Abstract
Long-lived mechanical oscillators are actively pursued as critical resources for quantum storage, sensing, and transduction. However, achieving deterministic quantum control while limiting mechanical dissipation remains a persistent challenge. Here, we demonstrate strong coupling between a transmon superconducting qubit and an ultra-long-lived nanomechanical oscillator (T1 ≈ 25 ms at 5 GHz, Q ≈ 0.8 × 10⁹) by leveraging the low acoustic loss in silicon and phononic bandgap engineering. The qubit-oscillator system achieves large cooperativity (C_T₁≈ 1.5×10⁵, C_T₂≈ 150), enabling the generation of non-classical states and the investigation of mechanisms underlying mechanical decoherence. We show that dynamical decouplingx2014implemented through the qubitx2014can mitigate decoherence, leading to a mechanical coherence time of T₂≈ 1 ms. These findings extend the exceptional storage capabilities of mechanical oscillators to the quantum regime, putting them forward as compact bosonic elements for future applications in quantum computing and metrology.