Maximizing information obtainable by quantum sensors with the Quantum Zeno Effect

Abstract

Quantum estimation theory can be exploited to use quantum systems as measurement devices. Wehave recently demonstrated that proper quantum dynamical control on a quantum sensor makes moreefficient the estimation of the parameters that characterize its environment at the molecular ornanometric scales [1-4]. We here consider a 1/2-spin as a magnetic field sensor, subjected to periodicprojective measurements. Projective measurements serve as a control tool, which turns a coherentoscillating evolution into an exponential decaying evolution, where the information of the coherent field isthen codified into the decay rate, instead of the oscillation frequency. We demonstrate with quantuminformation theory that when an off-resonance alternating magnetic field is probed, the projectiveevolution magnifies information on the magnetic field's strength [5]. We define the parameter regimeswhere this inference protocol outperforms the free evolution of the sensor. We show applications of themethod for determining molecular structures with quantum sensors.