Quantum entanglement explained and useful

[shunyadragon]

Source: https://www.msn.com/en-gb/entertainment/news/nobody-took-john-f-clausers-quantum-experiments-seriously-50-years-later-hes-collecting-a-nobel-prize/ar-AA156gHP

Nobody took John F. Clauser's quantum experiments seriously. 50 years later, he's collecting a Nobel Prize.


Story by Jonas Enander • Friday
React4 Comments|11 On Oct. 4, 80-year-old John F. Clauser woke up in his California home to the news that he had been awarded the Nobel Prize in physics. He will receive the prize at a ceremony in Stockholm, Sweden, on Dec. 10 together with Anton Zeilinger and Alain Aspect for their work on quantum entanglement.

It was a moment of celebration for Clauser, whose groundbreaking experiments with particles of light helped to prove key elements of quantum mechanics.

"Everybody wants to win a Nobel Prize," Clauser said. "I'm very happy."

But Clauser's journey to winning the biggest prize in science was not always straightforward.

In the 1960s, Clauser was a graduate physics student at Columbia University. By chance, he found an article in the university library that would shape his career and lead him to pursue the experimental work that eventually earned him the Nobel Prize.

The article, written by Irish physicist John Stewart Bell and published in the journal Physics in 1964, considered whether quantum mechanics gave a complete description of reality or not. At the heart of the question was the phenomenon of quantum entanglement.

Quantum entanglement happens when two or more particles link up in a certain way, and no matter how far apart they are in space, their states remain linked.

For example, imagine particle A flying off in one direction and particle B in the other. If the two particles are entangled — which means that they share a joint quantum state — a measurement of particle A will immediately determine the measurement outcome of particle B. It doesn't matter if the particles are a few feet or several light-years apart — their long-distance quantum affair is instantaneous.

This possibility was rejected by Albert Einstein and his colleagues in the 1930s. Instead, they argued that there exists an "element of reality" that is not accounted for in quantum mechanics.

In his 1964 article, Bell argued that it was possible to experimentally test whether quantum mechanics failed in describing such elements of reality. He called these unaccounted-for elements "hidden variables."

In particular, Bell had local variables in mind. This means that they only affect the physical setup in their immediate vicinity. As Clauser explained, "If you put stuff locally in a box and make a measurement in another box very far away, the experimental parameter choices made in one box can't affect the experimental results in the other box, and vice versa."

Clauser decided to test Bell's proposal. But when he wanted to do the experiment, his advisor urged him to reconsider.

"The hardest part initially was to get the opportunity," Clauser recalled. "Everybody was telling me that it was not possible, why bother!"

The quantum laboratory


In 1972, Clauser finally got a chance to test Bell's proposal while in a postdoctoral position at Lawrence Berkeley National Laboratory in California. He joined forces with doctoral student Stuart Freedman. Together they set up a laboratory filled with optical equipment.

"Nobody had done this before," Clauser said. "We didn't have any money to do anything. We had to build everything from scratch. I got my hands dirty, I got immersed in cutting oil, there were lots of wires and I built lots of electronics."

Clauser and Freedman managed to create entangled photons by manipulating calcium atoms. The particles of light, or photons, flew into polarizing filters that Clauser and Freedman could rotate relative to each other.

Quantum mechanics predicted that a higher amount of photons would simultaneously pass the filters than would be the case if the photons' polarization was determined by local and hidden variables.

Clauser's and Freedman's experiment showed that the predictions of quantum mechanics were correct. "We consider these results to be strong evidence against local hidden-variable theories," they wrote in 1972 in Physical Review Letters.

© Copyright Original Source

[Sparko]

Nowhere in that article does it explain how quantum entanglement works. Your title is click bait.

[shunyadragon]

Nowhere in that article does it explain how quantum entanglement works. Your title is click bait.

