Control of Molecular Rotation in Helium Nanodroplets with an Optical Centrifuge

We experimentally demonstrate that the rotation of molecules embedded in helium nanodroplets can be controlled with an optical centrifuge, allowing for the study of molecular dynamics inside the strongly interacting many-body environment of superfluid helium at variable levels of rotational excitation. By doping the droplets with dimers of nitric oxide, (NO)_{2}, and measuring the degree of their centrifuge-induced alignment as a function of time, we show both the forced in-field rotation of molecules in a continuous range of frequencies, as well as the field-free resonant rotation with a long nanosecond-scale decay. The ability to control and monitor the rotational dynamics of molecular rotors inside the superfluid medium may shed new light on superfluidity and the interaction of superfluids with defects at the atomic level.