81 research outputs found
Probing correlated phases of bosons in optical lattices via trap squeezing
We theoretically analyze the response properties of ultracold bosons in
optical lattices to the static variation of the trapping potential. We show
that, upon an increase of such potential (trap squeezing), the density
variations in a central region, with linear size of >~ 10 wavelengths, reflect
that of the bulk system upon changing the chemical potential: hence measuring
the density variations gives direct access to the bulk compressibility. When
combined with standard time-of-flight measurements, this approach has the
potential of unambiguously detecting the appearence of the most fundamental
phases realized by bosons in optical lattices, with or without further external
potentials: superfluid, Mott insulator, band insulator and Bose glass.Comment: 4 pages, 4 figure
The disordered-free-moment phase: a low-field disordered state in spin-gap antiferromagnets with site dilution
Site dilution of spin-gapped antiferromagnets leads to localized free
moments, which can order antiferromagnetically in two and higher dimensions.
Here we show how a weak magnetic field drives this order-by-disorder state into
a novel disordered-free-moment phase, characterized by the formation of local
singlets between neighboring moments and by localized moments aligned
antiparallel to the field. This disordered phase is characterized by the
absence of a gap, as it is the case in a Bose glass. The associated
field-driven quantum phase transition is consistent with the universality of a
superfluid-to-Bose-glass transition. The robustness of the
disordered-free-moment phase and its prominent features, in particular a series
of pseudo-plateaus in the magnetization curve, makes it accessible and relevant
to experiments.Comment: 4 pages, 4 figure
Pairing, crystallization and string correlations of mass-imbalanced atomic mixtures in one-dimensional optical lattices
We numerically determine the very rich phase diagram of mass-imbalanced
binary mixtures of hardcore bosons (or equivalently -- fermions, or
hardcore-Bose/Fermi mixtures) loaded in one-dimensional optical lattices.
Focusing on commensurate fillings away from half filling, we find a strong
asymmetry between attractive and repulsive interactions. Attraction is found to
always lead to pairing, associated with a spin gap, and to pair crystallization
for very strong mass imbalance. In the repulsive case the two atomic components
remain instead fully gapless over a large parameter range; only a very strong
mass imbalance leads to the opening of a spin gap. The spin-gap phase is the
precursor of a crystalline phase occurring for an even stronger mass imbalance.
The fundamental asymmetry of the phase diagram is at odds with recent
theoretical predictions, and can be tested directly via time-of-flight
experiments on trapped cold atoms.Comment: 4 pages, 4 figures + Supplementary Materia
Dynamical creation of a supersolid in asymmetric mixtures of bosons
We propose a scheme to dynamically create a supersolid state in an optical
lattice, using an attractive mixture of mass-imbalanced bosons. Starting from a
"molecular" quantum crystal, supersolidity is induced dynamically as an
out-of-equilibrium state. When neighboring molecular wavefunctions overlap,
both bosonic species simultaneously exhibit quasi-condensation and long-range
solid order, which is stabilized by their mass imbalance. Supersolidity appears
in a perfect one-dimensional crystal, without the requirement of doping. Our
model can be realized in present experiments with bosonic mixtures that feature
simple on-site interactions, clearing the path to the observation of
supersolidity.Comment: Accepted at Phys. Rev. Let
Off-diagonal correlations in a one-dimensional gas of dipolar bosons
We present a quantum Monte Carlo study of the one-body density matrix (OBDM)
and the momentum distribution of one-dimensional dipolar bosons, with dipole
moments polarized perpendicular to the direction of confinement. We observe
that the long-range nature of the dipole interaction has dramatic effects on
the off-diagonal correlations: although the dipoles never crystallize, the
system goes from a quasi-condensate regime at low interactions to a regime in
which quasi-condensation is discarded, in favor of quasi-solidity. For all
strengths of the dipolar interaction, the OBDM shows an oscillatory behavior
coexisting with an overall algebraic decay; and the momentum distribution shows
sharp kinks at the wavevectors of the oscillations, (where
is the atom density), beyond which it is strongly suppressed. This
\emph{momentum filtering} effect introduces a characteristic scale in the
momentum distribution, which can be arbitrarily squeezed by lowering the atom
density. This shows that one-dimensional dipolar Bose gases, realized e.g. by
trapped dipolar molecules, show strong signatures of the dipolar interaction in
time-of-flight measurements.Comment: 10 pages, 6 figures. v2: fixed a mistake in the comparison with Ref.
9, as well as several typos. Published versio
FFLO oscillations and magnetic domains in the Hubbard model with off-diagonal Coulomb repulsion
We observe the effect of non-zero magnetization m onto the superconducting
ground state of the one dimensional repulsive Hubbard model with correlated
hopping X. For t/2 < X < 2t/3, the system first manifests
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) oscillations in the pair-pair
correlations. For m = m1 a kinetic energy driven macroscopic phase separation
into low-density superconducting domains and high-density polarized walls takes
place. For m > m2 the domains fully localize, and the system eventually becomes
a ferrimagnetic insulator.Comment: IOP RevTeX class, 18 pages, 13 composite *.eps figure
Quantum Non-Demolition Detection of Polar Molecule Complexes: Dimers, Trimers, Tetramers
The optical nondestructive method for in situ detection of the bound states
of ultracold polar molecules is developed. It promises a minimally destructive
measurement scheme up to a physically exciting quantum non-demolition (QND)
level. The detection of molecular complexes beyond simple pairs of quantum
particles (dimers, known, e.g., from the BEC-BCS theory) is suggested,
including three-body (trimers) and four-body (tertramers) complexes trapped by
one-dimensional tubes. The intensity of scattered light is sensitive to the
molecule number fluctuations beyond the mean-density approximation. Such
fluctuations are very different for various complexes, which leads to radically
different light scattering. This type of research extends "quantum optics of
quantum gases" to the field of ultracold molecules. Merging the quantum optical
and ultracold gas problems will advance the experimental efforts towards the
study of the light-matter interaction at its ultimate quantum level, where the
quantizations of both light and matter are equally important.Comment: 6 pages, 2 figure
The effects of disorder in dimerized quantum magnets in mean field approximations
We study theoretically the effects of disorder on Bose-Einstein condensates
(BEC) of bosonic triplon quasiparticles in doped dimerized quantum magnets. The
condensation occurs in a strong enough magnetic field Hc, where the
concentration of bosons in the random potential is sufficient to form the
condensate. The effect of doping is partly modeled by delta - correlated
disorder potential, which (i) leads to the uniform renormalization of the
system parameters and (ii) produces disorder in the system with renormalized
parameters. These approaches can explain qualitatively the available
magnetization data in the Tl_(1-x)K_(x)CuCl_3 compound taken as an example. In
addition to the magnetization, we found that the speed of the Bogoliubov mode
has a peak as a function of doping parameter, x. No evidence of the pure Bose
glass phase has been obtained in the BEC regime.Comment: Includes 19 pages, 5 figure
Quantum polarization spectroscopy of correlations in attractive fermionic gases
We show how spin-spin correlations, detected in a non-destructive way via
spatially resolved quantum polarization spectroscopy, strongly characterize
various phases realized in trapped ultracold fermionic atoms. Polarization
degrees of freedom of the light couple to spatially resolved components of the
atomic spin. In this way quantum fluctuations of matter are faithfully mapped
onto those of light. In particular we demonstrate that quantum spin
polarization spectroscopy provides a direct method to detect the
Fulde-Ferrell-Larkin-Ovchinnikov phase realized in a one-dimensional imbalanced
Fermi system.Comment: 16 pages, 9 figure
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