Beating the shot-noise limit at finite temperatures with many-body systems

Beating the shot-noise limit at finite temperatures with many-body systems

Seminar author:Mohammad Mehboudi

Event date and time:03/16/2016 02:30:pm

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Parameter estimation in strongly correlated systems is gaining an increasing attention, due to the crucial role of the value of such parameters in determining the (phase) behaviour of many body systems. In this work we deal with the estimation of coupling constants of such systems at finite temperatures. To this end we use tools from quantum metrology and find the ultimate precision of estimation allowed by quantum mechanics. Then we suggest some protocols/observable using which one may achieve a reasonably precise estimation, compared to the ultimate bound.

Specially we prove the optimality of the collective angular momentums, being among the few simple observables one can measure practically, in the estimation of both the external magnetic field and the spin-spin interaction strength of the XX model. We show that, up to a constant, the quantum Fisher information associated to the magnetic field is equal to the well known physical quantity magnetic susceptibility. Although we observe that at finite temperatures the quantum Fisher information scales linearly with the resources, using an adaptive scheme the scaling power enhances by 1/3.