213 research outputs found
Phonon background versus analogue Hawking radiation in Bose-Einstein condensates
We determine the feasibility of detecting analogue Hawking radiation in a
Bose-Einstein condensate in the presence of atom loss induced heating. We find
that phonons created by three-body losses overshadow those due to analogue
Hawking radiation. To overcome this problem, three-body losses may have to be
suppressed, for example as proposed by Search et al. [Phys. Rev. Lett. 92
140401 (2004)]. The reduction of losses to a few percent of their normal rate
is typically sufficient to suppress the creation of loss phonons on the time
scale of a fast analogue Hawking phonon detection.Comment: 4 pages, no figures, revised versio
Quantum-field dynamics of expanding and contracting Bose-Einstein condensates
We analyze the dynamics of quantum statistics in a harmonically trapped
Bose-Einstein condensate, whose two-body interaction strength is controlled via
a Feshbach resonance. From an initially non-interacting coherent state, the
quantum field undergoes Kerr squeezing, which can be qualitatively described
with a single mode model. To render the effect experimentally accessible, we
propose a homodyne scheme, based on two hyperfine components, which converts
the quadrature squeezing into number squeezing. The scheme is numerically
demonstrated using a two-component Hartree-Fock-Bogoliubov formalism.Comment: 9 pages, 4 figure
Excitation transport through Rydberg dressing
We show how to create long range interactions between alkali-atoms in
different hyper-fine ground states, allowing coherent electronic quantum state
migration. The scheme uses off resonant dressing with atomic Rydberg states,
exploiting the dipole-dipole excitation transfer that is possible between
those. Actual population in the Rydberg state is kept small. Dressing offers
large advantages over the direct use of Rydberg levels: It reduces ionisation
probabilities and provides an additional tuning parameter for life-times and
interaction-strengths. We present an effective Hamiltonian for the ground-state
manifold and show that it correctly describes the full multi-state dynamics for
up to 5 atoms.Comment: 22 pages + 6 pages appendices, 8 figures, replaced with revised
version, added journal referenc
Newton's cradle and entanglement transport in a flexible Rydberg chain
In a regular, flexible chain of Rydberg atoms, a single electronic excitation
localizes on two atoms that are in closer mutual proximity than all others. We
show how the interplay between excitonic and atomic motion causes electronic
excitation and diatomic proximity to propagate through the Rydberg chain as a
combined pulse. In this manner entanglement is transferred adiabatically along
the chain, reminiscent of momentum transfer in Newton's cradle.Comment: 4 pages, 3 figures. Revised versio
Supersonic optical tunnels for Bose-Einstein condensates
We propose a method for the stabilisation of a stack of parallel vortex rings
in a Bose-Einstein condensate. The method makes use of a hollow laser beam
containing an optical vortex. Using realistic experimental parameters we
demonstrate numerically that our method can stabilise up to 9 vortex rings.
Furthermore we point out that the condensate flow through the tunnel formed by
the core of the optical vortex can be made supersonic by inserting a
laser-generated hump potential. We show that long-living immobile condensate
solitons generated in the tunnel exhibit sonic horizons. Finally, we discuss
prospects of using these solitons for analogue gravity experiments.Comment: 14 pages, 3 figures, published versio
Limits to the analogue Hawking temperature in a Bose-Einstein condensate
Quasi-one dimensional outflow from a dilute gas Bose-Einstein condensate
reservoir is a promising system for the creation of analogue Hawking radiation.
We use numerical modeling to show that stable sonic horizons exist in such a
system under realistic conditions, taking into account the transverse
dimensions and three-body loss. We find that loss limits the analogue Hawking
temperatures achievable in the hydrodynamic regime, with sodium condensates
allowing the highest temperatures. A condensate of 30,000 atoms, with
transverse confinement frequency omega_perp=6800*2*pi Hz, yields horizon
temperatures of about 20 nK over a period of 50 ms. This is at least four times
higher than for other atoms commonly used for Bose-Einstein condensates.Comment: 9 pages, 4 figures, replaced with published versio
Adiabatic entanglement transport in Rydberg aggregates
We consider the interplay between excitonic and atomic motion in a regular,
flexible chain of Rydberg atoms, extending our recent results on entanglement
transport in Rydberg chains [W\"uster et al., Phys.Rev.Lett 105 053004 (2010)].
