Composite oscillator systems for meeting user needs for time and frequency

Frequency standards are used in most navigation and telecommunications systems to provide a long term memory of either frequency, phase, or time epoch. From a systems point of view, the performance aspects of the frequency standard are weighed against other systems characteristics, such as overall performance, cost, size, and accessibility; a number of examples are very briefly reviewed. The theory of phase lock and frequency lock systems is outlined in sufficient detail that total oscillator system performance can be predicted from measurements on the individual components. As an example, details of the performance of a high spectral purity oscillator phase locked to a long term stable oscillator are given. Results for several systems, including the best system stability that can be obtained from present commercially available 5-MHz sources, are shown

Analysis of photon-atom entanglement generated by Faraday rotation in a cavity

Faraday rotation based on AC Stark shifts is a mechanism that can entangle the polarization variables of photons and atoms. We analyze the structure of such entanglement by using the Schmidt decomposition method. The time-dependence of entanglement entropy and the effective Schmidt number are derived for Gaussian amplitudes. In particular we show how the entanglement is controlled by the initial fluctuations of atoms and photons.Comment: 6 pages, 3 figure

Relationships Between the Performance of Time/Frequency Standards and Navigation/Communication Systems

The relationship between system performance and clock or oscillator performance is discussed. Tradeoffs discussed include: short term stability versus bandwidth requirements; frequency accuracy versus signal acquisition time; flicker of frequency and drift versus resynchronization time; frequency precision versus communications traffic volume; spectral purity versus bit error rate, and frequency standard stability versus frequency selection and adjustability. The benefits and tradeoffs of using precise frequency and time signals are various levels of precision and accuracy are emphasized

Alice falls into a black hole: Entanglement in non-inertial frames

Two observers determine the entanglement between two free bosonic modes by each detecting one of the modes and observing the correlations between their measurements. We show that a state which is maximally entangled in an inertial frame becomes less entangled if the observers are relatively accelerated. This phenomenon, which is a consequence of the Unruh effect, shows that entanglement is an observer-dependent quantity in non-inertial frames. In the high acceleration limit, our results can be applied to a non-accelerated observer falling into a black hole while the accelerated one barely escapes. If the observer escapes with infinite acceleration, the state's distillable entanglement vanishes.Comment: I.F-S published before with maiden name Fuentes-Guridi Replaced with published version. Phys. Rev. Lett. in pres

Nonequilibrium Langevin Approach to Quantum Optics in Semiconductor Microcavities

Recently the possibility of generating nonclassical polariton states by means of parametric scattering has been demonstrated. Excitonic polaritons propagate in a complex interacting environment and contain real electronic excitations subject to scattering events and noise affecting quantum coherence and entanglement. Here we present a general theoretical framework for the realistic investigation of polariton quantum correlations in the presence of coherent and incoherent interaction processes. The proposed theoretical approach is based on the {\em nonequilibrium quantum Langevin approach for open systems} applied to interacting-electron complexes described within the dynamics controlled truncation scheme. It provides an easy recipe to calculate multi-time correlation functions which are key-quantities in quantum optics. As a first application, we analyze the build-up of polariton parametric emission in semiconductor microcavities including the influence of noise originating from phonon induced scattering.Comment: some corrections in the presentation mad

The role of quantum fluctuations in the optomechanical properties of a Bose-Einstein condensate in a ring cavity

We analyze a detailed model of a Bose-Einstein condensate trapped in a ring optical resonator and contrast its classical and quantum properties to those of a Fabry-P{\'e}rot geometry. The inclusion of two counter-propagating light fields and three matter field modes leads to important differences between the two situations. Specifically, we identify an experimentally realizable region where the system's behavior differs strongly from that of a BEC in a Fabry-P\'{e}rot cavity, and also where quantum corrections become significant. The classical dynamics are rich, and near bifurcation points in the mean-field classical system, the quantum fluctuations have a major impact on the system's dynamics.Comment: 11 pages, 11 figures, submitted to PR

Photon-added coherent states as nonlinear coherent states

The states $|\alpha,m>$, defined as ${a^{\dagger}}^{m}|\alpha>$ up to a normalization constant and $m$ is a nonnegative integer, are shown to be the eigenstates of $f(\hat{n},m)\hat{a}$ where $f(\hat{n},m)$ is a nonlinear function of the number operator $\hat{n}$. The explicit form of $f(\hat{n},m)$ is constructed. The eigenstates of this operator for negative values of $m$ are introduced. The properties of these states are discussed and compared with those of the state $|\alpha,m >$.Comment: Rev Tex file with two figures as postscript files attached. Email: [email protected]

