Hunting for dark matter with quantum technologies

The highly sensitive nature of quantum sensing devices lends them to applications in the finest of measurements.

And what could be ‘finer’ than detecting dark matter?

Although direct detection remains elusive, cosmological observations and early Universe simulations allow us to infer the presence of dark matter, which is thought to constitute the vast majority of the total matter in our Universe.

All we know about dark matter is that it interacts with gravity (i.e. it has mass) and it doesn’t emit or absorb light (which is why we call it ‘dark’). Despite this, dark matter outweighs the ordinary matter that makes up stars, planets, and everything we see by a factor of five.

Fortunately for us, dark matter is believed to be present throughout the entire universe, surrounding galaxies like our own in a vast, invisible spherical ‘halo’.

We can exploit proposed interactions to search for dark matter. For example, we can use cutting-edge optomechanics (in the Optomechanical Dark-matter Instrument (ODIN) described below) to search for disturbances (phonons) in superfluid helium or look for candidate particles named axions in a resonant microwave cavity (Oscillating Resonant Group Axion, ORGAN).

In both cases, we require detection technologies and amplification with exceptional sensitivity, which can only be achieved through quantum technologies.

These quantum devices are designed to operate at or near the quantum limit, where they can detect the faintest signals with minimal added noise. This capability is crucial for isolating the tiny signals expected from axion-to-photon conversion, for example, which are otherwise easily overwhelmed by background noise.

Both ODIN and ORGAN operate in an ultracold environment in order to utilise quantum sensing devices.

At the same time as continuing the fundamental science challenge of detecting dark matter, such advances in optomechanics and amplification have translatable benefits in sensing and quantum instrumentation areas.

An optomechanical solution: phonon-based dark-matter detection (ODIN)

One proposed new quantum low-mass dark matter detector comes from an interdisciplinary collaboration between condensed-matter, quantum-optics and particle physicists, and builds on prior EQUS studies of elementary excitations in superfluid helium and advances in opto-mechanics1.

Led by EQUS Research Fellow Dr Chris Baker (UQ), in collaboration with EQUS Chief Investigator Dr Maxim Goryachev (UWA), the proposal hinges on direct detection of low-mass dark matter via its interactions with superfluid helium confined in an optomechanical cavity.

Maxim and Chris’ ODIN proposal utilises superfluid helium, in which dark-matter collisions would cause a mechanical ‘ringing’ effect (quantified as ‘phonons’).

A phonon is a collective excitation of particles, and the Quantum and Dark Matter Lab where Maxim works at UWA has significant experience in applying such quasiparticles’ properties to detect and understand other very low energy systems.

It is just one example of the application of sophisticated quantum technologies to precision metrology developed within EQUS’ Quantum- Enabled Diagnostics and Imaging program.

“The collective vibrations caused by low-mass dark-matter collisions would be extremely small,” says Maxim. “So these scattered phonons would be undetectable using current technologies.”

“That’s where the EQUS-forged links between our lab and the Queensland Quantum Optics Laboratory (QQOL) came in…”

Within EQUS, the UQ-based quantum optics lab has led studies in opto-mechanics, using light to control and probe mechanical motion.

At QQOL, Chris applied his expertise in superfluid opto-mechanics to develop an ‘amplification’ system based on transducing undetectable low-energy phonons into high-energy (detectable) photons.

The result is the Optomechanical Dark-matter Instrument, or ‘ODIN’.

The device, which can be implemented using well-established technology, would provide access to dark matter in the keV mass range, several orders of magnitude less energetic than existing experiments.

In addition to the contribution to dark-matter science, it is also notable as the first demonstration of applying opto-mechanics to detection of individual particles, i.e. detection of very rare scattering events. This broadens applications of opto-mechanics from being sensors of weak fields.

“We enjoyed the application of quantum instruments to exploration of such an important fundamental field of physics,” says Chris. “It is energising to consider wider applications of quantum, beyond more traditional fields such as computing and communications.”

EQUS alumni Prof Warwick Bowen and Dr Glen Harris (UQ) also contributed to the study.

