The search for dark matter in the form of axions hinges on cavity quality: the higher the quality factor, the faster the mass range can be scanned. Copper cavities are limited to quality factors around 10⁵ due to the anomalous skin effect, while conventional superconductors are degraded by vortices in strong fields. Neighboring works on the archive explore various approaches to detecting axions and dark photons using cavities, levitating magnets, and laser interferometers, but they do not solve the problem of a high-quality cavity in a multi-tesla field.
The authors used tapes of the high-temperature superconductor REBCO, which they mechanically peeled from the substrate, retaining a copper stabilizer 20–100 μm thick. This copper layer serves as a conducting base: the gaps between cavity segments become waveguides below the cutoff frequency, and the radio-frequency field decays exponentially without reaching the resistive substrate. To validate the concept, they fabricated two cavities: one with a fixed frequency of 5.40 GHz to achieve maximum quality factor, and another tunable at 2.3 GHz for integration into the CAPP-PACE helioscope.
The 5.40 GHz cavity achieved an unloaded quality factor of 1.4×10⁷ in an 8 T magnetic field, two orders of magnitude higher than a copper counterpart. The tunable 2.3 GHz cavity in the CAPP-PACE experiment showed a system noise temperature of 180 mK and a fivefold advantage in quality factor over copper. As a result, the scan rate increased by a factor of 8.4, and the sensitivity reached 1.4 times the KSVZ limit in the axion mass range of 9.4376–9.4914 μeV.
This work differs from neighboring studies in that it demonstrates for the first time a working high-temperature superconductor cavity in a real helioscope with sensitivity approaching the theoretical limit. Other works on the archive explore alternative detection methods but do not achieve this combination of high quality factor and large volume in a strong field. This opens the way to scaling to larger volumes for future experiments.
The technology can be scaled to cavities with volumes exceeding 30 liters for experiments like CAPP-12TB with a 12 T field. Further engineering will be needed to control the total seam length and deformations during thermal cycling. Also promising is the use of ultra-high-quality cavities with broadband parametric amplifiers to reduce signal loss during filtering.
The results will impact experiments searching for axions and other dark matter particles, as well as the development of accelerator cavities for future colliders and hybrid quantum systems.
The next step will be to create large-volume cavities with high quality factors for experiments with stronger magnets and to test their stability during long-term operation.
This work addresses a key problem in particle physics: how to achieve a high cavity quality factor in a strong magnetic field, which is necessary for detecting axions and solving the strong CP problem.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
This study presents a resonator made from the high-temperature superconductor REBCO, where the copper substrate serves as a conductive base that suppresses leakage through the gaps. A quality factor of 1.4×10⁷ was achieved in an 8 T field, two orders of magnitude higher than that of a copper counterpart. In the CAPP-PACE experiment, the scanning speed increased by a factor of 8.4, and the sensitivity reached 1.4 times the KSVZ limit.
Where its strength is
For the first time, a working HTS resonator has been demonstrated in a real helioscope with sensitivity close to the theoretical limit. This paves the way for scaling up to larger volumes.
Where it could go next
Worth trying
Why this may matter
The proposed approach could significantly accelerate axion searches in next-generation experiments, allowing large mass ranges to be scanned in a reasonable time.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.57, against a usual 0.64. It looks like few have drilled nearby.
A quality factor of 1.4×10⁷ means that the 5.4 GHz cavity has a linewidth of only about 400 Hz, which is 13 million times smaller than its resonant frequency.
The search for axions echoes the plot of the Strugatsky brothers' novel 'Roadside Picnic': scientists seek artifacts of an invisible world that could change our understanding of the universe.