Quantum oscillator noise spectroscopy via displaced cat states

TL;DR

This paper presents a new method for characterizing frequency noise in quantum harmonic oscillators by coupling them to a driven qubit and using convex optimization to reconstruct the noise spectrum, achieving high sensitivity in trapped ion systems.

Contribution

It introduces a novel noise spectroscopy technique utilizing displaced cat states and continuous qubit control, enabling detailed spectral analysis of oscillator frequency fluctuations.

Findings

Successfully identified intrinsic motional frequency noise in a trapped ion.

Achieved sensitivity to sub-Hz fluctuations in a spectral range up to 50 kHz.

Demonstrated the method's effectiveness in quantum oscillator noise characterization.

Abstract

Quantum harmonic oscillators are central to many modern quantum technologies. We introduce a method to determine the frequency noise spectrum of oscillator modes through coupling them to a qubit with continuously driven qubit-state-dependent displacements. We reconstruct the noise spectrum using a series of different drive phase and amplitude modulation patterns in conjunction with a data-fusion routine based on convex optimization. We apply the technique to the identification of intrinsic noise in the motional frequency of a single trapped ion with sensitivity to fluctuations at the sub-Hz level in a spectral range from quasi-DC up to 50 kHz.