Quantum supremacy

Quantum supremacy is the demonstration that a quantum computer can perform a computational task that no classical computer can perform in a feasible amount of time. The term was coined by John Preskill in 2012 and achieved experimentally by Google in 2019 with their Sycamore processor, which performed random circuit sampling on 53 qubits in 200 seconds — a task they claimed would take a classical supercomputer thousands of years. The achievement is not about solving a useful problem; random circuit sampling has no practical application. It is about establishing a computational phase transition: the point at which quantum systems become large enough and coherent enough that classical simulation is not merely slow but exponentially infeasible. The debate over whether this milestone has truly been reached is ongoing: IBM argued that classical simulation with better memory management could reduce the classical time, and the definition of supremacy itself is contested. The deeper question is whether supremacy is a meaningful category or merely a publicity milestone on the path to quantum advantage — the demonstration of a quantum computer solving a commercially or scientifically relevant problem better than classical alternatives. The field is currently in the awkward interregnum between supremacy and advantage, with no clear path from one to the other.