Thursday, April 1, 2021

Quantum Interference

FROM THE UNIVERSITY OF VIENNA


As Richard Feynman famously put it, “the double slit experiment is absolutely impossible to explain in any classical way and has in it the heart of quantum mechanics. In reality, it contains the only mystery.”

Indeed, in this experiment, a quantum particle behaves as if it was at two distinct locations at the same time, and exhibits paradigmatic wave-like phenomena such as interference. However, it was later noted that multi-slit experiments show that the degree of delocalization of quantum particles has its limits, and that in a certain sense, quantum particles cannot be simultaneously delocalized at more than two locations.

This limitation has created a puzzle that to this day has not yet been completely resolved. Researchers at the University of Vienna and IQOQI-Vienna (Austrian Academy of Sciences) have made a significant step towards understanding this problem by reformulating interference experiments in terms of information-theoretic games. Their analysis, which has recently appeared in the journal Quantum, provides an intuitive way of thinking about interference phenomena and its limitations, thereby paving the way towards solving the aforementioned puzzle.


One of the most striking features of quantum mechanics is the superposition principle. This principle can be most easily illustrated via the double-slit experiment, which involves a particle that is sent through a plate pierced with two slits. According to our common everyday intuitions, one might expect the particle to always pass either through one slit, or through the other.

However, quantum mechanics implies that the particle can in a certain sense pass through both slits at the same time, that is, it can be in a superposition of two locations at the same time. This possibility underlies the phenomenon of quantum interference, i.e. the striking wave-like behavior exhibited by quantum particles. Now, is there a way to quantify the degree to which quantum particles can be de-localized? Does quantum theory allow particles to traverse more than two paths at the same time? In order to understand these questions, physicists have analyzed “multi-slit experiments” (Sorkin, Rafael D. “Quantum mechanics as quantum measure theory.”  READ MORE

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