Long spin relaxation times in a single-beam blue-detuned optical trap

A scheme to trap atoms in a blue-detuned optical dipole trap, formed with a single laser beam and a holographic phase plate, is demonstrated. 105 rubidium atoms are trapped for (1/e lifetime) ∼300 msec, at temperatures of ∼24 μK. and a density of ∼7 × 10¹¹ atoms/cm³, for a trapping beam detuning of 0.1-30 nm. The time for a trapped atom to scatter one photon off the trapping beam is measured and found to be linear in the trapping laser detuning. At a detuning of 0.5 nm from resonance this time was measured to be ∼100 msec, indicating that the atoms are exposed on average only to ∼1/700 of the maximal light intensity in the trap. The use of a single laser beam allows for simple dynamical changes of the potential and large adiabatic compressions, while keeping the atoms mainly in the dark.