| We report the experimental results of a superconducting quantum bit coupled to a macroscopic mechanical resonator. The coupled sample was cooled in a dilution refrigerator to T = 25 mK. At this temperature, we measured the phonon occupation of the mechanical resonator and found it to be in the quantum ground state with high probability P 0 > 93%. We then excited the mechanical resonator from its ground state |0⟩ to the single phonon state |1⟩ by transferring a single quantum excitation from the quantum bit to the mechanical resonator. Using this ability, we probed the energy lifetime of the mechanical resonator, T1M = 6.1 ns, by monitoring the decay of a single phonon state. Next, we measured the decay of the superposed phonon state (|0⟩+|1⟩)/ 2 in order to extract the phase coherence time T 2M ≈ 2T1M. Finally, we explored higher phonon energy levels by directly exciting the mechanical resonator with a classical microwave source, thus creating a mechanical coherent state. |
