Acoustic Phonon Fock States and Phonon-mediated Quantum Entanglement*

Superconducting qubits are an excellent system for building quantum computing systems, due to their good individual qubit performance metrics, the availability of a high fidelity two-qubit entangling gate, and their easy lithographic scaling to large qubit numbers. In addition, these qubits provide unique opportunities as testbed systems for quantum communication as well as developing hybrid quantum systems. One compelling opportunity is provided by the ability to use superconducting qubits to control and measure acoustically-active structures, structures that can potentially serve to link these qubits to other two-level systems or to e.g. optical signals. I will describe our recent progress in coupling superconducting qubits to surface acoustic waves. In one experiment we have demonstrated the quantum control of a single microwave-frequency mechanical mode in a surface acoustic wave (SAW) resonator [1]. In a second experiment [2], we have launched and received itinerant phonons in a 2 mm long acoustic Fabry-Perot resonator, and generated a phonon-mediated entanglement between two qubits.
[1] K. J. Satzinger et al., “Quantum control of surface acoustic wave phonons”, Nature 563, 661–665 (2018)
[2] A. Bienfait et al., “Phonon-mediated quantum state transfer and remote qubit entanglement”, Science 364, 368-371 (2019)