The technique, described at the annual March Meeting of the American Physical Society,* ultimately could provide an empirical answer to a long-standing puzzle over how fast light crosses narrow gaps that do not permit the passage of conventional electromagnetic waves.
Alan Migdall and his colleagues set up a race course using “correlated” pairs of photons—indistinguishable photons created simultaneously. One photon passes through the sample to be tested while the other is directed along a path of adjustable length. The finish line is a so-called Hong-Ou-Mandel interferometer, a beamsplitter that the photons strike obliquely. Individual photons have a fifty-fifty chance of either passing through the beamsplitter or bouncing off it, but when two correlated photons arrive simultaneously, the rules of physics say they both must come out in the same direction.
As a result, this arrangement can detect when the first photon has taken exactly as long to get through the test object as the second photon did to traverse its path. This changes the difficult problem of measuring extraordinarily short intervals of time into the easier one of measuring distances. Through refinements to the design of their interferometer, Migdall and his colleagues can measure simultaneity with sub-femtosecond precision.
The team measured photon transit times through stacks consisting of alternating layers of material with high and low refractive index—the kind of arrangement that makes a light beam seem to bend as it crosses the boundary.
The new experiments verify the theoretical prediction** that photon transit time will vary significantly depending on how you arrange the stack. Migdall and his team found that a photon takes about 20 femtoseconds less to get through a stack of 31 layers, totaling a few microns across, when the stack begins and ends with high refractive index layers rather than the opposite. The shorter time delay is apparently superluminal i.e., shorter than the time needed for light in a vacuum to traverse the same distance. (This is possible because of a loophole in the speed-of-light limit that says that some wave-related phenomena can propagate superluminally if they do not transmit equivalent information faster than the speed of light.)
The team hopes to move on to a more perplexing case. Light striking the boundary between two refractive materials at a sufficiently shallow angle glances off completely as a reflection rather than passing through, but also creates a decaying field known as an evanescent wave on the other side of the boundary. This evanescent wave can reach across a narrow gap and strike up a new light wave in an adjacent medium. Theorists have presented discrepant calculations of how long light takes to traverse such a gap, but Migdall says the new system should be precise enough to measure such transits directly.
Ben Stein | EurekAlert!
Spintronics: Researchers show how to make non-magnetic materials magnetic
06.08.2020 | Martin-Luther-Universität Halle-Wittenberg
Manifestation of quantum distance in flat band materials
05.08.2020 | Institute for Basic Science
Scientists at the Fraunhofer Institute for Laser Technology ILT have come up with a striking new addition to contact stamping technologies in the ERDF research project ScanCut. In collaboration with industry partners from North Rhine-Westphalia, the Aachen-based team of researchers developed a hybrid manufacturing process for the laser cutting of thin-walled metal strips. This new process makes it possible to fabricate even the tiniest details of contact parts in an eco-friendly, high-precision and efficient manner.
Plug connectors are tiny and, at first glance, unremarkable – yet modern vehicles would be unable to function without them. Several thousand plug connectors...
An international research team has found a new approach that may be able to reduce bone loss in osteoporosis and maintain bone health.
Osteoporosis is the most common age-related bone disease which affects hundreds of millions of individuals worldwide. It is estimated that one in three women...
Traditional single-cell sequencing methods help to reveal insights about cellular differences and functions - but they do this with static snapshots only...
“Core-shell” clusters pave the way for new efficient nanomaterials that make catalysts, magnetic and laser sensors or measuring devices for detecting electromagnetic radiation more efficient.
Whether in innovative high-tech materials, more powerful computer chips, pharmaceuticals or in the field of renewable energies, nanoparticles – smallest...
An international research team with Prof. Cornelia Denz from the Institute of Applied Physics at the University of Münster develop for the first time light fields using caustics that do not change during propagation. With the new method, the physicists cleverly exploit light structures that can be seen in rainbows or when light is transmitted through drinking glasses.
Modern applications as high resolution microsopy or micro- or nanoscale material processing require customized laser beams that do not change during...
23.07.2020 | Event News
21.07.2020 | Event News
07.07.2020 | Event News
06.08.2020 | Earth Sciences
06.08.2020 | Power and Electrical Engineering
06.08.2020 | Life Sciences