83 research outputs found
Observation of heteronuclear atomic Efimov resonances
The Efimov effect represents a cornerstone in few-body physics. Building on
the recent experimental observation with ultracold atoms, we report the first
experimental signature of Efimov physics in a heteronuclear system. A mixture
of K and Rb atoms was cooled to few hundred nanoKelvins and
stored in an optical dipole trap. Exploiting a broad interspecies Feshbach
resonance, the losses due to three-body collisions were studied as a function
of the interspecies scattering length. We observe an enhancement of the
three-body collisions for three distinct values of the interspecies scattering
lengths, both positive and negative. We attribute the two features at negative
scattering length to the existence of two kind of Efimov trimers, namely KKRb
and KRbRb.Comment: 4 pages, 4 figure
Radio Frequency Selective Addressing of Localized Particles in a Periodic Potential
We study the localization and addressability of ultra cold atoms in a
combined parabolic and periodic potential. Such a potential supports the
existence of localized stationary states and we show that using a radio
frequency field allows to selectively address the atoms in these states. This
method is used to measure the energy and momentum distribution of the atoms in
the localized states. We also discuss possible extensions of this scheme to
address and manipulate particles in single lattice sites.Comment: 4 pages, 4 figure
Quantum normal-to-inhomogeneous superconductor phase transition in nearly two-dimensional metals
In multi-band systems, electrons from different orbitals coexist at the Fermi
surface. An attractive interaction among these quasi-particles gives rise to
inter-band or hybrid pairs which eventually condense in a superconducting
state. These quasi-particles have a natural mismatch of their Fermi
wave-vectors, , which depends on the strength of the hybridization
between their orbitals. The existence of this natural scale suggests the
possibility of inhomogeneous superconducting ground states in these systems,
even in the absence of an applied magnetic field. Furthermore, since
hybridization depends on pressure, this provides an external parameter to
control the wave-vectors mismatch at the Fermi surface. In this work, we study
the phase diagram of a two-dimensional, two-band metal with inter-band pairing.
We show that as the mismatch between the Fermi wave-vectors of the two hybrid
bands is reduced, the system presents a normal-to-inhomogeneous superconductor
quantum phase transition at a critical value of the hybridization
. The superconducting ground state for is characterized
by a wave-vector with magnitude . Here
is the superconducting gap in the homogeneous state and
the average Fermi velocity. We discuss the nature of the quantum critical point
(QCP) at and obtain the associated quantum critical exponents.Comment: 6 pages, 4 figure
Effect of optical disorder and single defects on the expansion of a Bose-Einstein condensate in a one-dimensional waveguide
We investigate the one-dimensional expansion of a Bose-Einstein condensate in
an optical guide in the presence of a random potential created with optical
speckles. With the speckle the expansion of the condensate is strongly
inhibited. A detailed investigation has been carried out varying the
experimental conditions and checking the expansion when a single optical defect
is present. The experimental results are in good agreement with numerical
calculations based on the Gross-Pitaevskii equation.Comment: 5 pages, 5 figure
Disorder-enhanced phase coherence in trapped bosons on optical lattices
The consequences of disorder on interacting bosons trapped in optical
lattices are investigated by quantum Monte Carlo simulations. At small to
moderate strengths of potential disorder a unique effect is observed: if there
is a Mott plateau at the center of the trap in the clean limit, phase coherence
{\it increases} as a result of disorder. The localization effects due to
correlation and disorder compete against each other, resulting in a partial
delocalization of the particles in the Mott region, which in turn leads to
increased phase coherence. In the absence of a Mott plateau, this effect is
absent. A detailed analysis of the uniform system without a trap shows that the
disordered states participate in a Bose glass phase.Comment: 4 pages, 4 figure
Three fermions in a box at the unitary limit: universality in a lattice model
We consider three fermions with two spin components interacting on a lattice
model with an infinite scattering length. Low lying eigenenergies in a cubic
box with periodic boundary conditions, and for a zero total momentum, are
calculated numerically for decreasing values of the lattice period. The results
are compared to the predictions of the zero range Bethe-Peierls model in
continuous space, where the interaction is replaced by contact conditions. The
numerical computation, combined with analytical arguments, shows the absence of
negative energy solution, and a rapid convergence of the lattice model towards
the Bethe-Peierls model for a vanishing lattice period. This establishes for
this system the universality of the zero interaction range limit.Comment: 6 page
Frequency metrology of helium around 1083 nm and determination of the nuclear charge radius
We measure the absolute frequency of seven out of the nine allowed
transitions between the 2{\it S} and 2{\it P} hyperfine manifolds in a
metastable He beam by using an optical frequency comb synthesizer-assisted
spectrometer. The relative uncertainty of our measurements ranges from to , which is, to our knowledge, the most precise
result for any optical He transition to date. The resulting {\it
P}-2{\it S} centroid frequency is kHz.
Comparing this value with the known result for the He centroid and
performing {\em ab initio} QED calculations of the He-He isotope shift,
we extract the difference of the squared nuclear charge radii of
He and He. Our result for fm disagrees by
about with the recent determination [R. van Rooij {\em et al.},
Science {\bf 333}, 196 (2011)].Comment: 4 pages, 3 figures, 3 table
Atomic wave packet dynamics in finite time-dependent optical lattices
Atomic wave packets in optical lattices which are both spatially finite and
time-dependent exhibit many striking similarities with light pulses in photonic
crystals. We analytically characterize the transmission properties of such a
potential geometry for an ideal gas in terms of a position-dependent band
structure. In particular, we find that at specific energies, wave packets at
the center of the finite lattice may be enclosed by pairs of band gaps. These
act as mirrors between which the atomic wave packet is reflected, thereby
effectively yielding a matter wave cavity. We show that long trapping times may
be obtained in such a resonator and investigate the collapse and revival
dynamics of the atomic wave packet by numerical evaluation of the Schr\"odinger
equation
Physics with Coherent Matter Waves
This review discusses progress in the new field of coherent matter waves, in
particular with respect to Bose-Einstein condensates. We give a short
introduction to Bose-Einstein condensation and the theoretical description of
the condensate wavefunction. We concentrate on the coherence properties of this
new type of matter wave as a basis for fundamental physics and applications.
The main part of this review treats various measurements and concepts in the
physics with coherent matter waves. In particular we present phase manipulation
methods, atom lasers, nonlinear atom optics, optical elements, interferometry
and physics in optical lattices. We give an overview of the state of the art in
the respective fields and discuss achievements and challenges for the future
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