630 research outputs found
Outcoupling from a Bose-Einstein condensate with squeezed light to produce entangled atom laser beams
We examine the properties of an atom laser produced by outcoupling from a
Bose-Einstein condensate with squeezed light. We model the multimode dynamics
of the output field and show that a significant amount of squeezing can be
transfered from an optical mode to a propagating atom laser beam. We use this
to demonstrate that two-mode squeezing can be used to produce twin atom laser
beams with continuous variable entanglement in amplitude and phase.Comment: 11 pages, 14 figure
Quantum field effects in coupled atomic and molecular Bose-Einstein condensates
This paper examines the parameter regimes in which coupled atomic and
molecular Bose-Einstein condensates do not obey the Gross-Pitaevskii equation.
Stochastic field equations for coupled atomic and molecular condensates are
derived using the functional positive-P representation. These equations
describe the full quantum state of the coupled condensates and include the
commonly used Gross-Pitaevskii equation as the noiseless limit. The model
includes all interactions between the particles, background gas losses,
two-body losses and the numerical simulations are performed in three
dimensions. It is found that it is possible to differentiate the quantum and
semiclassical behaviour when the particle density is sufficiently low and the
coupling is sufficiently strong.Comment: 4 postscript figure
Precise wavefunction engineering with magnetic resonance
Controlling quantum fluids at their fundamental length scale will yield
superlative quantum simulators, precision sensors, and spintronic devices. This
scale is typically below the optical diffraction limit, precluding precise
wavefunction engineering using optical potentials alone. We present a protocol
to rapidly control the phase and density of a quantum fluid down to the healing
length scale using strong time-dependent coupling between internal states of
the fluid in a magnetic field gradient. We demonstrate this protocol by
simulating the creation of a single stationary soliton and double soliton
states in a Bose-Einstein condensate with control over the individual soliton
positions and trajectories, using experimentally feasible parameters. Such
states are yet to be realized experimentally, and are a path towards
engineering soliton gases and exotic topological excitations.Comment: 8+ pages, 3 figures; revised parameters and added section about
optimisation of adiabatic, finite-duration pulses and analytic resolution
limi
Control of an atom laser using feedback
A generalised method of using feedback to control Bose-Einstein condensates
is introduced. The condensates are modelled by the Gross-Pitaevskii equation,
so only semiclassical fluctations can be suppressed, and back-action from the
measurement is ignored. We show that for any available control, a feedback
scheme can be found to reduce the energy while the appropriate moment is still
dynamic. We demonstrate these schemes by considering a condensate trapped in a
harmonic potential that can be modulated in strength and position. The
formalism of our feedback scheme also allows the inclusion of certain types of
non-linear controls. If the non-linear interaction between the atoms can be
controlled via a Feshbach resonance, we show that the feedback process can
operate with a much higher efficiency.Comment: 6 pages, 7 figure
Output of a pulsed atom laser
We study the output properties of a pulsed atom laser consisting of an
interacting Bose-Einstein condensate (BEC) in a magnetic trap and an additional
rf field transferring atoms to an untrapped Zeeman sublevel. For weak output
coupling we calculate the dynamics of the decaying condensate population, of
its chemical potential and the velocity of the output atoms analytically.Comment: 4 pages, RevTeX. Full ps file available on
http://mpqibmr1.mpq.mpg.de:5000/~man
Rotons and Quantum Evaporation from Superfluid 4He
The probability of evaporation induced by and rotons at the
surface of superfluid helium is calculated using time dependent density
functional theory. We consider excitation energies and incident angles such
that phonons do not take part in the scattering process. We predict sizable
evaporation rates, which originate entirely from quantum effects. Results for
the atomic reflectivity and for the probability of the roton change-mode
reflection are also presented.Comment: 11 pages, REVTEX, 3 figures available upon request or at
http://anubis.science.unitn.it/~dalfovo/papers/papers.htm
Modelling the force of infection for hepatitis B and hepatitis C in injecting drug users in England and Wales
BACKGROUND: Injecting drug use is a key risk factor, for several infections of public health importance, especially hepatitis B (HBV) and hepatitis C (HCV). In England and Wales, where less than 1% of the population are likely to be injecting drug users (IDUs), approximately 38% of laboratory reports of HBV, and 95% of HCV reports are attributed to injecting drug use. METHODS: Voluntary unlinked anonymous surveys have been performed on IDUs in contact with specialist agencies throughout England and Wales. Since 1990 more than 20,000 saliva samples from current IDUs have been tested for markers of infection for HBV, HCV testing has been included since 1998. The analysis here considers those IDUs tested for HBV and HCV (n = 5,682) from 1998–2003. This study derives maximum likelihood estimates of the force of infection (the rate at which susceptible IDUs acquire infection) for HBV and HCV in the IDU population and their trends over time and injecting career length. The presence of individual heterogeneity of risk behaviour and background HBV prevalence due to routes of transmission other than injecting are also considered. RESULTS: For both HBV and HCV, IDUs are at greatest risk from infection in their first year of injecting (Forces of infection in new initiates 1999–2003: HBV = 0.1076 95% C.I: 0.0840–0.1327 HCV = 0.1608 95% C.I: 0.1314–0.1942) compared to experienced IDUs (Force of infection in experienced IDUs 1999–2003: HBV = 0.0353 95% C.I: 0.0198–0.0596, HCV = 0.0526 95% C.I: 0.0310–0.0863) although independently of this there is evidence of heterogeneity of risk behaviour with a small number of IDUs at increased risk of infection. No trends in the FOI over time were detected. There was only limited evidence of background HBV infection due to factors other than injecting. CONCLUSION: The models highlight the need to increase interventions that target new initiates to injecting to reduce the transmission of blood-borne viruses. Although from the evidence here, identification of those individuals that engage in heightened at-risk behaviour may also help in planning effective interventions. The data and methods described here may provide a baseline for monitoring the success of public health interventions
Atom optical elements for Bose condensates
A simple model for atom optical elements for Bose condensate of trapped,
dilute alkali atomns is proposed and numerical simulations are presented to
illustrate its characteristics. We demonstrate ways of focusing and splitting
the condensate by modifying experimentally adjustable parameters. We show that
there are at least two ways of implementing atom optical elements: one may
modulate the interatomic scattering length in space, or alternatively, use a
sinusoidal, externally applied potential.Comment: 7 pages, 10 figure
Perfect weddings abroad
Approximately 16% of UK couples are currently married abroad. However, academic or practitioner focused research that explores the complex nature of a couple’s buying preferences or the development of innovative marketing strategies by businesses operating within the weddings abroad niche sector, is almost non-existent. This exploratory paper examines the role and relevance of marketing within the weddings abroad sector. The complex nature of customer needs in this high emotional and involvement experience, are identified and explored. A case study of Perfect Weddings Abroad Ltd highlights distinctive features and characteristics. Social networking and the use of home-workers, with a focus on reassurance and handholding are important tools used to develop relationships with customers. These tools and techniques help increase the tangibility of a weddings abroad package. Clusters of complementary services that are synergistic and provide sources of competitive advantage are identified and an agenda for future research is developed
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