Record-breakingly accurate energy measurement in Aalto, help even in the search for dark matter

An illustrator’s view of a calorimeter where the signal travels through superconductors and ordinary conductors. Picture: Ella Maru Studio

Quantum technology researchers have measured a very small amount of energy with record accuracy at Aalto University.

The new measurement method is used, for example, in quantum computers – and it could help, for example, in the search for a dark matter particle.

The measured amount of energy is so small that there is no real everyday comparison. However, it can be mentioned that it would be enough to lift a red blood cell a billionth of a meter.

“You can even say that the energy of a light particle is a hundredfold compared to the measured amount of energy. So we could count individual light particles,” says the academy professor Mikko Möttonen from Aalto University.

Amount of EnErgy was measured with a precision calorimeter, which is a type of thermometer. It was developed by a group led by Möttonen. The Technology Research Center VTT and the company developing quantum computers IQM were involved.

The researchers detected a very small electromagnetic pulse with their calorimeter. They measured microwave radiation, which also works with cell phones and microwave ovens.

The amount of radiation energy measured now was less than one thousandth trillionth of a joule, or zeptojoule. It has 20 zeros after the decimal point.

Thus measuring low signals is, in Möttönen’s words, “complicated”.

First of all, the calorimeter measured the amount of energy, i.e. the temperature associated with it, above 273 degrees below zero. Quantum technology devices are frozen near absolute cold because it minimizes interference.

The researchers sent microwave radiation to the sensor, which had two metals. It had a superconductor, where electric current flows unhindered, and a regular conductor, where electric current meets resistance.

“The superconductivity deteriorates immediately if the temperature in the very cold conductor rises at all,” says Möttönen.

The result was exactly 0.83 zeptojoules. According to Möttönen, it is the most accurate calorimetric measurement result in the world.

Now researchers can therefore count individual photons. According to Möttonen, this kind of measurement accuracy is needed.

“The equipment must be able to detect signals whose arrival time is unknown. This is important, for example, for searching for dark matter particles such as axions.”

The reference to actions is interesting, even though they are only supposed particles.

The actions got their name from the American physics Nobel laureate Frank Wilczekilta. According to him, the Earth moves in an action bubble, which is what dark matter is made of.

There is about five times as much dark matter as visible matter. It is still only detected by gravity. It’s what keeps galaxies together.

Even if the mass of axions is very small, there could be so many of them that they make up a significant part of the mass of the universe.

The search for axions has been based on the assumption that they can turn into photons in a magnetic field. Actions cannot be observed directly, but the new Calorimeter could count these rarely produced photons.

By the way, Wilczek came up with the name Aksion from a detergent package as a young mathematics student. To him, it seemed like a good name for a particle that, as it were, removes one of the problems of particle physics. Along with Wilczek, another American Nobel laureate developed the theory Steven Weinberg.

Möttönen has just arrived chosen nominated European Inventor Award as recipient. The prize is awarded by the European Patent Office.

The result of a recent study was published Nature Electronics in the journal.