We present a technique for recovering the spectrum of a non-Markovian bosonic bath and/or non- Markovian noises coupled to a harmonic oscillator. The treatment is valid under the conditions that the environment is large and hot compared to the oscillator, and that its temporal autocorrelation functions are symmetric with respect to time translation and reflection—criteria which we consider fairly minimal. We model a demonstration of the technique as deployed in the experimental scenario of a nanosphere levitated in a Paul trap, and show that it would effectively probe the spectrum of an electric field noise source from 102 to 106 Hz with a resolution inversely proportional to the measurement time. This technique may be deployed n quantum sensing, metrology, computing, and in experimental probes of foundational questions.
