Physicists at the University of Basel have succeeded in cooling a nanoelectronic chip to the unfathomable temperature of less than 3 millikelvin. Researchers from the Department of Physics and the Swiss Nanoscience Institute in collaboration with scientists from Germany and Finland used magnetic fields to eliminate heat from the electrical connections as well as the chip itself. Scientists all over the world have been working on techniques to reach as close to zero as possible. Absolute zero is referred to as 0 kelvin or -273.15°C. Reaching these blisteringly cold temperatures provides perfect conditions for quantum experiments and allows entirely new physical phenomena to be examined.
Multiple magnetic fields used to drop temperatures
The scientists, led by Basel physicist Professor Dominik Zumbühl have set this latest record by using magnetic cooling. Magnetic cooling works when a magnetic field is ramped down while external heat is avoided. The scientist used the ramped down magnetic field to chill the chip and its surrounds to 150 kelvins, they then use another separate magnetic field to cool down a Coulomb blockade thermometer. Because even the heat from the thermometer would be enough to stop them reaching their low-temperature goal. Once this heat source was dealt with the chip was able to set the very chilly record and actually stay cold for seven hours. “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.
Extreme cold opens doors to new research
This seven-hour window will allow scientists to conduct experiments in these conditions where particle motion virtually stops. Understanding the properties of physics in temperatures close to absolute zero has wide applications in many fields. Research done at extremely low temperatures have thrown up some results in the last few years.
One recent experiment found that molecules in an ultra-cold gas can chemically react at distances up to 100 times greater than they can at room temperature. When the same experiment was done at warmer temperatures the chemical reactions of the gas tended to slow down. But when the temperature was close to absolute zero (−273.15°C or 0 Kelvin) the molecules can still exchange atoms and forge new chemical bonds in the process. Deborah Jin from the University of Colorado in Boulder, who led the research that was reported in Science Journal says “It’s perfectly reasonable to expect that when you go to the ultra-cold regime there would be no chemistry to speak of. This paper says no, there’s a lot of chemistry going on.” Understanding how things work in these ultra cold environments may help us to understand our solar system and beyond. The coldest recorded temperature in the solar system was on the Moon.
In 2009, NASA’s Lunar Reconnaissance Orbiter measured areas permanently shadowed craters near the lunar south pole that were as low as −240°C. No doubt the race will continue in labs to try and achieve even lower temperatures than the recent record set by the Basel based group.