In such a Rydberg chain, similar to molecular aggregates, an electronic
excitation is delocalised due to long range dipole-dipole interactions among
the atoms. The transport of an exciton that is initially trapped by a chain
dislocation is strongly coupled to nuclear dynamics, forming a localised pulse
of combined excitation and displacement. This pulse transfers entanglement
between dislocated atoms adiabatically along the chain. Details about the
interaction and the preparation of the initial state are discussed. We also
present evidence that the quantum dynamics of this complex many-body problem
can be accurately described by selected quantum-classical methods, which
greatly simplify investigations of excitation transport in flexible chains
Collapsing Bose-Einstein condensates beyond the Gross-Pitaevskii approximation
We analyse quantum field models of the bosenova experiment, in which
Rb Bose-Einstein condensates were made to collapse by switching their
atomic interactions from repulsive to attractive. Specifically, we couple the
lowest order quantum field correlation functions to the Gross-Pitaevskii
function, and solve the resulting dynamical system numerically. Comparing the
computed collapse times with the experimental measurements, we find that the
calculated times are much larger than the measured values. The addition of
quantum field corrections does not noticeably improve the agreement compared to
a pure Gross-Pitaevskii theory.Comment: 8 pages, 4 figure
Multi-component gap solitons in spinor Bose-Einstein condensates
We model the nonlinear behaviour of spin-1 Bose-Einstein condensates (BECs)
with repulsive spin-independent interactions and either ferromagnetic or
anti-ferromagnetic (polar) spin-dependent interactions, loaded into a
one-dimensional optical lattice potential. We show that both types of BECs
exhibit dynamical instabilities and may form spatially localized
multi-component structures. The localized states of the spinor matter waves
take the form of vector gap solitons and self-trapped waves that exist only
within gaps of the linear Bloch-wave band-gap spectrum. Of special interest are
the nonlinear localized states that do not exhibit a common spatial density
profile shared by all condensate components, and consequently cannot be
described by the single mode approximation (SMA), frequently employed within
the framework of the mean-field treatment. We show that the non-SMA states can
exhibits Josephson-like internal oscillations and self-magnetisation, i.e.
intrinsic precession of the local spin. Finally, we demonstrate that
non-stationary states of a spinor BEC in a lattice exhibit coherent undamped
spin-mixing dynamics, and that their controlled conversion into a stationary
state can be achieved by the application of an external magnetic field.Comment: 12 pages, 13 figure
Dynamical formation and interaction of bright solitary waves and solitons in the collapse of Bose-Einstein condensates with attractive interactions
We model the dynamics of formation of multiple, long-lived, bright solitary
waves in the collapse of Bose-Einstein condensates with attractive interactions
as studied in the experiment of Cornish et al. [Phys. Rev. Lett. 96 (2006)
170401]. Using both mean-field and quantum field simulation techniques, we find
that while a number of separated wave packets form as observed in the
experiment, they do not have a repulsive \pi phase difference that has been
previously inferred. We observe that the inclusion of quantum fluctuations
causes soliton dynamics to be predominantly repulsive in one dimensional
simulations independent of their initial relative phase. However, indicative
three-dimensional simulations do not support this conclusion and in fact show
that quantum noise has a negative impact on bright solitary wave lifetimes.
Finally, we show that condensate oscillations, after the collapse, may serve to
deduce three-body recombination rates, and that the remnant atom number may
still exceed the critical number for collapse for as long as three seconds
independent of the relative phases of the bright solitary waves.Comment: 14 pages, 5 figure
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