  Quantum information can be stored in micromechanical resonators, encoded as
quanta of vibration known as phonons. The vibrational motion is then restricted
to the stationary eigenmodes of the resonator, which thus serves as local
storage for phonons. In contrast, we couple propagating phonons to an
artificial atom in the quantum regime, and reproduce findings from quantum
optics with sound taking over the role of light. Our results highlight the
similarities between phonons and photons, but also point to new opportunities
arising from the unique features of quantum mechanical sound. The low
propagation speed of phonons should enable new dynamic schemes for processing
quantum information, and the short wavelength allows regimes of atomic physics
to be explored which cannot be reached in photonic systems.

Mesoscale and Nanoscale Physics