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}.

We study several new magneto-optical trapping configurations in 87 Rb. These unconventional MOTs all use type-II transitions, where the angular momentum of the ground state is greater than or equal to that of the excited state, and they may use either red-detuned or blue-detuned light. We describe the conditions under which each new MOT forms. The various MOTs exhibit an enormous range of lifetimes, temperatures and density distributions. At the detunings where they are maximized, the lifetimes of the various MOTs vary from 0.1 to 15 s. One MOT forms large ring-like structures with no density at the centre. The temperature in the red-detuned MOTs can be three orders of magnitude higher than in the blue-detuned MOTs. We present measurements of the capture velocity of a blue-detuned MOT, and we study how the loss rate due to ultracold collisions depends on laser intensity and detuning. arXiv:1807.07655v1 [physics.atom-ph]

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