Single-photon measurements confirm Richard Feynman’s vision of quantum mechanics

Physicists have finally confirmed the two core principles of Richard Feynman’s path-integral approach to quantum mechanics through a groundbreaking experiment. This achievement follows nearly 80 years since Feynman first introduced his path-integral formulation, which describes how quantum systems evolve over time. While fundamental thought experiments have been explored in labs, no previous real-world experiment had directly tested the very foundations of Feynman’s theory.

In his 1948 postulates, Feynman proposed that quantum systems do not travel along a single path, but rather every possible path contributes to their overall trajectory. He also suggested that all these paths have equal probability amplitudes, differing only by a phase factor dependent on the path. The experiment, published in Science Advances, tested these postulates by measuring the probability amplitudes of over 1.4 million possible paths taken by single photons.

The researchers divided the path between the starting point and endpoint into a grid, connecting adjacent points with line segments and measuring the propagator for each segment. They identified 17^5, or 4,475,356, possible paths. By achieving a high level of precision in single-photon propagator fidelity, they successfully reconstructed the global structure of these path amplitudes.

The experiment validated Feynman’s first postulate with a mean absolute percentage error of 4.45% and a fidelity of 94.9%. It also confirmed the second postulate, which states that all paths have equal probability amplitudes differing only by a phase factor. This evidence supports the idea that quantum paths reflect physical reality rather than being mere mathematical artifacts.

The high-precision technique could be applied to studying quantum-to-classical transitions, decoherence mechanisms, and probing fundamental phenomena like entangled histories and curved spacetime.