Quantum locking will blow your mind — but how does it work?

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If case you haven't seen it yet, here's the quantum levitation (or, more accurately, quantum locking) video that's taken the internet by storm in the last 36 hours.

And while quantum locking (also known as "flux pinning") may not have anything to do with Weeping Angels, it's still pretty freaking amazing. But how does it work, and where the hell is your hoverboard?

Fortunately for all of us, Joe Hanson—who runs the awesome blog It's Okay to be Smart went out of his way to explain this phenomenon in more accessible terms:

What you start with is an inert [i.e. chemically inactive] disc, in this case a crystal sapphire wafer. That wafer is then coated with a superconductor called yttrium barium copper oxide. When superconductors get very cold (like liquid nitrogen cold) they conduct electricity with no loss of energy, which normal conducting materials like copper can't do.


Superconductors hate magnetic fields (when cold enough), and normally would just repel the magnetic force and float in a wobbly fashion. But because the superconductor is so thin in this case, tiny imperfections allow some magnetic forces through. These little magnetic channels are called flux tubes [pictured here].

The flux tubes cause the magnetic field to be "locked" in all three dimensions, which is why the disk remains in whatever position it starts in, levitating around the magnets.


Those of you with backgrounds in materials science, ceramics engineering or graduate-level physics may recognize this phenomenon as something similar to the Meissner-Ochsenfeld effect, though strictly speaking what you're witnessing is not a result of the Meissner effect.


In the Meissner effect, the superconductor that is placed within the magnetic field deflects the field entirely (see the image pictured here), such that none of the field passes through the object itself.

But as Hanson points out, the thinness of the superconductive coating featured in the quantum locking video allows for the magnetic field to penetrate it (albeit in discrete quantities) wherever there exist defects in the superconductor's molecular structure. This penetration gives rise to the "flux tubes" (again, pictured alongside Hanson's explanation), which pass through the inert crystal sapphire wafer and "trap" it in midair. This trapping provides the typically wobbly "levitation" characteristic of the Meissner effect a stiffer quality.


As for your hoverboard: as Hanson points out in his explanation, superconductors only possess their field-banishing properties at extremely cold temperatures, making hovering skateboards more or less impossible at this point. But for what it's worth, there's currently no evidence that says room-temperature superconductors can't exist—we just haven't haven't discovered them yet.

Edit: Down in the comments section, daen raises a good point that this effect would not have been observed had the crystal sapphire been coated with a Type I superconductor (yttrium barium copper oxide is what is known as a Type II superconductor).


For an explanation of why this matters, see the response to daen given in the comments. As I mention in my response, this isn't exactly my field, so feel free to weigh in on/correct any conclusions that I've drawn.


[Via It's Okay To Be Smart]