4 research outputs found
Camparison of the Hanbury Brown-Twiss effect for bosons and fermions
Fifty years ago, Hanbury Brown and Twiss (HBT) discovered photon bunching in
light emitted by a chaotic source, highlighting the importance of two-photon
correlations and stimulating the development of modern quantum optics . The
quantum interpretation of bunching relies upon the constructive interference
between amplitudes involving two indistinguishable photons, and its additive
character is intimately linked to the Bose nature of photons. Advances in atom
cooling and detection have led to the observation and full characterisation of
the atomic analogue of the HBT effect with bosonic atoms. By contrast, fermions
should reveal an antibunching effect, i.e., a tendency to avoid each other.
Antibunching of fermions is associated with destructive two-particle
interference and is related to the Pauli principle forbidding more than one
identical fermion to occupy the same quantum state. Here we report an
experimental comparison of the fermion and the boson HBT effects realised in
the same apparatus with two different isotopes of helium, 3He (a fermion) and
4He (a boson). Ordinary attractive or repulsive interactions between atoms are
negligible, and the contrasting bunching and antibunching behaviours can be
fully attributed to the different quantum statistics. Our result shows how
atom-atom correlation measurements can be used not only for revealing details
in the spatial density, or momentum correlations in an atomic ensemble, but
also to directly observe phase effects linked to the quantum statistics in a
many body system. It may thus find applications to study more exotic situations
>.Comment: Nature 445, 402 (2007). V2 includes the supplementary informatio
Simple method for producing Bose–Einstein condensates of metastable helium using a single-beam optical dipole trap
Ultracold metastable helium: Ramsey fringes and atom interferometry
We report on interference studies in the internal and external degrees of freedom of metastable triplet helium atoms trapped near quantum degeneracy in a 1:5 μm optical dipole trap. Applying a single π/2 rf pulse we demonstrate that 50% of the atoms initially in the m = +1 state can be transferred to the magnetic field insensitive m = 0 state. Two π/2 pulses with varying time delay allow a Ramseytype measurement of the Zeeman shift for a high precision measurement of the 2 3S1-2 1S0 transition frequency. We show that this method also allows strong suppression of mean-field effects on the measurement of the Zeeman shift, which is necessary to reach the accuracy goal of 0.1 kHz on the absolute transition frequencies. Theoretically the feasibility of using metastable triplet helium atoms in the m = 0 state for atom interferometry is studied demonstrating favorable conditions, compared to the alkali atoms that are used traditionally, for a non-QED determination of the fine structure constant