46 research outputs found
Ultracold atoms in optical lattices generated by quantized light fields
We study an ultracold gas of neutral atoms subject to the periodic optical
potential generated by a high- cavity mode. In the limit of very low
temperatures, cavity field and atomic dynamics require a quantum description.
Starting from a cavity QED single atom Hamiltonian we use different routes to
derive approximative multiparticle Hamiltonians in Bose-Hubbard form with
rescaled or even dynamical parameters. In the limit of large enough cavity
damping the different models agree. Compared to free space optical lattices,
quantum uncertainties of the potential and the possibility of atom-field
entanglement lead to modified phase transition characteristics, the appearance
of new phases or even quantum superpositions of different phases. Using a
corresponding effective master equation, which can be numerically solved for
few particles, we can study time evolution including dissipation. As an example
we exhibit the microscopic processes behind the transition dynamics from a Mott
insulator like state to a self-ordered superradiant state of the atoms, which
appears as steady state for transverse atomic pumping.Comment: 17 pages, 10 figures, Published versio
Probing superfluidity of periodically trapped ultracold atoms in a cavity by transmission spectroscopy
We study a system of periodic Bose condensed atoms coupled to cavity photons
using the input-output formalism. We show that the cavity will either act as a
through pass Lorentzian filter when the superfluid fraction of the condensate
is minimum or completely reflect the input field when the superfluid fraction
is maximum. We show that by monitoring the ratio between the transmitted field
and the reflected field, one can estimate the superfluid fraction.Comment: 3 page
Full quantum distribution of contrast in interference experiments between interacting one dimensional Bose liquids
We analyze interference experiments for a pair of independent one dimensional
condensates of interacting bosonic atoms at zero temperature. We show that the
distribution function of fringe amplitudes contains non-trivial information
about non-local correlations within individual condensates and can be
calculated explicitly using methods of conformal field theory. We point out
interesting relations between these distribution functions, the partition
function for a quantum impurity in a one-dimensional Luttinger liquid, and
transfer matrices of conformal field theories. We demonstrate the connection
between interference experiments in cold atoms and a variety of statistical
models ranging from stochastic growth models to two dimensional quantum
gravity. Such connection can be used to design a quantum simulator of unusual
two-dimensional models described by nonunitary conformal field theories with
negative central charges.Comment: 9 pages, 5 figures; Accepted for publication in Nature Physic
Quantum Non-Demolition Detection of Strongly Correlated Systems
Preparation, manipulation, and detection of strongly correlated states of
quantum many body systems are among the most important goals and challenges of
modern physics. Ultracold atoms offer an unprecedented playground for
realization of these goals. Here we show how strongly correlated states of
ultracold atoms can be detected in a quantum non-demolition scheme, that is, in
the fundamentally least destructive way permitted by quantum mechanics. In our
method, spatially resolved components of atomic spins couple to quantum
polarization degrees of freedom of light. In this way quantum correlations of
matter are faithfully mapped on those of light; the latter can then be
efficiently measured using homodyne detection. We illustrate the power of such
spatially resolved quantum noise limited polarization measurement by applying
it to detect various standard and "exotic" types of antiferromagnetic order in
lattice systems and by indicating the feasibility of detection of superfluid
order in Fermi liquids.Comment: Published versio
Probing quantum and thermal noise in an interacting many-body system
The probabilistic character of the measurement process is one of the most
puzzling and fascinating aspects of quantum mechanics. In many-body systems
quantum mechanical noise reveals non-local correlations of the underlying
many-body states. Here, we provide a complete experimental analysis of the
shot-to-shot variations of interference fringe contrast for pairs of
independently created one-dimensional Bose condensates. Analyzing different
system sizes we observe the crossover from thermal to quantum noise, reflected
in a characteristic change in the distribution functions from Poissonian to
Gumbel-type, in excellent agreement with theoretical predictions based on the
Luttinger liquid formalism. We present the first experimental observation of
quasi long-range order in one-dimensional atomic condensates, which is a
hallmark of quantum fluctuations in one-dimensional systems. Furthermore, our
experiments constitute the first analysis of the full distribution of quantum
noise in an interacting many-body system
Density correlations and dynamical Casimir emission of Bogoliubov phonons in modulated atomic Bose-Einstein condensates
We present a theory of the density correlations that appear in an atomic
Bose-Einstein condensate as a consequence of the dynamical Casimir emission of
pairs of Bogoliubov phonons when the atom-atom scattering length is modulated
in time. Different regimes as a function of the temporal shape of the
modulation are identified and a simple physical picture of the phenomenon is
discussed. Analytical expressions for the density correlation function are
provided for the most significant limiting cases. This theory is able to
explain some unexpected features recently observed in numerical calculations of
Hawking radiation from analog black holes
Detailed spectral and morphological analysis of the shell type SNR RCW 86
Aims: We aim for an understanding of the morphological and spectral
properties of the supernova remnant RCW~86 and for insights into the production
mechanism leading to the RCW~86 very high-energy gamma-ray emission. Methods:
We analyzed High Energy Spectroscopic System data that had increased
sensitivity compared to the observations presented in the RCW~86 H.E.S.S.
