Quantum state preparation, tomography, and entanglement of mechanical oscillators

TL;DR

This paper demonstrates the control, readout, and entanglement of two nanomechanical resonators using a superconducting qubit, advancing quantum acoustic processing capabilities with quantum state tomography and nonclassical state preparation.

Contribution

It introduces a method to control and measure multiple mechanical resonators with a single qubit, enabling quantum state manipulation and tomography of entangled mechanical states.

Findings

Successful quantum state control of two mechanical resonators.

Deterministic manipulation of mechanical states via swap operations.

Quantum tomography of nonclassical and entangled mechanical states.

Abstract

Precisely engineered mechanical oscillators keep time, filter signals, and sense motion, making them an indispensable part of today's technological landscape. These unique capabilities motivate bringing mechanical devices into the quantum domain by interfacing them with engineered quantum circuits. Proposals to combine microwave-frequency mechanical resonators with superconducting devices suggest the possibility of powerful quantum acoustic processors. Meanwhile, experiments in several mechanical systems have demonstrated quantum state control and readout, phonon number resolution, and phonon-mediated qubit-qubit interactions. Currently, these acoustic platforms lack processors capable of controlling multiple mechanical oscillators' quantum states with a single qubit, and the rapid quantum non-demolition measurements of mechanical states needed for error correction. Here we use a superconducting qubit to control and read out the quantum state of a pair of nanomechanical resonators. Our device is capable of fast qubit-mechanics swap operations, which we use to deterministically manipulate the mechanical states. By placing the qubit into the strong dispersive regime with both mechanical resonators simultaneously, we determine the resonators' phonon number distributions via Ramsey measurements. Finally, we present quantum tomography of the prepared nonclassical and entangled mechanical states. Our result represents a concrete step toward feedback-based operation of a quantum acoustic processor.