Quantum Phase Estimation Beyond the Gaussian Limit

Abstract

Quantum metrology aims to enhance measurement precision beyond the standard quantum limit (SQL), the benchmark set by classical resources, enabling advances in sensing, imaging, and fundamental physics. A critical milestone beyond the SQL is surpassing the Gaussian bound -- the fundamental precision limit achievable with any Gaussian state, such as optimally squeezed states. Certain non-Gaussian states, specifically asymmetric superpositions of coherent states (SCS) and superpositions of a vacuum and a Fock state (ON states), can outperform this Gaussian bound within an intermediate energy range. In particular, asymmetric SCS emerge as a highly practical resource for near-term quantum sensing architectures operating beyond the Gaussian limit due to their efficient preparation and processing via a constant-complexity protocol. Our comprehensive analysis under realistic loss, noise, and detection schemes quantifies the critical trade-off between achievable precision and the operational range of the non-Gaussian advantage. This work sheds light on the fundamental impact of non-Gaussianity and asymmetry on metrological tasks, and offers insights on how to leverage such resources in realistic near-term quantum enhanced sensors beyond the Gaussian limit.