Lecture Notes: Probing ultralight axion-like particles with quantum technology

TL;DR

The notes address ultralight ALP dark matter by treating it as a coherently oscillating classical field with mass‑dependent frequency. They connect an EFT description of ALP interactions, including dimension‑5 axion–photon couplings and higher‑dimensional quadratic effects, to concrete laboratory observables across haloscopes, helioscopes, atomic clocks, optical cavities, interferometers, and mechanical resonators. A central theme is the complementary reach across broad ALP masses, achieved by exploiting coherence, bandwidth, and noise properties of each platform, with detailed scaling laws and optimization criteria. The work emphasizes a unified framework that maps high‑scale ALP models to low‑energy signatures, guiding current and future laboratory searches and highlighting the potential for discovery in precision quantum technologies.

Abstract

We review the physics of ultralight axion-like particles (ALPs) as dark matter candidates and the experimental strategies used to search for them with precision and quantum technologies. In the ultralight regime, the enormous occupation number of the dark matter field motivates a classical description in terms of a coherently oscillating background, leading to distinctive, time-dependent signatures in laboratory observables. We discuss the effective field theory framework governing ALP interactions with Standard Model fields, and show how different operators give rise to qualitatively different experimental signals. The lecture notes cover both conversion-based searches enabled by the axion-photon coupling, such as haloscopes and helioscopes, and precision experiments sensitive to oscillations of fundamental constants and material properties. These include atomic and nuclear clocks, optical cavities, laser and unequal time-delay interferometers, and mechanical or solid state resonators. Emphasis is placed on the physical origin of the sensitivity of each platform, the role of coherence, bandwidth, and noise, and the complementarity between different technologies across a wide range of ALP masses. Together, these approaches provide broad and overlapping coverage of ultralight dark matter parameter space and define a rapidly evolving experimental programme with strong discovery potential.

Figures (24)

• Figure 1: A schematic overview of the possible mass ranges of dark matter candidates considered in the literature, illustrating the broad landscape from ultralight fields to macroscopic objects.
• Figure 2: Schematic illustration of a haloscope experiment for axion dark matter detection.
• Figure 3: Schematic of the MADMAX dielectric haloscope, illustrating axion-photon conversion and coherent emission from multiple dielectric interfaces in a strong magnetic field. Figure from Ref. PhysRevLett.118.091801.
• Figure 4: Comparison of static-field and driven SRF cavity schemes for axion dark matter detection, illustrating the resulting signal frequencies and power scaling. Figure from Ref. Berlin:2019ahk.
• Figure 5: Differential solar axion flux at Earth, showing the contributions from Primakoff, Compton, and bremsstrahlung production processes.