Dark matter accounts for 85% of the matter in the Universe, but we have little to no idea what it is. One of the best candidates is a hypothetical particle known as an axion. In 2023, EQUS researchers from the UWA Quantum Technologies and Dark Matter Laboratory—led by Chief Investigators Michael Tobar and Maxim Goryachev—developed and operated various dark matter detection experiments, bringing us closer to understanding one of the biggest mysteries in science. But more than that—by working to answer fundamental questions about our Universe, they developed technologies and made discoveries that will have broader benefit to society, including in the pharmaceutical industry.
One of the many challenges in searching for dark matter is that the mass of individual dark matter particles (assuming dark matter is even made up of particles) is unknown. Although we know the total mass of dark matter in the Universe, the possible mass of an axion spans 20 orders of magnitude (10-22–10-3 eV). With a range this enormous, no single experiment, detector or method is capable of searching for all axion masses. Instead, various experiments, using different detectors and detection methods, exist around the world, many of which EQUS researchers are leading or involved in.
A new device for ultralight axion detection
In 2023, the team—including Research Fellow Jeremy Bourhill and Honours student Emma Paterson—developed a device called an anyon twisted cavity resonator to search for ultralight axions. Its key feature is its electromagnetic helicity, which results from its unusual architecture. The device ‘twists’ light in either a clockwise or an anticlockwise direction inside a closed, hollow, metallic cavity—an effect previously observed only inside materials or on surfaces.
In axion direct-detection experiments, the particle mass a detector is sensitive to is equal to the difference between the frequencies of parallel electric and magnetic fields. In the case of the twisted resonator, the unique nature of the light means a single frequency resonance has parallel electric and magnetic fields, and the device is therefore sensitive from practically 0 eV up to 10-14 eV, which is well motivated by the theory but completely off-limits for other experiments. The axion mass that haloscope-based detectors (such as the ORGAN experiment, which uses a rectangular cavity) are sensitive to is inversely proportional to the size of the device, which means searching for lighter and lighter axions requires larger and larger devices. This restriction makes searching for ultralight axions essentially impossible, because the devices required would be unreasonably large.
The use of a twisted cavity also means an external magnet is not required to search for dark matter, contrary to haloscope-based detectors, so low-loss superconducting materials may be more readily used. However, the unusual architecture of the device is possible only because of the additive manufacturing technique used (metallic 3D printing). Achieving superconductivity at cryogenic temperatures—necessary to reach sufficient sensitivity to search for dark matter—in a 3D-printed device is extremely challenging.
To overcome these manufacturing challenges, the EQUS team are working with the Australian National Fabrication Facility on prototyping a device. In 2024, they will also begin construction of the feedback and circuitry to implement the low-noise readout necessary to detect the tiny dark matter signals.
From dark matter detection to pharmaceutical applications
As well as enabling searches for ultralight dark matter, the helicity of the new device means it has potential applications in future communication technologies, by increasing the robustness of signal transmission and/or adding another mechanism to use for signal encryption. More immediately relevant is the ability of the device to transfer angular momentum to chiral molecules—something the pharmaceutical industry is sorely in need of, because it enables the manipulation and separation of left- and right-handed enantiomers.
Molecular chirality (handedness) affects how a drug is metabolised in the human body. For example, one chirality of thalidomide suppresses cancer, whereas the other causes birth defects. Enantiomeric excess of one chirality over the other may also speed up the absorption of a drug. As a result, and to minimise side effects, more than half the new molecular entities approved by the US FDA are chirally pure.
However, the technology used to separate these drugs into their pure forms is currently inefficient and expensive because it relies on a surface effect and is therefore batch-limited.
The twisted resonator has the potential to offer high-efficiency separation of left- and right-handed molecules. By utilising the entire sample volume (rather than just the surface), it could greatly speed up the separation process, resulting in more affordable medicines, with fewer side-effects and more rapid absorption. To this end, in 2024, the team will investigate chemical feedthrough, perpetration and analysis for chiral separation.
Progress across the axion mass spectrum
EQUS researchers also made progress on other dark matter detection experiments in 2023.
The ORGAN experiment successfully undertook its second experimental scan, in an axion mass range of (1.07–1.12) × 10-4 eV. This scan set a new upper bound on the axion–photon coupling parameter, and was sensitive enough to exclude the axion-like particle cogenesis model for dark matter in this range. This result was achieved using a tunable rectangular cavity—mitigating practical issues that occur when conducting high-mass axion searches.
In a collaboration with researchers from the German Electron Synchrotron (DESY), EQUS researchers developed experiments to search for previously uncharacterised axion coupling parameters, using resonant and lumped-element haloscopes. They also used data from the first run of the ORGAN experiment to put limits on some of these terms, and on scalar dark matter and dark photons.
The UPLOAD experiment was operated for the first time as a power detection experiment. The results exclude axion masses of (1.12–1.20) × 10-6 eV for certain ranges of axion coupling parameters—an improvement of three orders of magnitude over previous results and the first limit on one of the axion coupling parameters.
As part of the ADMX collaboration, EQUS researchers helped to design a low-mass (around 1 × 10-6 eV) axion experiment using re-entrant cavities, showed that a travelling-wave parametric amplifier could be operated successfully with an axion haloscope to improve sensitivity, and performed a search for a dark-matter-induced cosmic axion background, the first experiment of its kind.
The future of dark matter detection
In 2024, the team will continue to develop quantum technologies for dark matter detection, and beyond. They will prototype and test the twisted cavity device, upgrade and operate axion dark matter experiments such as ORGAN, and work with Chief Investigators Arkady Fedorov and Tom Stace at UQ on developing single-photon counters to improve the sensitivity of axion dark matter detection. The team will also investigate ways to use acoustic resonances in quartz and other materials for dark matter detection, and for tests of quantum gravity and local Lorentz invariance (whether the laws of physics stay the same for all observers moving relative to one another).
This is an important point to emphasise—developing technologies for dark matter detection has benefits beyond understanding the nature of the majority of our Universe (itself a huge benefit). It’s a repeated pattern in fundamental science—trying to answer seemingly only academically interesting questions produces devices and technologies that benefit our society much more broadly. The potential benefits of the twisted cavity to the pharmaceutical industry would not have been discovered if the team weren’t developing technologies for dark matter detection. Further applications of the twisted cavity, and opportunities for commercialisation, are being explored as part of EQUS’ Translational Research Program.
This story was first published in the 2023 EQUS annual report, and was written by Kristen Harley.