[extropy-chat] splitting photons

[scerir]

J.J. Thorn et al., Am. J. Phys., v.72, p.1210 (2004).

[Abstract]

While the classical, wavelike behavior of light (interference
and diffraction) has been easily observed in undergraduate
laboratories for many years, explicit observation of the quantum
[or 'particle'] nature of light (i.e.,photons) is much
more difficult.

For example, while well-known phenomena such as the photoelectric
effect, and Compton scattering, strongly suggest the existence of
photons, they are not *definitive* proof of their existence.
[Leonard Mandel wrote the same, so: no doubt about it!]

Here we present an experiment, suitable for an undergraduate
laboratory, that unequivocally demonstrates the quantum nature of light.
Spontaneously downconverted light is incident on a *beamsplitter* and
the outputs are monitored with single-photon counting detectors
[2 detectors, plural].

We observe a near absence of *coincidence* counts between the two
detectors - a result inconsistent with a classical wave model of light,
but consistent with a quantum [particle] description in which individual
photons are incident on the beamsplitter. More explicitly, we measured
the degree of second-order coherence between the outputs to be
                       g(2)(0) = 0.0177±0.0026
which violates the classical inequality
                       g(2)(0)>=1
by 377 standard deviations.

[End of Abstract]

So, photons really do not split (but their wavefunctions ...).
"The hypothesis of light-quanta is not able to throw light
on the nature of radiation." - N. Bohr, 1922 Nobel Lecture.
(Lewis called "photons" these light quanta, in 1926).

A paper by John F. Clauser, in "Quantum [Un]speakables",
("unspeakable", you know, according to J.Bell, were
the unothodox quantum models, like hidden variables, etc.,
that orthodox physicists did not like at all, and journals
refused to publish), R.A.Bertlmann and A.Zeilinger eds., Springer,
2002, is titled "Early History of Bell's Theorem", pages 61-98,
and is very interesting.

Chapter 6.14 is devoted to "Splitting Photons?". Essentially
Clauser is discussing, in there, but very shortly, Schroedinger's
interpretation of Compton & Simon exp. (different from von Neumann's
idea), and also the simplistic Adam, Janossy, Varga experiments
(suggested by Schroedinger, references below), and also his own
experiment (reference below) which was a great improvement
of the A.J.V. experiments.

According to Clauser his experiment (similar to that above) already
showed that "both quantum mechanics and quantum electrodynamics hold
true, and photons do not split at a half-silvered mirror." and also
that the Cauchy-Schwarz inequality was, for the first time, violated
(in his experiment), which represents the "first observation of
sub-Poissonian statistics for light."

According to Clauser, his exp. resolves another problem that
Schroedinger himself stated: does the photoelectric effect
reveal a statistical (Bohr) or a precise (von Neumann)
conservation of energy? QED is formally based on an assumed strict
equality of h*nu (QM) and integral (over space) of EM field energy.
Clauser's exp. shows that the above equality holds and, thus,
necessarily, there is a precise conservation of energy.

References therein:
- E.Schroedinger, Physikalishe Zeits. 23 301 (1922);
  Die Naturwissenschaften 12 720 (1924); Nuovo Cimento
  9 162-170 (1958).
- A.Adam, L.Janossy, P.Varga, Acta Phys. Hung. 4 301 (1955);
  Ann. Phys. 16 408 (1956).
- J.F.Clauser, Phys. Rev. D-9 853 (1974).
- P.Grangier, G.Roger, A.Aspect, Europhys. Lett. 20 1061 (1986).