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Name: Justin
Status: educator
Grade: 9-12
Location: IL
Country: USA
Date: Winter 2012-2013


Question:
How does quantum locking work? I just saw an amazing video with a supercooled material that looks like magnetic levitation, but it works in many orientations. How can this be? https://www.youtube.com/watch?v=YAEhIAHyMX0

Replies:
Hi Justin,

This is an excellent question! Quantum locking (quantum pinning) is the result of several quantum phenomena acting at once. It is also a favorite demonstration of electrical, magnetic, semiconducting and low temperature effects.

Only Type II superconducting material may be used for pinning because these materials allow partial magnetic field penetration and they are superconducting with a critical temperature, Tc, above 77K (liquid N2). An example of Type II super conducting material is crystalline Yttrium Barium Copper Oxide(YBCO), YBa2Cu3O7-x.

The actual mechanism has not yet been elucidated for Type II material pinning, but is the subject of active research. Please allow this highly qualitative explanation for a thin super conducting disc:

When Tc is reached, electrons (e-) begin to move on the surface of any superconducting material. The e- flow and eddy currents have the effect of cancelling out the magnetic field component, repelling the magnetic field altogether (Meissner Effect). The Type I super conducting disc will simply float off of a tilted magnet.

However, for the YBCO (Type II) disc, the electrons also spin, forming a spin density wave. The density wave is a depression that a nearby e- may fall into, forming an e- pair, a Cooper pair. There may be a symmetry change or a Coulomb interaction as a result of these Cooper pairs forming. The end result is that the magnetic field does penetrate the YBCO in discrete quantities (quantum flux) and causes a well of flux around the disc. The flux has been described as flux tubes going through the disc and surrounding it (like fingers holding the edge of a book), holding it. Thereby the Type II disc will be held by the flux tubes within the flux well of a tilted (or turned over) magnet.

Hoping this helps! Peter E. Hughes, Ph.D. Milford, NH


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