115 research outputs found
Optimal trapping wavelengths of Cs molecules in an optical lattice
The present paper aims at finding optimal parameters for trapping of Cs
molecules in optical lattices, with the perspective of creating a quantum
degenerate gas of ground-state molecules. We have calculated dynamic
polarizabilities of Cs molecules subject to an oscillating electric field,
using accurate potential curves and electronic transition dipole moments. We
show that for some particular wavelengths of the optical lattice, called "magic
wavelengths", the polarizability of the ground-state molecules is equal to the
one of a Feshbach molecule. As the creation of the sample of ground-state
molecules relies on an adiabatic population transfer from weakly-bound
molecules created on a Feshbach resonance, such a coincidence ensures that both
the initial and final states are favorably trapped by the lattice light,
allowing optimized transfer in agreement with the experimental observation
Experimental Evidence for Efimov Quantum States
Three interacting particles form a system which is well known for its complex
physical behavior. A landmark theoretical result in few-body quantum physics is
Efimov's prediction of a universal set of weakly bound trimer states appearing
for three identical bosons with a resonant two-body interaction. Surprisingly,
these states even exist in the absence of a corresponding two-body bound state
and their precise nature is largely independent of the particular type of the
two-body interaction potential. Efimov's scenario has attracted great interest
in many areas of physics; an experimental test however has not been achieved.
We report the observation of an Efimov resonance in an ultracold thermal gas of
cesium atoms. The resonance occurs in the range of large negative two-body
scattering lengths and arises from the coupling of three free atoms to an
Efimov trimer. We observe its signature as a giant three-body recombination
loss when the strength of the two-body interaction is varied near a Feshbach
resonance. This resonance develops into a continuum resonance at non-zero
collision energies, and we observe a shift of the resonance position as a
function of temperature. We also report on a minimum in the recombination loss
for positive scattering lengths, indicating destructive interference of decay
pathways. Our results confirm central theoretical predictions of Efimov physics
and represent a starting point from which to explore the universal properties
of resonantly interacting few-body systems.Comment: 8 pages, 4 figures, Proceedings of ICAP-2006 (Innsbruck
Creating artificial magnetic fields for cold atoms by photon-assisted tunneling
This paper proposes a simple setup for introducing an artificial magnetic
field for neutral atoms in 2D optical lattices. This setup is based on the
phenomenon of photon-assisted tunneling and involves a low-frequency periodic
driving of the optical lattice. This low-frequency driving does not affect the
electronic structure of the atom and can be easily realized by the same means
which employed to create the lattice. We also address the problem of detecting
this effective magnetic field. In particular, we study the center of mass
wave-packet dynamics, which is shown to exhibit certain features of cyclotron
dynamics of a classical charged particle.Comment: EPL-style, 8 pages, 4 figure
Dark resonances for ground state transfer of molecular quantum gases
One possible way to produce ultracold, high-phase-space-density quantum gases
of molecules in the rovibronic ground state is given by molecule association
from quantum-degenerate atomic gases on a Feshbach resonance and subsequent
coherent optical multi-photon transfer into the rovibronic ground state. In
ultracold samples of Cs_2 molecules, we observe two-photon dark resonances that
connect the intermediate rovibrational level |v=73,J=2> with the rovibrational
ground state |v=0,J=0> of the singlet ground state potential.
For precise dark resonance spectroscopy we exploit the fact that it is possible
to efficiently populate the level |v=73,J=2> by two-photon transfer from the
dissociation threshold with the stimulated Raman adiabatic passage (STIRAP)
technique. We find that at least one of the two-photon resonances is
sufficiently strong to allow future implementation of coherent STIRAP transfer
of a molecular quantum gas to the rovibrational ground state |v=0,J=0>.Comment: 7 pages, 4 figure
Formation of ultracold RbCs molecules by photoassociation
The formation of ultracold metastable RbCs molecules is observed in a double
species magneto-optical trap through photoassociation below the
^85Rb(5S_1/2)+^133Cs(6P_3/2) dissociation limit followed by spontaneous
emission. The molecules are detected by resonance enhanced two-photon
ionization. Using accurate quantum chemistry calculations of the potential
energy curves and transition dipole moment, we interpret the observed
photoassociation process as occurring at short internuclear distance, in
contrast with most previous cold atom photoassociation studies. The vibrational
levels excited by photoassociation belong to the 5th 0^+ or the 4th 0^-
electronic states correlated to the Rb(5P_1/2,3/2)+Cs(6S_1/2) dissociation
limit. The computed vibrational distribution of the produced molecules shows
that they are stabilized in deeply bound vibrational states of the lowest
triplet state. We also predict that a noticeable fraction of molecules is
produced in the lowest level of the electronic ground state
Evidence for Efimov quantum states in an ultracold gas of cesium atoms
Systems of three interacting particles are notorious for their complex
physical behavior. A landmark theoretical result in few-body quantum physics is
Efimov's prediction of a universal set of bound trimer states appearing for
three identical bosons with a resonant two-body interaction.
