UW-Madison research provides basis for Nobel Prize in Physics
first time in Almost 10 yearsQuantum mechanics has re-emerged as the inspiration behind the Nobel Prize in Physics. In recognition of their work on quantum entanglement, this year’s most prestigious physics award has been divided in three ways between physicists Alain Aspect, John Clauser and Anton Zeilinger.
Quantum entanglement – a unique subatomic phenomenon that links the properties of two seemingly non-interacting particles – defies all known intuitions of our macroscopic world. This strange behavior, along with its association with real-world applications such as quantum computing and communications, has led to quantum entanglement to attract the minds of hobbyists and experts alike.
The newly announced Nobel Prize marks the next chapter in the field.
The three winners participated in the design and implementation of various experiments that deepened our understanding of quantum entanglement. Zeilinger, a professor of physics at the University of Vienna and designer of the latest set of experiments, was interested in understanding a strange side effect of quantum entanglement called quantum teleportation. In essence, Zeilinger’s experiments showed that by using two entangled particles, information could be shared over random distances, paving the way for a potentially highly secure commercial quantum network.
Zeilinger’s experiments were only possible because of experiments conducted by Clauser, a researcher at JF Clauser & Associates, and Aspect, a professor at the Institut Graduate School of Paris-Saclay University. Both physicists worked independently to design an instrument that could analyze the presence of quantum entanglement. Closer was the first to begin its tests in the 1970s.
Closer received promising results, but problems persisted. Ten years later, Aspect has successfully eliminated the remaining issues with an upgraded version of the original Clauser experience.
While that may be the extent of this year’s Nobel Prize in Physics, it constitutes only the latest stroke on a much larger picture of quantum entanglement.
To get to the beginning of this story, one needs to go back in time to the mid-1930s. It has only been 10 years since the field of quantum mechanics Endoscopy was done. The novelty and uniqueness of quantum mechanics has led to any discussion on this topic tearing the physics community apart like wildfire. Naturally, given the time period and subject matter, Albert Einstein made his way to the middle of this speech.
During the early 1930s, Einstein published a few papers discussing the various intricacies of quantum mechanics. However, in 1935, Einstein published one of his most influential papers on quantum mechanics. In collaboration with contemporary physicists Boris Podolsky and Nathan Rosen, the three have released a research paper titled Provocatively, “Can the quantum mechanical description of physical reality be considered complete?“
As the title might suggest, Einstein and his colleagues argued that some “physical irregularities” seemed so wild and unusual that the only logical conclusion was that quantum mechanics must be incomplete. What is the clearest of these violations? Quantum entanglement.
Einstein, Podolsky, and Rosen (EPR) built their thought experiment first using the idea of the Uncertainty Principle—a famous explanation that states that for a particular particle one can only know its position or momentum with absolute certainty, not both, like measuring one changes the other. Using this, physicists then established the idea of the interchangeability of two particles.
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Simply put, two factors – say, X and Y – are not interchangeable at XY ≠ YX. It may be useful to think of these operators as “actions” that are performed on something. In a mathematical context, these operators work on wave functions – the equations that represent atomic particles – to produce unique numerical results. However, comparisons in the real world, such as the Uncertainty Principle, are also useful for highlighting the same idea.
By replacing X and Y with the act of measuring position and momentum respectively, it becomes reasonable to argue that for a single particle, these two actions are not interchangeable. For example, if we measure the momentum of a particle, doing so will make it fly in a different direction, giving a different location from the original starting point when measured. If instead we measure the position first, it will be detected at the unadjusted starting point, already showing the inequality between XY and YX.
For supporters of quantum mechanics at the time, this idea was powerful. What made the EPR paper so shocking was that they were able to show, with a little math, that within the framework of quantum mechanics, standard physics begins to break down. It appears that “two physical quantities, with operators that do not travel, can have simultaneous realities,” describe Einstein and co-authors. This means that the two quantities whose interactions must be enveloped in a cloud of uncertainty are somehow connected, or rather intertwined, in such a way that knowing one changes the other predictably.
Theoretically, if two people at opposite ends of the universe were watching the same entangled pair of particles, and one person decided to change the quantum state of their particle, the other person would be able to see their particle interact with that change, seemingly far faster than the speed of light would allow. To EPR, this seemed physically impossible, and they concluded that quantum mechanics must be incomplete.
The idea of quantum entanglement, later described by Einstein as “scary remote workHe began a new approach toward a common understanding of quantum mechanics. For several decades after the paper was released, a leading theory suggested the existence of a set of “hidden variables” that explain this behaviour.
This would not be seriously challenged until 1964, when Northern Irish-born physicist John S. Bell works at the University of Wisconsin-Madison while on leave from the European Council for Nuclear Research (CERN). Bell happened to stumble upon a 1935 EPR paper, and upon reading his interpretation of quantum entanglement and hidden variables, Bell used relatively simple statistical principles to derive a set of inequalities that later became known as Bell’s inequalities.
Bell published his work in a paper titled “About the Einstein-Podolsky-Rosen paradox.Its contents have been carefully customized to prepare for gross inequalities. Roughly summing up, Bell’s inequalities were able to show that it was in fact possible to “discover” the existence of hidden quantum variables, all without knowing what they are.
If the hidden variables were really behind quantum entanglement, then Bell’s inequalities would still be true – validating the EPR interpretation. However, if the inequalities can be shown to be statistically incorrect, they can be taken as evidence that the original understanding of quantum entanglement is in fact correct.
For his part, Bell believed that the latter – that the inequalities would be violated – reinforced the earlier understanding of quantum mechanics. However, for now, Bill will have to wait for that confirmation.
Several years later, John Clauser, then a postdoctoral researcher at the University of California-Berkeley, discovered Bell’s work and began thinking about Experience That would eventually become the first trio of Nobel Prize laureates of the year.
To complete this experiment, Clauser created an instrument that can measure the variables required by Bell’s inequalities. To the surprise of many, Clauser’s empirical data violated Bell’s inequality, marking the first step in proving the “scare act” introduced by EPR 30 years ago.
John S. passed away. Bell in 1990, leaving him unable to see the recent progress his work had enabled him. However, the mathematics he left behind has cemented its place as an essential and vital part of this year’s Nobel Prize in Physics.
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