The humble helium atom has played a starring role in a number of pivotal discoveries since its first observation during the solar eclipse of 1868. Among these was the superfluidity of liquid helium, whose mechanism was promptly found to originate in the union of two foundational principles: The indistinguishability of identical particles and the fundamental connections between symmetry and statistics, married in the phenomenon of Bose-Einstein condensation (BEC). Much later, the realization of BEC in the laboratory in 1995 heralded the explosive growth of the field of ultracold atoms, which has since grown several burgeoning branches. One such branch reaches into metrology, the science of precision measurement, owing to the fact that cold-atom systems are created in exquisite isolation and under near-perfect control. Another branch is the use of BECs as testing grounds for theories concerning the emergence of ordered structure from systems of many interacting particles.
This seminar will focus on work I undertook within the Helium Condensate laboratory which build on these proud traditions. First, I will present some results of laser spectroscopy in helium which include order-of-magnitude gains in precision over previous measurements, and the first detection of certain weak transitions in helium. I will discuss the impetus and implications of these findings in the context of contemporary challenges to theories of fundamental physics. Second, with emphasis on our ability to detect individual helium atoms, I will describe a study of the quantum depletion of a BEC and its unexpected persistence after releasing the atoms from their trap.
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