QuSCo on-air: Prof Klaus Mølmer (AU) “Precision measurements – the noisier the better!”

Prof Klaus Mølmer kindly agreed to take part in our monthly seminars with a very insightful talk.


Much research has dealt with the sensitivity of measurement schemes based on the preparation, evolution, and final detection of non-classical states of a quantum system. In this talk, I shall discuss the analysis of continuous precision probing, i.e., the situation where a fluctuating signal is retrieved continuously in time from a single quantum system (the emitter). This is the typical situation, e.g., in spectroscopy, where we can use a master equation to predict the mean optical signal properties as a function of any system parameter, and thus we can infer its value from experimental data.

In a real experiment, the signal record fluctuates with time, and while this imposes measurement uncertainty, it also imposes a stochastic measurement back action: the system that emits the signal is constantly “quenched”. Analyses that takes this “permanently transient” dynamics explicitly into account yield much more information than the ones based on only mean signal values. It is (surprisingly) easy to derive the limit of sensitivity of any hypothetical measurement scheme on an emitted light signal, and it is (perhaps) surprising that this limit is actually reached by some of our standard detection methods in quantum optics.


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