MEASURING COHERENCE WHILE OBSERVING NOISE

We present a new approach to the measurement of coherence. By monitoring the quantum interference fluctuations in the population excited by a pair of time-delayed, randomly phased pulses, it is possible to extract information on internal dynamics, energy level splittings, and characteristic coherence decay times of the medium. As a proof of concept, we demonstrate the measurement of phase relaxation and doublet separation in atomic potassium. The principle of coherence observation by interference noise is very general, is shown to be robust and with inherent time resolution of a few optical cycles, and is proposed as an alternative to many;interferometric applications.