139 research outputs found
Transport of Bose-Einstein Condensates with Optical Tweezers
We have transported gaseous Bose-Einstein condensates over distances up to 44
cm. This was accomplished by trapping the condensate in the focus of an
infrared laser and translating the location of the laser focus with controlled
acceleration. Condensates of order 1 million atoms were moved into an auxiliary
chamber and loaded into a magnetic trap formed by a Z-shaped wire. This
transport technique avoids the optical and mechanical access constraints of
conventional condensate experiments and creates many new scientific
opportunities.Comment: 5 pages, 3 figure
Statistical Properties of Interacting Bose Gases in Quasi-2D Harmonic Traps
The analytical probability distribution of the quasi-2D (and purely 2D) ideal
and interacting Bose gas are investigated by using a canonical ensemble
approach. Using the analytical probability distribution of the condensate, the
statistical properties such as the mean occupation number and particle number
fluctuations of the condensate are calculated. Researches show that there is a
continuous crossover of the statistical properties from a quasi-2D to a purely
2D ideal or interacting gases. Different from the case of a 3D Bose gas, the
interaction between atoms changes in a deep way the nature of the particle
number fluctuations.Comment: RevTex, 10pages, 4 figures, E-mail: [email protected]
Spatial separation in a thermal mixture of ultracold Yb and Rb atoms
We report on the observation of unusually strong interactions in a thermal
mixture of ultracold atoms which cause a significant modification of the
spatial distribution. A mixture of Rb and Yb with a temperature
of a few K is prepared in a hybrid trap consisting of a bichromatic
optical potential superimposed on a magnetic trap. For suitable trap parameters
and temperatures, a spatial separation of the two species is observed. We infer
that the separation is driven by a large interaction strength between
Yb and Rb accompanied by a large three-body recombination rate.
Based on this assumption we have developed a diffusion model which reproduces
our observations
Topological vortex formation in a Bose-Einstein condensate
Vortices were imprinted in a Bose-Einstein condensate using topological
phases. Sodium condensates held in a Ioffe-Pritchard magnetic trap were
transformed from a non-rotating state to one with quantized circulation by
adiabatically inverting the magnetic bias field along the trap axis. Using
surface wave spectroscopy, the axial angular momentum per particle of the
vortex states was found to be consistent with or , depending
on the hyperfine state of the condensate.Comment: 5 pages, 3 figure
Damping of spin waves and singularity of the longitudinal modes in the dipolar critical regime of the Heisenberg-ferromagnet EuS
By inelastic scattering of polarized neutrons near the (200)-Bragg
reflection, the susceptibilities and linewidths of the spin waves and the
longitudinal spin fluctuations were determined separately. By aligning the
momentum transfers q perpendicular to both \delta S_sw and the spontaneous
magnetization M_s, we explored the statics and dynamics of these modes with
transverse polarizations with respect to q. In the dipolar critical regime,
where the inverse correlation length kappa_z(T) and q are smaller than the
dipolar wavenumber q_d, we observe:(i) the static susceptibility of \delta
S_sw^T(q) displays the Goldstone divergence while for \delta S_z^T(q) the
Ornstein-Zernicke shape fits the data with a possible indication of a
thermal(mass-)renormalization at the smallest q-values, i.e. we find
indications for the predicted 1/q divergence of the longitudinal
susceptibility; (ii) the spin wave dispersion as predicted by the
Holstein-Primakoff theory revealing q_d=0.23(1)\AA^{-1}in good agreement with
previous work in the paramagnetic and ferromagnetic regime of EuS; (iii) within
experimental error, the (Lorentzian) linewidths of both modes turn out to be
identical with respect to the q^2-variation, the temperature independence and
the absolute magnitude. Due to the linear dispersion of the spin waves they
remain underdamped for q<q_d. These central results differ significantly from
the well known exchange dominated critical dynamics, but are quantitatively
explained in terms of dynamical scaling and existing data for T>=T_C. The
available mode-mode coupling theory, which takes the dipolar interactions fully
into account, describes the gross features of the linewidths but not all
details of the T- and q-dependencies. PACS: 68.35.Rh, 75.40.GbComment: 10 pages, 7 figure
Two-species mixture of quantum degenerate Bose and Fermi gases
We have produced a macroscopic quantum system in which a Li-6 Fermi sea
coexists with a large and stable Na-23 Bose-Einstein condensate. This was
accomplished using inter-species sympathetic cooling of fermionic Li-6 in a
thermal bath of bosonic Na-23
Quantum gates with topological phases
We investigate two models for performing topological quantum gates with the
Aharonov-Bohm (AB) and Aharonov-Casher (AC) effects. Topological one- and
two-qubit Abelian phases can be enacted with the AB effect using charge qubits,
whereas the AC effect can be used to perform all single-qubit gates (Abelian
and non-Abelian) for spin qubits. Possible experimental setups suitable for a
solid state implementation are briefly discussed.Comment: 2 figures, RevTex
Wave Packet Echoes in the Motion of Trapped Atoms
We experimentally demonstrate and systematically study the stimulated revival
(echo) of motional wave packet oscillations. For this purpose, we prepare wave
packets in an optical lattice by non-adiabatically shifting the potential and
stimulate their reoccurence by a second shift after a variable time delay. This
technique, analogous to spin echoes, enables one even in the presence of strong
dephasing to determine the coherence time of the wave packets. We find that for
strongly bound atoms it is comparable to the cooling time and much longer than
the inverse of the photon scattering rate
- …