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Experiments with Quantum Degenerate Gases.

Dr. Andrew Truscott

Atomic and Molecular Physics Laboratories, RSPhysSE, Australian National University

10.00am, Monday 5 August 2002, Seminar Room (AR103), Graduate Research Centre, Swinburne

The experimental achievement of Bose-Einstein condensation (BEC) of trapped atomic gases 7 years ago catalyzed an explosion of research activity in atoms obeying Bose-Einstein statistics- that is, those with integer spin. In contrast, there are still only a few experimental realisations of quantum degenerate fermions.

Fermions must satisfy the Pauli exclusion principle, which forbids identical particles from occupying the same quantum state. This simple property gives rise to remarkable effects that include the structure of the periodic table of the elements, the nature of electrical conductivity in metals, and the quantum Hall effect. White Dwarf stars and neutron stars manifest the Pauli principle in a striking way. In both cases, the star has exhausted its nuclear fuel and is essentially "dead". Tremendous gravitational forces draw the star in on itself. Inside such a star, however, there is near-unity occupation of the available quantum states (i.e. quantum degeneracy), which provides a "Fermi pressure" that stabilises the star against collapse.

In this talk, I will describe the realisation of the first quantum degenerate mixture of bosons and fermions in a gas of trapped atoms [1]. In such a system the existence of Fermi pressure is striking, and causes the spatial extent of the Fermi cloud to be much larger than that of their bosonic counterpart.

I will also discuss more recent experiments at Rice University, in which, for the first time, bright soliton trains have been observed in a BEC [2].

1. Truscott, A.G., Strecker K.E., McAlexander W.I., Partridge G.B., and Hulet R.G., Observation of Fermi pressure in a gas of trapped atoms. Science, 2001. 291: p. 2570-2572.
2. Strecker, K.E., Partridge G.B., Truscott A.G., and Hulet R.G ., Formation and propagation of matter wave soliton trains. Submitted to Nature, 2002.

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