This a knee jerk biased reaction to his research that got him the Nobel Peace price. You need to specifically read and understand his research articals to remotely provide a constructive opinion. Did he absolutely fully explain every aspect of the behavior of particles concerning the uncertainty principle. No. He presented a working model to explain how the uncertainty principle works and practical applications.

[/cite=https://physics.aps.org/articles/v15/153]
The Nobel Prize in Physics this year recognizes efforts to take quantum weirdness out of philosophy discussions and to place it on experimental display for all to see. The award is shared by Alain Aspect, John Clauser, and Anton Zeilinger, all of whom showed a mastery of entanglement—a quantum relationship between two particles that can exist over long distances. Using entangled photons, Clauser and Aspect performed some of the first “Bell tests,” which confirmed quantum mechanics predictions while putting to bed certain alternative theories based on classical physics. Zeilinger used some of those Bell-test techniques to demonstrate entanglement control methods that can be applied to quantum computing, quantum cryptography, and other quantum information technologies.

Since its inception, quantum mechanics has been wildly successful at predicting the outcomes of experiments. But the theory assumes that some properties of a particle are inherently uncertain—a fact that bothered many physicists, including Albert Einstein. He and his colleagues expressed their concern in a paradox they described in 1935 [1]: Imagine creating two quantum mechanically entangled particles and distributing them between two separated researchers, characters later named Alice and Bob. If Alice measures her particle, then she learns something about Bob’s particle—as if her measurement instantaneously changed the uncertainty about the state of his particle. To avoid such “spooky action at a distance,” Einstein proposed that lying underneath the quantum framework is a set of classical “hidden variables” that determine precisely how a particle will behave, rather than providing only probabilities.

The hidden variables were unmeasurable—by definition—so most physicists deemed their existence to be a philosophical issue, not an experimental one. That changed in 1964 when John Bell of the University of Wisconsin-Madison, proposed a thought experiment that could directly test the hidden variable hypothesis [2]. As in Einstein’s paradox, Alice and Bob are each sent one particle of an entangled pair. This time, however, the two researchers measure their respective particles in different ways and compare their results. Bell showed that if hidden variables exist, the experimental results would obey a mathematical inequality. However, if quantum mechanics was correct, the inequality would be violated.

Bell’s work showed how to settle the debate between quantum and classical views, but his proposed experiment assumed detector capabilities that weren’t feasible. A revised version using photons and polarizers was proposed in 1969 by Clauser, then at Columbia University, along with his colleagues [3]. Three years later, Clauser and Stuart Freedman (both at the University of California, Berkeley) succeeded in performing that experiment [4].

Johan Jarnestad/Royal Swedish Academy of SciencesBell tested. The Freedman-Clauser experiment used entangled photons from excited calcium atoms. The photons traveled to two separate polarizers, which were set at specific orientations relative to each other. The rate at which both photons went throu... Show more
The Freedman-Clauser experiment used entangled photons obtained by exciting calcium atoms. When a calcium atom de-excites, it can emit two photons whose polarizations are aligned. The researchers installed two detectors (Alice and Bob) on opposite sides of the calcium source and measured the rate of coincidences—two photons hitting the detectors simultaneously. Each detector was equipped with a polarizer that could be rotated to an arbitrary orientation.

Freedman and Clauser showed theoretically that quantum mechanics predictions diverge strongly from hidden variable predictions when Alice and Bob’s polarizers are offset from each other by 22.5° or 67.5°. The researchers collected 200 hours of data and found that the coincidence rates violated a revamped Bell’s inequality, proving that quantum mechanics is right.

The results of the first Bell test were a blow to hidden variables, but there were “loopholes” that hidden-variable supporters could claim to rescue their theory. One of the most significant loopholes was based on the idea that the setting of Alice’s polarizer could have some influence on Bob’s polarizer or on the photons that are created at the source. Such effects could allow the elements of a hidden-variable system to “conspire” together to produce measurement outcomes that mimic quantum mechanics.

