Quantum information flow in feedback cooling of a nanoparticle

Feedback cooling is a method of reducing particle fluctuations by feeding back measurement results. Stochastic thermodynamics of such measurement and feedback systems are well studied, and it is known that the second law is extended with a quantity called the information flow in systems where continuous information processing takes place.

In this talk, we will present the relationship between the quantum information flow and the particle cooling limit in feedback cooling in nanoparticle systems. We consider a setup where continuous QND position measurements are made on a nanoparticle, and the measurement results are used to provide feedback on position and momentum. We will show that a tighter second law with quantum information flow holds, which gives the cooling limit. Specifically, we will show that the upper limit of the rate of work extracted from the system is given by the effective temperature of the particle and the quantum information flow.