© 2026 Aqora Quantum S.A.S.

Terms Privacy Legal Notice

Quantum and Semiclassical Optics Journal of the European Optical Society Part B

Superluminal and parelectric effects in rubidium vapour and ammonia gas

R. Y. Chiao, Eric L. Bolda, Jason L. Bowie, J. Boyce, J. C. Garrison, Morgan W. Mitchell

Published Jun 1, 1995• 14 citations

Abstract

Population inversion in an atomic or molecular medium leads to the possibility of superluminal propagation of off-resonance, finite-bandwidth electromagnetic wave packets, whose phase, group, energy, and 'signal' velocities, as defined by Sommerfield and Brillouin, all exceed the vacuum speed of light c. Einstein causality is not violated, since the front velocity is c. Here the authors propose an experiment to observe superluminal propagation of laser pulses detuned from a stimulated Raman transition in optically pumped rubidium vapour. The inversion of populations can also lead to a parelectric medium with negative DC electric susceptibility, thus implying the possibility of the levitation of an electrical charge in the vacuum above this medium. Stable electrostatic configurations of charges placed inside an evacuated cavity surrounded by this medium exist, in seeming violation of Earnshaw's theorem. An experiment is proposed to observe parelectricity in ammonia gas.

DOI: 10.1088/1355-5111/7/3/007

Related papers

Superluminal (but causal) propagation of wave packets in transparent media with inverted atomic populations

R. Y. Chiao

The propagation of limited-bandwidth signals, such as Gaussian wave packets, tuned to a transparent spectral region far below the resonance of an inverted two-level atomic medium, can be superluminal, i.e., with phase, group, and energy velocities all exceeding the vacuum speed of light c. Causality is not violated, however. Little distortion and gain can accompany this propagation.

Physical Review A•Jul 1, 1993•249 citations

Atomic coherence effects which produce superluminal (but causal) propagation of wavepackets

R. Y. Chiao

Analytic, limited-bandwidth signals, e.g. Gaussian wavepackets, whose frequencies lie in a transparent spectral window far below the resonance of an amplifying atomic medium, can propagate with phase, group, energy and 'signal' velocities (as defined by Sommerfeld and Brillouin) all exceeding the vacuum speed of light c. This 'superluminal' propagation may occur without significant distortion or gain. The front velocity, however, is not superluminal, and therefore Einstein causality is not violated. Applications will be discussed, including the possibility of using superluminal atomic coherence in condensed matter (e.g. macroscopic mass currents in superfluid helium which arise from vortex motions) for efficient gravitational antennae.

Quantum Optics Journal of the European Optical Society Part B•Aug 1, 1994•18 citations

One more experiment on "fast-light"

Roberto Assumpção

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.

arXiv:physics/0312068•Dec 11, 2003•0 citations

Signal Velocity, Causality, and Quantum Noise in Superluminal Light Pulse Propagation

A. Kuzmich, Arthur Dogariu, L. J. Wang +2 more

We consider pulse propagation in a linear anomalously dispersive medium where the group velocity exceeds the speed of light in vacuum ( c) or even becomes negative. A signal velocity is defined operationally based on the optical signal-to-noise ratio, and is computed for cases appropriate to the recent experiment where such a negative group velocity was observed. It is found that quantum fluctuations limit the signal velocity to values less than c.

arXiv:physics/0101068•Physical Review Letters•Apr 30, 2001•198 citations

On the Principle of Causality and Superluminal Signal Propagation Velocities

Nikolai S. Bukhman

Abstract This paper considers the question of superluminal (or negative) group velocities of signals in dispersive media, as well as negative group delay times of signals passing through linear filters. It is shown that information can be transmitted only with the help of jumps in the time dependence of a function or its derivatives and, therefore, the information propagation velocity in any (including dispersive, absorbing, or amplifying) medium exactly coincides with the speed of light in vacuum. As for the group velocity of a wave packet, it is only the propagation velocity of its infinitely differentiable envelope, by means of which the transmission of information, strictly speaking, is impossible. Therefore, in regions with anomalous dispersion, the group velocity can be superluminal or negative without violating the “light limitation” of the theory of relativity or the principle of causality. Examples of situations in which superluminal or negative group velocity occurs are given.

Journal of Communications Technology and Electronics•Mar 1, 2021•8 citations

Explanation of Superluminal Phenomena Based on Wave-Particle Duality and Proposed Optical Experiments

Hai-Long Zhao

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.

arXiv:1405.3364•May 14, 2014•0 citations

Population inversion in an atomic or molecular medium leads to the possibility of superluminal propagation of off-resonance, finite-bandwidth electromagnetic wave packets, whose phase, group, energy, and 'signal' velocities, as defined by Sommerfield and Brillouin, all exceed the vacuum speed of light c. Einstein causality is not violated, since the front velocity is c. Here the authors propose an experiment to observe superluminal propagation of laser pulses detuned from a stimulated Raman transition in optically pumped rubidium vapour. The inversion of populations can also lead to a parelectric medium with negative DC electric susceptibility, thus implying the possibility of the levitation of an electrical charge in the vacuum above this medium. Stable electrostatic configurations of charges placed inside an evacuated cavity surrounded by this medium exist, in seeming violation of Earnshaw's theorem. An experiment is proposed to observe parelectricity in ammonia gas.

Analytic, limited-bandwidth signals, e.g. Gaussian wavepackets, whose frequencies lie in a transparent spectral window far below the resonance of an amplifying atomic medium, can propagate with phase, group, energy and 'signal' velocities (as defined by Sommerfeld and Brillouin) all exceeding the vacuum speed of light c. This 'superluminal' propagation may occur without significant distortion or gain. The front velocity, however, is not superluminal, and therefore Einstein causality is not violated. Applications will be discussed, including the possibility of using superluminal atomic coherence in condensed matter (e.g. macroscopic mass currents in superfluid helium which arise from vortex motions) for efficient gravitational antennae.

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.

Abstract This paper considers the question of superluminal (or negative) group velocities of signals in dispersive media, as well as negative group delay times of signals passing through linear filters. It is shown that information can be transmitted only with the help of jumps in the time dependence of a function or its derivatives and, therefore, the information propagation velocity in any (including dispersive, absorbing, or amplifying) medium exactly coincides with the speed of light in vacuum. As for the group velocity of a wave packet, it is only the propagation velocity of its infinitely differentiable envelope, by means of which the transmission of information, strictly speaking, is impossible. Therefore, in regions with anomalous dispersion, the group velocity can be superluminal or negative without violating the “light limitation” of the theory of relativity or the principle of causality. Examples of situations in which superluminal or negative group velocity occurs are given.

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.