Taking the Knot out of Quantum Knots to Make a Topological Quantum Computer
Physicists capture first footage of quantum knots unraveling in superfluid
In brief…
+ The same team who tied the first “quantum knots” in a superfluid several years ago have now discovered that the knots decay, or “untie” themselves, fairly soon after forming, before turning into a vortex. The researchers also produced the first “movie” of the decay process in action, and they described their work in a recent paper in Physical Review Letters.
For now, at least, quantum knots remain a laboratory curiosity, but the research might have bearing on ongoing research into building topological quantum computers. Such a device would braid qubits in different topologically stable structures, making the computer more robust against errors. This latest finding indicates that time may be an important factor, given the knots’ rate of decay.
+ Hall and Möttönen used a quantum state of matter known as a Bose-Einstein Condensate (BEC) as their medium—technically a superfluid. 
Then they “tied” the knots by manipulating magnetic fields. If you think of the quantum field as points in space that each have an orientation—like arrows all pointing up, for instance—the core of a quantum knot would be a circle where the arrows all point down, similar to a god’s eye yarn pattern.
+ “If you followed the magnetic field line, it would go toward the center, but at the last minute it would peel away into a perpendicular direction,” Hall told Gizmodo in 2016. “It’s a particular way of rotating these arrows that gives you this linked configuration.”
+ For now, at least, quantum knots remain a laboratory curiosity, but the research might have bearing on ongoing research into building topological quantum computers. Such a device would braid qubits in different topologically stable structures, making the computer more robust against errors. This latest finding indicates that time may be an important factor, given the knots’ rate of decay.
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