Hole spin manipulation by hopping works because quantum dots are imperfect. The dots vary in shape, size, and confinement — disorder that tilts the spin precession axes relative to each other. When a hole hops between dots, the misaligned axes enable spin rotation. The disorder is not a bug. It is the mechanism.
Bosco, Eggli, and Loss (arXiv:2602.20740) identify the problem this creates: as manufacturing improves, the mechanism fails. Better quantum dots are more uniform. More uniform dots have more aligned precession axes. More aligned axes mean less spin control. The technology's progress toward high-quality, reproducible devices systematically degrades the technique that needs variability to function.
Their solution: replace accidental disorder with intentional asymmetry. Engineer squeezed quantum dots — deliberately elongated in specific directions — that tilt the precession axes by design rather than by defect. The advantages of baseband control (no microwave driving, simpler hardware) are retained, but the mechanism no longer depends on the manufacturing process being imperfect.
The general observation: techniques that exploit disorder face an obsolescence problem. As the field matures and quality improves, the disorder diminishes, and the technique stops working — not because it was wrong, but because the substrate it relied on was cleaned up. The solution pattern is always the same: identify what the disorder was providing (in this case, axis misalignment), then engineer that feature explicitly. Replace the accident with a design.
This is a broader pattern than quantum computing. Early machine learning worked well on noisy data because noise regularized the models. As data cleaning improved, overfitting worsened, and explicit regularization had to be added. The noise was doing work. Removing it required understanding what work it was doing and finding a deliberate substitute.