The shares of IonQ Inc. and other companies linked to quantum computing tumbled in extended trading on Tuesday after Nvidia Corp. Chief Executive Officer Jensen Huang said “very useful” quantum computers are likely decades away.

“If you kind of said 15 years for very useful quantum computers, that would probably be on the early side. If you said 30, it’s probably on the late side,” Huang said in a question-and-answer session during Nvidia’s analyst day. “If you picked 20, I think a whole bunch of us would believe it.”

QUANTUM CORP slid 15.78%; D-Wave Quantum Inc., Quantum Computing Inc. slid 14%; SEALSQ Corp, Rigetti , IonQ fell around 13%. The stocks have soared in recent months amid excitement about the potential of the technology, which was heightened last month following a quantum computing breakthrough by Alphabet Inc.

Quantum Computing shares had gained more than 1,800% over the past 12 months to $17.49 through Tuesday’s close. Rigetti rose more than 1,500% to $18.39 over the same span while D-Wave advanced nearly 1,000% to $9.55 and IonQ more than 300% to $49.59.

Alphabet Inc., whose shares in December posted their best month since May 2023, is down 0.3% in late trading after closing at $195.49.