Cool Kelvin

The School of Physics’ new cryogen-free dilution refrigerator can create the coldest macroscopic place in Victoria, cooling down to about 20 milli-Kelvin, almost the point of absolute zero, the null point of any temperature scale. Zero Kelvin is defined as −273.15°C.

The only refrigerator of its kind in Australia, the AU$600,000 machine was shipped from Leiden, the Netherlands, in May, and was up and running within a week after delivery.

It will advance research in some of the key fields the University’s physicists focus on including quantum systems and solid-state physics. Solid-state physics studies how the large-scale properties of solid materials result from their small-scale properties while quantum systems research examines how nanoscale structures behave differently from large-scale objects.

Senior Postdoctoral Research Fellow and lead of the University’s Quantum Measurement Program Dr Laurens Willems van Beveren says the machine was necessary to further the School’s research endeavours.

“What we’re striving for is better understanding of fundamental physics. At extremely low temperatures, some of the fundamental properties of certain materials appear, and we needed the refrigerator to create those temperatures.

“We’re striving for breakthrough science, and the fundamental improvement of our knowledge of the solid state.”

Dr Willems van Beveren explains the way in which extreme cooling allowed for specific experiments:

“Imagine you’re an electron and you’re leaving Flinders Street Station, and you’re trying to make it to University of Melbourne for a physics class, so you rush up Swanston Street, but it’s busy, traffic is bad and there are many people in the way.

“What happens is you try to divert around people and objects, and it slows you down – this is like the vibrations in the crystal of each molecule. If everything stood still, you could get to the University much faster – it would be a low resistance path. This is what cooling to a very low temperature does, it clears out these impediments and creates a clear path for the electrons to travel on.

“This lets researchers undertake very specific, detailed experiments. When you freeze samples like this, all the nice physical properties of the solid-state rise to the surface.

“This type of refrigerator is special, as it uses an electrical pump to cool down the system unlike a conventional dilution refrigerator, where a bath of liquid helium is used. Anticipating the increasing cost of liquid helium, which is a finite resource on Earth, this cryogen-free ‘dry’ fridge is ideally suited to keep low-temperature physics an ongoing discipline at the University of Melbourne in the future.”

This dilution refrigerator is unique in the world in that it includes a window, which allows researchers to shine (laser) light directly onto the cooled sample and learn more about what is happening during the experiment.

Dr Willems van Beveren sourced the machine from a company in Leiden, a city that has a long history of low temperature work. It was here that Professor Heike Kamerlingh Onnes was the first to liquefy helium, for which he was awarded the 1913 Nobel Prize in Physics.

He said as the physics community was celebrating the 100th anniversary of the discovery of superconductivity this year, it was particularly exciting the University now had this machine. The magnet inside the fridge is made of superconducting material.

Dr Willems van Beveren said the facility would benefit many members of the University and other Victorian university research communities, and would draw more researchers and PhD students from all over the world to the University of Melbourne.

He is applying for competitive ARC research grants to continue setting up a Quantum Measurement Group to attract high-quality Postgraduate and PhD students to the School of Physics to work on new fundamental physics projects.

Some of the studies the Quantum Measurement Program will look at may lead to many different practical applications, including new insights into the development of the next generation of solar cells.

http://physics.unimelb.edu.au/