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Veritasium
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Quantum cooling to (near) absolute zero
This video explains how zero point energy in helium-3 and helium-4 atoms means that atoms, even at absolute zero vibrate. The smaller size of the helium-3 means it vibrates more. In a mixture of helium-3 and helium-4 the helium-3 atoms can get closer to helium-4 than to other helium-3 (less vibration in helium-4). This means they can mix.
Using a U-tube it is shown that preferential evaporation of helium-3 from the mixture encourages more helium-3 to enter the helium-4 phase and this change in entropy takes thermal energy from the surroundings and so has a cooling effect. This apparatus is capable to reaching temperatures of 20milli Kelvin.
The technique is referred to as the dilution refrigeration technique. The technique is being used to detect changes in shape of a copper - aluminium mass as gravitational waves, produced in a supernova, pass through it.
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