The two photon problem defined by Vigier and Garuccio should be treated in the second quantization formalism; it is, thus, seen that the amplitude for finding one photon in the interference region of the two lasers remains the sum of the two interfering amplitudes.

In a two-channel interference experiment such as that considered in the preceding companion paper, a quantum may be localizable predominantly in one channel by a time-coincident experiment on a correlated quantum. The Copenhagen interpretation of quantum mechanics then requires a coincidence intensity prediction having the same reduced interference between channels as if the probability amplitude in the other channel had been attenuated by a filter. The quantum mechanical treatment of correlated systems originated by von Neumann does predict this reduced interference, (...) but avoids requiring a resulting direct locality violation by predicting that this reduced interference also occurs in a simple singles intensity observation. In contrast, de Broglie's locally causal interpretation of quantum mechanics requires that the experiment on the remote correlated system cannot change the amplitudes or phase relationship of coherent space-time wave propagating through the two channels, so that the full classical optics interference effect should be predicted for both singles and coincidence intensities. (shrink)

Fundamental experiments on the dual nature of atomic entities (photons, electrons, neutrons, etc.) can be interpreted in terms of “empty” waves not carrying energy and momentum. Similar points of view were advanced in famous papers by Einstein, de Broglie, Bohr, and Born. Recent proposals could lead to experimental tests of this idea, using low intensity photon beams, thanks to modern experimental apparatuses.