Quantum computing stocks fell in Wednesday trading after Nvidia Corp. Chief Executive Officer Jensen Huang said “very useful” quantum computers are likely decades away.

Rigetti Computing fell 41%; D-Wave Quantum fell 40%; QUBT fell 38%; IONQ fell 36%; QMCO fell 31%.

“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.”

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.