Autonomous dissipative Maxwell's demon in a diamond spin qutrit

Abstract

Engineered dynamical maps that combine not only coherent, but also unital and dissipative transformations of quantum states, have demonstrated a number of technological applications, and promise to be a beneficial tool also in quantum thermodynamic processes. Here, we exploit control of a spin qutrit to investigate energy exchange fluctuations of an open quantum system. The qutrit engineer dynamics can be understood as an autonomous feedback process, where random measurement events condition the subsequent dissipative evolution. To analyze this dynamical process, we introduce a generalization of the Sagawa-Ueda-Tasaki relation for dissipative dynamics and verify it experimentally. Not only we characterize the efficacy of the autonomous feedback protocol, but also find that the characteristic function of energy variations G(η) becomes insensitive to the process details at a single specific value of its argument. This allows us to demonstrate that a fluctuation theorem of the Jarzynski type holds for this general dissipative feedback dynamics, while previous relations were limited to unital dynamics. Moreover, in addition to the feedback efficacy, we find a witness of unitality associated with the fixed point of the dynamics.

Energy fluctuation relations and repeated quantum measurements

“…A recent effort in this direction has been conducted in Ref. [41] where a unified framework to describe energy fluctuations in quantum systems under controllable feedback mechanisms is presented. In such a case, indeed, the considered experimental system (a NV center in diamond) is repeatedly subject to random measurements and dissipative events (modelled by superoperator in Lindblad form [76]), whose occurrence is conditioned by the measurements' results.…”

“…Overall, in the quantum systems case, it has been determined that the fluctuations theorems still remain valid provided that (i) initially the system is at thermodynamic equilibrium [28]; (ii) the system's evolution is governed by a unital quantum map, whereby the identity is a fixed point of the map [29,30]. Moreover, it is worth also mentioning results and applications [31][32][33][34] concerning the quantum Zeno effect [35], and the works by Sagawa and Ueda [36,37], together with related studies [38][39][40][41], that deal with the informational aspect of nonequilibrium thermodynamics by studying the dynamics of a quantum system subject to closed-loop control. Finally, protocols involving only series of quantum measurements or cyclical repetitions of them, have shown also the ability to fuel quantum heat engines [42,43], provided that the right measurement observable is chosen [44].…”