After a brief theoretical introduction (based on the standard postulates of Special Relativity, and therefore extending it --or rather non-restricting it-- without any violations: in particular without any violations of the so-called Einstein causality), the main aim of this article is an updated presentation of the status-of-the-art of the
superluminal experiments. In particular, we devote such an article to the phenomena met in tunneling through quantum (and classical) barriers [e.g., referring to the Genelalized Hartman Effect]; and in connection with the Localized (nondiffracting) Solutions of the wave equations [e.g., of Maxwell equations]: especially of the X-shaped ones. The interested reader is provided with an extended Bibliography. This paper was written as a homage to E.C.G. Sudarshan, in connection with his pioneering work on the so-called tachyons. Actually, E.C.George Sudarshan, besides the originator of the V-A theory for weak-forces, of quantum optics --the quantum representation of coherent light--, of dynamical maps for open quantum systems, of the Zeno effect, etc., was a pioneer, in the sisties, also of the theory of Tachyons.
After a brief theoretical introduction (based on the standard postulates of Special Relativity, and therefore extending it --or rather non-restricting it-- without any violations: in particular without any violations of the so-called Einstein causality), the main aim of this article is an updated presentation of the status-of-the-art of the
superluminal experiments. In particular, we devote such an article to the phenomena met in tunneling through quantum (and classical) barriers [e.g., referring to the Genelalized Hartman Effect]; and in connection with the Localized (nondiffracting) Solutions of the wave equations [e.g., of Maxwell equations]: especially of the X-shaped ones. The interested reader is provided with an extended Bibliography. This paper was written as a homage to E.C.G. Sudarshan, in connection with his pioneering work on the so-called tachyons. Actually, E.C.George Sudarshan, besides the originator of the V-A theory for weak-forces, of quantum optics --the quantum representation of coherent light--, of dynamical maps for open quantum systems, of the Zeno effect, etc., was a pioneer, in the sisties, also of the theory of Tachyons.
This writing has been prepared on the occasion of the 75th birthday of E.C.George Sudarshan, who (besides the originator of the V-A theory for weak-forces, of quantum optics --the quantum representation of coherent light--, of dynamical maps for open quantum systems, of the Zeno effect, etc.) was a pioneer, already in the sisties, also of the theory of the so-called "tachyons". This paper wishes to be a homage to E.C.G.Sudarshan, in connection with the last-mentioned pioneering work of his. After a brief theoretical introduction (based on the standard postulates of Special Relativity, and therefore extending it --or rather non-restricting it-- without any violations: for example, without any violations of the so-called Einstein causality), the main aim of this article is an updated presentation of the status-of-the-art of the "superluminal" experiments. In particular, we devote such a review to the phenomena met in tunneling through quantum (and classical) barriers [e.g., referring to the Genelalized Hartman Effect]; and in connection with the "Localized (nondiffracting) Solutions" of the wave equantions [e.g., of Maxwell equations]: especially of the "X-shaped" ones. The interested reader is provided with an extended Bibliography.
Experiments at Berkeley and elsewhere which show that the process of tunneling is apparently superluminal will be reviewed. Conflicting theories for the tunneling time will be compared with experiment. The tunneling particle in the Berkeley experiments was the photon. The measurement of the tunneling time utilized a two-photon light source (spontaneous parametric down-conversion), a Hong-Ou-Mandel interferometer, and a coincidence counter of photon pairs. The tunnel barrier consisted of a photonic-bandgap medium excited at midgap. We find that the peak of a tunneling single-photon wave packet appeared on the far side of the barrier 1.47 ± 0.21 fs earlier than the peak of a wave packet which traveled an equal distance in air. Group velocities which exceed c can also occur in transparent media with inverted atomic populations. Tachyon-like excitations, i.e., collective normal modes of atoms coupled to electromagnetic radiation which possess tachyon-like dispersion relations, occur in these media. However, relativistic causality is not violated by any of these superluminal phenomena.
