Abstract
We present the properties and advantages of a new magneto-optical trap (MOT) where blue-detuned light drives "type-II" transitions that have dark ground states. Using ^{87}Rb, we reach a radiation-pressure-limited density exceeding 10^{11} cm^{-3} and a temperature below 30 μK. The phase-space density is higher than in normal atomic MOTs and a million times higher than comparable red-detuned type-II MOTs, making the blue-detuned MOT particularly attractive for molecular MOTs, which rely on type-II transitions. The loss of atoms from the trap is dominated by ultracold collisions between Rb atoms. For typical trapping conditions, we measure a loss rate of 1.8(4)×10^{-10} cm^{3} s^{-1}.
Highlights
We present the properties and advantages of a new magneto-optical trap (MOT) where blue-detuned light drives “type-II” transitions that have dark ground states
Applications of ultracold molecules [2] are sure to be advanced by recent demonstrations of molecular MOTs [3,4,5,6]
The dimensionless phasespace density is 6 × 10−6, about a million times higher than for a red-detuned type-II MOT [9]. This phasespace density is considerably higher than usually achieved in a normal type-I MOT and is similar to that achieved in the best dark spontaneous-force optical trap (SPOT) MOTs [14,15]
Summary
We present the properties and advantages of a new magneto-optical trap (MOT) where blue-detuned light drives “type-II” transitions that have dark ground states. All previous MOTs have been made using light red detuned from the atomic or molecular transition. We demonstrate a blue-detuned type-II MOT of 87Rb with a density exceeding 1011 cm−3
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