Squashed entanglement

Multipartite

Quantum network

Quantum mechanics

Engineering

Sensitivity (control systems)

Multipartite entanglement

Quantum metrology

Statistical physics

Gaussian

Metrology

Quantum entanglement

Observable

Quantum

Electronic engineering

Physics

Nonlinear system

Physical Review Letters

The well known metrological linear squeezing parameters (such as quadrature or spin squeezing) efficiently quantify the sensitivity of Gaussian states. Yet, these parameters are insufficient to characterize the much wider class of highly sensitive non-Gaussian states. Here, we introduce a class of metrological nonlinear squeezing parameters obtained by analytical optimization of measurement observables among a given set of accessible (possibly nonlinear) operators. This allows for the metrological characterization of non-Gaussian quantum states of discrete and continuous variables. Our results lead to optimized and experimentally-feasible recipes for high-precision moment-based estimation of a phase parameter and can be used to systematically construct multipartite entanglement and non-classicality witnesses for complex quantum states.

Metrological Nonlinear Squeezing Parameter