Title: Blue-detuned magneto-optical trap,
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$\mu$K. The phase-space
density is higher than in normal atomic MOTs, and a million times higher than
comparable red-detuned type-II MOTs, making it 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
$1.8(4)\times10^{-10}$cm$^{3}$s$^{-1}$.