Quantum annealing

Quantum computing promised revolutionary speedups, but building gate-based quantum computers proved extraordinarily difficult. Qubits were fragile, losing coherence in microseconds. Error correction schemes required thousands of physical qubits for each logical qubit. A different approach emerged: what if quantum effects could be harnessed for a specific computational task without requiring universal quantum gates?

Quantum annealing exploits quantum tunneling to find the lowest energy state of a system—mathematically equivalent to finding optimal solutions to certain combinatorial problems. Classical simulated annealing, a well-established optimization technique, works by gradually 'cooling' a system to settle into low-energy configurations. Quantum annealing replaces thermal fluctuations with quantum fluctuations, potentially allowing the system to tunnel through energy barriers rather than climbing over them.

D-Wave Systems, founded in 1999 in Burnaby, British Columbia, bet the company on this approach. While academic quantum computing research focused on gate-based systems, D-Wave built increasingly large quantum annealers: 128 qubits in 2011, 512 in 2013, over 5,000 by 2020. The devices looked nothing like laboratory quantum computers—massive dilution refrigerators housing superconducting circuits, sold to Google, NASA, and Lockheed Martin.

The adjacent possible for quantum annealing drew on different technologies than gate-based computing. Superconducting flux qubits didn't need the extreme coherence times of transmon qubits. Josephson junctions, developed for decades in superconducting electronics, provided the building blocks. And the adiabatic theorem from quantum mechanics guaranteed that systems evolved slowly enough would remain in their ground state—the theoretical basis for the approach.

Controversy surrounded D-Wave from the beginning. Was it really quantum? Early devices showed no clear speedup over classical optimization algorithms. Academic critics argued the systems might be sophisticated classical computers. Supporters countered that quantum effects were demonstrably present, even if practical advantage remained elusive. The debate illustrated how difficult it was to verify quantum computing claims.

Geographic factors shaped D-Wave's development. British Columbia's tech ecosystem, grown from the Vancouver area's software industry, provided a supportive environment outside the Stanford-MIT axis that dominated gate-based quantum research. Canadian government funding through various programs supplemented venture capital. The company's isolation from academic orthodoxy may have enabled its heterodox approach.

By 2025, the jury remained out. D-Wave had demonstrated quantum annealing at scale but had not conclusively proven quantum advantage for practical problems. Gate-based competitors from IBM and Google had made dramatic progress. Hybrid classical-quantum approaches blurred the lines. Quantum annealing occupied an uncertain niche: commercially available, undeniably impressive engineering, yet still searching for problems where it definitively outperformed classical alternatives.