Google Willow Demonstrates Verifiable Quantum Echoes Beyond Classical

Google researchers said on Oct. 22 that their Willow quantum processor ran a new algorithm, called Quantum Echoes, that performed a calculation they describe as verifiably beyond the reach of conventional supercomputers. The team reported that the computation, carried out on a 65‑qubit chip at Google Quantum AI, produced a result that would take an estimated 150 years of time on one of the world’s fastest classical supercomputers but required only days on Willow.

The experiment centers on a class of quantities known as out‑of‑time‑order correlators, or quantum echoes, which are signatures of chaotic behavior in quantum systems. To extract a stable, checkable signal from that chaos, researchers ran sequences of randomized operations on qubits, then reversed those operations to effectively run time backward while making small, controlled perturbations. The reversal strategy produces a complex interference pattern that the team says is difficult to simulate on classical hardware yet can be efficiently checked by another quantum device. "If I cant prove to you that the data is correct, how can I do anything with it?" physicist Tom OBrien of Google Quantum AI said during a recent...