1970: The world's first super-refrigerator is manufactured in Otaniemi
The Low Temperature Laboratory gained recognition for superfluidity research and record low temperatures.
In the spring of 1970, Otaniemi made scientific history: the first cryostat designed for research at ultra-low temperatures was completed at the Helsinki University of Technology’s new Low Temperature Laboratory. The construction of the super-refrigerator, seated on a suspended concrete slab weighing six tons, was led by the founder of the Low Temperature Lab, Professor and Academian Olli Lounasmaa (1930–2002).
The new cryostat was able to refrigerate samples to sub-millikelvin temperatures for the first time in world history. ‘At the time you couldn't get refrigeration units off the shelf, you had to build them yourself. Lounasmaa and his collaborators were very talented at that,’ says Aalto University professor Pertti Hakonen.
Many fascinating physical phenomena don't appear until the temperature approaches absolute zero: 0 Kelvin or –273,15 degrees Celsius.
For example, metals become superconductingat very low temperatures, allowing electric current to flow without loss. The gases helium-3 and helium-4 become superfluid liquids at low temperatures, losing all viscosity or internal friction. Superfluids can remain in constant motion and, for example, escape over the edge of a container.
Superconductivity and superfluidity are important phenomena in fundamental physics. The helium-3 superfluid, for example, can be used to investigate both turbulence and cosmology.
The Low Temperature Laboratory rose to international acclaim by validating the superfluidity of helium-3 in 1973. Its early scientific successes also included observing quantum vortices in rotating helium-3 superfluid in 1981.
‘Finding vortices was no surprise, but the number of different variants was,’ says Hakonen, who participated in measurements for the study.
The Low Temperature Laboratory became world famous when it achieved record low temperatures as a side product of its research. The world's coldest temperature in solid matter (0.1 nanokelvin) was also achieved in Otaniemi in 1999.
High-quality research and apprenticeship-like training
In addition to efficient refrigeration units, research at the Low Temperature Lab has produced other technologies, such as the SQUID sensors designed for measuring weak magnetic fields. These are used, for example, in magnetoencephalography (MEG) measuring the magnetic fields produced by neuronal currents and as the basis for qubits in a quantum computer.
The Low Temperature Laboratory is also the birthplace of the Helsinki-based company Bluefors, which manufactures tailor-made refrigerator units for research purposes and quantum computers used around the world.
Nowadays, the Low Temperature Laboratory is a globally recognized research unit for superconducting quantum technology and nanoelectronics. Hakonen’s research group is currently working to develop a LED light source based on the quantum entanglement of photon pairs. In the future, this research may enable interaction between quantum computers at a distance.
According to Hakonen, the priorities of the Low Temperature Laboratory are the same as they were in the early days. ‘First and foremost, we stand for high-quality research and apprenticeship-like training of graduate students,’ he says.
Text by Panu Räty