Photon production from the vacuum close to the super-radiant transition: When Casimir meets Kibble-Zurek

The dynamical Casimir effect (DCE) predicts the generation of photons from the vacuum due to the parametric amplification of the quantum fluctuation of an electromagnetic field\cite{casimir1,casimir2}. The verification of such effect is still elusive in optical systems due to the very demanding requirements of its experimental implementation. This typically requires very fast changes of the boundary conditions of the problem, such as the high-frequency driving of the positions of the mirrors of a cavity accommodating the field. Here, we show that an ensemble of two-level atoms collectively coupled to the electromagnetic field of a cavity (thus embodying the quantum Dicke model\cite{dicke}), driven at low frequencies and close to a quantum phase transition, stimulates the production of photons from the vacuum. This paves the way to an effective simulation of the DCE through a mechanism that has recently found an outstanding experimental demonstration\cite{esslinger}. The spectral properties of the emitted radiation reflect the critical nature of the system and allow us to link the detection of DCE to the Kibble-Zurek mechanism for the production of defects when crossing a continuous phase transition\cite{KZ1,KZ2}. We illustrate the features of our proposal by addressing a simple cavity quantum-electrodynamics (cQED) setting of immediate experimental realisation.Comment: 4+1 pages, major changes in the second part of the paper. To appear in Physical Review Letter

Protein-Energy Undernutrition Among Elderly Hospitalized Patients: A Prospective Study

Context: Numerous studies have identified strong correlations between the severity of nutritional deficits and an increased risk of subsequent morbid events among the hospitalized elderly, but whether inadequate nutrient intake during hospitalization contributes to such nutritional deficits or the risk of adverse outcomes is not known. Objectives: To identify the distribution of average daily nutrient intake among the nonter–minally ill hospitalized elderly, ascertain what factors contribute to persistently low intakes, and determine whether the adequacy of nutrient intake correlates with the risk of mortality. Design: Prospective cohort study conducted from 1994 to 1997. Setting: University-affiliated Department of Veterans Affairs hospital. Patients: A total of 497 patients 65 years or older (mean [SD] age, 74 [6] years; 97% male; 86% white) with a length of stay of 4 days or more. Main Outcome Measures: Daily in-hospital nutrient intake, in-hospital mortality, and 90-day mortality. Results: A total of 102 patients (21%) had an average daily in-hospital nutrient intake of <50% of their calculated maintenance energy requirements. Admission illness severity, average length of stay, and admission albumin and prealbumin levels for this low nutrient group did not differ significantly from those of the remaining patients. However, the low nutrient group had lower mean (SD) discharge serum total cholesterol (154 [44] mg/dL [4 [1.1] mmol/L] vs 173 [42] mg/dL [4.5 [1.1] mmol/L]; p = .001), albumin (29.1 [6.7] vs 33.2 [6.1] g/L, p = .001), and prealbumin (162 [69] vs 205 [68] mg/L;p = .001) concentrations and a higher rate of in-hospital mortality (relative risk, 8.0; 95% confidence interval, 2.8 to 22.6) and 90-day mortality (relative risk, 2.9; 95% confidence interval, 1.4 to 6.1). Contributing to the problem of inadequate nutrient intake, patients were frequently ordered to have nothing by mouth and were not fed by another route. Neither canned supplements nor nutrition support were used effectively. Conclusions: Throughout their hospitalization, many elderly patients were maintained on nutrient intakes far less than their estimated maintenance energy requirements, which may contribute to an increased risk of mortality. Given the difficulties reversing established nutritional deficits in the elderly, greater efforts should be made to prevent the development of such deficits during hospitalization. (JAMA 281:2013–2019, 1999)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68391/2/10.1177_088453369901400610.pd

Quantum Trajectory method for the Quantum Zeno and anti-Zeno effects

We perform stochastic simulations of the quantum Zeno and anti-Zeno effects for two level system and for the decaying one. Instead of simple projection postulate approach, a more realistic model of a detector interacting with the environment is used. The influence of the environment is taken into account using the quantum trajectory method. The simulation of the measurement for a single system exhibits the probabilistic behavior showing the collapse of the wave-packet. When a large ensemble is analysed using the quantum trajectory method, the results are the same as those produced using the density matrix method. The results of numerical calculations are compared with the analytical expressions for the decay rate of the measured system and a good agreement is found. Since the analytical expressions depend on the duration of the measurement only, the agreement with the numerical calculations shows that otherparameters of the model are not important.Comment: 12 figures, accepted for publication in Phys. Rev. A replaced with single-spaced versio