Observing the emergence of a quantum phase transition shell by shell.

Many-body physics describes phenomena that cannot be understood by looking only at the constituents of a system. Striking examples are broken symmetry, phase transitions and collective excitations. To understand how such collective behaviour emerges as a system is gradually assembled from individual particles has been a goal in atomic, nuclear and solid-state physics for decades.

Measurement of Identical Particle Entanglement and the Influence of Antisymmetrization.

We explore the relationship between symmetrization and entanglement through measurements on few-particle systems in a multiwell potential. In particular, considering two or three trapped atoms, we measure and distinguish correlations arising from two different physical origins: antisymmetrization of the fermionic wave function and interaction between particles. We quantify this through the entanglement negativity of states, and the introduction of an antisymmetric negativity, which allows us to understand the role that symmetrization plays in the measured entanglement properties.

High-Contrast Interference of Ultracold Fermions.

Many-body interference between indistinguishable particles can give rise to strong correlations rooted in quantum statistics. We study such Hanbury Brown-Twiss-type correlations for number states of ultracold massive fermions. Using deterministically prepared ^{6}Li atoms in optical tweezers, we measure momentum correlations using a single-atom sensitive time-of-flight imaging scheme.

Density Oscillations Induced by Individual Ultracold Two-Body Collisions.

Access to single-particle momenta provides new means of studying the dynamics of a few interacting particles. In a joint theoretical and experimental effort, we observe and analyze the effects of a finite number of ultracold two-body collisions on the relative and single-particle densities by quenching two ultracold atoms with an initial narrow wave packet into a wide trap with an inverted aspect ratio. The experimentally observed spatial oscillations of the relative density are reproduced by a parameter-free zero-range theory and interpreted in terms of cross-dimensional flux.

High-temperature pairing in a strongly interacting two-dimensional Fermi gas.

The nature of the normal phase of strongly correlated fermionic systems is an outstanding question in quantum many-body physics. We used spatially resolved radio-frequency spectroscopy to measure pairing energy of fermions across a wide range of temperatures and interaction strengths in a two-dimensional gas of ultracold fermionic atoms. We observed many-body pairing at temperatures far above the critical temperature for superfluidity.

Computer access and Internet use by urban and suburban emergency department customers.

Background: Patients are increasingly using the Internet (43% in 2000 vs. 70% in 2006) to obtain health information, but is there a difference in the ability of urban and suburban emergency department (ED) customers to access the Internet?

Study Objective: To assess computer and Internet resources available to and used by people waiting to be seen in an urban ED and a suburban ED.

Methods: Individuals waiting in the ED were asked survey questions covering demographics, type of insurance, access to a primary care provider, reason for their ED visit, computer access, and ability to access the Internet for health-related matters.

Genetic analysis of isolates of Rickettsia rickettsii that differ in virulence.

We examined the degree of intraspecies genetic polymorphisms present among 13 R. rickettsii strains isolated from the blood of patients and ixodid ticks from North and South America. Preliminary confirmation of these isolates as R.