Ground-state cooling of a mechanical resonator by single- and two-phonon processes

Abstract

A scheme for ground-state cooling of a mechanical resonator by single- and two-phonon processes is analyzed. The mechanical resonator is coupled to two coupled quantum dots forming an effective Λ-type three-level structure and connected with two normal metal leads. The quantum dots are driven by two light fields; by choosing appropriate parameters, the electron can be trapped in the dark state of the system, a superposition of the two ground states. When the single-phonon absorption and emission processes are dominant, under the weak (strong) driving field circumstances, the mechanical resonator is cooled through absorbing a phonon when the electron jumps from dark state to bright state (one of the dressed states) and then tunnels out of the two coupled dots. Net cooling of the resonator to its ground state is possible in the absence of the electron-phonon dephasing via single-phonon processes. When the two-phonon processes are tuned to be stronger than the single-phonon processes, the mechanical resonator can be cooled to its nonclassical state.