We have recently constructed a photon position operator with commuting components. This was long thought to be impossible, but our position eigenvectors have a vortex structure like twisted light. Thus they are not spherically symmetric and the position operator does not transform as a vector, so that previous non-existence arguments do not apply. We find two classes of position eigenvectors and obtain photon wave functions by projection onto the bases of position eigenkets that they define, following the usual rules of quantum mechanics. The hermitian position operator, r⁁⁽⁰⁾, leads to a Landau-Peierls wave function, while field-like eigenvectors of the nonhermitian position operator and its adjoint lead to a biorthonormal basis. These two bases are equivalent in the sense that they are related by a similarity transformation. The eigenvectors of the nonhermitian operators r⁁^(±½) lead to a field-potential wave function pair. These field-like positive frequency wave functions satisfy Maxwell's equations, and thus justify the supposition that MEs describe single photon wave mechanics. The expectation value of the number operator is photon density with undetected photons integrated over, consistent with Feynman's conclusion that the density of non-interacting particles can be interpreted as probability density.

Date Published: 31 August 2007
PDF: 11 pages
Proc. SPIE 6664, The Nature of Light: What Are Photons?, 666408 (31 August 2007); doi: 10.1117/12.730703

Published in SPIE Proceedings Vol. 6664:
The Nature of Light: What Are Photons?
Chandrasekhar Roychoudhuri; Al F. Kracklauer; Katherine Creath, Editor(s)