Physicists embark on six-year hunt for dark matter particle

Aalto University researchers will probe the secrets of dark matter using a quantum detector of unprecedented sensitivity.

In the pitch dark of the cosmos lurks an invisible kind of matter. Its presence is seen in the rippling ebb and flow of galaxies, but it’s never been directly observed. What secrets lie beneath the surface, brewing in the deep?

Physicists have long theorized about the composition of dark matter, which is thought to be five times more abundant than regular matter. Among competing hypotheses, one particle has emerged as a promising candidate: the axion.

Researchers at Aalto University are setting out on a six-year project to find evidence for the existence of axions. They will do so as part of a newly founded consortium called DarkQuantum, alongside researchers at the University of Zaragoza, who are coordinating the project, as well as researchers at the French National Centre for Scientific Research, Karlsruhe Institute of Technology, and other partner institutions.

This new consortium will be the first to use the latest quantum technologies to build sensors with unprecedented scanning sensitivity. DarkQuantum was awarded €12.9 million on October 26 by the European Research Council, of which roughly €2 million is set aside for Aalto University Senior Lecturer and Docent Sorin Paraoanu and his Superconducting Qubits and Circuit QED (KVANTTI) research group.

‘We are peering into a deep, dark pit. If it exists, the axion goes beyond the standard model of elementary particles,’ Paraoanu says. ‘Such an observation would be comparable in significance to the Higgs boson discovery in the early 2010s. But at least with the Higgs boson, they knew where to start looking!’

‘The nature of dark matter is one of the biggest mysteries in modern science,’ adds University of Zaragoza Professor Igor Garcia Irastorza, who also heads the DarkQuantum consortium. ‘If dark matter is made of axions, we have a real chance of detecting it with this project.’

Although there have been attempts to observe axions in the past, this latest endeavor will capitalize on quantum phenomena to enable researchers to better filter out noise and repeat their experiments with greater fidelity. That’s where Paraoanu and his team come in.

Moving mountains

Zoom into our small corner of the Milky Way galaxy, deep under the mountains spanning the border between Spain and France. This is the site of the Canfranc Underground Laboratory, which will house a high-frequency sensor the DarkQuantum researchers plan to build. The other, low-frequency sensor will be located at the German Electron Synchrotron (DESY) in Hamburg.

Paraoanu and his KVANTTI group are primarily responsible for building and tuning the high-frequency sensor, as well as writing the algorithms and software to use it. This sensor, called a haloscope, will probe the depths of the galactic halo in search of axions.

Putting the sensor deep underground helps eliminate cosmic background radiation, and it may offer a unique opportunity to simultaneously study certain noise-reduction techniques for quantum computing.

‘Our high-frequency sensor will be 10-100 times more sensitive than previous iterations, and it will be able to scan on the scale of a few microelectron volts. It will use superconducting qubits—the same qubits used in quantum computers—but they will serve in a different role as detectors in this haloscope,’ Paraoanu says.

Previous attempts to detect axions have used linear amplifiers, which tend to introduce noise and effectively absorb particles into the system. Paraoanu’s sensor will rely on quantum nondemolition measurements, which will allow for repeated experiments with the same particles.

‘The theory suggests that, in an ultra-cold environment, we can introduce a magnetic field that will cause any axions present to decay into photons. If we detect any photons in the cavity, then we can conclude that axions are present in the system, and that they do indeed exist,’ Paraoanu says.

Synergy Grant

The European Research Council’s Synergy Grant is prestigious, and Paraoanu and his team are only the second in Aalto University’s history to receive the grant—the first was awarded to Professor Risto Ilmoniemi for his ongoing ConnectToBrain project.

The six-year project will be broken into two parts: a four-year scaling up phase, which includes the construction, tuning and transportation of the haloscopes; and a two-year experimental phase, in which the team will gather data. Paraoanu expects to have openings for several researcher positions in the project in the coming years.

Other partner institutions named in the Synergy Grant include the Max Planck Society for the Advancement of the Sciences, the Polytechnic University of Cartagena, and the Spanish National Research Council.

Paraoanu and the KVANTTI research group will carry out their work using OtaNano equipment. OtaNano is Finland’s national research infrastructure for micro-, nano-, and quantum technologies. Specifically, Paraoanu will perform his work at the Low Temperature Laboratory, founded by Finnish physicist Olli V. Lounasmaa. Paraoanu is also involved in InstituteQ and in the new Finnish Quantum Flagship (FQF).