Ken. Let's just focus on the more substantial Photoelectric Effect. Dr. Neumaier
was claiming that Einstein was wrong that a photon was particle. Here he
explains how pure photon field can trigger the detector. I think you are expert
in waves as seen in your weak measurement trajectory defence in the qm forum. So
please comment on the following in his original presentation. Please take time
on it as it is crucial in establishing the decision whether or not to get back
Einstein Nobel Prize for deceiving the world photons are particles. Remember de
Broglie got the idea matter are wave from Einstein conjecture. And wave/particle
duality has confused the world for over a century. Which part of the following
do you agree and not?
http://arnold-neumaier.at/physfaq/topics/photodetection
------------------------ The photoelectric effect ------------------------
The photoelectric effect
http://en.wikipedia.org/wiki/Photoelectric_effect is
usually explained (following Einstein, who received the Nobel price for this
explanation) by saying that a sufficiently energetic photon falling on a
photosensitive substance causes the latter to eject a single electron, which is
then magnified by a photomultiplier to produce a macroscopic and hence
observable effect - the ''click'' of the detector. This is commonly used in
discussions of experiments on entangled photons carried out by Alice and Bob,
who make statistics on clicks to prove or disprove things, or to communicate
secret information.
In the semiclassical picture known to Einstein 1905, currents are produced by
discrete electrons. In 1905, when Einstein proposed his explanation, the
photoelectric effect was a clear indication of the particle nature of light,
since no other model was available that could have explained the process.
Einstein's explanation was so important for the development of the subject that
he got 1921 the Nobel prize for it, a few years before modern quantum mechanics
was born. The modern concept of a photon was created only later (Lewis 1926,
Dirac 1927).
According to today's knowledge, just like Bohr's atomic model, Einstein's
explanation of the photoeffect is too simplistic, and is not conclusive. Now,
100 years later, his picture is known to be approximate only, and that currents
in metals are in fact produced by the continuous electron fields of QED.
Discrete semiclassical particles are just very rough approximations.
Indeed, the argument of Einstein put forward for the discrete nature of
radiation is spurious, since it ignores the quantum nature of the detector
(which was of course completely unknown at the time). As one can read in the
standard reference for quantum optics, L. Mandel and E. Wolf, Optical Coherence
and Quantum Optics, Cambridge University Press, 1995. the clicks in a photon
detector are an artifact of photodetection caused by the quantum nature of
matter, rather than proof of single photons arriving.
Mandel and Wolf write (on p.629, in the context of localizing photons), about
the temptation to associate with the clicks of a photodetector a concept of
photon particles: ''Nevertheless, the temptation to interpret the electronic
signal registered by a photodetector as due to a photon that is localized in
some sense is quite strong.'' The wording suggests that one should resist the
temptation, although this advice is usually not heeded. However, the advice is
sound since a photodetector clicks even when it detects only classical light!
This follows from the standard analysis of a photodetector, which treats the
light classically and only quantizes the detector.
Sections 9.1-9.5 show that the electron field responds to a classical external
electromagnetic radiation field by emitting electrons according to Poisson-law
probabilities, very much like that interpreted by Einstein in terms of light
particles. Thus the quantum detector produces discrete Poisson-distributed
clicks, although the source is completely continuous, and there are no photons
at all in the quantum mechanical model. The state space of this quantum system
consists of multi-electron states only. So here the multi-electron system
(followed by a macroscopic decoherence process that leads to the multiple dot
localization of the emitted electron field) is responsible for the creation of
the dot pattern. This proves that the clicks cannot be taken to be a proof of
the existence of photons.
Note that initially, only single photoelectrons are emitted, which would leave
no experimental trace without being magnified. A macroscopic magnification is
needed to make the photoelectrons observable. In a photodetector, a
photomultiplier is used to produce an observable current. In the case of
detection by a photographic plate, the detector is a photoemulsion, and the
photoelectrons are magnified via a chemical reaction that produces tiny dots
whose density is proportional to the incident intensity of the electromagnetic
radiation.
(The table of contents of the book by Mandel & Wolf is at
http://www.cambridge.org:80/servlet/...TEM_ENT_ID=233 If you are new to quantum
optics and want to have a shortcut through this book of over 1100 pages: At
first, you need enough classical background. To update your math, read or review
Sections 2.1-2.3 and 3.1 and go back to the pieces from Chapter 1 that you need
to make sense of these sections. Classical physics in a simplified setting
without polarization starts in Chapter 4 and 5, where you need at first only
4.1-4.3 and 5.6-5.7 -- again, reading omitted stuff you need for understanding
that as you go along. Full classical electromagnetism is covered in Chapters
6-8. You need 6.1-6.5. The quantum part starts in Chapter 9. You'd read 9.1-9.5,
10.1-10.5, 10.9, 10.10, 11.1-8, 11.13, 12.1-12.4, 12.10, 13.1-13.3, 14.1-14.6.,
15.1-3, 18.1-4, 20.1-6, 22.4. Then you have an overview over the central part of
quantum optics, and are well prepared to start a second, thorough reading of the
whole book.)
Section 12.11 is about the problems with photon position, and that there is no
associated operator, but only a POVM. It is in this section that they made the
remark referred to above. Sections 14.1-14.5 show that the semiclassical picture
of Chapter 9 holds with small corrections also in the quantum case, and is
virtually unaltered in case of coherent light.
We conclude that the discreteness of the clicks must be caused by the quantum
nature of matter, since there is nothing discrete in an incident classical
external radiation field.
I discussed the situation in some more detail in a public lecture given in 2008,
http://arnold-neumaier.at/ms/lightslides.pdf See Section 3 (pp.35-44);
names in smallcaps are accompanied by references, given at the end of the
slides.
Note that this holds even for very faint light. In deep-field astronomy,
'photographs' of perhaps several billion light years distant astronomical
objects using CCD detectors is routine. The time interval between individual
events on a CCD array of a few cm^2 can be several minutes or more in some
cases.
To explain the image, it is enough that the detector elements on the plate
respond locally according to a Poisson process with probability rate determined
by the incident energy density. This means it fires randomly at the rate
determined at each moment from the incident faint field. No memory is needed,
and energy loss is irrelevant (except for the efficiency of the process). The
local detector elements will respond independently and rarely but occasionally,
and waiting long enough will precisely reproduce the averaged intensity profile
- the goal of the imaging.
It doesn't make sense to somehow count photons classically and pretend that each
of the myriads of photons created in a distant star is a spherical wave
spreading out through space to be ''collapsed'' when entering the CCD detector.
The detector doesn't see the myriads of these extremely faint spherical waves
and decides to collapse just one of them. Instead, it ''sees'' the energy
density; according to its value, it feels more or less ''motivated'' to respond,
resulting in a Poisson statistics. The reason is that in QED, the local mean
energy density is an observable field, whereas the concept of a photon number
density cannot even be meaningfully defined.