The chief obstacle in building quantum computers is that superposition is very difficult to maintain. They derive this speed advantage by taking advantage of superposition, the ability of tiny particles - such as the atoms spinning in both directions at once - to inhabit more than one physical state at a time. Physical systems that correlate spin and velocity could open the door to a novel approach to quantum computers, largely hypothetical devices that would perform some types of computations exponentially faster than conventional computers. “Quantum mechanics provides a surprising answer: They can simultaneously spin both ways.” “What about the atoms moving with a velocity in between these extremes?” Zwierlein asks. In the process of sorting themselves into separate quantum states, the atoms moving very fast to the left end up spinning one way, while those moving very fast to the right end up spinning the other way. Just like electrons, the atoms in the gas are fermions, particles that cannot share the same quantum state as a consequence, each atom has to have a different combination of spin and velocity. The MIT team, led by Martin Zwierlein, an associate professor of physics and a principal investigator in the Research Laboratory of Electronics (RLE), produced this spin-velocity correlation in an ultracold, dilute gas of atoms. The correlation between spin and direction of motion is crucial to creating a so-called topological superfluid, a key ingredient of some quantum-computing proposals. Physical materials with this distinctive property could be used in “spintronic” circuit devices that rely on spin rather than electrical current for transferring information. In work reported this week in the journal Physical Review Letters, MIT physicists have imposed a stringent set of traffic rules on atomic particles in a gas: Those spinning clockwise can move in only one direction, while those spinning counterclockwise can move only in the other direction. Elementary particles have a property called “spin” that can be thought of as rotation around their axes.
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