119 research outputs found
High-resolution imaging of ultracold fermions in microscopically tailored optical potentials
We report on the local probing and preparation of an ultracold Fermi gas on
the length scale of one micrometer, i.e. of the order of the Fermi wavelength.
The essential tool of our experimental setup is a pair of identical,
high-resolution microscope objectives. One of the microscope objectives allows
local imaging of the trapped Fermi gas of 6Li atoms with a maximum resolution
of 660 nm, while the other enables the generation of arbitrary optical dipole
potentials on the same length scale. Employing a 2D acousto-optical deflector,
we demonstrate the formation of several trapping geometries including a tightly
focussed single optical dipole trap, a 4x4-site two-dimensional optical lattice
and a 8-site ring lattice configuration. Furthermore, we show the ability to
load and detect a small number of atoms in these trapping potentials. A site
separation of down to one micrometer in combination with the low mass of 6Li
results in tunneling rates which are sufficiently large for the implementation
of Hubbard-models with the designed geometries.Comment: 15 pages, 6 figure
Phase 1 study of sirolimus in combination with oral cyclophosphamide and topotecan in children and young adults with relapsed and refractory solid tumors.
PurposeTo determine the maximum tolerated dose (MTD), toxicities, and pharmacodynamics effects of sirolimus combined with oral metronomic topotecan and cyclophosphamide in a pediatric population.Materials and methodsPatients who were 1 to 30 years of age with relapsed/refractory solid tumors (including CNS) were eligible. Patients received daily oral sirolimus and cyclophosphamide (25-50 mg/m2/dose) on days 1-21 and oral topotecan (0.8 mg/m2/dose) on days 1-14 in 28-day cycles. Sirolimus steady-state plasma trough concentrations of 3-7.9 ng/mL and 8-12.0 ng/mL were evaluated, with dose escalation based on a 3+3 phase 1 design. Biomarkers of angiogenesis were also evaluated.ResultsTwenty-one patients were treated (median age 18 years; range 9-30). Dose-limiting toxicities included myelosuppression, ALT elevation, stomatitis, and hypertriglyceridemia. The MTD was sirolimus with trough goal of 8-12.0 ng/mL; cyclophosphamide 25 mg/m2/dose; and topotecan 0.8 mg/m2/dose. No objective responses were observed. Four patients had prolonged stable disease > 4 cycles (range 4-12). Correlative biomarker analyses demonstrated reductions in thrombospondin-1 (p=0.043) and soluble vascular endothelial growth factor receptor-2 plasma concentrations at 21 days compared to baseline.ConclusionsThe combination of oral sirolimus, topotecan, and cyclophosphamide was well tolerated and biomarker studies demonstrated modulation of angiogenic pathways with this regimen
Localization of the Grover walks on spidernets and free Meixner laws
A spidernet is a graph obtained by adding large cycles to an almost regular
tree and considered as an example having intermediate properties of lattices
and trees in the study of discrete-time quantum walks on graphs. We introduce
the Grover walk on a spidernet and its one-dimensional reduction. We derive an
integral representation of the -step transition amplitude in terms of the
free Meixner law which appears as the spectral distribution. As an application
we determine the class of spidernets which exhibit localization. Our method is
based on quantum probabilistic spectral analysis of graphs.Comment: 32 page
Single-Atom Resolved Fluorescence Imaging of an Atomic Mott Insulator
The reliable detection of single quantum particles has revolutionized the
field of quantum optics and quantum information processing. For several years,
researchers have aspired to extend such detection possibilities to larger scale
strongly correlated quantum systems, in order to record in-situ images of a
quantum fluid in which each underlying quantum particle is detected. Here we
report on fluorescence imaging of strongly interacting bosonic Mott insulators
in an optical lattice with single-atom and single-site resolution. From our
images, we fully reconstruct the atom distribution on the lattice and identify
individual excitations with high fidelity. A comparison of the radial density
and variance distributions with theory provides a precise in-situ temperature
and entropy measurement from single images. We observe Mott-insulating plateaus
with near zero entropy and clearly resolve the high entropy rings separating
them although their width is of the order of only a single lattice site.
