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> If it were possible to measure the phase of a photon after a beam splitter in a nondestructive way "Non-destructive measurement" is an oxymoron. It's not a r

> If it were possible to measure the phase of a photon after a beam splitter in a nondestructive way "Non-destructive measurement" is an oxymoron. It's not a real measurement if it doesn't destroy the coherence of entanglement. Weak measurements do destroy some entanglement, just not "all" of it.

westurner 1y ago
> "Non-destructive measurement" is an oxymoron. It's not a real measurement if it doesn't destroy the coherence of entanglement. If there were no loopholes to Bell's theorem I would agree. > Weak measurements do destroy some entanglement, just not "all" of it. IDK if that's true. Are all methods of observing probabilistic states destructive forms of measurement? Does a camera on a candle diminish the candle, or does it take energy (and information) from the "wake" of the field moments or field disturbances? I don't think that anyone realizes that it's possible to infer photonic phase from intensity (by Huygens-Steiner).
- westurner 1y ago
  > Weak measurements do destroy some entanglement, just not "all" of it. Which measure of degree of entanglement best characterizes state linkage across spacetime? Depending on definition, doesn't a laser pointer entangle phase states across spacetime, but only slower than c (the speed of transverse photonic waves in a total vacuum)? Are the states synchronized with a constant delay? Quantum discord: https://en.wikipedia.org/wiki/Quantum_discord https://en.wikipedia.org/wiki/Quantum_discord : > In quantum information theory, quantum discord is a measure of nonclassical correlations between two subsystems of a quantum system. It includes correlations that are due to quantum physical effects but do not necessarily involve quantum entanglement. Quantum mutual information: https://en.wikipedia.org/wiki/Quantum_mutual_information https://en.wikipedia.org/wiki/Quantum_mutual_information

westurner 1y ago

> "Non-destructive measurement" is an oxymoron. It's not a real measurement if it doesn't destroy the coherence of entanglement. If there were no loopholes to Bell's theorem I would agree. > Weak measurements do destroy some entanglement, just not "all" of it. IDK if that's true. Are all methods of observing probabilistic states destructive forms of measurement? Does a camera on a candle diminish the candle, or does it take energy (and information) from the "wake" of the field moments or field disturbances? I don't think that anyone realizes that it's possible to infer photonic phase from intensity (by Huygens-Steiner).

westurner 1y ago
> Weak measurements do destroy some entanglement, just not "all" of it. Which measure of degree of entanglement best characterizes state linkage across spacetime? Depending on definition, doesn't a laser pointer entangle phase states across spacetime, but only slower than c (the speed of transverse photonic waves in a total vacuum)? Are the states synchronized with a constant delay? Quantum discord: https://en.wikipedia.org/wiki/Quantum_discord https://en.wikipedia.org/wiki/Quantum_discord : > In quantum information theory, quantum discord is a measure of nonclassical correlations between two subsystems of a quantum system. It includes correlations that are due to quantum physical effects but do not necessarily involve quantum entanglement. Quantum mutual information: https://en.wikipedia.org/wiki/Quantum_mutual_information https://en.wikipedia.org/wiki/Quantum_mutual_information