Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A sub-femtosecond stop watch for 'photon finish' races

17.03.2008
Using a system that can compare the travel times of two photons with sub-femtosecond precision, scientists at the Joint Quantum Institute (a partnership of the National Institute of Standards and Technology (NIST) and the University of Maryland) and Georgetown University have found a remarkably large difference in the time it takes photons to pass through nearly identical stacks of materials with different arrangements of refractive layers.

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!
Further information:
http://www.nist.gov

More articles from Physics and Astronomy:

nachricht Listening to the quantum vacuum
26.03.2019 | Louisiana State University

nachricht The taming of the light screw
22.03.2019 | Max-Planck-Institut für Struktur und Dynamik der Materie

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: New gene potentially involved in metastasis identified

Gene named after Roman goddess Minerva as immune cells get stuck in the fruit fly’s head

Cancers that display a specific combination of sugars, called T-antigen, are more likely to spread through the body and kill a patient. However, what regulates...

Im Focus: The taming of the light screw

DESY and MPSD scientists create high-order harmonics from solids with controlled polarization states, taking advantage of both crystal symmetry and attosecond electronic dynamics. The newly demonstrated technique might find intriguing applications in petahertz electronics and for spectroscopic studies of novel quantum materials.

The nonlinear process of high-order harmonic generation (HHG) in gases is one of the cornerstones of attosecond science (an attosecond is a billionth of a...

Im Focus: Magnetic micro-boats

Nano- and microtechnology are promising candidates not only for medical applications such as drug delivery but also for the creation of little robots or flexible integrated sensors. Scientists from the Max Planck Institute for Polymer Research (MPI-P) have created magnetic microparticles, with a newly developed method, that could pave the way for building micro-motors or guiding drugs in the human body to a target, like a tumor. The preparation of such structures as well as their remote-control can be regulated using magnetic fields and therefore can find application in an array of domains.

The magnetic properties of a material control how this material responds to the presence of a magnetic field. Iron oxide is the main component of rust but also...

Im Focus: Self-healing coating made of corn starch makes small scratches disappear through heat

Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.

Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are...

Im Focus: Stellar cartography

The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.

A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

International Modelica Conference with 330 visitors from 21 countries at OTH Regensburg

11.03.2019 | Event News

Selection Completed: 580 Young Scientists from 88 Countries at the Lindau Nobel Laureate Meeting

01.03.2019 | Event News

LightMAT 2019 – 3rd International Conference on Light Materials – Science and Technology

28.02.2019 | Event News

 
Latest News

Listening to the quantum vacuum

26.03.2019 | Physics and Astronomy

The struggle for life in the Dead Sea sediments: Necrophagy as a survival mechanism

26.03.2019 | Earth Sciences

Mangroves and their significance for climate protection

26.03.2019 | Earth Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>