A recent study on D‑Wave Advantage 4.1 quantum annealers used a fast‑anneal protocol that shortens the anneal time to 0.005 µs—well below the device’s coherence time. The experiment probed one‑dimensional Ising spin chains whose ends are fixed in opposite directions, a configuration that forces domain walls—locations where neighboring spins flip—to form in the middle of the chain. For chains run at the slow, 20 µs anneal time, the observed distribution of domain walls is U‑shaped. This profile matches a classical model that averages over random static fields and incorporates thermal noise. However, when the anneal time is shortened to 0.005–0.03 µs, the distribution approaches the sine‑squared shape predicted by a quantum particle‑in‑a‑box model. The match is imperfect at the shortest time, where the data still show a distorted U‑shaped profile with a truncated tail, indicating that coherent dynamics are not yet fully established. The experiment therefore demonstrates that ultra‑fast annealing can access a coherent quantum regime distinct from the classical thermal regime, but that the device still has limits: even at 0.005 µs the distribution does not yet converge to the ideal sine‑squared form. The study highlights the usefulness of the domain‑wall distribution tail as a metric for coherence time and noise levels in quantum annealers.

The hardware used in the work is the Advantage 4.1 system, whose fast‑anneal protocol allows anneal times down to 0.005 µs—about a hundred times shorter than the previous minimum of 0.5 µs. All experiments were programmed with the D‑Wave Ocean SDK and the Ising Hamiltonian was encoded as a binary quadratic model (BQM) using the Dimod package. The fast‑anneal experiments reveal quantum behavior that emerges only when the dynamics are faster than the device’s decoherence processes.

The transition from the thermalised U‑shaped profile to the quantum sine‑squared shape illustrates how measurement of the domain‑wall distribution can act as a platform‑independent diagnostic for both coherence time and noise levels. The work underscores that while faster anneals improve quantum features, complete convergence to the ideal distribution is still limited by the hardware’s coherence properties.