(NewScientist) Google has shown that its Sycamore quantum computer can detect and fix computational errors, an essential step for large-scale quantum computing, but its current system generates more errors than it solves.
Error-correction is a standard feature for ordinary, or classical, computers, which store data using bits with two possible states: 0 and 1. Transmitting data with extra “parity bits” that warn if a 0 has flipped to 1, or vice versa, means such errors can be found and fixed.
Julian Kelly at Google AI Quantum and his colleagues have demonstrated the concept on Google’s Sycamore quantum computer, with logical qubits ranging in size from five to 21 physical qubits, and found that logical qubit error rates dropped exponentially for each additional physical qubit. The team was able to make careful measurements of the extra qubits that didn’t collapse their state but, when taken collectively, still gave enough information to deduce whether errors had occurred.
Kelly says that this means it is possible to create practical, reliable quantum computers in the future. “This is basically our first half step along the path to demonstrate that,” he says. “A viable way of getting to really large-scale, error-tolerant computers. It’s sort of a look ahead for the devices that we want to make in the future.”
Peter Knight at Imperial College London says Google’s research is progress towards something essential for future quantum computers. “If we couldn’t do this we’re not gonna have a large scale machine,” he says. “I applaud the fact they’ve done it, simply because without this, without this advance, you will still have uncertainty about whether the roadmap towards fault tolerance was feasible. They removed those doubts.”