Planar quantum squeezing in spin-1/2 systems

Abstract

Planar quantum squeezed (PQS) states, i.e. quantum states which are squeezed in two orthogonal spin components on a plane, have recently attracted attention due to their applications in atomic interferometry and quantum information [1, 2]. In this paper we present an application of the framework described by Puentes et al [3] for planar quantum squeezing via quantum nondemolition (QND) measurement, for the particular case of spin-1/2 systems and nonzero covariance between orthogonal spin components. Our regime, consisting of spin-1/2 entangled planar-squeezed (EPQS) states, is of interest as it can present higher precision for quantum parameter estimation and quantum magnetometry at finite intervals. We show that entangled planar-squeezed states (EPQS) can be used to reconstruct a specific quantum parameter, such as a phase or a magnetic field, within a finite interval with higher precision than PQS states, and without iterative procedures. EPQS is of interest in cases where limited prior knowledge about the specific subinterval location for a phase is available, but it does not require knowledge of the exact phase a priori, as in the case of squeezing on a single spin component.