In the First Part of this paper [that was submitted for pub. in 1991 and appeared in print in Phys. Reports 214 (1992) 339] we critically review the main theoretical definitions and calculations of the sub-barrier tunnelling and reflection times. Moreover, within conventional QM, we propose a new definition of such durations, on the basis of a recent general formalism of ours. At last, we discuss a surprising result: that QM predicts tunnelling through opaque barriers to take place with Superluminal group-velocities. In the Second Part [that appeared in print later, in J. de Physique-I 5 (1995) 1351] we, e.g., present the results of some numerical calculations (based on our equations) on the penetration and return times during tunnelling INSIDE a rectangular potential barrier, and set forth suitable definitions also of the variances, or dispersions, for the transmission and reflection time-durations. The numerical evaluations confirm that our approach implied, and implies, the existence of Superluminal tunnelling (that we called "Hartman effect"): an effect that in these days is receiving --at Cologne, Berkeley, Florence and Vienna-- indirect, but interesting, experimental verifications. More detailed reviews of the same topics are in the LANL Archive cond-mat/9802126 (and in an Appendix to physics/9712051, where the data are summarized of the experiments that --in four different sectors of physics-- seem to indicate the existence of Superluminal motions).
In the last decade decoherence has become a very popular topic mainly due to the progress in experimental techniques which allow monitoring of the process of decoherence for single microscopic or mesoscopic systems. The other motivation is the rapid development of quantum information and quantum computation theory where decoherence is the main obstacle in the implementation of bold theoretical ideas. All that makes the second improved and extended edition of this book very timely. Despite the enormous efforts of many authors decoherence with its consequences still remains a rather controversial subject. It touches on, namely, the notoriously confusing issues of quantum measurement theory and interpretation of quantum mechanics. The existence of different points of view is reflected by the structure and content of the book. The first three authors (Joos, Zeh and Kiefer) accept the standard formalism of quantum mechanics but seem to reject orthodox Copenhagen interpretation, Giulini and Kupsch stick to both while Stamatescu discusses models which go beyond the standard quantum theory. Fortunately, most of the presented results are independent of the interpretation and the mathematical formalism is common for the (meta)physically different approaches. After a short introduction by Joos followed by a more detailed review of the basic concepts by Zeh, chapter 3 (the longest chapter) by Joos is devoted to the environmental decoherence. Here the author considers mostly rather `down to earth' and well-motivated mechanisms of decoherence through collisions with atoms or molecules and the processes of emission, absorption and scattering of photons. The issues of decoherence induced superselection rules and localization of objects including the possible explanation of the molecular structure are discussed in details. Many other topics are also reviewed in this chapter, e.g., the so-called Zeno effect, relationships between quantum chaos and decoherence, the role of decoherence in quantum information processing and even decoherence in the brain. The next chapter, written by Kiefer, is devoted to decoherence in quantum field theory and quantum gravity which is a much more speculative and less explored topic. Two complementary aspects are studied in this approach: decoherence of particle states by the quantum fields and decoherence of field states by the particles. Cosmological issues related to decoherence are discussed, not only within the standard Friedmann cosmology, but also using the elements of the theory of black holes, wormholes and strings. The relations between the formalism of consistent histories defined in terms of decoherence functionals and the environmental decoherence are discussed in chapter 5, also written by Kiefer. The Feynman--Vernon influence functional for the quantum open system is presented in detail as the first example of decoherence functional. Then the general theory is outlined together with possible interpretations including cosmological aspects. The next chapter by Giulini presents an overview of the superselection rules arising from physical symmetries and gauge transformations both for nonrelativistic quantum mechanics and quantum field theory. Critical discussion of kinematical superselection rules versus dynamical ones is illustrated by numerous examples like Galilei invariant quantum mechanics, quantum electrodynamics and quantum gravity. The introduction to the theory of quantum open systems and its applications to decoherence models is given in chapter 7 by Kupsch. Generalized master equations, Markovian approximation and a few Hamiltonian models relevant for decoherence are discussed. Some mathematical tools, e.g., complete positivity and entropy inequalities are also presented. The last chapter by Stamatescu is devoted to stochastic collapse models which can be interpreted either as certain representations of the dynamics of open quantum systems or as fundamental modifications of the Schr\"odinger equation. The final part of the book consists of remarks by Zeh on related concepts and methods and seven appendices. The broad spectrum, mathematically-friendly presentation, inclusion of the very recent developments and the extensive bibliography (about 550 references) make this book a valuable reference for all researchers, graduate and PhD students interested in the foundations of quantum mechanics, quantum open systems and quantum information. The relative independence of the chapters and numerous redundancies allow for selective reading, which is very helpful for newcomers to this field.
