Cavity-free quantum optomechanical cooling by atom-modulated radiation

We theoretically study how the mechanical motion of an oscillating mirror reacts to electromagnetic radiation which is modulated by remotely trapped Λ-level atoms. When illuminated by continuous-wave radiation, the mirror motion will induce red and blue sideband radiation fields that respectively increases and reduces phonon excitation. We find that by suitably driving the atoms, specific frequencies of radiation could be effectively reflected back to the mirror by a four-wave mixing process. Such process allows us to manipulate the heating and cooling effects of the mirror. Particularly, if the red sideband fields accumulates a π phase during the round-trip, the heating effects can be eliminated, thus the mirror could be cooled to the ground motional state. Without the necessity of cavity installation and perfect alignment, our proposal complements other efforts in quantum cooling of macroscopic objects.