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Can a disc really float above a magnet and lock in place?

Fun fact · The viral "quantum levitation" and "quantum locking" videos

Faithful. A working physicist would nod.

What the scene or the claim says

A small disc hovers over a magnetic track, stays exactly where you put it, even upside-down, and glides along the track without touching it.

What is real

This is real, and the name is fair. A thin superconducting disc is cooled below its critical temperature inside a magnetic field. In a type-II superconductor, magnetic field lines get trapped in quantised tubes of flux, pinned at tiny defects in the material, and the pinning holds the disc where it was cooled, in position and orientation. The usual material, YBCO, superconducts below about 90 K, so liquid nitrogen at 77 K is enough to run it.

What stops it working that way

• It only works while the disc stays cold. Left alone, it warms up and drops.
• It locks where it was field-cooled. Cool it above the track and it stays there; move it and it resists.
• The video's "quantum" is a macroscopic effect: quantised flux, and a superconducting state that is a quantum state of a very large number of electrons together.

If you wanted it to work

The same physics underlies MRI magnets and particle-accelerator magnets. A material that stayed superconducting at room temperature would let you keep the disc floating on a kitchen table, and see the LK-99 card for why that has not happened yet.

Sources

• Wu et al. 1987, superconductivity at 93 K in Y-Ba-Cu-O
• Blatter et al. 1994, vortices in high-temperature superconductors

See it in the swipe deck, with the other cards.