Room-temperature spin registers

The appeal was a quantum register with no cryostat — a device that works on a desk. Enough distinct material platforms were being proposed for it that the question looked open rather than settled.

We ran eight candidates against prior art before building anything, on the rule that a direction has to survive a literature check before it earns a single line of code.

All eight died. Six to prior art, two to a fabrication dependency, none to physics — and every one terminated in the same place.

Magnetic coupling between spin qubits needs ≲30–50 nm. Optical readout needs ≳250 nm by diffraction. The windows do not overlap: a factor of 5–10 in distance, 10²–10³ in coupling. Everything else in the field is a workaround for that gap, and every workaround we could reach either was already taken or required a sample we could not make. The scissors held across NV, SiC, quMOF and hBN, which is why we treat it as general rather than as a defect of one platform.

The honest assessment written at the time was that none of it clears the bar for a paper — not the wavelength observation, not the pulse ordering, not the synthesis. Two days, $0, and the output is the eight kills and the process rules they produced. That is worth more than the marginal note would have been, and it is the whole reason this page exists.