Google just made it much harder to build a serious quantum computer

Google is racing to create the first quantum computer capable of solving a problem ordinary computers cannot – and it has just made that challenge much harder.

Achieving “quantum supremacy”, as it is known, involves building a device that can solve a problem faster than any non-quantum computer.

In 2016, a team led by Sergio Boixo at Google published a paper showing that even with state-of-the-art supercomputers, it would be infeasible to simulate the behaviour of a quantum circuit with 48 qubits (quantum bits) at a circuit depth of 40, a…