1,991 research outputs found
Correlated hopping of bosonic atoms induced by optical lattices
In this work we analyze a particular setup with ultracold atoms trapped in
state-dependent lattices. We show that any asymmetry in the contact interaction
translates into one of two classes of correlated hopping. After deriving the
effective lattice Hamiltonian for the atoms, we obtain analytically and
numerically the different phases and quantum phase transitions. We find for
weak correlated hopping both Mott insulators and charge density waves, while
for stronger correlated hopping the system transitions into a pair superfluid.
We demonstrate that this phase exists for a wide range of interaction
asymmetries and has interesting correlation properties that differentiate it
from an ordinary atomic Bose-Einstein condensate.Comment: 24 pages with 9 figures, to appear in New Journal of Physic
Detecting ground state qubit self-excitations in circuit QED: slow quantum anti-Zeno effect
In this work we study an ultrastrong coupled qubit-cavity system subjected to
slow repeated measurements. We demonstrate that even under a few imperfect
measurements it is possible to detect transitions of the qubit from its free
ground state to the excited state. The excitation probability grows
exponentially fast in analogy with the quantum anti-Zeno effect. The dynamics
and physics described in this paper is accessible to current superconducting
circuit technology.Comment: 6 pages, 6 figures. v2: extended published versio
Limits to the analogue Hawking temperature in a Bose-Einstein condensate
Quasi-one dimensional outflow from a dilute gas Bose-Einstein condensate
reservoir is a promising system for the creation of analogue Hawking radiation.
We use numerical modeling to show that stable sonic horizons exist in such a
system under realistic conditions, taking into account the transverse
dimensions and three-body loss. We find that loss limits the analogue Hawking
temperatures achievable in the hydrodynamic regime, with sodium condensates
allowing the highest temperatures. A condensate of 30,000 atoms, with
transverse confinement frequency omega_perp=6800*2*pi Hz, yields horizon
temperatures of about 20 nK over a period of 50 ms. This is at least four times
higher than for other atoms commonly used for Bose-Einstein condensates.Comment: 9 pages, 4 figures, replaced with published versio
Power law tails of time correlations in a mesoscopic fluid model
In a quenched mesoscopic fluid, modelling transport processes at high
densities, we perform computer simulations of the single particle energy
autocorrelation function C_e(t), which is essentially a return probability.
This is done to test the predictions for power law tails, obtained from mode
coupling theory. We study both off and on-lattice systems in one- and
two-dimensions. The predicted long time tail ~ t^{-d/2} is in excellent
agreement with the results of computer simulations. We also account for finite
size effects, such that smaller systems are fully covered by the present theory
as well.Comment: 11 pages, 12 figure
On the shape of vortices for a rotating Bose Einstein condensate
For a Bose-Einstein condensate placed in a rotating trap, we study the
simplified energy of a vortex line derived in Aftalion-Riviere Phys. Rev. A 64,
043611 (2001) in order to determine the shape of the vortex line according to
the rotational velocity and the elongation of the condensate. The energy
reflects the competition between the length of the vortex which needs to be
minimized taking into account the anisotropy of the trap and the rotation term
which pushes the vortex along the z axis. We prove that if the condensate has
the shape of a pancake, the vortex stays straight along the z axis while in the
case of a cigar, the vortex is bent
Scattering of coherent states on a single artificial atom
In this work we theoretically analyze a circuit QED design where propagating
quantum microwaves interact with a single artificial atom, a single Cooper pair
box. In particular, we derive a master equation in the so-called transmon
regime, including coherent drives. Inspired by recent experiments, we then
apply the master equation to describe the dynamics in both a two-level and a
three-level approximation of the atom. In the two-level case, we also discuss
how to measure photon antibunching in the reflected field and how it is
affected by finite temperature and finite detection bandwidth.Comment: 18 pages, 7 figure
Three-dimensional vortex configurations in a rotating Bose Einstein condensate
We consider a rotating Bose-Einstein condensate in a harmonic trap and
investigate numerically the behavior of the wave function which solves the
Gross Pitaevskii equation. Following recent experiments [Rosenbuch et al, Phys.
Rev. Lett., 89, 200403 (2002)], we study in detail the line of a single
quantized vortex, which has a U or S shape. We find that a single vortex can
lie only in the x-z or y-z plane. S type vortices exist for all values of the
angular velocity Omega while U vortices exist for Omega sufficiently large. We
compute the energy of the various configurations with several vortices and
study the three-dimensional structure of vortices
Variational ansatz for the superfluid Mott-insulator transition in optical lattices
We develop a variational wave function for the ground state of a
one-dimensional bosonic lattice gas. The variational theory is initally
developed for the quantum rotor model and later on extended to the Bose-Hubbard
model. This theory is compared with quasi-exact numerical results obtained by
Density Matrix Renormalization Group (DMRG) studies and with results from other
analytical approximations. Our approach accurately gives local properties for
strong and weak interactions, and it also describes the crossover from the
superfluid phase to the Mott-insulator phase.Comment: Entirely new and more precise variational metho
Quantitative performance characterization of three-dimensional noncontact fluorescence molecular tomography
© 2016 The Authors.Fluorescent proteins and dyes are routine tools for biological research to describe the behavior of genes, proteins, and cells, as well as more complex physiological dynamics such as vessel permeability and pharmacokinetics. The use of these probes in whole body in vivo imaging would allow extending the range and scope of current biomedical applications and would be of great interest. In order to comply with a wide variety of application demands, in vivo imaging platform requirements span from wide spectral coverage to precise quantification capabilities. Fluorescence molecular tomography (FMT) detects and reconstructs in three dimensions the distribution of a fluorophore in vivo. Noncontact FMT allows fast scanning of an excitation source and noninvasive measurement of emitted fluorescent light using a virtual array detector operating in free space. Here, a rigorous process is defined that fully characterizes the performance of a custom-built horizontal noncontact FMT setup. Dynamic range, sensitivity, and quantitative accuracy across the visible spectrum were evaluated using fluorophores with emissions between 520 and 660 nm. These results demonstrate that high-performance quantitative three-dimensional visible light FMT allowed the detection of challenging mesenteric lymph nodes in vivo and the comparison of spectrally distinct fluorescent reporters in cell culture
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