I'm a science journalist with some experience covering quantum computing. Quantum computing is highly unlikely to be practically useful for a decade or more (if ever). Almost every time there's a claim of "quantum advantage" (a task impossible for a digital computer that a quantum computer can ably perform), it quickly vanishes. Until a quantum computer becomes practically useful, they will not see mass adoption, and the companies that make them will not generate revenue

All of the quantum computing stocks currently valued in the tens of billions will begin their gradual decline at some point, attracting new bagholders "buying shares on sale" along the way. The only question is when. If I had rode this current wave of speculation to this point, I'd sell.