[Paper Review] Is the Interpretation of Delayed-Choice Experiments Misleading?

Pierre Roussel, I. Stefan|ArXiv.org|Jun 18, 2007

Quantum Mechanics and Applications6 references3 citations

TL;DR

This paper challenges the widely accepted interpretation of delayed-choice experiments, arguing that the notion of a photon 'choosing' its path after emission is a misinterpretation of quantum mechanics. It contends that wave function collapse is not retroactively influenced by later measurement choices, and that the observed behavior is fully consistent with standard quantum theory without invoking retrocausality or observer-dependent reality.

ABSTRACT

The interpretation of an experimental realization of Wheeler's delayed-choice gedanken experiment is discussed and called into question.

Motivation & Objective

• To question the validity of the delayed-choice effect interpretation in Wheeler’s gedanken experiment as presented in recent experimental realizations.
• To argue that the idea of a photon 'choosing' its path after emission contradicts standard quantum mechanics and introduces unwarranted retrocausality.
• To demonstrate that the wave function does not change retroactively due to later measurement settings, and that the measurement outcome is determined by the full experimental context.
• To emphasize that the wave function is not a physical entity with definite trajectories, but a tool for predicting probabilities.
• To clarify that the complementarity principle does not imply that the initial state is altered by later choices, but rather that measurement settings define the observable properties.

Proposed method

• Analyzes the Mach-Zehnder interferometer setup in both 'closed' (with BS2) and 'open' (without BS2) configurations to compare detection probabilities.
• Applies the standard quantum mechanical description of superposition and wave function evolution, showing that the state remains coherent until measurement.
• Uses historical quotes from Einstein, Bohr, and Schrödinger to argue that the wave function is not a physical trajectory but a probability amplitude.
• Emphasizes that wave function collapse occurs only at measurement, not before, and that no change occurs in the state between BS1 and BS2 due to later decisions.
• Contrasts the claimed 'delayed choice' effect with the actual quantum formalism, showing that the outcome depends only on the final measurement setting.
• Argues that the use of Bohr’s complementarity principle is misapplied when suggesting that the initial state is altered by later choices.

Experimental results

Research questions

• RQ1 Does the delayed-choice experiment truly demonstrate retrocausal influence on a photon’s path, as commonly interpreted?
• RQ2 Is the claim that a photon 'travels both routes' or 'one route' after the fact consistent with standard quantum mechanics?
• RQ3 Can the wave function be considered a physical entity with definite trajectories, or is it merely a tool for predicting measurement outcomes?
• RQ4 Does the presence or absence of BS2 after the photon passes BS1 alter the photon’s past state, or is the outcome determined solely by the final measurement setting?
• RQ5 Is the complementarity principle correctly applied in the delayed-choice interpretation, or does it misrepresent the role of measurement settings?

Key findings

• The delayed-choice effect as commonly interpreted—where a measurement choice retroactively determines the photon’s path—is not supported by quantum mechanics.
• The wave function does not change between BS1 and BS2 due to later decisions about BS2; the state evolves unitarily until measurement.
• The probability amplitude for detection is one-half in each arm before BS2, regardless of whether BS2 is later inserted or removed.
• The idea that a photon 'travels both routes' or 'one route' is a classical misinterpretation; no definite trajectory exists between measurements.
• Wave function collapse occurs only at detection, and the choice of measurement setting determines the observable, not the past state of the system.
• The experiment exemplifies wave packet reduction in a non-traditional setting, but not retrocausal influence—only the standard quantum measurement process is at work.