Novel technique for producing ultracold 4He beams

We have developed a technique for producing ultracold beams of ground state 4He atoms by evaporation from a film at subkelvin temperature in a dilution refrigerator. Our analysis shows that we have cooled atoms to below 700 μK and that the cooling process can be continued to below 100 μK. This new technique has great promise for determining the He-He interaction potential to high precision and searching for 4He dimer formation. It might also be used to study quantum reflection off surfaces and to search for Bose-Einstein condensation in a dilute gas of 4He