The Core Assumption of Every Known Single Photon Experiment is Wrong.
Dr. Valentin Voroshilov, firstname.lastname@example.org
Recent paper (R. Chaves, G. Barreto Lemos, J. Pienaar; 2018) describes “statistics generated …
by a photon in the Mach-Zehnder interferometer” in “the Wheeler’s delayed-choice experiment”,
or its modified version.
In the original thought experiment (J. A. Wheeler, 1978), a photon enters an interferometer at the
location of a beam splitter BS1, and “the experimenter chooses whether or not to remove the
beam splitter BS2 after a photon has entered a Mach- Zehnder interferometer (at BS1).”
(Figure is used with the permission of the publisher)
The authors “treat the photon in the Mach-Zehnder interferometer as a two-level quantum
system”. The statistics is to be supplied using “photon counting … detector(s)”.
The authors offer a quote (H. Paul, 1982) “It is essential that a single photon source is used, such
that both detectors never click simultaneously. This guarantees that each photon cannot be
modeled as a classical wave that is quantized only at the detector”.
The discussion essentially revolves around different possible descriptions of a photon traveling
along only one possible path or (as a manifestation of its wave-like properties) along two paths at
the same time.
A beam splitter is a device an interaction with which may open for a photon two possible paths
to travel along. For the original or a modified experiment, all versions of reasoning about
possible outcomes of an experiment are based on the assumption that the photon entering an
interferometer (at beam splitter BS1) eventually enters a detector.
This assumption, however, is wrong.
A beam splitter is a macroscopic optical device which consists of a large number of atoms or
When a photon is encountering a device, it does not interact with the device as a whole, it only
interacts with a specific atom. As the result of that interaction the photon can be scattered or
absorbed. In the former case, the photon may encounter another atom, and interact with it. There
is always non-zero probability that the original photon will be absorbed by the device, and a
photon leaving the device will be produced by an atom in the device. Hence, in the latter case,
the device does not open for a photon two different paths; a photon does not take one path or
another, or both. An original photon gets absorbed, disappears. But, as the result of complicated
interactions inside a device, the device emits a new photon, which may encounter another optical
Exactly same situation will be happening when a photon interacts with any optical device,
including (but not limited) a fully reflective mirror, a lens, a prism, a polarizer, a fiber optical
Under these circumstance, any statement about the fate of the original photon entering a detector
is wrong, because there is always non-zero, and not accounted for, probability that the photon
entering a detector is not the original one, but the one emitted by an optical device (at least one
of several existing between the very first device and a detector).
An optical device, any optical device, simply cannot be used to make a definite (known)
alternation (from a set of possible alternations) in the behavior of a photon entering that device,
because there is always non-zero probability of the photon being absorbed.
The result of an action of an optical device on light i.e. (reflection, refraction, polarization) is
statistical, and based on the interactions between light in form of a wave (i.e. a large number of
photons) and the charges in the device.
Without accounting for the exact interaction between a single photon and an optical device in its
entirety, any statement regarding how an optical device may affect the behavior of a single
photon is meaningless.
This realization negates all conclusions from all experiments (thought or actual) based on a
“single photon – optical device” interaction.
1. Rafael Chaves, Gabriela Barreto Lemos, and Jacques Pienaar; “Causal Modeling the Delayed-
Choice Experiment”, Phys. Rev. Lett. 120, 190401 – Published 7 May 2018
2. J. A. Wheeler, in Mathematical Foundations of Quantum Theory, edited by R. Marlow
(Academic Press, New York, 1978).
3. H. Paul, Photon antibunching, Rev. Mod. Phys. 54, 1061 (1982).