Superluminal speed
In one application, the optical touch key was used on shop windows, on the inside of which the keyboard was semi-permanently glued in optical contact, as shown in Figure 1. In this type of non-mechanical key, the finger interfered with the evanescent field at total internal reflection in a rectangular prism as illustrated in Figure 1, Figure 2a and Figure 2b. One practical application of the evanescent field was the optical touch key – a forerunner to the touch keys in present-day iPads and the like – which was patented in 1978 and marketed by OptiSensor AB. Superluminal Speed of the Evanescent Field? Wikipedia has extensive articles on “Faster-than-light” and “Quantum_entanglement”, which are recommended as sources for further references in this vibrant field. A macroscopic equivalent to quantum tunnelling is the evanescent field at total internal reflection, which will here now first be discussed. Before that, tunnelling in quantum mechanics, which is another possible example involving such superluminal velocities, will be discussed in Sec. One such example is quantum entanglement – what Einstein called ‘spukhafte Fernwirkung’ (‘spooky action at a distance’), and which will here be discussed at some length in Sec. However, it now also seems clear – even if maybe not fully understood – that some physical phenomena would seem to transcend the limitation thus imposed by the speed of light. According to Einstein’s theory of special relativity, the speed of light would also seem to be the maximum speed with which information can travel, otherwise we would seem to be at risk to get involved into problems about cause and effect with regard to reference systems with different relativistic velocities. Physical Review Letters, published online April 26, 2012.From Maxwell’s equations follow that electromagnetic waves in vacuum propagate with the speed of light.
Stimulated generation of superluminal light pulses via four-wave mixing. By performing measurements of quantum discord between fast beams and reference beams, the group hopes to determine how useful this fast light could be for the transmission and processing of quantum information. Quantum discord mathematically defines the quantum information shared between two correlated systems-in this case, the seed and conjugate pulses. One immediate application that the group would like to explore for this system is quantum discord. In the experiment, the pulses' peaks arrived 50 nanoseconds faster than light traveling through a vacuum. Its peak, too, can travel faster or slower depending on how the laser is tuned and the conditions inside the laser. At the same time, photons from the inserted beams interact with the vapor to generate a second pulse, called the "conjugate" because of its mathematical relationship to the seed. The vapor amplifies the seed pulse and shifts its peak forward so that it becomes superluminal. In four-wave mixing, researchers send 200-nanosecond-long "seed" pulses of laser light into a heated cell containing atomic rubidium vapor along with a separate "pump" beam at a different frequency from the seed pulses. Four-wave mixing produces cleaner, less noisy pulses with a greater increase in speed by "re-phasing" or rearranging the light waves that make up the pulse.
The method introduces a great deal of noise with no great increase in the apparent speed.
Recent experiments have generated "uninformed" faster-than-light pulses by amplifying the leading edge of the pulse and attenuating, or cutting off, the back end. The leading edge of that curve can't exceed the speed of light, but the main hump, the peak of the pulse, can be skewed forward or backward, arriving sooner or later than it normally would. A short burst of light arrives as a sort of (usually) symmetric curve like a bell curve in statistics. No information can travel faster than light.īut there's kind of a loophole. The new method could be used to improve the timing of communications signals and to investigate the propagation of quantum correlations.Īccording to Einstein's special theory of relativity, light traveling in a vacuum is the universal speed limit.
Researchers at the National Institute of Standards and Technology (NIST) have developed a novel way of producing light pulses that are "superluminal"-in some sense they travel faster than the speed of light.* The technique, called four-wave mixing, reshapes parts of light pulses and advances them ahead of where they would have been had they been left to travel unaltered through a vacuum.