror
vibrations to a narrow internal optical transition of an ensemble of two level
systems. The particles represented by a collective mesoscopic spin model
implement, together with the cavity, an efficient, frequency tailorable zero
temperature loss channel which can be turned to a gain channel of pump. As
opposed to the case of resolved-sideband cavity cooling requiring a small
cavity linewidth, one can work here with low finesses and very small cavity
volumes to enhance the light mirror and light atom coupling. The tailored loss
and gain channels provide for efficient removal of vibrational quanta and
suppress reheating. In a simple physical picture of sideband cooling, the atoms
shape the cavity profile to enhance/inhibit scattering into higher/lower energy
sidebands. The method should be applicable to other cavity based cooling
schemes for atomic and molecular gases as for molecular ensembles coupled to
stripline cavities
The impact of the first COVID-19 lockdown on weight management practices in UK adults: a self-regulation perspective
This study aimed to identify the impact of the first UK COVID-19 lockdown on individuals’ weight management attempts (WMA). A self-regulation theoretical framework was used to identify predictors of continuing with a WMA, and weight change during the lockdown. An online retrospective cross-sectional study was conducted after the first UK COVID-19 lockdown. The sample consisted of 166 UK adults (M:31.08, SD:12.15) that were trying to manage their weight before the lockdown started. The survey assessed changes in WMA and practices, and measured perceived stress, flexible/rigid restraint, uncontrolled eating, craving control, and self-compassion. Results showed that 56% of participants reported disruption to their WMA during the lockdown. Participants with lower levels of perceived stress and higher flexible restraint were more likely to continue their WMA. Flexible restraint was a significant predictor of weight change. Interventions that promote flexibility in weight management may be beneficial for at-risk individuals under lockdown conditions
Robust entanglement of a micromechanical resonator with output optical fields
We perform an analysis of the optomechanical entanglement between the
experimentally detectable output field of an optical cavity and a vibrating
cavity end-mirror. We show that by a proper choice of the readout (mainly by a
proper choice of detection bandwidth) one can not only detect the already
predicted intracavity entanglement but also optimize and increase it. This
entanglement is explained as being generated by a scattering process owing to
which strong quantum correlations between the mirror and the optical Stokes
sideband are created. All-optical entanglement between scattered sidebands is
also predicted and it is shown that the mechanical resonator and the two
sideband modes form a fully tripartite-entangled system capable of providing
practicable and robust solutions for continuous variable quantum communication
protocols
Radiation-pressure self-cooling of a micromirror in a cryogenic environment
We demonstrate radiation-pressure cavity-cooling of a mechanical mode of a
micromirror starting from cryogenic temperatures. To achieve that, a
high-finesse Fabry-Perot cavity (F\approx 2200) was actively stabilized inside
a continuous-flow 4He cryostat. We observed optical cooling of the fundamental
mode of a 50mu x 50 mu x 5.4 mu singly-clamped micromirror at \omega_m=3.5 MHz
from 35 K to approx. 290 mK. This corresponds to a thermal occupation factor of
\approx 1x10^4. The cooling performance is only limited by the mechanical
quality and by the optical finesse of the system. Heating effects, e.g. due to
absorption of photons in the micromirror, could not be observed. These results
represent a next step towards cavity-cooling a mechanical oscillator into its
quantum ground state
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