Tuesday, June 28, 2011

Which Path? That Path

A few years ago we (Neil J. Gunther, Edoardo Charbon, Dmitri Boiko, and me) where interested in quantum imaging and experiments confirming Bohr's principle (click the quantum imaging tag in the tag cloud at right). We came up with the concept of photon twinning and understood well how the various order correlation functions relate, which led to a single photon detection camera developed at the University of Delft by Edoardo Charbon, which by postselection can distinguish the photons of its flash light from those of the ambient light (sun).

Maximal values of respective correlation functions for incoherent, coherent and thermal light states
correlation function
photon states
incoherent
coherent
chaotic
g(1)(x, 0)
0
1
1
g(2)(x, 0)
1
1
2
∆g(2)(x, 0)
0
0
1

Those results are published in the two papers http://www.iop.org/EJ/abstract/1367-2630/11/1/013001 and http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-17-15087. The paper Observing the Average Trajectories of Single Photons in a Two-Slit Interferometer by Sacha Kocsis et al. in Science magazine of 3 June reports on related work:

A consequence of quantum mechanics and the Heisenberg uncertainty principle is that complementary variables (for example, position and momentum) cannot both be determined precisely. Measuring one variable necessarily results in loss of information about the other. The best example is the two-slit interferometer and the interference pattern that occurs when light or single photons or electrons are transmitted through it. Determining which slit the particle goes through (position) destroys the interference pattern (momentum). Kocsis et al. implement a recent theoretical proposal in which an experimental protocol involving weak measurements could answer the "which path did the photon take" question. The results may impact the foundations of quantum and classical physics and potentially find practical application in metrology.

Science 3 June 2011: Vol. 332 no. 6034 pp. 1170-1173 DOI: 10.1126/science.1202218