The Controlled Phase Shifts of Photons in the Mach-Zehnder Interferometer

The Mach-Zehnder interferometer (MZI) is a two-path phase-to-intensity transducer that becomes “mysterious” mainly when one conflates operational facts, minimal predictive calculus, and ontological storytelling. Controlled phase shifts are the central “knob” of the MZI: a tunable relative phase Φ converts directly into complementary output intensities at the two ports. In this model, photons enter the MZI with classical instructions: the “white” photons with E2 = 1 (where E is the electric field of the sinusoidal electromagnetic wave at the given moment) are reflected on the beamsplitters, the “grey” photons with E2 = 0.5 can be both reflected and transmitted through the beamsplitters (with 50:50 ratio), and the “black” photons with E2 = 0 transmit through the beamsplitters. The movable mirrors and the second beamsplitter modify the “color” of photons. The 50:50 mixture of “white” and “black” photons at the input is separated by the first beamsplitter. The phase shifts are modified by movable mirrors so that the second beamsplitter organizes the resulting structure of photons at the two detectors. The interference patterns have been formed from two sub-ensembles of photons with their relative phase shift ΔΦ = π at the given port. We assume that this classical behavior of photons in the MZI can clarify the “riddle-like” discussions (e.g., delayed choice switching, the meaning of a dark port, and the role of which-way information).

Keywords: Classical instructions for Photons, Interference of two Sub-Ensembles of Photons, Mach-Zehnder Interferometer, “Riddle-like” Discussions.