Helium rain inside metallic hydrogen within Jupiter, conditions and experiments?
Different sources give significantly different values for the conditions under which hydrogen shifts from molecular to metallic. See the discussion in the comments associated with this question. Pressures from about 20 to 300 GPa and temperatures very broadly around 10 000 K seem to be the most common.  

Experiments can only just reach these pressures, at lower temperatures, for tiny volumes of material, and the question of whether anyone has made metallic hydrogen at all remains controversial. Certainly no one can make it repeatably. (wikipedia has a reasonable summary of the history) or make enough of it and keep it for long enough to check to what extent, if any, helium is soluble in it.

That said, analysing from theory whether it will be soluble shouldn't be that hard, since both hydrogen and helium are relatively simple atoms. An early paper concludes that the hydrogen would be at or close to the limit of how much helium could be dissolved. I'm sure there is more accurate recent work, but I couldn't find it quickly.