discovery publication. Studies of the morphological correlation between the
0.5-1~keV X-ray band, the 2-5~keV X-ray band, radio, and gamma-ray emissions
have been performed as well as broadband modeling of the spectral energy
distribution with two different emission models. Results:We present the first
conclusive evidence that the TeV gamma-ray emission region is shell-like based
on our morphological studies. The comparison with 2-5~keV X-ray data reveals a
correlation with the 0.4-50~TeV gamma-ray emission.The spectrum of RCW~86 is
best described by a power law with an exponential cutoff at TeV and a spectral index of ~. A static
leptonic one-zone model adequately describes the measured spectral energy
distribution of RCW~86, with the resultant total kinetic energy of the
electrons above 1 GeV being equivalent to 0.1\% of the initial kinetic
energy of a Type I a supernova explosion. When using a hadronic model, a
magnetic field of ~100G is needed to represent the measured data.
Although this is comparable to formerly published estimates, a standard
E spectrum for the proton distribution cannot describe the gamma-ray
data. Instead, a spectral index of ~1.7 would be required, which
implies that ~erg has been transferred into
high-energy protons with the effective density cm^-3. This
is about 10\% of the kinetic energy of a typical Type Ia supernova under the
assumption of a density of 1~cm^-3.Comment: accepted for publication by A&
A reference human induced pluripotent stem cell line for large-scale collaborative studies
Human induced pluripotent stem cell (iPSC) lines are a powerful tool for studying development and disease, but the considerable phenotypic variation between lines makes it challenging to replicate key findings and integrate data across research groups. To address this issue, we sub-cloned candidate human iPSC lines and deeply characterized their genetic properties using whole genome sequencing, their genomic stability upon CRISPR-Cas9-based gene editing, and their phenotypic properties including differentiation to commonly used cell types. These studies identified KOLF2.1J as an all-around well-performing iPSC line. We then shared KOLF2.1J with groups around the world who tested its performance in head-to-head comparisons with their own preferred iPSC lines across a diverse range of differentiation protocols and functional assays. On the strength of these findings, we have made KOLF2.1J and its gene-edited derivative clones readily accessible to promote the standardization required for large-scale collaborative science in the stem cell field
Upgrading electron temperature and electron density diagnostic diagrams of forbidden line emission
Context. Diagnostic diagrams of forbidden lines have been a useful tool
for observers for many decades now. They are used to obtain information on the basic
physical properties of thin gaseous nebulae. Some diagnostic diagrams are in wavelength
domains that were difficult to apply either due to missing wavelength coverage or the low
resolution of older spectrographs. Furthermore, most of the diagrams were calculated using
just the species involved as a single atom gas, although several are affected by
well-known fluorescence mechanisms as well. Additionally, the atomic data have improved up
to the present time.
Aims. The aim of this work is to recalculate well-known, but also
sparsely used, unnoted diagnostics diagrams. The new diagrams provide observers with
modern, easy-to-use recipes for determining electron temperature and densities.
Methods. The new diagnostic diagrams were calculated using large grids
of parameter space in the photoionization code CLOUDY. For a given basic parameter (e.g.,
electron density or temperature), the solutions with cooling-heating-equilibrium were
chosen to derive the diagnostic diagrams. Empirical numerical functions were fitted to
provide formulas usable in, e.g., data reduction pipelines.
Results. The resulting diagrams differ significantly from those used up
to now and will improve thermodynamic calculations. To our knowledge, detailed, directly
applicable fit formulas are given for the first time, leading to the calculation of
electron temperature or density from the line ratios