High-tech refrigerators have been used to reach temperatures as close to absolute zero as possible — 0 kelvin or -273.15 °C. Physicists aim to cool equipment to as close to absolute zero as possible, because these extremely low temperatures offer the ideal conditions for quantum experiments, and allow entirely new physical phenomena to be examined.

A chip with a Coulomb blockade thermometer on it is prepared for experiments at extremely low temperatures. (University of Basel)

A nanoelectronic chip was successfully cooled to a temperature lower than 3 millikelvin using magnetic cooling to cool the electrical connections as well as the chip itself. The researchers had previously suggested utilizing the principle of magnetic cooling in nanoelectronics in order to cool nanoelectronic devices to unprecedented temperatures close to absolute zero.

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 efficient magnetic cooling.

The new method successfully incorporates a combination of two cooling systems, both of which are based on magnetic cooling. All of the chip’s electrical connections were cooled to 150 micro-kelvin — a temperature that is less than a thousandth of a degree away from absolute zero. Then, a second cooling system was integrated directly into the chip itself, and a Coulomb blockade thermometer was placed on the chip. The construction and the material composition also enabled the thermometer to be magnetically cooled to a temperature almost as low as absolute zero.

The same method could be used to reach 1 millikelvin. The extremely low temperatures can be maintained for a period of seven hours, providing enough time to conduct various experiments that will help to understand the properties of physics close to absolute zero.

For more information, contact Professor Dominik Zumbühl, Department of Physics, at This email address is being protected from spambots. You need JavaScript enabled to view it.; +41 61 207 36 93.

Tech Briefs Magazine

This article first appeared in the March, 2018 issue of Tech Briefs Magazine.

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