CH110 Study Guide - Final Guide: Quantum Electrodynamics, Quantum Field Theory, Dmitry Shirkov
The photon is one of the basic notions in quantum
electrodynamics. In quantum electrodynamics,
however, the photon is by no means a tiny particle. The
photon is an elementary excitation of the
electromagnetic field, the excitation that concerns the
whole of the volume occupied by the system in
question. Berestetskii et al. [7] underline that the wave
function of a photon does not altogether signify the
same thing as does the wave function of
2
an ordinary particle in quantum mechanics, and the
notion of coordinates of the photon has no physical
meaning at all (see also [8], Sec. 5c). According to
Bogoliubov and Shirkov [9], Sec. 6.2, by a particle in
quantum field theory is meant an excitation of an
oscillator, so that a nth excited state of the oscillator is
referred to by convention as a state with n particles, the
photons in our case. From [9] it follows as well that, in
a coordinate space, to the photon corresponds a plane
wave exp[i(ωt−kx)] filling the overall volume of a big
cube V. Nowhere in quantum electrodynamics does one
resort to the concept of a point-like photon, and the
photon in quantum electrodynamics is a wave pure and
simple. In this connection Lamb [3] proposes to give
up the use of the word ‘photon’ that often leads to
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Document Summary
The photon is one of the basic notions in quantum electrodynamics. In quantum electrodynamics, however, the photon is by no means a tiny particle. The photon is an elementary excitation of the electromagnetic field, the excitation that concerns the whole of the volume occupied by the system in question. [7] underline that the wave function of a photon does not altogether signify the same thing as does the wave function of. 2 an ordinary particle in quantum mechanics, and the notion of coordinates of the photon has no physical meaning at all (see also [8], sec. In this connection lamb [3] proposes to give up the use of the word photon" that often leads to confusion. An adequate terminology is always useful, of course, while a more important point emerges from the foregoing. The question of another sort arises in connection with the concept of the photon.