Lamb 1969 states,
A misconception which most physicists acquire in their formative years is that the photoelectric effect requires the quantization of the electromagnetic field for its explanation. […] In fact we shall see that the photoelectric effect may be completely explained without invoking the concept of "light quanta."
The paper gives a description in which an atom is ionized by light, with the atom being treated quantum-mechanically but the light being treated as a classical wave.
Is it true that all the standard treatments in textbooks are getting this wrong?
Lamb and Scully "The photoelectric effect without photons," in "Polarization, Matière et Rayonnement," Volume in Honour of A. Kastler (Presses Universitaires de France, Paris, 1969) — can be found online by googling
Best Answer
Yes, the photoelectric effect can be explained without photons!
One can read it in
L. Mandel and E. Wolf, Optical Coherence and Quantum Optics, Cambridge University Press, 1995,
a standard reference for quantum optics. 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.
An interesting collection of articles explaining different current views is in
Further discussion is given in the entry ''The photoelectric effect'' of my theoretical physics FAQ at http://arnold-neumaier.at/physfaq/physics-faq.html . See also the slides of my lectures http://arnold-neumaier.at/ms/lightslides.pdf and http://arnold-neumaier.at/ms/optslides.pdf .
QED and photons are of course needed to explain special quantum effects of light revealed in modern experiments (discussed in the Optics and Photonics News issue cited above) such as nonclassical states of light or parametric down conversion, but not for the photoelectric effect.