Coherent Interaction-free Detection of Noise

Abstract: 

Characterizing noise at certain frequencies is essential for the development of quantum technologies. We propose interaction-free measurements (IFMs) as a noise-detection technique and explore two conceptually different schemes: the coherent (cIFM) and the projective (pIFM) realizations. These detectors consist of a qutrit whose second transition is coupled to a resonant oscillatory field that may have noise in amplitude or phase. For comparison, we consider a paradigmatic detector based on absorption, consisting of a single qubit interacting resonantly with the field. If the noise field has reasonably strong coupling with the detector qubit, then the state of the qubit will be influenced in the presence of noise. We find that the qutrit scheme offers clear advantages compared to the qubit detector, allowing precise detection and characterization of the noise. Moreover, under certain circumstances, the cIFM detector can distinguish between clustered noise signals and other arbitrarily correlated noises, which the qubit and pIFM detector cannot. As such, we study the signature of noise correlations in the cIFM detector’s signal.