975 research outputs found
Dynamical quantum phase transitions in the dissipative Lipkin-Meshkov-Glick model and proposed realization in optical cavity QED
We present an optical cavity QED configuration that is described by a
dissipative version of the Lipkin-Meshkov-Glick model of an infinitely
coordinated spin system. This open quantum system exhibits both first- and
second-order non-equilibrium quantum phase transitions as a single, effective
field parameter is varied. Light emitted from the cavity offers measurable
signatures of the critical behavior, including that of the spin-spin
entanglement.Comment: 4 pages, 4 figures, typos corrected and other minor change
The impact of new signals on precise marine navigation - initial results from an experiment in Harwich Harbour
The General Lighthouse Authorities of the United Kingdom and Ireland (GLAs) are supporting a project at University College London (UCL) to study whether it is possible to meet the International Maritime Organisation’s (IMO) future requirements for port and harbour approach using future GNSS constellations, as detailed in IMO resolution A.915. This paper presents the results of a trial focusing on the accuracy, integrity, availability and continuity of port navigation, port approach, and docking. Abstract The required accuracy for docking is 0.1 m (95\%), which currently necessitates the use of Real Time Kinematic (RTK) processing. We consider the single-epoch geometry-based approach, which is robust against loss of lock and will fully benefit from the additional satellites. The trial was held at the beginning of May 2008 and saw THV Alert navigate into Harwich Harbour while satellite observation data were recorded from the vessel and from shore-based reference stations. Additional data were obtained from nearby Ordnance Survey reference stations, and two total stations were used to track the vessel’s passage to provide a truth model. Several modernised GPS satellites were tracked. The data were processed under different scenarios, using software developed at UCL, and the positioning performance analysed. Abstract Providing integrity for single-epoch RTK is particularly difficult. The identification of phase observation outliers is not possible before the integer ambiguities are resolved, but an undetected outlier could prevent successful ambiguity resolution. However, it will not always be necessary to fix every ambiguity to achieve the required precision, particularly with a multi-GNSS constellation. This paper introduces a new algorithm for partial ambiguity resolution in the presence of measurement bias that has been developed and tested at UCL. This algorithm results in an improved ambiguity resolution success rate at the expense of computation time
Entanglement and entropy engineering of atomic two-qubit states
We propose a scheme employing quantum-reservoir engineering to controllably
entangle the internal states of two atoms trapped in a high finesse optical
cavity. Using laser and cavity fields to drive two separate Raman transitions
between metastable atomic ground states, a system is realized corresponding to
a pair of two-state atoms coupled collectively to a squeezed reservoir.
Phase-sensitive reservoir correlations lead to entanglement between the atoms,
and, via local unitary transformations and adjustment of the degree and purity
of squeezing, one can prepare entangled mixed states with any allowed
combination of linear entropy and entanglement of formation.Comment: 4 pages, 5 figures, REVTe
Proposal for teleportation of the wave function of a massive particle
We propose a scheme for teleporting an atomic center-of-mass wave function
between distant locations. The scheme uses interactions in cavity quantum
electrodynamics to facilitate a coupling between the motion of an atom trapped
inside a cavity and external propagating light fields. This enables the
distribution of quantum entanglement and the realization of the required
motional Bell-state analysis.Comment: 4 pages, 3 figure
Rapid Steady State Convergence for Quantum Systems Using Time-Delayed Feedback Control
We propose a time-delayed feedback control scheme for open quantum systems
that can dramatically reduce the time to reach steady state. No measurement is
performed in the feedback loop, and we suggest a simple all-optical
implementation for a cavity QED system. We demonstrate the potential of the
scheme by applying it to a driven and dissipative Dicke model, as recently
realized in a quantum gas experiment. The time to reach steady state can then
reduced by two orders of magnitude for parameters taken from experiment, making
previously inaccessible long time attractors reachable within typical
experimental run times. The scheme also offers the possibility of slowing down
the dynamics, as well as qualitatively changing the phase diagram of the
corresponding physical system.Comment: 25 pages, 9 figures. Invited paper in "Focus on Coherent Control of
Complex Quantum Systems", Eds. B. Whaley and G. Milburn. PS: Preview on OSX
struggles with opening some of the figures with a lot of data in the
The relationship between muscular power and functional fitness among older adults
The purpose of the study was to determine whether functional fitness is a good predictor of average and peak muscular power among adults over the age of 65. The 30-second chair stand and 8-foot-up-and-go test were used to define functional fitness and were administered to 57 older adults. Muscular power output was measured using the Tendo Weightlifting Analyzer during 5 chair stands. Relative average and peak power were used in the analyses. An independent t-test was run on all variables to distinguish differences between men and women, and multiple regression analyses were performed to detect the relationship between the two functional fitness variables and muscular power. There were no differences between genders, and 53.5% variance in both relative average and peak power was accounted for by the functional fitness measures (p ≤ .05). Functional fitness, defined as 30-second chair stand and 8-foot-up-and-go test, is a good predictor of average and peak muscular power
- …