Broadband detection of a weak oscillatory field with unknown carrier frequency underlies magnetometry, axion searches and gravitational-wave sensing. We show that the Grover-like integration-time lower bound for this task is a geometric corollary an upper bound on the integrated quantum Fisher information, a metrological constraint. We further give an all-analog multi-resonant protocol based on a randomized Su-Schrieffer-Heeger control Hamiltonian and an m-register GHZ probe and verify near-optimal scaling through simulation.
@article{arxiv.2601.19816,
title = {Simple broadband signal detection at the fundamental limit},
author = {Anthony M. Polloreno and Graeme Smith},
journal= {arXiv preprint arXiv:2601.19816},
year = {2026}
}