Axion Dark Matter Searches: From High-Q Cavities to Quantum-Limited Probing (CARAMEL)

by Yannis K. Semertzidis (Brookhaven National Laboratory)

Tuesday 21 Apr 2026, 10:30 → 12:00 Europe/Rome

1/1-2 - Aula "C. Voci" (Dipartimento di Fisica e Astronomia - Edificio Marzolo)

The search for axion dark matter has entered a mature and
rapidly evolving phase, driven by significant advances in high-Q
resonant systems, quantum-limited amplification, and system integration.
I will begin by reviewing the progress achieved at IBS-CAPP, where a
broad program of haloscope experiments has demonstrated world-leading
sensitivity in the GHz range through the development of superconducting
cavities, ultra-low-noise detection chains, and large-scale cryogenic
infrastructure. I will then briefly discuss the ongoing efforts within
DMAG to extend this reach toward higher frequencies and new detection
paradigms.

A central challenge in the field remains the efficient exploration of
wide frequency ranges while maintaining sensitivity at or near the
quantum limit. In this context, I will introduce the CARAMEL approach
(Cosmic Axions Revealed via Amplified Modulation of the Ellipticity of a
Laser, PRD 113, 032012, 2026), a probing-based detection scheme that
departs from conventional power-detection methods. Instead of relying on
passive signal extraction, CARAMEL employs an active, phase-sensitive
probing field, enabling a heterodyne-like measurement that enhances
sensitivity and enables rapid scanning.

I will discuss how this method can bridge the gap between current
haloscope techniques and future single-photon detection strategies,
offering a practical intermediate path with significant gains in scan
speed and robustness against technical noise. Particular emphasis will
be placed on how existing experimental infrastructures—such as those at
Padova—can leverage their expertise in precision measurements and
low-noise detection to play a leading role in this next phase of axion
searches.

The talk will conclude with an outlook on the achievable sensitivity and
the potential for extending axion searches across a broad frequency
range, from sub-GHz to tens of GHz, using a combination of resonant
enhancement and quantum-limited probing.