Jan 8 (Reuters) - Quantum computing stocks sank on

Wednesday, pausing a year-long rally, after Nvidia ( NVDA ) CEO

Jensen Huang said the technology's practical use was likely two

decades away.

The long wait outlined by Huang for "very useful quantum

computers" throws cold water on a sector that was already

expected to spend millions more on the technology, which can

only perform niche calculations so far.

"If you kind of said 15 years ... that'd probably be on the

early side. If you said 30, it is probably on the late side. But

if you picked 20, I think a whole bunch of us would believe it,"

he told an investor conference on Tuesday.

Shares of Rigetti Computing ( RGTI ) and Quantum Computing ( QUBT )

fell more than 17% each in trading before the bell,

while IonQ ( IONQ ) and D-Wave Quantum ( QBTS ) fell 9.4% and

14%, respectively.

The companies were in total set to lose about $3 billion in

market value, if losses hold.

Stocks of all the companies had risen at least three-fold

last year, driven by a high-profile breakthrough at

Alphabet-owned Google and increasing computing needs brought on

by generative AI applications.

Google had in December unveiled a new generation chip that

it said solved in five minutes a computing problem that would

take a classical computer more time than the history of the

universe, sparking a rally in its shares.

In April 2024, Microsoft and Quantinuum said they had

achieved a key step in making quantum computers a commercial

reality, but did not comment on how many more years it would

take to beat a conventional supercomputer using the tech.

(Reporting by Arsheeya Bajwa in Bengaluru; Editing by Anil

D'Silva)