Scientists from the oldest University of Basel in Switzerland established new temperature record for ultra-strong cooling of matter. But the most valuable development promises to be the ability to adapt the approach used to cool quantum processors and even conventional semiconductors.
The proposed solution is a chain of an array of copper islands on a silicon substrate. The same or similar circuit works like a thermometer – measuring a record low temperature is as difficult as reaching it. The sample was cooled using two technologies: using magnetic fields and using liquid helium.
The main refinement of the refrigeration unit was a very “rigid” fixation of the sample, which made it possible to get rid of the “thermal” influence from the refrigeration system. During operation, the helium-based refrigerator creates vibrations that are transmitted to the sample and do not allow it to cool as much as it could. Recall that to cool a substance to temperatures close to absolute zero means to slow down the vibrations of the atoms of this substance as much as possible. In fact, the laws of quantum mechanics come into play, and quantum states are destroyed by any “sneeze”.
A firmly fixed sample was first covered with a strong magnetic field, which ordered the spins of the copper atoms and made it possible to effectively cool the material, and then gradually cooled it using dilution refrigerator (sample fixing played at this stage). At the third stage, the magnetic field was gradually reduced to nothing, which reduced the magnetic energy of the sample and further reduced the oscillations of the copper atoms (and cooled the sample a little more).
Combined cooling made it possible to achieve a new record minimum temperature of 220 μK, or only 220 millionths of a degree above absolute zero. In the future, the researchers want to use their method to reduce temperatures another tenfold and, in the future, adapt it to cool semiconductor materials. This will pave the way for the study of new quantum effects and diverse applications such as qubit optimization in quantum computers. Let’s add work published in Physical Review Research.
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