An explanation for superluminal phenomena based on wave-particle duality of photons is suggested. A single photon may be regarded as a wave packet, whose spatial extension is its coherence volume. As a photon propagates as a wave train in vacuum, its velocity is just the speed of light. When it tunnels through a barrier as a particle, its wave function collapses and it will travel faster than light. Superluminal motion can occur only within the coherence length and the time constrained by uncertainty principle. A massive particle cannot be superluminal during the tunneling process. So superluminality does not violate causality. As for the superluminal and negative group velocities in anomalously dispersive medium, they are merely reshaping effect of the pulse, and they will become subluminal at large distances. A couple of experiments are proposed to test the superluminal phenomena.
Preface. Introduction to the Conference. A Quantum of Light Shed on a Classical Problem C.K. Whitney. A Classical Photon Model R.J. Beil. Stationary Vacuum-Polarization 'P Fields': the Missing Element in Electromagnetism and Quantum Mechanics M.H. MacGregor. Electrons and Photons as Soliton-Waves G. Hunter. Topological Solitons in Non-Linear Electrodynamics G. Kalbermann. A Particle or a Photon in a Field T.W. Marshall, E. Santos. Could the Photon be Superfluous? M. Sachs. Fluctuation-Dissipation Quantum Electrodynamics G.F. Efremov, et al. Einstein-de-Broglie-Proca Theory of Light and Simultaneous Existence of Transverse and Longitudinal Photons S. Roy, M. Roy. Origin, Observation and Consequences of the B(3) Field M.W. Evans. Opto-Magnetic Effects in Non-Absorbing Media: Problems of Measurement and Interpretation S. Jeffers, et al. Generalized Equations of Electrodynamics of Continuous Media V.M. Dubovik, et al. Maxwellian Analysis of Reflection and Refraction R.D. Prosser, et al. Solutions of Maxwell Equations for a Hollow Curved Wave Conductor N. Bashkov, A. Tchernomorov. Maxwell's Equations Directly from the Dynamics of Point Particles G.N. Ord. Obtaining the Schrodinger and Dirac Equations from the Einstein/KAC Model of Brownian Motion by Projection G.N. Ord. Derivation of the Schrodinger Equation T.B. Andrews. An Appraisal of Stochastic Interpretations of Quantum Mechanics M. Baublitz, Jr. Compatible Statistical Interpretation of Quantum Beats M. Bozic. Stochastic Non-Markov Model of Quantum Mechanical Behaviour S.R. Vatsya. A Fundamental Force as the Deterministic Explanation of Quantum Mechanics B.J. Dalton. A Geometric Approach to the Quantum Mechanics of the Broglie and Vigier W.R. Wood, G. Papini. Stable Orbits as Limit Cycles S. Bergia. The Correspondence Principle: Periodic Orbits from Quantum Mechanics D. Provost. Neutron Interferometric Experiments on Quantum Mechanics G. Badurek. Enigmatic Neutrons V.K. Ignatovich. Experiments to Test the Reality of De Broglie Waves J.R. Croca. Preselected Quantum Optical Correlations M. Pavicic. Apparent Contradiction in EPR Correlations L.C. Ryff. The Wave- particle Duality E. Bitsakis. Quantum Mechanical Tunneling in a Causal Interpretation M. Clarkson. Quantum Uncertainty, Wave-particle Duality and Fundamental Symmetries P. Rowlands. On the Contradiction between Quantum Mechanics and Relativity: a Superluminal Quantum Morse Telegraph A. Garuccio. Incompatibility between Einstein's Relativity and Lorentz's Equations P. Marmet. On Self-Interaction and (Non-)Perturbative Quantum GRT H.-H. von Borzeszkowski. Classical Physics Foundations for Quantum Physics L. Motz, D.W. Kraft. Inertial Transformations: A Review F. Selleri. The Lorentz Invariance Revisited M. Surdin. A New Type of Massive Spin-One Boson: And Its Relation with Maxwell Equations D.V. Ahluwalia. Implications of Extended Models of the Electron for Particle Theory and Cosmology E.J. Sternglass. The Takabayasi Moving Frame, from the A Potential to the Z Boson R. Boudet. The Nature of the Cosmological Redshift M. Moles. A Quantum Digital Theory of Light N.V. Pope. Toward a Comprehensible Physical Theory: Gravity and Quantum Mechanics H. Yilmaz. Hidden Background Field and Quantum Non-Locality R. Ramanathan. Einstein-Podolsky-Rosen Correlations within Bell Region R. Horodecki. Electromagnetic Gauge as Integration Condi