On 23 October 2019 Nature published a paper titled 'Quantum supremacy using a programmable superconducting processor'. The Sycamore processor, developed at Google's Santa Barbara lab, held 53 superconducting qubits cooled to within a hundredth of a degree of absolute zero. The task was deliberately narrow: sampling from random quantum circuits — a problem of no practical use, but one that exploits superposition and entanglement to the limit. Sycamore finished it in 200 seconds. By Google's reckoning, the world's most powerful classical supercomputer (Summit at Oak Ridge) would need 10,000 years to do the same.

The concept had been named in 2012 by John Preskill of Caltech: 'quantum supremacy' is the moment a quantum device, on any task — useful or not — exceeds the reach of classical computers. Sycamore's result was not an application but a proof of principle: a theoretical premise about quantum processors was now experimentally demonstrated. IBM responded within a week, arguing that with a more efficient memory architecture their own supercomputer could finish the same problem in 2.5 days. The supremacy claim remained contested, and the community gravitated toward the more careful 'quantum advantage'.

But the direction of travel was clear. From 2020 the race accelerated: IBM unveiled the 127-qubit Eagle in 2021, the 433-qubit Osprey in 2022, and the 1,121-qubit Condor in 2023. A Chinese group at USTC claimed an independent supremacy result in 2020 using a photonic system (Jiuzhang) on Gaussian boson sampling. IonQ and Quantinuum pursued a separate hardware path with trapped ions. Microsoft worked on topological qubits, AWS offered hybrid cloud services, and Canada's Xanadu pushed photonic qubits. A quantum computer — until the 2010s a 'will it ever work?' question — became, in the 2020s, a mid-stage hardware race.

Useful applications remain distant. For a quantum processor to surpass classical ones on a real problem (chemistry simulation, cryptography, optimisation), error-corrected logical qubits are needed, which require millions of physical qubits. Even so, Sycamore was the first major concrete step in which quantum mechanics — alive in laboratories for nearly a century — was translated into the language of computer science. From Shor's algorithm that could shake the foundations of RSA encryption, to molecular simulation in drug design, the signpost for the next generation of computing was planted on 23 October 2019.