1/fnoise for intermittent quantum dots exhibits non-stationarity and critical exponents

The power spectrum of quantum dot (QD) fluorescence exhibits noise, related to the intermittency of these nanosystems. As in other systems exhibiting noise, this power spectrum is not integrable at low frequencies, which appears to imply infinite total power. We report measurements of individual QDs that address this long-standing paradox. We find that the level of noise decays with the observation time. The change of the spectrum with time places a bound on the total power. These observations are in stark contrast with most measurements of noise in macroscopic systems which do not exhibit any evidence for non-stationarity. We show that the traditional description of the power spectrum with a single exponent β is incomplete and three additional critical exponents characterize the dependence on experimental time.