Adaptive Quantum Nondemolition Measurement of a Photon Number
Bruno Peaudecerf, T. Rybarczyk, Stefan Gerlich, S. Gleyzes, J. M. Raimond, S. Haroche, I. Dotsenko, M. Brune · Physical Review Letters · 2014
In many quantum measurements, information is acquired incrementally by the successive interaction of meters with the measured system. Adaptive measurements minimize the use of resources (meters) by adjusting the measurement settings according to available information. We demonstrate an adaptive measurement for nondestructive photon counting in a cavity, based on Ramsey interferometry for Rydberg atoms interacting with the field. Tuning the interferometer in real time, we speed up the measurement by up to 45%. Such adaptive methods are promising for quantum metrology, state preparation, and feedback.