Can a Photon Be Separated from Its Wave?

Louis Sica

doi:10.4236/jmp.2018.93032

Abstract

An experiment is proposed in which the overall path taken by a photon is indicated by the timing of a twin herald photon, while a particular segment of that path is determined by interference. The experiment is to be carried out in two parts. In the first, coincident pairs of photons generated by type I spontaneous- parametric-down-conversion are diffracted by a large-width grating to increase the coherence length of their associated waves, and to produce two sources of coincident photons. Upon experimental confirmation that coincidences have been maintained, one of the sources is used to furnish timing heralds, and the other to send photons to an unequal path interferometer. A photon path through the interferometer via the short arm is indicated by count synchronization with the herald. The exit output port used and final detection location are determined by the phase in the long arm. If output port usage can thus be controlled by the phase in the photon free arm, the path of the photon as particle will have been controlled by interference with an accompanying photon-empty wave.

Highlights

Among Feynman’s more quoted statements is that the most fundamental quantum mystery [1] is that exhibited by the two-slit experiment and its demonstration of wave-particle duality
This is because the bandwidth of the resulting one-photon states would be expected to be determined by that of the laser, as opposed to the large bandwidth of one-photon states not derived from two-photon states. (Note: one-photon state photons would be eliminated by using only synchronized counts.) Using this second strategy, the experiment of Section 4 appears to be considerably more feasible than using the first strategy
Recent experiments such as [17] [18] show that a two-photon state may be formed in the degenerate co-linear output of a Type I SPDC, and that its position is distinguishable in diffraction grating output from the wideband radiation consisting of pairs of one-photon states generated by the nonlinear process

Summary

Introduction

Among Feynman’s more quoted statements is that the most fundamental quantum mystery [1] is that exhibited by the two-slit experiment and its demonstration of wave-particle duality. A thin wire grating with wires placed in the fringe zero-intensity minima allowed the existence of fringes in the region of two-beam superposition to be monitored while counts from the two detectors remained anti-correlated While for some, this experiment and its offshoots [4] seem to demonstrate that which-path information and interference can be obtained from the same set of events, others have found the experimental outcome insufficient to warrant their abandonment of the usual quantum interpretation [5]. It would follow that interference due to the chosen phase of a wave in a photon-empty interferometer arm can determine the output port for a photon that has taken the other path to a final interferometer beam splitter If observed, this outcome would be consistent with the idea that light consists of both particles and waves, rather than an entity that switches between the two. It is related to “Welcher Weg” and quantum eraser experiments such as those described in [12] [13]

Action of a Diffraction Grating Filter in a Particle-Coupled-To-Wave Picture

Expected Coherence Length from a Grating in Two Cases

Can Which-Path Information and Wave Interference Exist Simultaneously?

Discussion and Conclusions