University of Basel physicists has successfully cooled a nanoelectronic chip to a temperature lower than 3 millikelvin. The scientists from the Department of Physics and the Swiss Nanoscience Institute set this record in collaboration with other physicists from Germany and Finland. The team used magnetic cooling to cool the electrical connections, as well as the chips itself.

There have been numerous working groups around the world using high-tech refrigerators to attempt to reach temperatures that are as close to absolute zero as possible. Physicists want to reach absolute zero because the extremely low temperatures are the ideal conditions for quantum experiments and allow entirely new physical phenomena to be examined.

The group was led by Basel physics professor Dominik Zumbühl. They had previously suggested utilizing the principle of magnetic cooling in nanoelectronics to cool devices to temperatures as close to absolute zero as possible. Magnetic cooling is based on the fact that a system can cool down when an applied magnetic field is ramped down, while any external heat flow is avoided. Before ramping down, the heat of magnetization needs to be removed with another method to obtain effective magnetic cooling.

This is how Zumbühl’s team succeeded in cooling a nanoelectronic chip to a temperature below 2.0 millikelvin, a low-temperature record. Dr. Marioi Palma, lead author of the study, and his colleague, Christian Scheller, have successfully used a combination of two cooling systems that were both based on magnetic cooling. They cooled all of the chip’s electrical connections to temperatures of 150 microkelvin. This is a temperature less than a thousandth of a degree away from absolute zero.

The researchers then integrated a second cooling system directly onto the chip and placed a Coulomb blockade thermometer on it. This construction and material consumption allowed the team to cool the thermometer to a temperature near absolute zero.

"The combination of cooling systems allowed us to cool our chip down to below 3 millikelvin, and we are optimistic that we can use the same method to reach the magic 1 millikelvin limit," says Zumbühl.

It is also amazing that the scientists are in a position to maintain these low temperatures for around seven hours. This is enough time to conduct a lot of experiments that will help to understand the properties of physics close to absolute zero.

The paper on this research was published in Applied Physics Letters.