30 research outputs found
Localization by Dissipative Disorder: a Deterministic Approach to Position Measurements
We propose an approach to position measurements based on the hypothesis that
the action of a position detector on a quantum system can be effectively
described by a dissipative disordered potential. We show that such kind of
potential is able, via the dissipation-induced Anderson localization, to
contemporary localize the wavefunction of the system and to dissipate
information to modes bounded to the detector. By imposing a diabaticity
condition we demonstrate that the dissipative dynamics between the modes of the
system leads to a localized energy exchange between the detector and the rest
of the environment -the "click" of the detector- thus providing a complete
deterministic description of a position measurement. We finally numerically
demonstrate that our approach is consistent with the Born probability rule
A cold-atom random laser
Conventional lasers make use of optical cavities to provide feedback to gain
media. Conversely, mirrorless lasers can be built by using disordered
structures to induce multiple scattering, which increases the effective path
length in the gain medium and thus provides the necessary feedback. These
so-called random lasers potentially offer a new and simple mean to address
applications such as lighting. To date, they are all based on condensed-matter
media. Interestingly, light or microwave amplification by stimulated emission
occurs also naturally in stellar gases and planetary atmospheres. The
possibility of additional scattering-induced feedback (that is, random lasing)
has been discussed and could explain unusual properties of some space masers.
Here, we report the experimental observation of random lasing in a controlled,
cold atomic vapour, taking advantage of Raman gain. By tuning the gain
frequency in the vicinity of a scattering resonance, we observe an enhancement
of the light emission of the cloud due to random lasing. The unique possibility
to both control the experimental parameters and to model the microscopic
response of our system provides an ideal test bench for better understanding
natural lasing sources, in particular the role of resonant scattering feedback
in astrophysical lasers
Observation of local temporal correlations in trapped quantum gases
We measure the temporal pair correlation function of a
trapped gas of bosons above and below the critical temperature for
Bose-Einstein condensation. The measurement is performed {\it in situ} using a
local, time-resolved single-atom sensitive probing technique. Third and fourth
order correlation functions are also extracted. We develop a theoretical model
and compare it with our experimental data, finding good quantitative agreement
and highlighting the role of interactions. Our results promote temporal
correlations as new observables to study the dynamics of ultracold quantum
gases
Thermodynamics of Strongly Correlated One-Dimensional Bose Gases
We investigate the thermodynamics of one-dimensional Bose gases in the
strongly correlated regime. To this end, we prepare ensembles of independent 1D
Bose gases in a two-dimensional optical lattice and perform high-resolution in
situ imaging of the column-integrated density distribution. Using an inverse
Abel transformation we derive effective one-dimensional line-density profiles
and compare them to exact theoretical models. The high resolution allows for a
direct thermometry of the trapped ensembles. The knowledge about the
temperature enables us to extract thermodynamic equations of state such as the
phase-space density, the entropy per particle and the local pair correlation
function.Comment: 4 pages, 5 figure
Cross-dimensional phase transition from an array of 1D Luttinger liquids to a 3D Bose-Einstein condensate
We study the thermodynamic properties of a 2D array of coupled
one-dimensional Bose gases. The system is realized with ultracold bosonic atoms
loaded in the potential tubes of a two-dimensional optical lattice. For
negligible coupling strength, each tube is an independent weakly interacting 1D
Bose gas featuring Tomonaga Luttinger liquid behavior. By decreasing the
lattice depth, we increase the coupling strength between the 1D gases and allow
for the phase transition into a 3D condensate. We extract the phase diagram for
such a system and compare our results with theoretical predictions. Due to the
high effective mass across the periodic potential and the increased 1D
interaction strength, the phase transition is shifted to large positive values
of the chemical potential. Our results are prototypical to a variety of
low-dimensional systems, where the coupling between the subsystems is realized
in a higher spatial dimension such as coupled spin chains in magnetic
insulators.Comment: 5 pages, 5 pictures, final version, Phys. Rev. Lett. in print (2014
Distributed quasi-Bragg beam splitter in crossed atomic waveguides
AbstractWe perform an experimental and theoretical study of a novel distributed quasi-Bragg splitter for cold atoms propagating in crossed optical waveguides. The atoms are guided by horizontal red-detuned laser beams which cross with an angle of roughly 90°. The lattice formed by the interference between the two waveguides is used as a quasi-Bragg splitter to continuously deflect the atomic flux from one waveguide into the other. In the limit of strong waveguide confinement and depending on the velocity of the cloud, three main regimes are observed corresponding (1) to the absence of reflection, (2) to partial reflection and (3) to full reflection into the second waveguide. In view of the application to atom interferometry, the condition to split the cloud into mainly two equally-populated fragments is only met in the highest velocity regime, where the fraction of reflected and transmitted atoms can be controlled by tuning the lattice height. A diagnostic of the momentum distribution shows that a quasi-Bragg splitter with the occupation of mainly two momentum states is achieved in this regime. This behaviour can be understood by considering the band structure associated with the potential in the crossing region and agrees with numerical simulations of the atomic dynamics.</jats:p
Data for "Generation of optical potentials for ultracold atoms using a superluminescent diode"
The dataset consists of images for dynamic and static potentials produced by the SLD with atoms loaded into the potentials and mages produced by the combination of the DMD each light source, SLD and Laser. These images are taken at and around the focal point in the vacuum cell. There is also an origin spectra file containing the measured spectrum of the SLD light before and after the tapered amplifie