Publications - Magneto-Optical Traps
Cold collisions in a high-gradient magneto-optical trap, J. Phys. B: At. Mol. Opt. Phys. 35, 4899 (2002)BibTeX
We present a detailed analysis of the cold collision measurements performed in
a high-gradient magneto-optical trapwith a few trapped Cs atomsfirst presented
in Ueberholz et al (J. Phys. B: At.Mol. Opt. Phys. 33 (2000) L135). The ability
to observe individual loss events allows us to identify two-body collisions that
lead to the escape of only one of the colliding atoms (up to 10% of all collisional
losses). Possible origins of these events are discussed here. We also observed
strong modifications of the total loss rate with variations in the repumping laser
intensity. This is explained by a simple semiclassical model based on optical
suppression of hyperfine-changing collisions between ground-state atoms.
A single trapped atom: Light-matter interaction at the microscopic level, Ann. Phys. (Leipzig) 10, 9-18 (2001)BibTeX
For a single trapped atom the fluctuations of resonance fluorescence reveal its dynamic evolution at all relevant time scales. We review experimental results, extend interpretations and express expectations for future systems with fully controlled quantum properties.
Quantum Fluctuations of a Single Trapped Atom: Transient Rabi Oscillations and Magnetic Bistability, IEEE J. of Quantum Electronics 36, 1358 (2000)arXivBibTeX
Isolation of a single atomic particle and monitoring its resonance fluorescence is a powerful tool for studies of quantum effects in radiation-matter interactions. We present observations of quantum dynamics of an isolated neutral atom stored in a magneto-optical trap. By means of photon orrelations in the atom's resonance fluorescence we demonstrate the well-known phenomenon of photon antibunching which corresponds to transient Rabi oscillations in the atom. Through polarization-sensitive photon correlations, we show a novel example of resolved quantum fluctuations: pontaneous magnetic orientation of an atom. These effects can only be observed with a single atom.
Counting Cold Collisions, J. Phys. B: At. Mol. Opt. Phys. 33, L135 (2000)arXivBibTeX
We have experimentally explored a novel possibility to study exoergic cold atomic collisions. Trapping of small countable atom numbers in a shallow magneto-optical trap and monitoring of their temporal dynamics allows us to directly observe isolated two-body atomic collisions and provides detailed information on loss statistics. A substantial fraction of such cold collisional events has been found to result in the loss of one atom only. We have also observed for the first time a strong optical suppression of ground-state hyperfine-changing collisions in the trap by its repump laser field.
Magneto-optical trap as an optical lattice, Phys. Rev. A 61, 013409 (1999)BibTeX
We study the magneto-optical trap (MOT) as an optical lattice with a setup providing full phase control for all light fields. Although completely different light fields are possible for various phases, we have found experimental evidence that stored atoms are generally localized in micropotentials of the six-beam lattice. The influence of the phase variation is surprisingly small, suggesting that the robust behavior of the MOT is a consequence of this fact. We find furthermore good agreement of our experimental data with a simple theoretical model which reduces the complicated MOT to a description of steady-state atoms localized at points of the deepest adiabatic light-shift potential.
Single-atom dynamics revealed by photon correlations, Phys. Rev. A 58, R1657 (1998)BibTeX
We have studied a single neutral atom stored in a magneto-optical trap by recording arrival times of fluorescence photons emitted by the atom. Photon correlations at nanosecond scales (Rabi oscillations), at microseconds (intensity and polarization correlations), and also at milliseconds (position correlations) reveal the dynamical behavior of the atomic excitation, of the atomic orientation, and of its transport in the trap at both the optical wavelength scale and the trap size.
Decoding the dynamics of a single trapped atom from photon correlations, Appl. Phys. B 67, 689 (1998)BibTeX
Information on the dynamics of a single neutral atom can be decoded from fluctuations in the resonance fluorescence.
We have measured two-time photon correlations
of individual cesium atoms stored in a magneto-optical trap. We observe strong correlations at nanosecond scales (Rabi
oscillations), at microseconds (intensity and polarization correlations),
and also at milliscconds (position correlations) revealing the dynamical behavior of the atomic excitation, of
the atomic orientation, and of its transport in the trap at both the optical wavelength scale and the trap size. In this article
we compare our experimental results with a simplified model of an atom moving through an optical lattice. We investigate
the influence of light-field topogaphy and of the multilevel character of the atom on the shape and the visibility of the
Standing light fields for cold atoms with intrinsically stable and variable time phases, Opt. Comm. 148, 45 (1998)BibTeX
We present a novel method to realise a standing light field with a stable configuration in two or three dimensions. A single standing wave formed by two counterpropagating beams is folded and brought into intersection with itself. The values of the relative timephases are stable, a priori known, and can be altered arbitrarily by means of retardation plates. The polarisation configurations of three orthogonal standing waves include the standard magnetooptical trap and a novel three-dimensional pure polarisation lattice which we have investigated in a first spectroscopic measurement, providing strong evidence for atomic localisation in both cases.
Diffraction by cold atoms, Opt. Comm. 145, 57 (1997)BibTeX
We have observed diffraction of a laser probe beam by a trapped sample of cold atoms. The effect is only visible in the vicinity of a resonance line. The observed diffraction pattern arises from interference of the incident and scattered light wave, allowing reconstruction of geometric properties of the trapped sample from the holographic record.
Magnetostatic traps for charged and neutral particles, Hyperfine Interactions 109, 281-292 (1997)BibTeX
We have constructed magnetostatic traps from permanent magnets for trapping charged and neutral atoms. Two storage experiments are presented: a compact Penning trap for light ions and magnetic trapping of single neutral atoms. The dynamics of cold neutral atoms and their loss mechanisms in a quadrupole magnetostatic trap are discussed.
Observation of individual neutral atoms in magnetic and magneto-optical traps, Europhys. Lett. 34, 663 (1996)BibTeX
We have identified and photographed individual cesium atoms in a magneto-optical trap with steep magnetic gradients. By switching off the trapping light fields, single atoms were released to a bound state of the magnetic potential. A storage time of 38 s was measured for purely magnetic trapping, whereas a storage time of 147 s was observed in the corresponding magneto-optical trap.