Unconditional two-mode squeezing of separated atomic ensembles

We propose schemes for the unconditional preparation of a two-mode squeezed state of effective bosonic modes realized in a pair of atomic ensembles interacting collectively with optical cavity and laser fields. The scheme uses Raman transitions between stable atomic ground states and under ideal conditions produces pure entangled states in the steady state. The scheme works both for ensembles confined within a single cavity and for ensembles confined in separate, cascaded cavities.Comment: 4 pages, 2 figure

Collective spin systems in dispersive optical cavity QED: Quantum phase transitions and entanglement

We propose a cavity QED setup which implements a dissipative Lipkin-Meshkov-Glick model -- an interacting collective spin system. By varying the external model parameters the system can be made to undergo both first-and second-order quantum phase transitions, which are signified by dramatic changes in cavity output field properties, such as the probe laser transmission spectrum. The steady-state entanglement between pairs of atoms is shown to peak at the critical points and can be experimentally determined by suitable measurements on the cavity output field. The entanglement dynamics also exhibits pronounced variations in the vicinities of the phase transitions.Comment: 19 pages, 18 figures, shortened versio

Coupling of effective one-dimensional two-level atoms to squeezed light

A cavity QED system is analyzed which duplicates the dynamics of a two-level atom in free space interacting exclusively with broadband squeezed light. We consider atoms in a three or four-level Lambda-configuration coupled to a high-finesse optical cavity which is driven by a squeezed light field. Raman transitions are induced between a pair of stable atomic ground states via the squeezed cavity mode and coherent driving fields. An analysis of the reduced master equation for the atomic ground states shows that a three-level atomic system has insufficient parameter flexibility to act as an effective two-level atom interacting exclusively with a squeezed reservoir. However, the inclusion of a fourth atomic level, coupled dispersively to one of the two ground states by an auxiliary laser field, introduces an extra degree of freedom and enables the desired interaction to be realised. As a means of detecting the reduced quadrature decay rate of the effective two-level system, we examine the transmission spectrum of a weak coherent probe field incident upon the cavity

Counter-Intuitive Vacuum-Stimulated Raman Scattering

Vacuum-stimulated Raman scattering in strongly coupled atom-cavity systems allows one to generate free-running single photon pulses on demand. Most properties of the emitted photons are well defined, provided spontaneous emission processes do not contribute. Therefore, electronic excitation of the atom must not occur, which is assured for a system adiabatically following a dark state during the photon-generation process. We experimentally investigate the conditions that must be met for adiabatic following in a time-of-flight driven system, with atoms passing through a cavity and a pump beam oriented transverse to the cavity axis. From our results, we infer the optimal intensity and relative pump-beam position with respect to the cavity axis.Comment: 4 pages, 4 figure

Propagation management for no-acknowledge HF communications links

The problems in the engineering of no-acknowledge HF links are reviewed with particular application to naval applications. Models for predicting the performance of the ionospheric path and techniques for measurement of channel quality are considered. Manual methods of propagation management are found to be limited by speed and accuracy in conducting measurements. Automation of the channel quality measurement process allowed observation of short term behaviour of the link for comparison with predictions. Long term behaviour tends toward the prediction but large deviations are found in the short term. Techniques for improving the estimates of the remote ionosphere were investigated. Updating predictions using a derived ionospheric index and the use of a backscatter sounder were attempted with limited success. Concepts for improvement in no-acknowledge links include networking between transmitting stations, modulation diversity and coding techniques, and development of 'intelligent receiving terminals with facilities for rapid selection of operating channels and overcoming unwanted signal interference. Recommendations for further work to investigate these concepts is presented

Surgeons or Scribes? The Role of United States Court of Appeals Law Clerks in Appellate Triage

Using original survey data, we explore how federal courts of appeals judges select and use their law clerks—a question that we answered in an earlier article about federal district court clerks. As with that first article, we do not intend to tackle such normative issues as whether courts of appeals law clerks possess too much influence over the judicial process or whether the selection criteria used by these judges is appropriate. What we will present, however, is descriptive data on the criteria that courts of appeals judges use to pick their law clerks as well as the tasks assigned to those clerks. We believe that our findings, namely, that courts of appeals judges delegate substantial job duties to their clerks, should serve as the springboard for a future debate over the wisdom of such delegation

