Quantum control of surface acoustic wave phonons

TL;DR

This paper demonstrates full quantum control of a macroscopic mechanical resonator using surface acoustic waves coupled to a superconducting qubit, enabling superpositions of phonon states and advancing quantum acoustic technologies.

Contribution

It introduces a method for controlling and measuring quantum states of surface acoustic wave phonons via superconducting qubits, achieving superpositions and state mapping.

Findings

Generated superpositions of zero and one phonon states.

Performed Wigner tomography of mechanical quantum states.

Established a platform for quantum acoustic applications.

Abstract

The superposition of quantum states is one of the hallmarks of quantum physics, and clear demonstrations of superposition have been achieved in a number of quantum systems. However, mechanical systems have remained a challenge, with only indirect demonstrations of mechanical state superpositions, in spite of the intellectual appeal and technical utility such a capability would bring. This is due in part to the highly linear response of most mechanical systems, making quantum operation difficult, as well as their characteristically low frequencies, making it difficult to reach the quantum ground state. In this work, we demonstrate full quantum control of the mechanical state of a macroscopic mechanical resonator. We strongly couple a surface acoustic wave resonator to a superconducting qubit, using the qubit to control and measure quantum states in the mechanical resonator. Most notably, we generate a quantum superposition of the zero and one phonon states and map this and other states using Wigner tomography. This precise, programmable quantum control is essential to a range of applications of surface acoustic waves in the quantum limit, including using surface acoustic waves to couple disparate quantum systems.