Refining the search for axions ORGAN

Another EQUS approach to quantum-based dark matter detection focused on the hypothetical particle known as the ‘axion’, which is one of the most compelling candidates for dark matter2.

The ORGAN axion haloscope exploits proposed interactions to detect axions in the laboratory, particularly their ability to convert into photons (particles of light) when exposed to a strong magnetic field.

The study builds on previous EQUS advances, with EQUS Chief Investigator Prof Mike Tobar’s group at UWA building the most sensitive dark matter detector to date in the particular mass range searched, in 2021.

Like a radio antenna picking up faint radio-frequency signals, ORGAN uses a highly sensitive detector to search for photons coming from axion-photon conversions inside a strong magnetic field.

The detector utilises a resonant microwave cavity (typically made from copper) and a very strong magnetic field (up to 11.5 Tesla) to search for axions.

When passing through a magnetic field, axions may convert into photons, producing a faint but detectable signal at a specific frequency that is proportional to the axion mass.

ORGAN systematically scans these frequencies, searching for evidence of axions and thus helping to refine the parameter space for where they might exist.

One challenge is knowing where to look in the electro-magnetic spectrum. “It could be an AM radio station, FM radio station, or at WiFi frequencies and above (i.e. microwave)” says the study’s lead author EQUS alumni Dr Aaron Quiskamp.

In those axion-to-photon conversions, the frequency of the photon generated is related to the axion mass. “And since we don’t know the mass of the axion, we don’t know what photon frequency to tune our detector to, explains Aaron.

“You could imagine ORGAN as a radio receiver looking for an unknown music station. Instead of tuning in to known frequencies, it’s scanning a wide range of potential ‘stations’ (or axion masses) where the signal might be hidden.”

However, as with a radio receiver, when the detector isn’t tuned to the correct frequency (the right axion mass), all we “hear” is white noise.

This means we must carefully adjust and refine our search to zero in on the right frequency where the axion signal might hide, beneath the noise. If no signal is detected at a given frequency, we can confidently conclude—based on the sensitivity of our detector—that axions with that specific mass are unlikely to exist. We then set an ‘exclusion limit’ ruling out that particular range of masses, and inform the axion community, guiding future searches toward unexplored regions.

Many searches are needed to ‘scan’ the wide range of possible frequencies, with all of these searches narrowing down the future search space, and honing in, hopefully, on eventual detection.

The team also searched the 25 μeV mass range using a near quantum-noise-limited parametric amplifier (aptly named ORGAN-Q where Q stands for quantum). This was a big step in the sensitivity of the experiment, pushing the detection threshold lower and searching for even fainter signals than ever before.

This latest iteration of ORGAN operated at millikelvin temperatures for the first time, marking a significant milestone in the experiment’s capabilities. Achieving such ultra-low temperatures is crucial for minimising thermal noise and enhancing the sensitivity of the experiment.

Moving forward, the team will use quantum-noise-limited detectors to push the sensitivity of the experiment even further, with upgrades such as new cavity designs, gigahertz single photon counting, superconducting cavities, and a larger magnet probing even deeper into the parameter space between 15–50 GHz.

Quantum contributions: fundamental, discovery science and future sensing applications

EQUS’ significant contributions to dark matter science are an example of how fundamental, ‘discovery’ research also advances current technologies.

The successful detection of dark matter, and/ or discovery of axions, would have profound implications for both fundamental physics and our understanding of the universe.

“We would solve one of the most significant mysteries in cosmology, deepening our understanding of how the universe evolved after the Big Bang”, says coauthor Maxim Goryachev.

At the same time, the immediate impact of this work is the advancement of experimental techniques in quantum instrumentation.

For example, the quantum-noise-limited amplifiers and single-photon detector technologies being developed for the ORGAN experiment will improve the sensitivity and precision of a wide range of other physics experiments and engineering applications.

“The exquisitely sensitive quantum technologies required to detect weakly interacting dark matter can also be used to detect and measure all sorts of other weak signals, such as other quantum sensing applications, like detecting gravity gradients for example,” says Mike.

This story was first published in the 2024 EQUS annual report.