Simple broadband signal detection at the fundamental limit

TL;DR

This paper establishes fundamental quantum limits for broadband weak signal detection and proposes an all-analog multi-resonant protocol that approaches these limits, with potential applications in magnetometry, axion searches, and gravitational-wave sensing.

Contribution

It introduces a new quantum metrological bound for broadband detection and presents a novel all-analog protocol that nearly achieves this limit.

Findings

Derived a geometric lower bound on integration time for detection.

Designed a randomized Su-Schrieffer-Heeger control protocol.

Verified near-optimal scaling through simulation.

Abstract

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.