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AIP conference proceedings

Superluminal energy and information transport?

A. A. Stahlhofen, H. Druxes

Published Jan 1, 1999• 0 citations
Publisher

Abstract

The widespread belief, that energy and signal velocities are bounded by the speed of light in vacuum has been challenged in recent years by observations of superluminal propagation of classical evanescent modes in tunneling time experiments. These experiments thus provide a frame for testing the limits of transport velocities physically achievable. Obvious and hidden time-scales involved in tunneling time experiments are discussed focussing on optical tunneling in frustrated total internal reflection. A suggestion for a direct test of the energy transport velocity—also of interest in future hyper-fast space travel—is presented. Related questions touching our current understanding of some fundamental concepts in physics are addressed.

DOI
10.1063/1.57717

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The widespread belief, that energy and signal velocities are bounded by the speed of light in vacuum has been challenged in recent years by observations of superluminal propagation of classical evanescent modes in tunneling time experiments. These experiments thus provide a frame for testing the limits of transport velocities physically achievable. Obvious and hidden time-scales involved in tunneling time experiments are discussed focussing on optical tunneling in frustrated total internal reflection. A suggestion for a direct test of the energy transport velocity—also of interest in future hyper-fast space travel—is presented. Related questions touching our current understanding of some fundamental concepts in physics are addressed.
Contemporary observational and theoretical studies on the temporal nature of microscopic measurements renewed the discussion about the fundamental constants, leading to the possibility of light speed variation and superluminal pulse propagation. Gain assisted experiments using anomalous dispersion near an absorption line in atomic gas, a "fast - light" medium, seem to lead to a wave group velocity vG exceeding c, the vacuum speed of light; moreover, definition of the information velocity vi sets the question of interpretation of the three speeds: one view is that vi = vG, but this violates Causality; another view is that vi = c in all situations, but this limits, a priori, the transport of information. Another view is that vi, vG and c are distinct. This contribution follows the last possibility. A draft discussion on space-time is given.
Evanescent modes or the tunnelling process are characterized by an imaginary wave number. These special solutions of the Helmholtz and of the Schrödinger equations first noticed in connection with the total reflection were said to have no physical meaning about 200 years ago. Last century the tunnelling problem in quantum mechanics has been described by the phase time approach. The phase time approach yields the group velocity of a wave packet (see e.g. Hartman, 1962). Nowadays the phase time approach is used in network analyzers to determine the group velocity of an electromagnetic wave in devices. We have reported about superluminal signal velocities in photonic tunnelling. It was observed that the superluminal photonic tunnelling time data measured in the time domain are in agreement with the calculated phase time data. This result is also in agreement with the definition of the barrier transition time given in the Federal Standard 1037 C (NTIA, USA 2000). Thus we have added further credibility to the assumption that the photonic tunnelling results are representative for quantum mechanical tunnelling of particles.
Photonic tunnelling experiments have shown that i) the Einstein energy relation is violated, ii) the tunnelling process is non‐local, iii) the signal velocity is faster than light, i.e. superluminal, iv) the tunnelling signal is not observable, since photonic tunnelling is described by virtual photons, and v) according to the experimental results the signal velocity is infinite inside the barriers, implying that tunnelling instantaneously acts at a distance. We think these properties are not compatible with the claims of many text books on Special Relativity, see for instance Refs. [1].
Superluminal signal velocity is widely assumed to confront Einstein causality and thus the Special Theory of Relativity (STR). Actually, there is only the tunneling mechanism known to permit superluminal signal velocities at present. The demonstrated negative group velocity experiments don't represent superluminal signal velocities. In those experiments only the signal's peak traveled faster than light and the signal was reshaped. In this Note we shall discuss why tunneling allows superluminal signal velocities. However, opposed to text books on STR we have shown that a superluminal signal beam does not allow the design of a time machine.
We describe a series of atom optics experiments underway at Toronto for investigating tunnelling interaction times of various sorts. We begin by discussing some outstanding issues and confusions related to the question of whether or not superluminal tunnelling can be construed as true faster-than-light “signal propagation,” a question which we answer in the negative. We then argue that atom optics is an arena ideally suited for addressing a variety of remaining questions about how, where, and for how long a particle interacts with a tunnel barrier. We present recent results on a modified “delta-kick cooling” scheme which we have used to prepare Rubidium atoms with one-dimensional de Broglie wavelengths on the order of an optical wavelength, along with simulations showing that from these temperatures, we will be able to use acousto-optically modulated dipole-force barriers to velocity-select ultracold atom samples ideal for future tunnelling experiments.