Quantum Oscillator Noise Spectroscopy via Displaced Cat States
Alistair R. Milne, Cornelius Hempel, Li Li, Claire Edmunds, Harry J. Slatyer, Harrison Ball, Michael Hush, Michael J. Biercuk
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.