Propagation-Distance Limit for a Classical Nonlocal Optical System

TL;DR

This paper derives quantum-speed-limit bounds for nonlocal optical beams, establishing a fundamental propagation-distance limit for mode distinguishability, and demonstrates practical applications in beam shaping and high-sensitivity metrology.

Contribution

It introduces a classical optical analogue of quantum speed limits, providing analytic bounds on propagation distance for mode conversion and enabling high-precision sensing.

Findings

Derived closed-form bounds for optical propagation distance

Designed a beam shaper achieving mode conversion within millimeters

Achieved high index and temperature sensitivities for metrology

Abstract

We derive closed-form analog quantum-speed-limit (QSL) bounds for highly nonlocal optical beams whose paraxial propagation is mapped to a reversed (inverted) harmonic-oscillator generator. Treating the longitudinal coordinate $z$ as an evolution parameter (propagation distance), we construct the propagator, evaluate the Bures distance, and obtain analytic Mandelstam--Tamm and Margolus--Levitin bounds that fix a propagation-distance limit $z_{\mathrm{PDL}}$ to reach a prescribed mode distinguishability. This distance-domain constraint is the classical optical analogue of the minimal orthogonality time in quantum mechanics. We then propose a compact self-defocusing PDL beam shaper that achieves strong transverse-mode conversion within millimeter scales. We further show that small variations in refractive index, beam power, or temperature shift $z_{\mathrm{SL}}$ with high leverage, enabling speed-limit-based metrology with index sensitivities down to $10^{-7}$ RIU and temperature resolutions of order $1$ mK. The results bridge distance-domain QSL geometry and practical photonic applications.