Quantum metrology with critical driven-dissipative collective spin system

Abstract

We propose a critical dissipaive quantum metrology schemes for single parameter estimation which are based on a quantum probe consisting of coherently driven ensemble of N spin-1/2 particles under the effect of squeezed, collective spin decay. The collective spin system exhibits a dissipative phase transition between thermal and ferromagnetic phases, which is characterized with nonanalytical behavior of the spin observables. We show that thanks to the dissipative phase transition the sensitivity of the parameter estimation can be significantly enhanced. Furthermore, we show that our steady state is an entangled spin squeezed state which allow to perform parameter estimation with sub shot-noise limited measurement uncertainty.

Quantum thermodynamics of boundary time-crystals

“…Despite these profound insights on their emergent dynamics, much less is known about thermodynamic properties of time-crystalline phases (see related issues for nonequilibrium engines [27][28][29]). Understanding and controlling heat currents, power exchanges and irreversible entropy production in these systems is, however, both of fundamental interest and of practical relevance, for instance for exploring efficiency measures and thermodynamic costs of possible applications of time-crystals as resources for quantum sensing [30][31][32]. The main challenge for such a quantum thermodynamic analysis lies in the fact that, given that these systems are genuinely out of equilibrium, they are not described by thermal open quantum dynamics [33].…”

Entangled time-crystal phase in an open quantum light-matter system

“…It consists of a collective many-body spin model which allows for both efficient numerical simulations [43][44][45][46][47][48] and exact analytical solutions [38,[49][50][51][52][53][54]. This model features quantum correlations between spins in its stationary phase -witnessed by non-zero spin-squeezing and two-qubit entanglementbut only classical correlations in the time-crystal regime [38,52,53,[55][56][57][58], which is described by highly mixed and effectively classical states [39,52,53,59]. It thus remains an open question whether (boundary) time-crystal phases can host quantum effects or whether these phases are essentially purely classical dynamical regimes.…”

“…Explicitly taking into account the light field further allows us -to best of our knowledge for the first time -to observe the emergence of quantum correlations, including entanglement, in a time-crystal regime. The existence of these correlations may motivate the development of alternative strategies for exploiting these phases for enhanced metrological applications [57,58].…”

Continuous Sensing and Parameter Estimation with the Boundary Time Crystal

“…Alternative quantum metrology approaches try to harness nonequilibrium phenomena in order to enhance the sensitivity of parameter estimation [38]. For instance, this is the case of protocols exploiting dissipative phase transitions [38][39][40][41][42][43][44][45][46]. Another key idea is to exploit the information contained in the emissions of open quantum systems via continuous monitoring protocols [38,[47][48][49][50][51][52][53][54].…”

“…In this work we show how dissipative time-crystals can be exploited for sensing applications, reaching a sensitivity which can surpass the standard quantum limit. Recent works have studied BTCs from the perspective of critically enhanced sensing [44,45], focusing on prop-erties of the system alone, while Ref. [65] considered a discrete time-crystal for sensing time-dependent fields.…”