Abstract
We introduce a method to construct a quantum battery and a quantum Otto heat engine using a Nitrogen-Vacancy (NV) center spin coupled to a mechanical oscillator in a highly detuned regime. By precisely controlling the NV spin, we enable efficient energy exchange despite significant detuning, challenging conventional assumptions. This leads to a robust mechanical quantum battery and a cooling scheme driving the oscillator toward its ground state. Leveraging this, we implement a quantum Otto engine that produces mechanical work at maximum efficiency without decoupling from the hot bath, paving the way for practical quantum thermal machines.