No abstract

In an ensemble of two-level atoms that can be described in terms of a collective spin, entangled states can be used to enhance the sensitivity of interferometric precision measurements. While non-Gaussian spin states can produce larger quantum enhancements than spin-squeezed Gaussian states, their use requires the measurement of observables that are nonlinear functions of the three components of the collective spin. In this paper we develop strategies that achieve the optimal quantum enhancements using non-Gaussian states produced by a nonlinear one-axis-twisting Hamiltonian, and show that measurement-afterinteraction techniques, known to amplify the output signals in quantum parameter estimation protocols, are effective in measuring nonlinear spin observables. Including the presence of the relevant decoherence processes from atomic experiments, we determine analytically the quantum enhancement of non-Gaussian over-squeezed states as a function of the noise parameters for arbitrary atom numbers.Résumé. Dans un ensemble d'atomes à deux niveaux descriptible par un spin collectif, on peut utiliser les états intriqués pour améliorer la sensibilité des mesures interférométriques. Bien que les états de spin non gaussiens puissent produire des améliorations quantiques plus importantes que les habituels état comprimés de spin, gaussiens, leur utilisation nécessite la mesure d'observables non linéaires en les trois composantes du spin collectif. Nous expliquons ici comment maximiser le gain quantique en utilisant des états non gaussiens surcomprimés produits par un hamiltonien non linéaire de torsion à un axe, et nous montrons que les techniques de mesure après intéraction, connues pour amplifier les signaux de sorties

We show that a significant quantum gain corresponding to squeezed or over-squeezed spin states can be obtained in multiparameter estimation by measuring the Hadamard coefficients of a 1D or 2D signal. The physical platform we consider consists of two-level atoms in an optical lattice in a squeezed-Mott configuration, or more generally by correlated spins distributed in spatially separated modes. Our protocol requires the possibility to locally flip the spins, but relies on collective measurements. We give examples of applications to scalar or vector field mapping and compressed sensing.

No abstract