Measurements of a quantum bulk acoustic resonator using a superconducting qubit

TL;DR

This paper demonstrates quantum control of a piezoelectric bulk acoustic resonator coupled to a superconducting qubit, highlighting its potential for quantum acoustics and hybrid quantum systems at cryogenic temperatures.

Contribution

It introduces a high-Q, GHz-frequency quantum bulk acoustic resonator coupled to a superconducting qubit using a flip-chip technique, enabling quantum control of mechanical states.

Findings

Achieved large electromechanical coupling at 4.88 GHz

Demonstrated quantum control of mechanical modes

High intrinsic mechanical quality factor (~4.3×10^4)

Abstract

Phonon modes at microwave frequencies can be cooled to their quantum ground state using conventional cryogenic refrigeration, providing a convenient way to study and manipulate quantum states at the single phonon level. Phonons are of particular interest because mechanical deformations can mediate interactions with a wide range of different quantum systems, including solid-state defects, superconducting qubits, as well as optical photons when using optomechanically-active constructs. Phonons thus hold promise for quantum-focused applications as diverse as sensing, information processing, and communication. Here, we describe a piezoelectric quantum bulk acoustic resonator (QBAR) with a 4.88 GHz resonant frequency that at cryogenic temperatures displays large electromechanical coupling strength combined with a high intrinsic mechanical quality factor $Q_i \approx 4.3 \times 10^4$. Using a recently-developed flip-chip technique, we couple this QBAR resonator to a superconducting qubit on a separate die and demonstrate quantum control of the mechanics in the coupled system. This approach promises a facile and flexible experimental approach to quantum acoustics and hybrid quantum systems.