43 research outputs found
Atomic Interactions in Precision Interferometry Using Bose-Einstein Condensates
We present theoretical tools for predicting and reducing the effects of
atomic interactions in Bose-Einstein condensate (BEC) interferometry
experiments. To address mean-field shifts during free propagation, we derive a
robust scaling solution that reduces the three-dimensional Gross-Pitaevskii
equation to a set of three simple differential equations valid for any
interaction strength. To model the other common components of a BEC
interferometer---condensate splitting, manipulation, and recombination---we
generalize the slowly-varying envelope reduction, providing both analytic
handles and dramatically improved simulations. Applying these tools to a BEC
interferometer to measure the fine structure constant (Gupta, et al., 2002), we
find agreement with the results of the original experiment and demonstrate that
atomic interactions do not preclude measurement to better than part-per-billion
accuracy, even for atomic species with relatively large scattering lengths.
These tools help make BEC interferometry a viable choice for a broad class of
precision measurements.Comment: 8 pages, 6 figures, revised based on reviewer comment
Quantum Degenerate Mixture of Ytterbium and Lithium Atoms
We have produced a quantum degenerate mixture of fermionic alkali 6Li and
bosonic spin-singlet 174Yb gases. This was achieved using sympathetic cooling
of lithium atoms by evaporatively cooled ytterbium atoms in a far-off-resonant
optical dipole trap. We observe co-existence of Bose condensed (T/T_c~0.8)
174Yb with 2.3*10^4 atoms and Fermi degenerate (T/T_F~0.3) 6Li with 1.2*10^4
atoms. Quasipure Bose-Einstein condensates of up to 3*10^4 174Yb atoms can be
produced in single-species experiments. Our results mark a significant step
toward studies of few and many-body physics with mixtures of alkali and
alkaline-earth-like atoms, and for the production of paramagnetic polar
molecules in the quantum regime. Our methods also establish a convenient scheme
for producing quantum degenerate ytterbium atoms in a 1064nm optical dipole
trap.Comment: 4 pages, 3 figure
Two-Photon Spectroscopy of the NaLi Triplet Ground State
We employ two-photon spectroscopy to study the vibrational states of the
triplet ground state potential () of the NaLi
molecule. Pairs of Na and Li atoms in an ultracold mixture are photoassociated
into an excited triplet molecular state, which in turn is coupled to
vibrational states of the triplet ground potential. Vibrational state binding
energies, line strengths, and potential fitting parameters for the triplet
ground potential are reported. We also observe rotational
splitting in the lowest vibrational state.Comment: 7 pages, 3 figure
Collisional Cooling of Ultracold Molecules
Since the original work on Bose-Einstein condensation, quantum degenerate
gases of atoms have allowed the quantum emulation of important systems from
condensed matter and nuclear physics, as well as the study of novel many-body
states with no analog in other fields of physics. Ultracold molecules in the
micro- and nano-Kelvin regimes promise to bring powerful new capabilities to
quantum emulation and quantum computing, thanks to their rich internal degrees
of freedom compared to atoms. They also open new possibilities for precision
measurement and the study of quantum chemistry. Quantum gases of atoms were
made possible by collision-based cooling schemes, such as evaporative cooling.
For ultracold molecules, thermalization and collisional cooling have not been
realized. With other techniques such as supersonic jets and cryogenic buffer
gases, studies have been limited to temperatures above 10 mK. Here we show
cooling of NaLi molecules at micro- and nano-Kelvin temperatures through
collisions with ultracold Na atoms, both prepared in their stretched hyperfine
spin states. We find a lower bound on the elastic to inelastic collision ratio
between molecules and atoms greater than 50 -- large enough to support
sustained collisional cooling. By employing two stages of evaporation, we
increase the phase-space density (PSD) of the molecules by a factor of 20,
achieving temperatures as low as 220 nK. The favorable collisional properties
of a Na and NaLi mixture show great promise for making deeply quantum
degenerate dipolar molecules and suggest the potential for such cooling in
other systems
Sympathetic cooling in an optically trapped mixture of alkali and spin-singlet atoms
We report on the realization of a stable mixture of ultracold lithium and
ytterbium atoms confined in a far-off-resonance optical dipole trap. We observe
sympathetic cooling of 6Li by 174Yb and extract the s-wave scattering length
magnitude |a6Li-174Yb| = (13 \pm 3)a0 from the rate of inter-species
thermalization. Using forced evaporative cooling of 174Yb, we achieve reduction
of the 6Li temperature to below the Fermi temperature, purely through
inter-species sympathetic cooling.Comment: 4 pages, 3 figure
Magnetic trapping of ultracold molecules at high density
Trapping ultracold molecules in conservative traps is essential for
applications -- such as quantum state-controlled chemistry, quantum
simulations, and quantum information processing. These applications require
high densities or phase-space densities. We report magnetic trapping of NaLi
molecules in the triplet ground state at high density () and ultralow temperature (). Magnetic
trapping at these densities allows studies on both atom-molecule and
molecule-molecule collisions in the ultracold regime in the absence of trapping
light, which has often lead to undesired photo-chemistry. We measure the
inelastic loss rates in a single spin sample and spin-mixtures of fermionic
NaLi as well as spin-stretched NaLiNa mixtures. We demonstrate sympathetic
cooling of NaLi molecules in the magnetic trap by radio frequency evaporation
of co-trapped Na atoms and observe an increase in the molecules' phase-space
density by a factor of .Comment: 8 pages, 4 figure
Spin-Orbit Coupling and Spin Textures in Optical Superlattices
We proposed and demonstrated a new approach for realizing spin orbit coupling
with ultracold atoms. We use orbital levels in a double well potential as
pseudospin states. Two-photon Raman transitions between left and right wells
induce spin-orbit coupling. This scheme does not require near resonant light,
features adjustable interactions by shaping the double well potential, and does
not depend on special properties of the atoms. A pseudospinor Bose-Einstein
condensate spontaneously acquires an antiferromagnetic pseudospin texture which
breaks the lattice symmetry similar to a supersolid