Source: : October 26, 2023 Subject: Review of key concepts from "Quantum Entanglement Explained”
This podcast explores the concept of quantum entanglement, describing it as a defining characteristic of quantum mechanics where two or more particles become linked, sharing a single wave function regardless of distance. Unlike classical correlations, measuring the properties of one entangled particle instantaneously influences the properties of the other, a phenomenon once deemed "spooky action at a distance." The text explains that this isn't faster-than-light communication but rather a demonstration of quantum nonlocality, highlighting how entanglement is fundamental to the development of quantum computing and quantum cryptography.
Quantum Entanglement Explained.mp4
The debate remained unresolved until John Bell in 1964 devised a clever experiment to test whether hidden variables existed. Bell's theorem predicted stronger correlations in measurement outcomes for quantum mechanics than for any hidden variable theory:
"It wasn’t until almost 30 years later, in 1964, that Irish physicist John Bell figured out how to set up a clever experiment to determine who was right... Bell proved that quantum mechanics predicted stronger statistical correlations in the outcomes of these measurements than any hidden variable theory possibly could."
Experiments conducted in the 1970s by John Clauser and Stuart Freedman confirmed Bell's predictions, demonstrating the absence of hidden variables:
"...it showed that there was no sign of hidden variables, and that indeed, outcomes are determined only by the act of measurement itself. And in the ensuing years, this aspect of quantum mechanics has proven to be correct over and over again. Bohr was right, and EPR were wrong."
The source then pivots to explain what entanglement truly is, moving beyond the "spooky action at a distance" idea. The core concept is that entangled particles are not separate objects but rather two parts of a single object described by a single wave function:
"But once objects are entangled, they’re not separate. They are, in a sense, two parts of a single object... if we entangle two particles, they are then described by a single wave function. And since two entangled objects are being described by the same wave function, they are mathematically speaking the same object. That’s really what entanglement means, and it’s why the particles’ properties are then interdependent."
This unified description explains why measuring one particle instantaneously affects the other; the measurement changes the single wave function describing the entire system. The interaction that creates entanglement causes the wave functions of the individual particles to become inseparable:
"So once two particles are entangled, we can’t say anything about one of them without considering the whole wave function. It’s as if their properties are now spread out over both."