Reality Doesn’t Exist Until You Measure It, Quantum Parlor Trick Confirms

posted by hubie on Saturday July 30 2022, @12:26AM

from the I'm-a-Copenhagen-junkie dept.

Two players leverage quantum rules to achieve a seemingly telepathic connection:

A quantum particle can exist in two mutually exclusive conditions at once. For example, a photon can be polarized so that the electric field in it wriggles vertically, horizontally, or both ways at the same time—at least until it's measured. [...] The polarization emerges only with the measurement.
That last bit rankled Albert Einstein, who thought something like a photon's polarization should have a value independent of whether it is measured. He suggested particles might carry "hidden variables" that determine how a two-way state will collapse. However, in 1964, British theorist John Bell found a way to prove experimentally that such hidden variables cannot exist by exploiting a phenomenon known as entanglement.
Two photons can be entangled so that each is in an uncertain both-ways state, but their polarizations are correlated so that if one is horizontal the other must be vertical and vice versa. Probing entanglement is tricky. To do so, Alice and Bob must each have a measuring apparatus. Those devices can be oriented independently, so Alice can test whether her photon is polarized horizontally or vertically, while Bob can cant his detector by an angle. The relative orientation of the detectors affects how much their measurements are correlated.
Bell envisioned Alice and Bob orienting their detectors randomly over many measurements and then comparing the results. If hidden variables determine a photon's polarization, the correlations between Alice's and Bob's measurements can be only so strong. But, he argued, quantum theory allows them to be stronger. Many experiments have seen those stronger correlations and ruled out hidden variables, albeit only statistically over many trials.

[...] Now, Xi-Lin Wang and Hui-Tian Wang, physicists at Nanjing University, and colleagues have made the point more clearly through the Mermin-Peres game. In each round of the game, Alice and Bob share not one, but two pairs of entangled photons on which to make any measurements they like. [...]
If hidden variables predetermine the results of the measurements, Alice and Bob can't win every round [...] and on average, they can win at most eight out of nine rounds.
[...] Generating two pairs of entangled photons simultaneously is impractical, Xi-Lin Wang says. So instead, the experimenters used a single pair of photons that are entangled two ways—through polarization and so-called orbital angular momentum, which determines whether a wavelike photon corkscrews to the right or to the left. The experiment isn't perfect, but Alice and Bob won 93.84% of 1,075,930 rounds, exceeding the 88.89% maximum with hidden variables, the team reports in a study in press at Physical Review Letters.
[...] Xi-Lin Wang says the experiment was meant mainly to show the potential of the team's own favorite technology—photons entangled in both polarization and angular momentum. "We wish to improve the quality of these hyperentangled photons."

arXiv paper: Jia-Min Xu, Yi-Zheng Zhen, Yu-Xiang Yang, et al., Experimental Demonstration of Quantum Pseudotelepathy, arXiv:2206.12042v1 [quant-ph] 24 Jun 2022

Original Submission

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