Geometry-tunable directional ground-state cooling in an optomechanical resonator

We propose a theoretical scheme for geometry-tunable directional ground-state cooling in a whispering-gallery-mode optomechanical resonator. By coherently suppressing intrinsic backscattering with an auxiliary nanoparticle and applying a mode-selective parametric drive, the system acquires a strongly asymmetric cooling response for the two driving directions. As a result, ground-state cooling remains achievable in the backward-driving configuration even deep in the unresolved-sideband regime, whereas the forward-driving case reduces to conventional and much less efficient optomechanical cooling. We further show that the directional cooling contrast is enhanced by increasing the cavity dissipation rate and, within the regime where ground-state cooling remains valid, also by increasing the environmental temperature. These results identify coherent scattering control combined with parametric reservoir engineering as an effective strategy for directional cooling and chiral quantum control in whispering-gallery-mode optomechanical platforms.