Question

When an electron tunnels from one place to another, does in happen instantaneously, or does it require a finite amount of time? Can things other than electrons tunnel?

Asked by: Phil Reedy

 Answer

Well, there is a nice piece of work done by Markus Buettiker from Geneva (CH) concerning the travel time of tunneling electrons. He has a web page where you can find some references: http://mykonos.unige.ch/~buttiker/

For the second part of the question, photons can tunnel as well. There is a nice experiment call Newton's experiment which demonstrate the tunneling effect of photons: You launch a laser beam on a prism such that a total reflection occurs (that means that the angle of incidence respect to the normal of the hypotenuse should be greater than the critical angle of the media). In this configuration no light is transmitted, all the intensity is reflected. now, if you approach very close a second prism towards the hypotenuse of the first one, without touching it you will frustrate the total reflection and a beam will be transmitted to the second prism, though there is no light between the two hypotenuse. I don't want to go into detail, but the phenomena can be explained by Maxwell's equation and evanescent waves. Actually a lot of research is done on this field, namely in Scanning Near-Field Optical Microscopy (SNOM) which uses the tunneling of photons . (see for instance: http://monet.physik.unibas.ch/snom/)

Answered by: Alex, Ph.D Physics

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