Quantum computers work in a fundamentally different way to the computer in your phone or laptop.
They harness quantum mechanics – the strange behaviour of ultra-tiny particles – to crack problems far faster than traditional computers.
It’s hoped quantum computers might eventually be able to use that ability to vastly speed up complex processes, such as creating new medicines.
There are also fears it could be used for ill – for example to break some types of encryption used to protect sensitive data.
In February Apple announced, external that the encryption that protects iMessage chats is being made “quantum proof” to stop them being read by powerful future quantum computers.
Hartmut Neven leads Google’s Quantum AI lab that created Willow and describes himself as the project’s “chief optimist.”
He told the BBC that Willow would be used in some practical applications – but declined, for now, to provide more detail.
But a chip able to perform commercial applications would not appear before the end of the decade, he said.
Initially these applications would be the simulation of systems where quantum effects are important
“For example, relevant when it comes to the design of nuclear fusion reactors to understand the functioning of drugs and pharmaceutical development, it would be relevant for developing better car batteries and another long list of such tasks”.