Measurement of a quantum system using spin-mechanical conversion

TL;DR

This paper demonstrates converting quantum spin measurements in diamond defects into macroscopic mechanical rotations, enabling high-contrast readout and coherent control for advanced sensing and quantum state manipulation.

Contribution

It introduces a novel spin-mechanical coupling method in levitated diamonds, linking quantum spin states to measurable mechanical motion at room temperature.

Findings

Achieved over 70% spin readout contrast.

Demonstrated pulsed detection of Rabi oscillations and spin-echo interferometry.

Measured spin torque-induced reorientation with high temporal resolution.

Abstract

Levitated macroscopic particles exhibiting quantum mechanical effects are garnering increased attention as a means for precision sensing and testing quantum mechanics. Defects in diamond, such as the nitrogen-vacancy (NV) centre possess optically-addressable spins with long coherence times at room temperature and offer an intriguing system to examine quantum spin dynamics coupled to a macroscopic classical particle. In this work, we convert the outcome of a quantum measurement on an ensemble of spins into a macroscopic rotation of the host particle via spin-mechanical coupling. Following a sequence of green laser and microwave control pulses, spin-mechanical coupling between the final qubit spin state and the host particle -- an electrically-levitated diamond -- exerts a torque on the particle that deflects a weak near-infra-red laser beam. We measure spin readout contrast in excess of 70\%, and demonstrate pulsed mechanical detection of coherent Rabi oscillations, spin-echo interferometry and $T_1$-induced relaxation. We directly measure with temporal resolution the particle reorientation from a 60\,attonewton-metre spin torque induced by flipping the spins. Our results open up interesting new opportunities for levitated spin-mechanical systems using pulsed control, from improved sensing to the prospect of realising macroscopic quantum superposition states.