Treversal
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Quantum Tunneling Is Not Instantaneous, Physicists Show
A new experiment tracks the transit time of particles burrowing through barriers, revealing previously unknown details of a deeply counterintuitive phenomenon
www.scientificamerican.com
Ever since its discovery, experimentalists have strived for a clearer understanding of exactly what happens during tunneling. In 1993, for example, Steinberg, Paul Kwiat and Raymond Chiao, all then at the University of California, Berkeley, detected photons tunneling through an optical barrier (a special piece of glass that reflected 99 percent of the incident photons; 1 percent of them tunneled through). The tunneling photons arrived earlier, on average, than photons that traveled the exact same distance but were unimpeded by a barrier. The tunneling photons seemed to be traveling faster than the speed of light.