Google says its new quantum chip, dubbed "Willow", incorporates key "breakthroughs" and "paves the way to a useful, large-scale quantum computer."

However experts say Willow is, for now, a largely experimental device, meaning a quantum computer powerful enough to solve a wide range of real-world problems is still years - and billions of dollars - away.

Google had chosen a problem to use as a benchmark of performance that was, "tailor-made for a quantum computer" and this didn't demonstrate "a universal speeding up when compared to classical computers".

In very simple terms the more useful a quantum computer is, the more qubits it has.

Errors are a significant obstacle in creating more powerful quantum computers and the development was "encouraging for everyone striving to build a practical quantum computer" Prof Woodward said.