Quantix

Quantix, an ice monk of The SI Guard, steps across a frozen superconducting lake of vortex stones, each holding one quantum of flux.

The Physics

In a superconducting ring the electrons pair up into Cooper pairs and share a single macroscopic wavefunction. The phase must come back to itself around the loop, so the fluxoid (the flux, plus a small supercurrent term) is quantised in whole multiples of Φ₀. In a type-II superconductor the field enters as Abrikosov vortices, each carrying one Φ₀, arranged in a triangular lattice.

Φ₀ = h/2e ≈ 2.067 833 848 × 10⁻¹⁵ Wb

• Φ₀: magnetic flux quantum (Wb)
• h: Planck constant (exact)
• 2e: charge of a Cooper pair

Since the 2019 SI fixed h and e, Φ₀ is exact (CODATA lists it as exact; the digits shown are truncated). Its inverse, K_J = 2e/h, is the Josephson constant behind the world's voltage standards. The factor 2 was confirmed in 1961 (Deaver & Fairbank; Doll & Näbauer).

Honest caveat: The 2e is the pair charge, not one electron's. Flux is quantised only in superconductors, and in a thin ring it is strictly the fluxoid, not the bare flux, that comes in whole units.

On the sticker

Quantix holds a glowing vortex swirl, with the triangular vortex lattice behind him. Printed text: QUANTIX with the line Φ0 = h/2e. Pixel-art kiss-cut vinyl sticker, white, in 2″, 3″, 4″ and 6″ sizes.