Quantum Tunneling and the Hogwart’s Express; Tunneling is Not Instantaneous

Layperson’s explanation for quantum tunneling is well done in this Scientific American work. Recommend reading from the source. Because Quantum is Coming. Qubit

Quantum Tunneling Is Not Instantaneous, Physicists Show

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+  Researchers have showed that quantum tunneling is not instantaneous—at least, in one way of thinking about the phenomenon—despite recent headlines that have suggested otherwise. “This is a beautiful experiment,” says Igor Litvinyuk of Griffith University in Australia, who works on quantum tunneling but was not part of this demonstration. “Just to do it is a heroic effort.”

Some media reports controversially claimed that the Griffith University experiment had shown tunneling to be instantaneous. The confusion has a lot to do with theoretical definitions of tunneling time. The type of delay the team measured was certainly almost zero, but that result was not the same as saying the electron spends no time in the barrier. Litvinyuk and his colleagues had not examined that aspect of quantum tunneling.

+  Careful analysis revealed that it was, mathematically speaking, the peak of the tunneling photons’ wave functions (the most likely place to find the particles) that was traveling at superluminal speed. The leading edges of the wave functions of both the unimpeded photon and the tunneling photon reach their detectors at the same time, however—so there is no violation of Einstein’s theories of relativity. “The peak of the wave function is allowed to be faster than light without information or energy traveling faster than light,” Steinberg says.

+  They also verified another strange prediction of quantum mechanics: the lower the energy, or slower the movement, of a tunneling particle, the less time it spends in the barrier. This result is counterintuitive, because in our everyday notion of how the world works, a slower particle would be expected to remain in the barrier for a longer stretch of time. + Litvinyuk is impressed by the measurements of the rotation of the clock hand. “I see no holes in this,” he says. But he remains cautious. “How, ultimately, it relates to the tunneling time is still up for interpretation,” he says.

Source:  Scientific American.  Anil Ananthaswamy,  Quantum Tunneling Is Not Instantaneous, Physicists Show…

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