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THIS ITEM began with my trying to learn about quantum entanglement. This physics term describes the way particles can interact from afar, something that Albert Einstein referred to as “spooky action at a distance.” However, to get a full flavor of quantum entanglement, I had first to untangle my misunderstanding of Heisenberg’s Uncertainty Principle.
Wouldn’t you know, it turns out I’ve been confusing this principle with another tidbit of science called the Observer Effect.
In his 1927 paper, Werner Heisenberg used the term Ungenauigkeit, indeterminacy, to describe the impossibility of simultaneously determining both a particle’s position and its trajectory. Later in an endnote, and in the 1930 English translation, Ungenauigkeit was replaced by Unsicherheit, uncertainty. And, from then on, I suspect, people like me misunderstood what Heisenberg meant.
That is, what’s impossible is simultaneous determination of a particle’s position, speed and direction. It’s not uncertainty in the sense of accuracy of measurements.
This latter describes the Observer Effect, that measurements in certain systems cannot be made without affecting the systems. Loosely, and this is as far as I’ve ever ventured into quantum mechanics, when one tries to measure something, the measurement instrument gets in the way of the result. (Come to think of it, this used to happen to me all the time in Physics 101.)
In any case, Heisenberg’s Uncertainty Principle describes how quantum systems behave. It’s not about observational success.
Richard Feynman had a great quote in this regard: “Nature does not know what you are looking at, and she behaves the way she is going to behave whether you bother to take down the data or not.”
Having cleared this up, more or less, let’s touch on quantum entanglement. In assessing Breakthroughs of the Year, Science magazine, December 18, 2015, included “Quantum Weirdness Confirmed,” an item written by Adrian Cho.
The weirdness discussed is the principle of quantum entanglement, Einstein’s spooky action at a distance. As Cho notes, “Measuring the property of one quantum particle, such as a photon, can instantly determine the state of another quantum particle, even if it’s light-years away.”
This has been tough to accept, because it would seem to contradict relativity’s postulate that nothing can travel faster than the speed of light.
However, back in 1964, British theoretical physicist John Bell proposed a theoretical test, Bell’s Theorem, challenging elements of this paradoxical action at a distance. Over the years, his theoretical views of quantum physical features have been confirmed, experiment by experiment. Bell died, at age 62, of a cerebral hemorrhage in 1990. Unknown to him, he had been nominated that year for a Nobel Prize (which is never awarded posthumously).
In “More Evidence to Support Quantum Theory’s ‘Spooky Action at a Distance,'” Science, August 28, 2015, Adrian Cho describes an example of entanglement with A and B, in the guise of two familiar pals Alice and Bob: Suppose Alice and Bob have two electrons that are entangled; that is, their spins, with 50/50 probability of being up or down, are correlated. If Alice measures her electron and happens to find it spinning upward, then she knows instantly that Bob’s is spinning downward, even if he’s a galaxy away.
Or maybe only 0.8 mile apart. In Nature, August 27, 2015, Zeeya Merali’s “Quantum ‘Spookiness’ Passes Toughest Test Yet” describes the most recent confirmation. A team led by Ronald Hanson of the Netherland’s Delft University of Technology started with two unentangled electrons posed 0.8 mile apart in different labs of their Delft campus. Each electron was individually entangled with a photon, and both photons were then sent to a third location. There, the two photons were entangled with each other, and, as proof of quantum action at a distance, this caused their partner electrons to become entangled back at their separate labs too.
“The results won’t surprise many physicists,” Cho notes in Science, December 18, 2015, “but it could pave the way for exotic technologies such as a quantum Internet.”
Merali cites an application in cryptography: “Companies already sell systems that use quantum mechanics to block eavesdroppers. The systems produce entangled pairs of photons, sending one photon of each pair to the first user and the other photon to the second user. The two users then turn these photons into a cryptographic key that only they know.”
It’s appears certain that I must now untangle my understanding of quantum computing…. from afar. ds
© Dennis Simanaitis, SimanaitisSays.com, 2016