209 research outputs found
Lattice supersolid phase of strongly correlated bosons in an optical cavity
We numerically simulate strongly correlated ultracold bosons coupled to a
high-finesse cavity field, pumped by a laser beam in the transverse direction.
Assuming a weak classical optical lattice added in the cavity direction, we
model this system by a generalized Bose-Hubbard model, which is solved by means
of bosonic dynamical mean-field theory. The complete phase diagram is
established, which contains two novel self-organized quantum phases, lattice
supersolid and checkerboard solid, in addition to conventional phases such as
superfluid and Mott insulator. At finite but low temperature, thermal
fluctuations are found to enhance the buildup of the self-organized phases. We
demonstrate that cavity-mediated long-range interactions can give rise to
stable lattice supersolid and checkerboard solid phases even in the regime of
strong s-wave scattering. In the presence of a harmonic trap, we discuss
coexistence of these self-organized phases, as relevant to experiments.Comment: 4 pages, 3 figure
Dynamic Kosterlitz-Thouless transition in 2D Bose mixtures of ultra-cold atoms
We propose a realistic experiment to demonstrate a dynamic
Kosterlitz-Thouless transition in ultra-cold atomic gases in two dimensions.
With a numerical implementation of the Truncated Wigner Approximation we
simulate the time evolution of several correlation functions, which can be
measured via matter wave interference. We demonstrate that the relaxational
dynamics is well-described by a real-time renormalization group approach, and
argue that these experiments can guide the development of a theoretical
framework for the understanding of critical dynamics.Comment: 5 pages, 6 figure
Finite temperature analysis of a quasi2D dipolar gas
We present finite temperature analysis of a quasi2D dipolar gas. To do this,
we use the Hartree Fock Bogoliubov method within the Popov approximation. This
formalism is a set of non-local equations containing the dipole-dipole
interaction and the condensate and thermal correlation functions, which are
solved self-consistently. We detail the numerical method used to implement the
scheme. We present density profiles for a finite temperature dipolar gas in
quasi2D, and compare these results to a gas with zero-range interactions.
Additionally, we analyze the excitation spectrum and study the impact of the
thermal exchange
Contrast Interferometry Using Bose-Einstein Condensates to Measure h/m and the Fine Structure Constant
The kinetic energy of an atom recoiling due to absorption of a photon was
measured as a frequency using an interferometric technique called ``contrast
interferometry''. Optical standing wave pulses were used as atom-optical
elements to create a symmetric three-path interferometer with a Bose-Einstein
condensate. The recoil phase accumulated in different paths was measured using
a single-shot detection technique. The scheme allows for additional photon
recoils within the interferometer and its symmetry suppresses several random
and systematic errors including those from vibrations and ac Stark shifts. We
have measured the photon recoil frequency of sodium to ppm precision, using
a simple realization of this scheme. Plausible extensions should yield a
sufficient precision to bring within reach a ppb-level determination of
and the fine structure constant
Observation of Bose-Einstein Condensation of Molecules
We have observed Bose-Einstein condensation of molecules. When a spin mixture
of fermionic Li-6 atoms was evaporatively cooled in an optical dipole trap near
a Feshbach resonance, the atomic gas was converted into Li_2 molecules. Below
600 nK, a Bose-Einstein condensate of up to 900,000 molecules was identified by
the sudden onset of a bimodal density distribution. This condensate realizes
the limit of tightly bound fermion pairs in the crossover between BCS
superfluidity and Bose-Einstein condensation.Comment: 4 pages, 3 figure
Fifty-fold improvement in the number of quantum degenerate fermionic atoms
We have produced a quantum degenerate Li-6 Fermi gas with up to 7 x 10^7
atoms, an improvement by a factor of fifty over all previous experiments with
degenerate Fermi gases. This was achieved by sympathetic cooling with bosonic
Na-23 in the F=2, upper hyperfine ground state. We have also achieved
Bose-Einstein condensation of F=2 sodium atoms by direct evaporation
Quantum degenerate Bose-Fermi mixture of chemically different atomic species with widely tunable interactions
We have created a quantum degenerate Bose-Fermi mixture of 23Na and 40K with
widely tunable interactions via broad interspecies Feshbach resonances. Twenty
Feshbach resonances between 23Na and 40K were identified. The large and
negative triplet background scattering length between 23Na and 40K causes a
sharp enhancement of the fermion density in the presence of a Bose condensate.
As explained via the asymptotic bound-state model (ABM), this strong background
scattering leads to a series of wide Feshbach resonances observed at low
magnetic fields. Our work opens up the prospect to create chemically stable,
fermionic ground state molecules of 23Na-40K where strong, long-range dipolar
interactions will set the dominant energy scale
Observation of Weak Collapse in a Bose-Einstein Condensate
We study the collapse of an attractive atomic Bose-Einstein condensate prepared in the uniform potential of an optical-box trap. We characterize the critical point for collapse and the collapse dynamics, observing universal behavior in agreement with theoretical expectations. Most importantly, we observe a clear experimental signature of the counterintuitive weak collapse, namely, that making the system more unstable can result in a smaller particle loss. We experimentally determine the scaling laws that govern the weak-collapse atom loss, providing a benchmark for the general theories of nonlinear wave phenomena.The GeForce GTX TITAN X used for the numerical simulations was donated by the NVIDIA Corporation. This work was supported by the Royal Society, EPSRC (Grant No. EP/ N011759/1), ERC (QBox), AFOSR, and ARO. A. L. G. and N. N. acknowledge support from Trinity College, Cambridge
Collisional properties of ultracold K-Rb mixtures
We determine the inter-species s-wave triplet scattering length a3 for all
K-Rb isotopic mixtures by measuring the cross-section for collisions between
41K and 87Rb in different temperature regimes. The positive value
a3=+163(+57,-12)a0 ensures the stability of binary 41K-87Rb Bose-Einstein
condensates. For the fermion-boson mixture 40K-87Rb we obtain a large and
negative scattering length which implies an efficient sympathetic cooling of
the fermionic species down to the degenerate regime.Comment: 4 pages, 4 figures; revised version (references added and small
changes
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