  Measurement-based control has emerged as an important technique to prepare
mechanical resonators in pure quantum states for applications in quantum
information processing and quantum sensing. Conventionally this has required
two separate channels, one for probing the motion and another one acting back
on the resonator. In this work, we analyze and experimentally demonstrate a
technique of single-laser feedback cooling, where one laser is used for both
probing and controlling the mechanical motion. We show using an analytical
model and experiments that feedback cooling is feasible in this mode as long as
certain stability requirements are fulfilled. Our results demonstrate that, in
addition to being more experimentally feasible construction, the interference
effects of the single-laser feedback can actually be used to enhance cooling at
some parameter regimes.
