Jeremy O’Brien, The Physicist Who Bet Quantum Computing On A Chip Foundry

The experimentalist who made two photons do logic, then argued that the remaining problem was not physics but a production line. In 2003 Nature published a quantum logic gate made entirely out of light. The first author was Jeremy O’Brien, then a research fellow at the University of Queensland, and the device was a controlled-NOT gate assembled from beam splitters and single photons on an optical bench, reported with his colleagues Geoff Pryde, Andrew White, Tim Ralph and David Branning. Photons had always been the easiest quantum objects to make and the hardest to make interact, which is why they had been treated as messengers rather than as processors. What that experiment showed was that the missing interaction could be manufactured out of interference and measurement instead of being found in nature, and it opened a line of work that occupied the next fifteen years of his career. Thirteen years after the gate paper he co-founded a company whose central claim was that physics was no longer the interesting part. PsiQuantum was built on the premise that a quantum computer becomes commercially useful only once it can run error correction, that error correction needs something close to a million physical…