Generation of two-mode nonclassical states and a quantum phase gate operation in trapped ion cavity QED

We propose a scheme to generate nonclassical states of a quantum system, which is composed of the one-dimensional trapped ion motion and a single cavity field mode. We show that two-mode SU(2) Schr\"odinger-cat states, entangled coherent states, two-mode squeezed vacuum states and their superposition can be generated. If the vibration mode and the cavity mode are used to represent separately a qubit, a quantum phase gate can be implemented.Comment: to appear in PR

Static and dynamic characteristics of an hydrodynamic journal bearing

Hydrodynamic oil film bearings exhibit lateral flexibility which influences the dynamics of rotors they support. This lateral flexibility is specified by coefficients which relate forces generated by the oil film to the instantaneous journal centre velocity and its displacement from an equilibrium position. Previous investigators adopted a linear treatment by taking uniform viscosity with small displacement and velocity increments. Relatively large journal centre velocities are possible in rotating machinery. Therefore, this thesis investigates the non-linear behaviour of these oil film coefficients. Coefficient calculations allowed viscosity to vary with temperature and pressure rendering the governing Reynolds Equation non-linear. A range of positive and negative displacement and velocity increments were examined. Novel experimental techniques have been developed which allow determination of coefficient variation with respective displacement and velocity. Coefficients were deduced from specially chosen, imposed vibration orbits arising from two mutually perpendicular external oscillating forces of variable relative magnitude and phase. Journal centre displacement and velocity were measured using high speed data logging equipment. A unique feature was the ability to obtain, experimental displacement coefficients from the results of both dynamic and incremental loading. It was found necessary to establish the bearing centre separately for each warm-up/load combination. Journal clearance in the hot rotating condition could not be measured to the precision required by its sensitivity to calculated load. Clearance and cavitation zone pressures were deduced from simultaneous predictions of the measured vertical load and attitude angle. Theoretical oil film tensile forces were necessary, a proposition supported by recently published experimental findings. Theoretical results for an equivalent uniform viscosity combined with experimental data gave a simple static locus design procedure. A temperature profile was assumed for theoretical work but choice thereof was found to be not critical. Coefficients are defined in terms of a "zero" value and linear gradient. Using realistic criteria, measured coefficient variation was found to be significant at eccentricity ratios greater than 0.78. Theory adequately predicted most "zero" values but not gradients. It is concluded that improvement in the coefficient prediction willPh

Surgeons or Scribes? The Role of United States Court of Appeals Law Clerks in Appellate Triage

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Mimicking a Squeezed Bath Interaction: Quantum Reservoir Engineering with Atoms

The interaction of an atomic two-level system and a squeezed vacuum leads to interesting novel effects in atomic dynamics, including line narrowing in resonance fluorescence and absorption spectra, and a suppressed (enhanced) decay of the in-phase and out-of phase component of the atomic polarization. On the experimental side these predictions have so far eluded observation, essentially due to the difficulty of embedding atoms in a 4 pi squeezed vacuum. In this paper we show how to ``engineer'' a squeezed-bath-type interaction for an effective two-level system. In the simplest example, our two-level atom is represented by the two ground levels of an atom with angular momentum J=1/2 -> J=1/2 transition (a four level system) which is driven by (weak) laser fields and coupled to the vacuum reservoir of radiation modes. Interference between the spontaneous emission channels in optical pumping leads to a squeezed bath type coupling, and thus to symmetry breaking of decay on the Bloch sphere. With this system it should be possible to observe the effects predicted in the context of squeezed bath - atom interactions. The laser parameters allow one to choose properties of the squeezed bath interaction, such as the (effective) photon number expectation number N and the squeezing phase phi. We present results of a detailed analytical and numerical study.Comment: 24 pages, 8 figure