A thin superconductor layer (~1µm thick) is coated on a sapphire wafer. Quantum physics tells us that the magnetic field penetrates into the superconductor in the form of discrete flux tubes. The superconductor strongly pins these tubes, causing it to float in midair. This effect is called ‘quantum levitation’.
In this video, the locking phenomenon is nicely demonstrated using two different magnet configurations, and then a crude train track is used to show its potential in transportation.
As Jason Kottke puts it, “You can almost hear your tiny mind explode when the ‘train’ goes upside-down.”