Ultimate precision limit of noise sensing and dark matter search

TL;DR

This paper establishes the fundamental quantum limits of noise sensing for axion dark matter detection, demonstrating that entanglement-assisted strategies and photon counting can significantly enhance search sensitivity.

Contribution

It derives the ultimate precision bounds for noise sensing in dark matter searches and proposes optimal measurement strategies using entanglement and photon counting.

Findings

Two-mode squeezed vacuum achieves near-optimal sensitivity.

Single-mode squeezing is limited by loss and underperforms vacuum limit.

Entanglement assistance and photon counting are crucial for optimal dark matter detection.

Abstract

The nature of dark matter is unknown and calls for a systematical search. For axion dark matter, such a search relies on finding feeble random noise arising from the weak coupling between dark matter and microwave haloscopes. We model such process as a quantum channel and derive the fundamental precision limit of noise sensing. An entanglement-assisted strategy based on two-mode squeezed vacuum is thereby demonstrated optimal, while the optimality of a single-mode squeezed vacuum is found limited to the lossless case. We propose a `nulling' measurement (squeezing and photon counting) to achieve the optimal performances. In terms of the scan rate, even with 20-decibel of strength, single-mode squeezing still underperforms the vacuum limit which is achieved by photon counting on vacuum input; while the two-mode squeezed vacuum provides large and close-to-optimum advantage over the vacuum limit, thus more exotic quantum resources are no longer required. Our results highlight the necessity of entanglement assistance and microwave photon counting in dark matter search.