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A Point source of light has radial symmetry.

If the source gets attenuated so that only a single photon is leaving each hour, can I still argue, that the field of the single photon is radial but the photon is detected on an arbitrary (random) point on the sphere, like it is the case for the wave function of a material particle?

In this case there could be interference caused by spatially very distant interfering objects (e.g. gravitation of stars, ...)

Or does the emitted photon have a narrow radiation coil from beginning?

MichaelW
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A single photon can be emitted with an outgoing "spherical" wavefront. I put "spherical" in quotes because most emission processes will produce a photon with a wavefunction that may have less symmetry but that is still significant in practically all directions, in close analogy with classical EM radiation. (This close analogy is not a coincidence, as illustrated quantitatively in another post.)

A photon is something that can be counted, not necssarily something that is localized or traveling in a narrow direction. However, if a source located in the middle of a large spherical cavity emits single a "spherically"-symmetric photon, and if the spherical wall of the cavity is lined with localized photon-detectors, then only one of those detectors will register the photon. This is a property of the measurement, and it does not imply that the photon had any narrow direction prior to the measurement.

Chiral Anomaly
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