Model Explores the Hallmarks of Quantum Behavior

Could the way we categorize nonintuitive phenomena such as quantum interference and quantum entanglement be a result of our cognitive limitations, that is, the ways in which we study the world? Not nature, but our lack of full knowledge about the system, could be causing the phenomena observed in the system to acquire the features of unexplainable exoticism. What then, are the real hallmarks of quantum behavior?

Professor Pawel Blasiak from the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN) addresses this question in a recent paper, in which he shows how to construct, from the building blocks of classical physics, broadly understood optical interferometric systems that reproduce quantum predictions for single particles. Blasiak presents a model that shows why quantum mechanics is needed and what quantum mechanics can tell us about our surrounding reality that is new. Blasiak suggests that if a quantum effect has a simple classical explanation, one should not go looking for any particularly “quantum” secret in it. Blasiak’s model also demonstrates why quantum theory becomes essential when multiple particles are involved.

Recent research explores the foundation of quantum reality. Courtesy of IFJ PAN.

Blasiak’s paper outlines the principles of constructing models of any complex optical systems built of elements functioning according to the principles of classical physics, with the addition of certain local hidden variables, to which the researcher would have only indirect access. Blasiak shows that for single particles, the model faithfully reproduces all the phenomena commonly regarded as an obvious sign of quantum behavior, including collapse of the wave function, quantum interference, and contextuality. Moreover, the classical analogies of these phenomena turn out to be quite simple, according to the model.

However, this model cannot reproduce the characteristic features of quantum entanglement, the occurrence of which requires at least two quantum particles. This would seem to indicate that entanglement and the associated nonlocality may be a more fundamental property of the quantum world than quantum interference.

“This type of approach allows us to avoid the terrible practice of evasive answers and waving our hands around in discussions about the fundamentals and interpretation of quantum mechanics,” Blasiak said. “We have the tools to formulate such questions and solve them precisely. The constructed model aims to show that ontological models with limited access to information have at least the potential possibility of explaining most of the exotic quantum phenomena within broadly understood classical physics. The only real quantum mystery to remain would be quantum entanglement.”

The research was published in Physical Review A (https://doi.org/10.1103/PhysRevA.98.012118).