Counterintuitively, these states even exist in the absence of a corresponding
two-body bound state. Since the formulation of Efimov's problem in the context
of nuclear physics 35 years ago, it has attracted great interest in many areas
of physics. However, the observation of Efimov quantum states has remained an
elusive goal. Here we report the observation of an Efimov resonance in an
ultracold gas of cesium atoms. The resonance occurs in the range of large
negative two-body scattering lengths, arising from the coupling of three free
atoms to an Efimov trimer. Experimentally, we observe its signature as a giant
three-body recombination loss when the strength of the two-body interaction is
varied. We also detect a minimum in the recombination loss for positive
scattering lengths, indicating destructive interference of decay pathways. Our
results confirm central theoretical predictions of Efimov physics and represent
a starting point with which to explore the universal properties of resonantly
interacting few-body systems. While Feshbach resonances have provided the key
to control quantum-mechanical interactions on the two-body level, Efimov
resonances connect ultracold matter to the world of few-body quantum phenomena.Comment: 18 pages, 3 figure
Superfluidity of flexible chains of polar molecules
We study properties of quantum chains in a gas of polar bosonic molecules
confined in a stack of N identical one- and two- dimensional optical lattice
layers, with molecular dipole moments aligned perpendicularly to the layers.
Quantum Monte Carlo simulations of a single chain (formed by a single molecule
on each layer) reveal its quantum roughening transition. The case of finite
in-layer density of molecules is studied within the framework of the J-current
model approximation, and it is found that N-independent molecular superfluid
phase can undergo a quantum phase transition to a rough chain superfluid. A
theorem is proven that no superfluidity of chains with length shorter than N is
possible. The scheme for detecting chain formation is proposed.Comment: Submitted to Proceedings of the QFS2010 satellite conference "Cold
Gases meet Many-Body Theory", Grenoble, August 7, 2010. This is the expanded
version of V.
Pinning quantum phase transition for a Luttinger liquid of strongly interacting bosons
One of the most remarkable results of quantum mechanics is the fact that
many-body quantum systems may exhibit phase transitions even at zero
temperature. Quantum fluctuations, deeply rooted in Heisenberg's uncertainty
principle, and not thermal fluctuations, drive the system from one phase to
another. Typically, the relative strength of two competing terms in the
system's Hamiltonian is changed across a finite critical value. A well-known
example is the Mott-Hubbard quantum phase transition from a superfluid to an
insulating phase, which has been observed for weakly interacting bosonic atomic
gases. However, for strongly interacting quantum systems confined to
lower-dimensional geometry a novel type of quantum phase transition may be
induced for which an arbitrarily weak perturbation to the Hamiltonian is
sufficient to drive the transition. Here, for a one-dimensional (1D) quantum
gas of bosonic caesium atoms with tunable interactions, we observe the
commensurate-incommensurate quantum phase transition from a superfluid
Luttinger liquid to a Mott-insulator. For sufficiently strong interactions, the
transition is induced by adding an arbitrarily weak optical lattice
commensurate with the atomic granularity, which leads to immediate pinning of
the atoms. We map out the phase diagram and find that our measurements in the
strongly interacting regime agree well with a quantum field description based
on the exactly solvable sine-Gordon model. We trace the phase boundary all the
way to the weakly interacting regime where we find good agreement with the
predictions of the 1D Bose-Hubbard model. Our results open up the experimental
study of quantum phase transitions, criticality, and transport phenomena beyond
Hubbard-type models in the context of ultracold gases
Bound Chains of Tilted Dipoles in Layered Systems
Ultracold polar molecules in multilayered systems have been experimentally
realized very recently. While experiments study these systems almost
exclusively through their chemical reactivity, the outlook for creating and
manipulating exotic few- and many-body physics in dipolar systems is
fascinating. Here we concentrate on few-body states in a multilayered setup. We
exploit the geometry of the interlayer potential to calculate the two- and
three-body chains with one molecule in each layer. The focus is on dipoles that
are aligned at some angle with respect to the layer planes by means of an
external eletric field. The binding energy and the spatial structure of the
bound states are studied in several different ways using analytical approaches.
The results are compared to stochastic variational calculations and very good
agreement is found. We conclude that approximations based on harmonic
oscillator potentials are accurate even for tilted dipoles when the geometry of
the potential landscape is taken into account.Comment: 10 pages, 6 figures. Submitted to Few-body Systems special issue on
Critical Stability, revised versio
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