Furthermore, we show how a Mott insulator melts for increasing temperatures due
to a proliferation of local defects. Our experiments open a new avenue for the
manipulation and analysis of strongly interacting quantum gases on a lattice,
as well as for quantum information processing with ultracold atoms. Using the
high spatial resolution, it is now possible to directly address individual
lattice sites. One could, e.g., introduce local perturbations or access regions
of high entropy, a crucial requirement for the implementation of novel cooling
schemes for atoms on a lattice
Spatial Light Modulators for the Manipulation of Individual Atoms
We propose a novel dipole trapping scheme using spatial light modulators
(SLM) for the manipulation of individual atoms. The scheme uses a high
numerical aperture microscope to map the intensity distribution of a SLM onto a
cloud of cold atoms. The regions of high intensity act as optical dipole force
traps. With a SLM fast enough to modify the trapping potential in real time,
this technique is well suited for the controlled addressing and manipulation of
arbitrarily selected atoms.Comment: 9 pages, 5 figure
Quantum walk on distinguishable non-interacting many-particles and indistinguishable two-particle
We present an investigation of many-particle quantum walks in systems of
non-interacting distinguishable particles. Along with a redistribution of the
many-particle density profile we show that the collective evolution of the
many-particle system resembles the single-particle quantum walk evolution when
the number of steps is greater than the number of particles in the system. For
non-uniform initial states we show that the quantum walks can be effectively
used to separate the basis states of the particle in position space and
grouping like state together. We also discuss a two-particle quantum walk on a
two- dimensional lattice and demonstrate an evolution leading to the
localization of both particles at the center of the lattice. Finally we discuss
the outcome of a quantum walk of two indistinguishable particles interacting at
some point during the evolution.Comment: 8 pages, 7 figures, To appear in special issue: "quantum walks" to be
published in Quantum Information Processin
Random Time-Dependent Quantum Walks
We consider the discrete time unitary dynamics given by a quantum walk on the
lattice performed by a quantum particle with internal degree of freedom,
called coin state, according to the following iterated rule: a unitary update
of the coin state takes place, followed by a shift on the lattice, conditioned
on the coin state of the particle. We study the large time behavior of the
quantum mechanical probability distribution of the position observable in
when the sequence of unitary updates is given by an i.i.d. sequence of
random matrices. When averaged over the randomness, this distribution is shown
to display a drift proportional to the time and its centered counterpart is
shown to display a diffusive behavior with a diffusion matrix we compute. A
moderate deviation principle is also proven to hold for the averaged
distribution and the limit of the suitably rescaled corresponding
characteristic function is shown to satisfy a diffusion equation. A
generalization to unitary updates distributed according to a Markov process is
also provided. An example of i.i.d. random updates for which the analysis of
the distribution can be performed without averaging is worked out. The
distribution also displays a deterministic drift proportional to time and its
centered counterpart gives rise to a random diffusion matrix whose law we
compute. A large deviation principle is shown to hold for this example. We
finally show that, in general, the expectation of the random diffusion matrix
equals the diffusion matrix of the averaged distribution.Comment: Typos and minor errors corrected. To appear In Communications in
Mathematical Physic
Correlated Markov Quantum Walks
We consider the discrete time unitary dynamics given by a quantum walk on
performed by a particle with internal degree of freedom, called coin
state, according to the following iterated rule: a unitary update of the coin
state takes place, followed by a shift on the lattice, conditioned on the coin
state of the particle. We study the large time behavior of the quantum
mechanical probability distribution of the position observable in for
random updates of the coin states of the following form. The random sequences
of unitary updates are given by a site dependent function of a Markov chain in
time, with the following properties: on each site, they share the same
stationnary Markovian distribution and, for each fixed time, they form a
deterministic periodic pattern on the lattice.
We prove a Feynman-Kac formula to express the characteristic function of the
averaged distribution over the randomness at time in terms of the nth power
of an operator . By analyzing the spectrum of , we show that this
distribution posesses a drift proportional to the time and its centered
counterpart displays a diffusive behavior with a diffusion matrix we compute.
Moderate and large deviations principles are also proven to hold for the
averaged distribution and the limit of the suitably rescaled corresponding
characteristic function is shown to satisfy a diffusion equation.
An example of random updates for which the analysis of the distribution can
be performed without averaging is worked out. The random distribution displays
a deterministic drift proportional to time and its centered counterpart gives
rise to a random diffusion matrix whose law we compute. We complete the picture
by presenting an uncorrelated example.Comment: 37 pages. arXiv admin note: substantial text overlap with
arXiv:1010.400
Far-from-equilibrium quantum many-body dynamics
The theory of real-time quantum many-body dynamics as put forward in Ref.
[arXiv:0710.4627] is evaluated in detail. The formulation is based on a
generating functional of correlation functions where the Keldysh contour is
closed at a given time. Extending the Keldysh contour from this time to a later
time leads to a dynamic flow of the generating functional. This flow describes
the dynamics of the system and has an explicit causal structure. In the present
work it is evaluated within a vertex expansion of the effective action leading
to time evolution equations for Green functions. These equations are applicable
for strongly interacting systems as well as for studying the late-time
behaviour of nonequilibrium time evolution. For the specific case of a bosonic
N-component phi^4 theory with contact interactions an s-channel truncation is
identified to yield equations identical to those derived from the 2PI effective
action in next-to-leading order of a 1/N expansion. The presented approach
allows to directly obtain non-perturbative dynamic equations beyond the widely
used 2PI approximations.Comment: 20 pp., 6 figs; submitted version with added references and typos
corrected
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