When superfluidity meets superconductivity in the extraction of ³He isotope from liquid helium

The world needs clean energy. One of the most promising ways of producing it in large amounts is the helium3-deuterium (³ $\text{He-D}$ ) fusion reaction. Although there are numerous sources of ³ $\text{He}$ on Earth, most of them are either difficult to access or unprofitable to operate. The main problem underlying the shortage of ³ $\text{He}$ is the lack of an effective method of obtaining this isotope. Here we report the results of quantum filtration of ³ $\text{He}$ 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 $\text{He}$ concentration downstream, where only pure $_{}^4\text{He}$ 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 $\text{He-D}$ fusion. This method should be easy to upscale and could be used in space (with less energy input) as ³ $\text{He}$ , the crucial isotope for future energy, is also sought beyond the Earth.