Chris Ballance, The British Quantum Entrepreneur Who Put Ion Traps On A Chip

The physicist who pushed the trapped-ion quantum logic gate to its most accurate, then decided accuracy was not the problem. In December 2015 a small group in a basement laboratory on Parks Road in Oxford submitted a paper reporting a two-qubit quantum logic gate that worked correctly 99.9 times out of a hundred, and a single-qubit gate that worked correctly 99.9934 times out of a hundred. The first author was Chris Ballance, then a doctoral student and postdoctoral researcher in the university’s ion trap group. The result was published in Physical Review Letters the following year, and for about five years it stood among the highest two-qubit gate fidelities recorded on any quantum computing platform, matched at the time by a group at the National Institute of Standards and Technology whose paper appeared in the same issue. Four years later he left to start a company, and the company was not about making the gate better. It was about the observation that a gate this good was already good enough, and that the thing standing between the laboratory and a useful quantum computer was not physics at all. It was wiring. Chris Ballance had spent a decade proving that trapped…