First results from a microwave cavity axion search at 24 micro-eV (1610.02580v3)

Abstract: We report on the first results from a new microwave cavity search for dark matter axions with masses above $20~\mu\text{eV}$. We exclude axion models with two-photon coupling $g_{a\gamma\gamma} \gtrsim 2\times10^{-14}~\text{GeV}^{-1}$ over the range $23.55~\mu\text{eV} < m_a < 24.0~\mu\text{eV}$. These results represent two important achievements. First, we have reached cosmologically relevant sensitivity an order of magnitude higher in mass than any existing limits. Second, by incorporating a dilution refrigerator and Josephson parametric amplifier, we have demonstrated total noise approaching the standard quantum limit for the first time in an axion search.

• The paper excludes axion models with gₐγγ ≳ 2×10⁻¹⁴ GeV⁻¹ for masses between 23.55–24.0 μeV, marking a sensitivity breakthrough.
• The study employs a microwave cavity detector enhanced by a dilution refrigerator and a Josephson parametric amplifier to achieve near-quantum-limited noise.
• The innovative approach sets a foundation for future high-mass axion searches by advancing cryogenic and quantum electronics techniques.

Overview of Microwave Cavity Axion Search Results at 24 $\mu$eV

The paper presents significant advancements in the search for dark matter axions, focusing on a mass range above 20 $\mu\text{eV}$. The research was conducted through a novel microwave cavity experiment at Yale Wright Laboratory, addressing the challenge of detecting axions within this previously unexplored mass range, utilizing enhanced quantum electronics technologies.

Key Findings and Methodologies

Two crucial developments emerge from the results:

1. The exclusion of axion models with a two-photon coupling $$g_{a\gamma\gamma} \gtrsim 2\times10^{-14}~\text{GeV}^{-1}$$ for axion masses within the range of $23.55 < m_a < 24.0~\mu\text{eV}$. This represents an advancement in sensitivity—an order of magnitude higher in mass than previous constraints.
2. The integration of a dilution refrigerator and a Josephson parametric amplifier (JPA) into the experimental apparatus achieved noise levels approaching the standard quantum limit for the first time in axion searches.

The experimental setup involved a cavity axion detector, leveraging the principle of Primakoff conversion. Axions in the galactic halo convert into microwave photons within a high-Q cavity inside a strong magnetic field, a process resonantly enhanced under specific conditions. The configuration comprised a tunable microwave cavity linked to a low-noise receiver housed in the bore of a superconducting magnet, operating under cryogenic conditions managed by a dilution refrigerator.

Experimental Achievements

The application of quantum-limited amplification with the JPA is particularly noteworthy. The apparatus achieved an unprecedented level of noise reduction, which is crucial for its sensitivity to axion signals. By minimizing system noise and employing an innovative receiver design, the researchers managed to edge closer to the purportedly elusive axion interaction parameters.

The experiment spanned several months during 2016, collecting and analyzing extensive data. The methodology included synthetic axion signal injections and thorough recalibration procedures to ensure the integrity and reliability of measurements.

Implications and Future Prospects

The results underscore the possibility of pushing forward the boundaries of axion searches into higher mass regions with cosmological relevance. The refinement of techniques such as cryogenic cooling, coupled with advancements in signal amplification technology, sets a precedent for future work aimed at exploring axion parameter space with greater precision.

While this paper places new constraints on axion models, ongoing and future experiments will benefit from the technical innovations demonstrated. Enhancements in cavity design and further quantum noise reduction strategies might enable the detection of dark matter axions with even weaker couplings.

The paper significantly contributes to the theoretical and practical evolution within the field, augmenting the strategies required to tackle the formidable challenge of dark matter detection. Consequently, these results form a critical building block for future explorations in the ongoing search for axions and the broader dark matter problem.