  We experimentally demonstrate, for the first time, noise diagnostics by
repeated quantum measurements. Specifically, we establish the ability of a
single photon, subjected to random polarisation noise, to diagnose
non-Markovian temporal correlations of such a noise process. In the frequency
domain, these noise correlations correspond to colored noise spectra, as
opposed to the ones related to Markovian, white noise. Both the noise spectrum
and its corresponding temporal correlations are diagnosed by probing the photon
by means of frequent, (partially-)selective polarisation measurements. Our main
result is the experimental demonstration that noise with positive temporal
correlations corresponds to our single photon undergoing a dynamical regime
enabled by the quantum Zeno effect (QZE), while noise characterized by negative
(anti-) correlations corresponds to regimes associated with the anti-Zeno
effect (AZE). This demonstration opens the way to a new kind of noise
spectroscopy based on QZE and AZE in photon (or other single-particle) state
probing.

Quantum Physics