In lab, Quantinuum's logical qubits gain over 10x per size step

Quantum computers are built from hardware qubits, and those are fragile: they make errors. To run complicated algorithms, several of them must be linked into a single logical qubit, a unit able to detect and correct errors among its members. The trade-off is simple to state and hard to beat. More hardware qubits per logical qubit give more chances to spot errors, but also more places where errors can start. Below a certain error rate, growing the logical qubit helps. Above it, growing the logical qubit makes things worse.

Researchers call that crossover breakeven. Several companies have now built hardware whose error rate is low enough to clear it. The gains, though, have been modest. Pushing error rates down to the levels complex algorithms will need would mean adding a number of hardware qubits to each logical qubit that the reporting describes as completely impractical.

On Monday, Quantinuum announced that its current generation of hardware can keep scaling well beyond breakeven. At each step up in the size of its logical qubits, some measures of their performance improved by a factor of over 10. The figure concerns some measures, not all of them, and it comes from the company's own announcement.

For teams aiming at algorithms that need very low error rates, the question moves from whether scaling helps to how far this generation can be pushed. The announcement gives no date for machines built on it, and no price.