Cold Atoms and Quantum Gases

Applying narrowband continuous-wave lasers at a wavelength of 1083 nm we cool a gas of helium atoms in a long-lived state to temperatures one millionth of a degree above absolute zero. We trap about a million atoms of both isotopes of helium, 3He, which is a fermion, and 4He, which is a boson, either at the minimum of a magnetic field or in the centre of two focused laser beams (crossed dipole trap) in ultrahigh vacuum. At the temperatures and densities that can be realized in these traps Bose-Einstein condensation is realized for 4He and Fermi degeneracy for 3He. This has allowed several studies employing the wave nature and the small velocities of the atoms at these temperatures:

(1)   Tests of Quantum Statistical Mechanics for bosons and fermions with weak  and tunable interparticle interactions (in contrast to Condensed matter systems)
(2)   Tests of Quantum Electrodynamics measuring the frequency of ultranarrow atomic transitions in helium with a frequency comb laser
(3)   Tests of Quantum Atom Optics via the Hanbury Brown Twiss effect (see Fig.1)


Contact: Dr. Wim Vassen. Email: w.vassen@few.vu.nl
Physics of Light and Matter, Department of Physics and Astronomy        

 vassen

Fig. 1: Experimental setup (left) and the observed correlation function (right) for 4He (bosons, in red) and 3He (fermions, in blue). A cold helium cloud at T=0.5mK (at S) is released and the atoms fall under the influence of gravity onto a time-resolved and position-sensitive microchannel plate detector that detects single atoms. Horizontal (Dx andDy) and vertical (Dz) pair separations are recorded. The measured two-particle correlation function shows that identical bosons, like photons, show a bunching effect, whereas identical fermions show anti-bunching (related to the Pauli principle).

From: Nature 445, 402 (2007)