A Rydberg-dressed Magneto Optical Trap

We Rydberg dress a magneto-optical trap of strontium atoms, mixing Rydberg character into atoms as they are cooled and confined. A recently developed tunable high-power narrow-linewidth 319 nm laser is used to excite and characterise triplet Rydberg states in strontium. Off-resonantly dressing a cloud of atoms in a narrow-line MOT operating on the 5s2 1S0 - 5s5p 3P1 transition, we observe a one-body AC Stark shift on the cloud, which we characterise to identify a regime in which only Rydberg dressed atoms are trapped in the MOT. In this cloud the Rydberg dressed atoms are both trapped and cooled. Increasing atomic density in the dressed MOT, plasma formation is observed at densities lower than the density necessary for observation of Rydberg dressed atoms. This plasma is caused by a build-up of charges due to spontaneous ionisation of Rydberg atoms, which then DC Stark shift the Rydberg state onto resonance with the coupling laser. The high charge density of the plasma then results in strong Rydberg excitation that causes rapid depletion of atoms. Regimes using optimum Rydberg states and charge-extracting electric fields are identified that may prevent plasma formation, and allow the interacting regime to be reached. Such a regime, with cooling, confinement, and tunable interactions, may form the basis of a quantum simulator for dissipative many-body systems.