Universality in Three- and Four-Body Bound States of Ultracold Atoms

Under certain circumstances, three or more interacting particles may form bound states. While the general few-body problem is not analytically solvable, the so-called Efimov trimers appear for a system of three particles with resonant two-body interactions. The binding energies of these trimers are predicted to be universally connected to each other, independent of the microscopic details of the interaction. By exploiting a Feshbach resonance to widely tune the interactions between trapped ultracold lithium atoms, we find evidence for two universally connected Efimov trimers and their associated four-body bound states. A total of eleven precisely determined three- and four-body features are found in the inelastic loss spectrum. Their relative locations on either side of the resonance agree well with universal theory, while a systematic deviation from universality is found when comparing features across the resonance.

Temporal Extent of Surface Potentials between Closely Spaced Metals

Variations in the electrostatic surface potential between the proof mass and electrode housing in the space-based gravitational wave mission LISA is one of the largest contributors of noise at frequencies below a few mHz. Torsion balances provide an ideal testbed for investigating these effects in conditions emulative of LISA. Our apparatus consists of a Au coated Cu plate brought near a Au coated Si plate pendulum suspended from a thin W wire. We have measured a white noise level of $30, uVhz$ above approximately 0.1, mHz, rising at lower frequencies, for the surface potential variations between these two closely spaced metals.