634 research outputs found
Accessing Rydberg-dressed interactions using many-body Ramsey dynamics
We demonstrate that Ramsey spectroscopy can be used to observe
Rydberg-dressed interactions. In contrast to many prior proposals, our scheme
operates comfortably within experimentally measured lifetimes, and accesses a
regime where quantum superpositions are crucial. The key idea is to build a
spin-1/2 from one level that is Rydberg-dressed and another that is not. These
levels may be hyperfine or long-lived electronic states. An Ising spin model
governs the Ramsey dynamics, for which we derive an exact solution. Due to the
structure of Rydberg interactions, the dynamics differs significantly from that
in other spin systems. As one example, spin echo can increase the rate at which
coherence decays. The results also apply to bare (undressed) Rydberg states as
a special case, for which we quantitatively reproduce recent ultrafast
experiments without fitting
Many-body physics in the radio frequency spectrum of lattice bosons
We calculate the radio-frequency spectrum of a trapped cloud of cold bosonic
atoms in an optical lattice. Using random phase and local density
approximations we produce both trap averaged and spatially resolved spectra,
identifying simple features in the spectra that reveal information about both
superfluidity and correlations. Our approach is exact in the deep Mott limit
and in the deep superfluid when the hopping rates for the two internal spin
states are equal. It contains final state interactions, obeys the Ward
identities (and the associated conservation laws), and satisfies the -sum
rule. Motivated by earlier work by Sun, Lannert, and Vishveshwara [Phys. Rev. A
\textbf{79}, 043422 (2009)], we also discuss the features which arise in a
spin-dependent optical lattice.Comment: 6 pages, 4 figures, 13 subfigure
High temperature thermodynamics of fermionic alkaline earth atoms in optical lattices
We calculate experimentally relevant properties of trapped fermionic alkaline
earth atoms in an optical lattice, modeled by the SU(N) Hubbard model. Our
calculation is accurate when the temperature is much larger than the tunneling
rate, similar to current regimes in ultracold atom experiments. In addition to
exploring the Mott insulator-metal crossover, we calculate final temperatures
achieved by the standard experimental protocol of adiabatically ramping from a
non-interacting gas, as a function of initial gas temperature and final state
lattice parameters. Of particular experimental interest, we find that
increasing gives substantially \textit{colder} Mott insulators, up to more
than a factor of five for relevant parameters. This cooling happens for all
, fixing the initial entropy, or for all N \lsim 20 (the exact value
depends on dimensionality), fixing the initial temperature.Comment: 4+ pages main text, 2 figures. 3 pages supplementary information, 2
figures. v2: added citatio
Accessory genetic content in Campylobacter jejuni ST21CC isolates from feces and blood
Campylobacter jejuni is an important foodborne pathogen and the most commonly reported bacterial cause of gastroenteritis. C. jejuni is occasionally found in blood, although mechanisms important for invasiveness have remained unclear. C. jejuni is divided into many different lineages, of which the ST21 clonal complex (CC) is widely distributed. Here, we performed comparative genomic and in vitro analyses on 17C. jejuni ST21CC strains derived from human blood and feces in order to identify features associated with isolation site. The ST21CC lineage is divided into two large groups; centered around ST-21 and ST-50. Our clinical strains, typed as ST-50, showed further microevolution into two distinct clusters. These clusters were distinguished by major differences in their capsule loci and the distribution of accessory genetic content, including C. jejuni integrated elements (CJIEs) and plasmids. Accessory genetic content was more common among fecal than blood strains, whereas blood strains contained a hybrid capsule locus which partially consisted of C. jejuni subsp. doylei-like content. In vitro infection assays with human colon cell lines did not show significant differences in adherence and invasion between the blood and fecal strains. Our results showed that CJIEs and plasmid derived genetic material were less common among blood isolates than fecal isolates; in contrast, hybrid capsule loci, especially those containing C. jejuni subsp. doylei-like gene content, were found among many isolates derived from blood. The role of these findings requires more detailed investigation.Peer reviewe
High-intensity two-frequency photoassociation spectroscopy of a weakly bound molecular state: theory and experiment
We investigate two-frequency photoassociation of a weakly bound molecular
state, focusing on a regime where the ac Stark shift is comparable to the
halo-state energy. In this "high-intensity" regime, we observe features absent
in low-intensity two-frequency photoassociation. We experimentally measure the
spectra of Sr atoms coupled to the least bound state of the
Sr ground electronic channel through an intermediate electronically
excited molecular state. We compare the spectra to a simple three-level model
that includes a two-frequency drive on each leg of the transition. With
numerical solution of the time-dependent Schrodinger equation, we show that
this model accurately captures (1) the existence of experimentally observed
satellite peaks that arise from nonlinear processes, (2) the locations of the
two-photon peak in the spectrum, including ac Stark shifts, and (3) in some
cases, spectral lineshapes. To better understand these numerical results, we
develop an approximate treatment of this model, based on Floquet and
perturbation theory, that gives simple formulas that accurately capture the
halo-state energies. We expect these expressions to be valuable tools to
analyze and guide future two-frequency photoassociation experiments.Comment: 12 pages, 7 figure
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