Johan Jarnestad/Royal Swedish Academy of SciencesLoophole closed. For their updated Bell test, Aspect and his colleagues installed—for each of the entangled photons—a switching system that randomly changed the photon’s path between two branches. Each branch had a polarizer with a different orientat... Show more
To close this so-called locality loophole, Aspect and his colleagues at the Institute of Optics Graduate School in France performed an updated Bell test in 1982, using an innovative method for randomly changing the polarizer orientations [5]. The system worked like a railroad switch, rapidly diverting photons between two separate “tracks,” each with a different polarizer. The changes were made as the photons were traveling from the source to the detectors, so there was not enough time for coordination between supposed hidden variables.

Zeilinger, who is now at the University of Vienna, has also worked on removing loopholes from Bell tests (see Viewpoint: Closing the Door on Einstein and Bohr’s Quantum Debate, written by Aspect). In 2017, for example, he and his collaborators devised a way to use light from distant stars as a random input for setting polarizer orientations (see Synopsis: Cosmic Test of Quantum Mechanics).

APS/A. Stonebraker/D. EhrensteinCan you repeat? The entanglement swapping developed by Zeilinger and colleagues could send entanglement over long distances. In such a quantum repeater setup, two sets of entangled photons are created (red), with one photon from each pair sent to a c... Show more
Zeilinger also used the techniques of entanglement control to explore practical applications, such as quantum teleportation and entanglement swapping. For the latter, he and his team showed in 1998 that they could create entanglement between two photons that were never in contact [6]. In this experiment, two sets of entangled photon pairs are generated at two separate locations. One from each pair is sent to Alice and Bob, while the other two photons are sent to a third person, Cecilia. Cecilia performs a Bell-like test on her two photons, and when she records a particular result, Alice’s photon winds up being entangled with Bob's. This swapping could be used to send entanglement over longer distances than is currently possible with optical fibers (see Research News: The Key Device Needed for a Quantum Internet).

“Quantum entanglement is not questioned anymore,” says quantum physicist Jean Dalibard from the College of France. “It has become a tool, in particular in the emerging field of quantum information processing, and the three nominated scientists can be considered as the godfathers of this new domain.”

Quantum information specialist Jian-Wei Pan of the University of Science and Technology of China in Hefei says the winners are fully deserving of the prize. He has worked with Zeilinger on several projects, including a quantum-based satellite link (see Focus: Intercontinental, Quantum-Encrypted Messaging and Video). “Now, in China, we are putting a lot of effort into actually turning these dreams into reality, hoping to make the quantum technologies practically useful for our society.”

–Michael Schirber

Michael Schirber is a Corresponding Editor for Physics Magazine based in Lyon, France.
References

1. A. Einstein et al., “Can quantum-mechanical description of physical reality be considered complete?” Phys. Rev. 47, 777 (1935).
2. J. S. Bell, “On the Einstein Podolsky Rosen paradox,” Physics 1, 195 (1964).
3. J. F. Clauser et al., “Proposed experiment to test local hidden-variable theories,” Phys. Rev. Lett. 23, 880 (1969).
4. S. J. Freedman and J. F. Clauser, “Experimental test of local hidden-variable theories,” Phys. Rev. Lett. 28, 938 (1972).
5. A. Aspect et al., “Experimental test of Bell’s inequalities using time-varying analyzers,” Phys. Rev. Lett. 49, 1804 (1982).
6. J. W. Pan et al., “Experimental entanglement swapping: Entangling photons that never interacted,” Phys. Rev. Lett. 80, 3891 (1998). [/cite]

[Sparko]

He just proved there were no hidden variable. He did not explain HOW quantum entanglement works. Why one particle can affect another at a distance with zero time lag. Are they in fact the same particle existing in two locations at the same time for example? Nobody knows.

[shunyadragon]

He just proved there were no hidden variable. He did not explain HOW quantum entanglement works. Why one particle can affect another at a distance with zero time lag. Are they in fact the same particle existing in two locations at the same time for example? Nobody knows.

