Photonic polarization gears for ultra-sensitive angular measurements

TLDR

Quantum metrology promises enhanced precision but is unlikely to be practical soon, yet its concepts inspire immediate classical or hybrid methods and motivate surpassing standard measurement limits for more precise physical estimation. This work presents a single‑photon scheme that measures light rotation angles with super‑resolution precision by borrowing NOON‑state quantum metrology concepts. The authors implement a photonic gear that amplifies a mechanical rotation θ to mθ in optical polarization using NOON‑like states up to m = 100, combine this gear effect with entanglement‑based quantum enhancement, and thereby achieve super‑resolving Malus' law. The gear effect yields single‑photon angular measurements matching the precision of m‑photon polarization‑only quantum strategies while being robust to losses, and the high gear ratio boosts optical non‑contact angular measurement precision by nearly two orders of magnitude.

Abstract

Quantum metrology bears a great promise in enhancing measurement precision, but is unlikely to become practical in the near future. Its concepts can nevertheless inspire classical or hybrid methods of immediate value. Here we demonstrate NOON-like photonic states of m quanta of angular momentum up to m=100, in a setup that acts as a 'photonic gear', converting, for each photon, a mechanical rotation of an angle θ into an amplified rotation of the optical polarization by mθ, corresponding to a 'super-resolving' Malus' law. We show that this effect leads to single-photon angular measurements with the same precision of polarization-only quantum strategies with m photons, but robust to photon losses. Moreover, we combine the gear effect with the quantum enhancement due to entanglement, thus exploiting the advantages of both approaches. The high 'gear ratio' m boosts the current state of the art of optical non-contact angular measurements by almost two orders of magnitude. Beating the standard measurement limits is a goal of metrology, as it would allow for more precise estimation of physical quantities. Borrowing concepts from NOON-state quantum metrology, this work presents a single-photon scheme to measure rotation angles of light with super-resolution precision.