Quantum advantage (also called quantum supremacy, though this term has fallen out of favor) refers to a quantum computer solving a problem that is practically impossible for any classical computer, or solving a practical problem significantly faster or better than classical alternatives. The concept exists on a spectrum from narrow computational demonstrations to broad practical utility.
Google claimed the first quantum advantage in 2019 with its 53-qubit Sycamore processor, performing a random circuit sampling task in 200 seconds that they estimated would take a classical supercomputer 10,000 years. IBM disputed this estimate, arguing that classical simulation with sufficient memory could complete the task in 2.5 days. Google strengthened its claim with the 2024 Willow chip, performing random circuit sampling on 70+ qubits that would require an estimated 10^25 years of classical computation. Chinese groups have demonstrated quantum advantage with photonic and superconducting systems for boson sampling and related tasks.
These demonstrations, while scientifically significant, involve artificial problems with no practical application. The more important milestone — practical quantum advantage, where a quantum computer solves a commercially or scientifically relevant problem better than classical alternatives — has not yet been achieved. Leading candidates include molecular simulation for drug discovery, optimization problems in logistics and finance, and cryptographic applications. The timeline for practical quantum advantage is uncertain, with estimates ranging from 2-5 years for narrow applications (with error mitigation or early fault tolerance) to 10+ years for broad applicability.