The world needs clean energy. One of the most promising ways of producing it in large amounts is the helium3-deuterium (3 \(\hbox {He-D}\) ) fusion reaction. Although there are numerous sources of 3 \(\hbox {He}\) on Earth, most of them are either difficult to access or unprofitable to operate. The main problem underlying the shortage of 3 \(\hbox {He}\) is the lack of an effective method of obtaining this isotope. Here we report the results of quantum filtration of 3 \(\hbox {He}\) from liquid helium in a superfluid state (below the \(\lambda\) -transition), with the use of an entropy filter made of a high-temperature superconductor YBCO-123. During the operation of so-called fountain effect generated with this filter, unlike the other filters, we observed a strong increase of 3 \(\hbox {He}\) concentration downstream, where only pure \(^{4}\hbox {He}\) was expected. This effect occurred due to the unique combination of two quantum phenomena—superfluidity and superconductivity, leading to the observation of a low-temperature rectification-like process. Rectification of helium isotopes does not require lowering the temperature below the \(\lambda\) -transition, so the process can be more economical than filtration. Moreover, micro-superconductors could be applied also to the extraction of deuterium, thus allowing the same method to be used for both crucial components of the 3 \(\hbox {He-D}\) fusion. This method should be easy to upscale and could be used in space (with less energy input) as 3 \(\hbox {He}\) , the crucial isotope for future energy, is also sought beyond the Earth.
