It's not a cube and it's not subatomic but I believe it is the smallest twisty puzzle ever made.
It's 6mm high and has a diameter also of 6mm. Excluding stickers it's volume is fractionally less than 170 cubic mm.
I made it from one of Callum's incredible 6mm Subatomic Cubes. I considered using a Dremel to cut it down but quickly dismissed that as plain idiotic. So I cut the cube down using a sharp knife and smoothed it with wet & dry sand paper. I then cut the stickers by hand and put them on using my normal method. This is where I use a pin to apply a tiny blob of Super Glue. I then use tweezers to add the stickers. This works though at such a tiny scale the glue often just won't stick. It's very annoying because you think the puzzle is finished but a few seconds into using it you find one or two stickers have come off.
Since the sticker material at this scale is quite thick (in comparison) it doesn't bend around the curved surface of the puzzle as it should. This means it creates the illusion that the puzzle is an octagonal prism rather than a true cylinder. The puzzle however is a true cylinder. VIDEO
Subatomic Cylinder Cube
Subatomic Cylinder Cube next to the Callum's 6mm Subatomic Cube it was made from
My three Cylinder Cubes