45 research outputs found
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
Long-Lived Ultracold Molecules with Electric and Magnetic Dipole Moments
We create fermionic dipolar NaLi molecules in their triplet ground
state from an ultracold mixture of Na and Li. Using
magneto-association across a narrow Feshbach resonance followed by a two-photon
STIRAP transfer to the triplet ground state, we produce
ground state molecules in a spin-polarized state. We observe a lifetime of
in an isolated molecular sample, approaching the -wave
universal rate limit. Electron spin resonance spectroscopy of the triplet state
was used to determine the hyperfine structure of this previously unobserved
molecular state.Comment: 5 pages, 5 figure
Photoassociation of Ultracold NaLi
We perform photoassociation spectroscopy in an ultracold Na-Li
mixture to study the excited triplet molecular potential. We
observe 50 vibrational states and their substructure to an accuracy of 20 MHz,
and provide line strength data from photoassociation loss measurements. An
analysis of the vibrational line positions using near-dissociation expansions
and a full potential fit is presented. This is the first observation of the
potential, as well as photoassociation in the NaLi system.Comment: 6 pages, 3 figure
New Directions in Degenerate Dipolar Molecules via Collective Association
We survey results on the creation of heteronuclear Fermi molecules by tuning
a degenerate Bose-Fermi mixture into the neighborhood of an association
resonance, either photoassociation or Feshbach, as well as the subsequent
prospects for Cooper-like pairing between atoms and molecules. In the simplest
case of only one molecular state, corresponding to either a Feshbach resonance
or one-color photoassociation, the system displays Rabi oscillations and rapid
adiabatic passage between a Bose-Fermi mixture of atoms and fermionic
molecules. For two-color photoassociation, the system admits stimulated Raman
adiabatic passage (STIRAP) from a Bose-Fermi mixture of atoms to stable Fermi
molecules, even in the presence of particle-particle interactions. By tailoring
the STIRAP sequence it is possible to deliberately convert only a fraction of
the initial atoms, leaving a finite fraction of bosons behind to induce
atom-molecule Cooper pairing via density fluctuations; unfortunately, this
enhancement is insufficient to achieve a superfluid transition with present
ultracold technology. We therefore propose the use of an association resonance
that converts atoms and diatomic molecules (dimers) into triatomic molecules
(trimers), which leads to a crossover from a Bose-Einstein condensate of
trimers to atom-dimer Cooper pairs. Because heteronuclear dimers may possess a
permanent electric dipole moment, this overall system presents an opportunity
to investigate novel microscopic physics.Comment: 10 pages, 5 figures, 77+ references, submitted to Euro. Phys. J.
topical issue on "Ultracold Polar Molecules: Formation and Collisions
Photoassociation inside an optical dipole trap: absolute rate coefficients and Franck-Condon factors
We present quantitative measurements of the photoassociation of cesium
molecules inside a far-detuned optical dipole trap. A model of the trap
depletion dynamics is derived which allows to extract absolute photoassociation
rate coefficients for the initial single-photon photoassociation step from
measured trap-loss spectra. The sensitivity of this approach is demonstrated by
measuring the Franck-Condon modulation of the weak photoassociation transitions
into the low vibrational levels of the outer well of the 0g- state that
correlates to the 6s+6p3/2 asymptote. The measurements are compared to
theoretical predictions. In a magneto-optical trap these transitions have
previously only been observed indirectly through ionization of ground state
molecules
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
Feynman diagrams versus Fermi-gas Feynman emulator
Precise understanding of strongly interacting fermions, from electrons in
modern materials to nuclear matter, presents a major goal in modern physics.
However, the theoretical description of interacting Fermi systems is usually
plagued by the intricate quantum statistics at play. Here we present a
cross-validation between a new theoretical approach, Bold Diagrammatic Monte
Carlo (BDMC), and precision experiments on ultra-cold atoms. Specifically, we
compute and measure with unprecedented accuracy the normal-state equation of
state of the unitary gas, a prototypical example of a strongly correlated
fermionic system. Excellent agreement demonstrates that a series of Feynman
diagrams can be controllably resummed in a non-perturbative regime using BDMC.
This opens the door to the solution of some of the most challenging problems
across many areas of physics
Many-Body Physics with Ultracold Gases
This article reviews recent experimental and theoretical progress on
many-body phenomena in dilute, ultracold gases. Its focus are effects beyond
standard weak-coupling descriptions, like the Mott-Hubbard-transition in
optical lattices, strongly interacting gases in one and two dimensions or
lowest Landau level physics in quasi two-dimensional gases in fast rotation.
Strong correlations in fermionic gases are discussed in optical lattices or
near Feshbach resonances in the BCS-BEC crossover.Comment: revised version, accepted for publication in Rev. Mod. Phy
Variational Monte Carlo analysis of the Hubbard model with a confining potential: one-dimensional fermionic optical lattice systems
We investigate the one-dimensional Hubbard model with a confining potential,
which may describe cold fermionic atoms trapped in an optical lattice.
Combining the variational Monte Carlo simulations with the new stochastic
reconfiguration scheme proposed by Sorella, we present an efficient method to
systematically treat the ground state properties of the confined system with a
site-dependent potential. By taking into account intersite correlations as well
as site-dependent on-site correlations, we are able to describe the coexistence
of the metallic and Mott insulating regions, which is consistent with other
numerical results. Several possible improvements of the trial states are also
addressed.Comment: 7 pages, 15 figures; removed unnecessary graphs (p.8-p.32 in the old
version are removed