Adds background on PsiQuantum, details on how funds will be used, paragraphs 3-8

By Anna Tong, Max A. Cherney, Stephen Nellis

SAN FRANCISCO, March 24 (Reuters) - Quantum computing startup PsiQuantum is raising at least $750 million at a $6 billion pre-money valuation, according to two people familiar with the matter.

BlackRock BLK.N is leading the fundraising effort, which has not yet been completed, one of the people said.

Unlike some quantum computing startups using exotic materials, PsiQuantum is aiming to modify traditional manufacturing techniques from the semiconductor industry. The company uses existing photonics technology - the same kind of chipmaking used to make the fiber-optic connections for internet communications - at a factory run by GlobalFoundries GFS.O in New York, saying it plans to make millions of quantum chips.

Scaling up those plans to make a high volume of quantum computing processors is a costly, complex endeavor and requires fundraising, one of the people said.

Startups and major tech firms alike are chasing quantum computing, which can solve complex problems that would take conventional computers thousands or millions of years, such as predicting how atoms and molecules will interact. Scientists hope to use quantum machines to develop new materials for batteries and new drugs.

In recent months, Alphabet's GOOGL.O Google, Microsoft MSFT.O and Amazon AMZN.O have all unveiled new quantum computing chips. Last week, Nvidia NVDA.O, the world's biggest chip firm, said that it will establish a quantum computing research center in Boston.

PsiQuantum is working with the governments in Australia and the United States to build two quantum computers in the coming years - one in Brisbane, Australia, and the other in Chicago.

Quantum computers have been around for decades but have produced too many errors to be more useful than conventional computers. In recent years, companies have made advances in making better quantum chips and correcting those errors, with PsiQuantum saying it believes it will have a useful machine by 2029 or sooner and Google saying earlier this year that it will have useful quantum applications within five years.

(Reporting by Max A. Cherney, Anna Tong and Stephen Nellis in San Francisco; Editing by Chris Reese and Matthew Lewis)

((max.cherney@thomsonreuters.com; 415-404-2697; @chernandburn on Twitter/X))