Still not comprehending the results of the research involved.

[Sparko]

Still not comprehending the results of the research involved.

Well then maybe you should study more.

[shunyadragon]

Well then maybe you should study more.

The following is more complete understanding about what the results of the research is.

Still not comprehending the results of the research involved, and what is meant by explained. Basically or maybe simply the uncertainty principle concerning the relationship between particles needs no further explanation and just functions as observed and this functional behavior is useful in practical applications. Scientist in the past have been trying to find other hidden reasons and there are none. Much of research in Quantum Mechanics is simple how do particles and energy behave at the Quantum level. As noted that scientist have not found other "underlying" causes for the Quantum behavior for the uncertainty principle. This is essentially true of all Quantum Mechanics behavior they have no "underlying" explanations for Quantum behavior beyond the consistency and predictability of Quantum particle and energy behavior.

This is what explained means.

[Sparko]

The following is more complete understanding about what the results of the research is.

Still not comprehending the results of the research involved, and what is meant by explained. Basically or maybe simply the uncertainty principle concerning the relationship between particles needs no further explanation and just functions as observed and this functional behavior is useful in practical applications. Scientist in the past have been trying to find other hidden reasons and there are none. Much of research in Quantum Mechanics is simple how do particles and energy behave at the Quantum level. As noted that scientist have not found other "underlying" causes for the Quantum behavior for the uncertainty principle. This is essentially true of all Quantum Mechanics behavior they have no "underlying" explanations for Quantum behavior beyond the consistency and predictability of Quantum particle and energy behavior.

This is what explained means.

So your explanation is that there isn't one?

[shunyadragon]

So your explanation is that there isn't one?

Like all quantum Mechanics we DO NOT have an underlying explanation beyond the predictability and consistency of the behavior of the Quantum properties of the Quantum levels of matter and energy. What Clauser and later others demonstrated is that

We DO NOT know HOW Quantum Mechanics works beyond the predictability and consistency of the behavior of particle and energy at Quantum scale. One thing Clauser did and others later confirmed is he was able to recreate and replicate the behavior of particles uncertainty principle and verify that present day math and physics is adaquite to explain their behavior and use this knowledge in practical ways without any underlying hidden variable. That is all that can be expected in Quantum Mechanics.

[Sparko]

Like all quantum Mechanics we DO NOT have an underlying explanation beyond the predictability and consistency of the behavior of the Quantum properties of the Quantum levels of matter and energy. What Clauser and later others demonstrated is that

We DO NOT know HOW Quantum Mechanics works beyond the predictability and consistency of the behavior of particle and energy at Quantum scale. One thing Clauser did and others later confirmed is he was able to recreate and replicate the behavior of particles uncertainty principle and verify that present day math and physics is adaquite to explain their behavior and use this knowledge in practical ways without any underlying hidden variable. That is all that can be expected in Quantum Mechanics.

so then I was right when I said your title was just clickbait.

[shunyadragon]

so then I was right when I said your title was just clickbait.

No.

[Sparko]

No.

You just admitted that nobody knows how quantum entanglement actually works, yet your title suggests that it has been explained. Clickbait.

[shunyadragon]

You just admitted that nobody knows how quantum entanglement actually works, yet your title suggests that it has been explained. Clickbait.

Again NO! Misquoting me out of context. I clearly stated 'We DO NOT know how Quantum Mechanics works.' All we know is Quantum Mechanics and Quantum entanglement has been demonstrated to work consistently and predictably based on the known math and falsified hypothesis beginning with Clauser. Quantum entanglement has been reproduced, and observed under laboratory conditions. More references to follow concerning research since Clauser that confirmed his work.

At present we only can observe the behavior of matter and energy at the quantum scale and confirm this by the consistency and predictability of the Quantum World. We have not been able to determine the how or cause of Quantum Mechanics behavior beyond this. That is the nature of Quantum Mechanics.

[Machinist]

Quantum entanglement is how quantum computers work.