Weakly invasive metrology: quantum advantage and physical implementations

Abstract

We consider the estimation of a Hamiltonian parameter of a set of highly photosensitive samples, which are damaged after a few photons Nabs are absorbed, for a total time T. The samples are modelled as a two mode photonic system, where photons simultaneously acquire information on the unknown parameter and are absorbed at a fixed rate. We show that arbitrarily intense coherent states can obtain information at a rate that scales at most linearly with Nabs and T, whereas quantum states with finite intensity can overcome this bound. We characterise the quantum advantage as a function of Nabs and T, as well as its robustness to imperfections (non-ideal detectors, finite preparation and measurement rates for quantum photonic states). We discuss an implementation in cavity QED, where Fock states are both prepared and measured by coupling atomic ensembles to the cavities. We show that superradiance, arising due to a collective coupling between the cavities and the atoms, can be exploited for improving the speed and efficiency of the measurement.

Understanding and Improving Critical Metrology. Quenching Superradiant Light-Matter Systems Beyond the Critical Point

“…Quenching across a transition further allows one to sidestep the issue of critical slowing down encountered when preparing states near a critical point (i.e., adiabatic critical quantum metrology). Therefore, an alternative aim of quantum metrology in systems exhibiting a superradiant phase transition could be to quench far beyond the critical point and imprint information into the macroscopically populated field (however, the coupling to highly sensitive systems such as biological samples may not be suitable for such a protocol [44]). Given the prevalence of superradiant phase transitions in light-matter systems [45], we expect that the protocol we present in the following will be applicable to a wide range of scenarios.…”

Gaussian quantum metrology in a dissipative environment

“…It can be physically realized by two optomechanical cavities [35] or nanomechanical resonators [36]. To measure the physical quantity κ of certain classical system, we couple the probe to the system such that the measured quantity κ is encoded into the probe state via the dynamics of the probe governed by the Hamiltonian ( = 1) [37]…”

Average number is an insufficient metric for interferometry

“…In practice, a more intricate model explicitly factoring in some absorption (damage) dynamic may be desirable both in quantifying a state's metrological performance and the potential damage it may cause by its application. Whether a given level of exposure, or absorption or damage is considered can give rise to different precisions [10,64].…”