667 research outputs found
Density modulations in an elongated Bose-Einstein condensate released from a disordered potential
We observe large density modulations in time-of-flight images of elongated
Bose-Einstein condensates, initially confined in a harmonic trap and in the
presence of weak disorder. The development of these modulations during the
time-of-flight and their dependence with the disorder are investigated. We
render an account of this effect using numerical and analytical calculations.
We conclude that the observed large density modulations originate from the weak
initial density modulations induced by the disorder, and not from initial phase
fluctuations (thermal or quantum).Comment: Published version; 4+ pages; 4 figure
Quantum glass phases in the disordered Bose-Hubbard model
The phase diagram of the Bose-Hubbard model in the presence of off-diagonal
disorder is determined using Quantum Monte Carlo simulations. A sequence of
quantum glass phases intervene at the interface between the Mott insulating and
the Superfluid phases of the clean system. In addition to the standard Bose
glass phase, the coexistence of gapless and gapped regions close to the Mott
insulating phase leads to a novel Mott glass regime which is incompressible yet
gapless. Numerical evidence for the properties of these phases is given in
terms of global (compressibility, superfluid stiffness) and local
(compressibility, momentum distribution) observables
Optimal quantum control of Bose Einstein condensates in magnetic microtraps
Transport of Bose-Einstein condensates in magnetic microtraps, controllable
by external parameters such as wire currents or radio-frequency fields, is
studied within the framework of optimal control theory (OCT). We derive from
the Gross-Pitaevskii equation the optimality system for the OCT fields that
allow to efficiently channel the condensate between given initial and desired
states. For a variety of magnetic confinement potentials we study transport and
wavefunction splitting of the condensate, and demonstrate that OCT allows to
drastically outperfrom more simple schemes for the time variation of the
microtrap control parameters.Comment: 11 pages, 7 figure
Mach-Zehnder interferometry with interacting trapped Bose-Einstein condensates
We theoretically analyze a Mach-Zehnder interferometer with trapped
condensates, and find that it is surprisingly stable against the nonlinearity
induced by inter-particle interactions. The phase sensitivity, which we study
for number squeezed input states, can overcome the shot noise limit and be
increased up to the Heisenberg limit provided that a Bayesian or
Maximum-Likelihood phase estimation strategy is used. We finally demonstrate
robustness of the Mach-Zehnder interferometer in presence of interactions
against condensate oscillations and a realistic atom counting error.Comment: 4 pages, 5 figures, minor revision
Trapping and manipulating neutral atoms with electrostatic fields
We report on experiments with cold thermal Li atoms confined in combined
magnetic and electric potentials. A novel type of three-dimensional trap was
formed by modulating a magnetic guide using electrostatic fields. We observed
atoms trapped in a string of up to six individual such traps, a controlled
transport of an atomic cloud over a distance of 400m, and a dynamic
splitting of a single trap into a double well potential. Applications for
quantum information processing are discussed.Comment: 4 pages, 4 figure
Superfluidity versus Anderson localization in a dilute Bose gas
We consider the motion of a quasi one dimensional beam of Bose-Einstein
condensed particles in a disordered region of finite extent. Interaction
effects lead to the appearance of two distinct regions of stationary flow. One
is subsonic and corresponds to superfluid motion. The other one is supersonic,
dissipative and shows Anderson localization. We compute analytically the
interaction-dependent localization length. We also explain the disappearance of
the supersonic stationary flow for large disordered samples.Comment: 4 pages, 3 figures, final published versio
Spontaneous creation of non-zero angular momentum modes in tunnel-coupled two-dimensional degenerate Bose gases
We investigate the dynamics of two tunnel-coupled two-dimensional degenerate
Bose gases. The reduced dimensionality of the clouds enables us to excite
specific angular momentum modes by tuning the coupling strength, thereby
creating striking patterns in the atom density profile. The extreme sensitivity
of the system to the coupling and initial phase difference results in a rich
variety of subsequent dynamics, including vortex production, complex
oscillations in relative atom number and chiral symmetry breaking due to
counter-rotation of the two clouds.Comment: 7 pages, 5 figure
Spectral Properties and Lifetimes of Neutral Spin-1/2-Fermions in a Magnetic Guide
We investigate the resonant motion of neutral spin-1/2-fermions in a magnetic
guide. A wealth of unitary and anti-unitary symmetries is revealed in
particular giving rise to a two-fold degeneracy of the energy levels. To
compute the energies and decay widths of a large number of resonances the
complex scaling method is employed. We discuss the dependence of the lifetimes
on the angular momentum of the resonance states. In this context the existence
of so-called quasi-bound states is shown. In order to approximately calculate
the resonance energies of such states a radial Schr\"odinger equation is
derived which improves the well-known adiabatic approximation. The effects of
an additionally applied homogeneous Ioffe field on the resonance energies and
decay widths are also considered. The results are applied to the case of the
atom in the hyperfine ground state.Comment: accepted for publication in PR
Trapping atoms on a transparent permanent-magnet atom chip
We describe experiments on trapping of atoms in microscopic magneto-optical
traps on an optically transparent permanent-magnet atom chip. The chip is made
of magnetically hard ferrite-garnet material deposited on a dielectric
substrate. The confining magnetic fields are produced by miniature magnetized
patterns recorded in the film by magneto-optical techniques. We trap Rb atoms
on these structures by applying three crossed pairs of counter-propagating
laser beams in the conventional magneto-optical trapping (MOT) geometry. We
demonstrate the flexibility of the concept in creation and in-situ modification
of the trapping geometries through several experiments.Comment: Modifications: A) Reference I. Barb et al., Eur. Phys. JD, 35, 75
(2005) added. B)Sentence rewritten: We routinely capture more than 10^6 atoms
in a micro-MOT on a magnetized pattern. C) The magnetic field strengths are
now given in Teslas. D) The second sentence in the fourth paragraph has been
rewritten in order to more clearly describe the geometry and purpose of the
compensation coils.E) In the seventh paragraph we have rewritten the sentence
about the creation of the external magnetic field for the magnetic-domain
patterning. F) In the ninth paragraph, we clarify the way to shift the trap
center. G) Caption of Fig. 4 changed. H) We have modified paragraph 12 to
improve the description on the guiding of the trap center along a toroidal
pattern. I) The last two sentences of the manuscript have been rewritte
Trapping cold atoms using surface-grown carbon nanotubes
We present a feasibility study for loading cold atomic clouds into magnetic
traps created by single-wall carbon nanotubes grown directly onto dielectric
surfaces. We show that atoms may be captured for experimentally sustainable
nanotube currents, generating trapped clouds whose densities and lifetimes are
sufficient to enable detection by simple imaging methods. This opens the way
for a novel type of conductor to be used in atomchips, enabling atom trapping
at sub-micron distances, with implications for both fundamental studies and for
technological applications
- …