Quantum acoustic systems, in which superconducting qubits are coupled to quantized me- chanical degrees of freedom, offer a unique paradigm for the investigation of the fundamental properties of phonons as well as the development of quantum technologies based on phonons. This thesis presents several experiments that demonstrate the interaction between a super- conducting transmon qubit and a high-frequency surface acoustic wave (SAW) resonator. We use classical modeling techniques to design the electrical conductance of the SAW res- onator, which encodes the spectral properties of the phononic modes hosted by the SAW device. These spectral features are then investigated by leveraging the extreme sensitivity of the qubit to its local environment, and highlight the complex mode structure of surface phonons in our experiments. Furthermore, by considering the full phononic density of states, we identify interference effects between resonant and lossy phonon modes, which act as the primary source of decoherence for the qubit. These phonons that are not confined within the SAW cavity act as an engineered dissipation channel, which we use advantageously as a mechanism for the dynamical quantum state preparation and stabilization of high-purity qubit states. The results of this thesis highlight the versatility of quantum acoustics sys- tems in both the strong and weak coupling regimes, and emphasize the ability to engineer phononic interference and dissipation in the quantum regime.
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