Theoretical Way to Overcome Photon Shot Noise Limits

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Nature publishes a fairly theoretical paper by Hoi-Kwan Lau & Aashish A. Clerk from University of Chicago "Fundamental limits and non-reciprocal approaches in non-Hermitian quantum sensing." The paper points to a way to overcome what is considered to be a fundamental limit - photon shot noise. The authors also plan to attack thermal noise in their future research.

"In a quantum setting, optical sensors are typically limited because light is made up of particles, and this discreteness leads to unavoidable noise. But this study revealed an unexpected method to combat that limitation... We think we’ve uncovered a new strategy for building extremely powerful quantum sensors."

Unfortunately, this revolution will not happen overnight. Everything in this paper is highly theoretical. A sensing system nonreciprocity is said to be the key factor in increasing the signal while keeping the same noise:

In conclusion, the authors say: "We... discussed a new method for enhancing dispersive measurement using effective non-Hermitian physics, namely the use of nonreciprocity to enhance sensing. We show that nonreciprocity allows one to arbitrarily exceed the fundamental bound on the measurement rate of a reciprocal sensor, and discussed a simple implementation that does not require any amplification processes. We also show that nonreciprocity can enhance the sensitivity of mode-splitting type sensor.

Finally, we note that the general theory developed in this work could be easily applied to more general kinds of sensing problems. For example, the same formalism could be used to understand the performance of non-Hermitian sensors when thermal noise dominates (as would be the case for systems deep in the classical limit).


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