How do you cool superfluid 3He to 2.5 mK?

[fresh_42]

I've just read about the second sound and that this phenomenon can be seen in superfluid ³He at 2.5 mK. How do they manage to come that close to 0?
A short hint about the methods would be nice to read. Normally you hear that things are cooled by fluid nitrogen or helium. But mK are out of reach by those.

 

[Vanadium 50]

See

https://en.wikipedia.org/wiki/Dilution_refrigerator
https://en.wikipedia.org/wiki/Magnetic_refrigeration

 

[fresh_42]

See

https://en.wikipedia.org/wiki/Dilution_refrigerator
https://en.wikipedia.org/wiki/Magnetic_refrigeration

Thank you. Btw. I was led to the question by reading here about the Pauli pressure.