Demonstrating Wave-Particle Duality In Photodetection
One feature of quantum theory is that objects should have both particle and wave properties: Things usually encountered as particles, such as
electrons or atoms, show their quantum, or nonclassical, nature in the form of wavelike effects.
Conversely, light, which can usually be described by a wave equation, shows its nonclassical side by acting like a particle.
In most optics experiments, even those involving lasers, the light produces only classical effects, which can be described using 19th century
electromagnetism. For example, a grocery scanner diode laser emits about 10^15 photons per second. When such a stream encounters a half-silvered
mirror, half of the light will be reflected and half transmitted. With so many photons, the individual particle nature is hidden when the photons are
detected at photodiodes sitting behind each exit port of the beamsplitter.
If the original laser beam is replaced with a source of single photons, then the story is different: A lone photon might well have an equal chance of
going towards either detector, but it will ultimately register in only one -- a sure sign of quantum behavior.
One can probe these issues more deeply by using entangled photon pairs.
Kevin Resch, Jeff Lundeen and Aephraim Steinberg at the University of Toronto send ultraviolet (UV) light into a special crystal in which a single UV
photon can produce two red photons in a process called down-conversion.
One of the red photons is vertically polarized and the other is horizontally polarized. The photons can be time-delayed relative to one another by
varying the thickness of birefringent material (which can swivel a light wave's orientation) traversed by the photon.
By adjusting the delay between the photons, the researchers were able to change the number of photon pairs emerging from an interferometer without
changing the intensity, or brightness, of the beam.
Thanks to the intrinsic nonlinear response of the detectors, this quantum interference effect then became apparent in the counting rate at a single
detector -- an effect never before observed -- and not just in the coincidence rate between a pair of photodetectors.
The researchers believe that the ability to observe such nonlinear responses in photodetection at the single photon level may be useful to the study
of decoherence in photodetection and for providing an experimental basis for developing a more accurate theoretical description for photodetection.
(Reference: Physical Review A, 1 February 2001.)
(Editor's Note: This article is adapted from PHYSICS NEWS UPDATE, the American Institute of Physics Bulletin of Physics News Number 519, January 4,
2000, by Phillip F. Schewe and Ben Stein.)
Simply stated James even space can be understood from the contex of a substance. Spacetime James is no different
What are your thoughts?