Information Speed in Controllable Light Velocity

Daniel J. Gauthier, Michael D. Stenner, Mark Allen Neifeld

Frédéric Bouchard, Jérémie Harris, Harjaspreet Mand +2 more

Einstein's theory of relativity establishes the speed of light in vacuum, c, as a fundamental constant. However, in optically dense media, light can be made to travel at speeds lower than c, e.g. light in water propagates at 3/4c. More dramatically, the speed of light pulses can be altered by orders of magnitude in dispersive media such as cold atomic clouds [1], atomic vapours [2] and structurally engineered materials [3]. Under exotic conditions, the velocity of these pulses can be rendered greater or smaller than c, or even negative [4]. While significant control can be exerted over the speed of light in dispersive media, no experimental demonstration of altered light speed has hitherto been achieved in vacuum for propagating physical beams of finite energy. Here we show that pulsed beams of twisted light can exhibit sub-luminal velocities upon vacuum propagation. Our experiment reveals changes in the range of 0.1% in the velocity of propagating twisted pulsed beams relative to c. Though our work poses no challenge to relativity theory, it experimentally confirms a counterintuitive body of theoretical work on the group velocity of structured pulses in vacuum, and introduces a novel theory of pulse velocity for twisted light. Our results are particularly important given the recent surge of interest in the application of structured beams to telecommunication [5], quantum key distribution [6] and quantum information [7].

Daniel J. Gauthier, Michael D. Stenner

Chuyi Wan

In the double-slit interference experiment with light, once one of the slits is instantaneously closed, the point H on the screen directly opposite the other slit will experience a change in the intensity of light at that point. Moreover, the time it takes for the intensity of light at point H to change after the slit is closed is shorter than the time it takes for light from the slit to reach point H. This indicates that information is transmitted from the slit to point H on the screen at a speed faster than the speed of light c. This does not violate Relativity, as it does not conflict with the Principle of Constancy of Light Velocity. The transmission speed of information within a wave packet of photons is not solely determined by the Principle of Constancy of Light Velocity. Information is transmitted at varying speeds within the wave packet. In the direction parallel to the propagation of the photons, the speed of information transmission matches c. However, in other directions, the speed of information transmission can exceed c.

Chuyi Wan

In the double-slit interference experiment with light, once one of the slits is instantaneously closed, the point H on the screen directly opposite the other slit will experience a change in the intensity of light at that point. Moreover, the time it takes for the intensity of light at point H to change after the slit is closed is shorter than the time it takes for light from the slit to reach point H. This indicates that information is transmitted from the slit to point H on the screen at a speed faster than the speed of light c. This does not violate Relativity, as it does not conflict with the Principle of Constancy of Light Velocity. The transmission speed of information within a wave packet of photons is not solely determined by the Principle of Constancy of Light Velocity. Information is transmitted at varying speeds within the wave packet. In the direction parallel to the propagation of the photons, the speed of information transmission matches c. However, in other directions, the speed of information transmission can exceed c.

Michael D. Stenner, Daniel J. Gauthier, Mark Allen Neifeld