MadSci Network: Physics

Re: Does quantum tunnelling transfer info faster than the speed of light

Date: Wed Mar 4 02:28:55 1998
Posted By: Georg Hager, Grad student, Theoretical Particle Physics
Area of science: Physics
ID: 887896067.Ph

Dear Steve!

You have to differentiate two things here: First, the experiments with ``quantum tunnelling'' (actually damped microwave propagation, that's why it's calles ``electromagnetic tunnelling'') performed by Prof. Nimtz at the University of Cologne (which involved the ``Mozart'' stuff) does not conflict with Special Relativity and can be explained entirely on the grounds of classical electrodynamics, which is known to conform with SR. GŁnter Nimtz has accepted that his experiments do not violate Einstein causality and has published a paper on that:

Heitmann, W. and G. Nimtz 1994: "On causality proofs of superluminal barrier traversal of frequency band limited wave packets" in Phys. Lett. A 196, p. 154.

Second, the problem how the speed of quantum tunnelling can be defined is not quite settled. In fact, hardly anybody believes that superluminal transport of information might be possible - and everybody seems to agree that the experiments are correct. The difficulty is that we do not exactly know how information is transmitted in a tunnelling process. It seems that the correct criterion for the speed of pulse transmission through a barrier should be set by the so-called front velocity, the velocity of the ``leading edge'' of the pulse. Till today, no experiment could measure front velocities greater than c (Nimtz in his ``Mozart'' setup used the pulse maximum as the criterion).

Many people are still working on this problem, and there is lots of recent literature around. The following web page gives some basic introduction and many references to articles and books:

Faster-than-light speeds in tunneling experiments: an annotated bibliography

Hope that helps,

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