Fingerprints of Qubit Noise in Transient Cavity Transmission

TL;DR

This paper demonstrates that transient cavity transmission measurements can reveal the spectral density of qubit noise, offering a new method to characterize noise in quantum systems.

Contribution

It provides analytical expressions linking noise spectral density to cavity transmission and proposes a practical method for noise spectral density extraction from measurements.

Findings

Transient transmission reflects noise spectral features.

Analytical formulas for various noise types are derived.

A method for spectral density extraction with bounded error is proposed.

Abstract

Noise affects the coherence of qubits and thereby places a bound on the performance of quantum computers. We theoretically study a generic two-level system with fluctuating control parameters in a photonic cavity and find that basic features of the noise spectral density are imprinted in the transient transmission through the cavity. We obtain analytical expressions for generic noise and proceed to study the cases of quasistatic, white and $1/f^{\alpha}$ noise in more detail. Additionally, we propose a way of extracting the spectral density for arbitrary noise in a frequency band only bounded by the range of the qubit-cavity detuning and with an exponentially decaying error due to finite measurement times. Our results suggest that measurements of the time-dependent transmission probability represent a novel way of extracting noise characteristics.