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Yes, the article seems to imply that homodyne detectors are some kind of magical machines that can determine whether a particle is quantum entangled without hav
by gpvos 12y ago
Yes, the article seems to imply that homodyne detectors are some kind of magical machines that can determine whether a particle is quantum entangled without having it collapse into a single state. Which would go against all QM knowledge that I have (little though it is). A quick check of the Wikipedia articles doesn't confirm that, but it leaves me confused.
- tjradcliffe 12y agoCurrent thinking is that "collapse" is a hack. We've always talked about the wavefunction collapsing but never been able to describe the onotology of collapse. Non-locality seemed for a time to explain why that is so: because collapse happened non-locally, it could happily violate the law of non-contradiction from the viewpoint of a Lorentz-invariant observer. The alternative to collapse is decoherence due to entanglement with a heat bath. There are still unexplained issues with this, in my view, but that may simply be because I don't fully understand how the ontology of the classical world is constructed by this process, or why once that ontology is constructed the beings that are governed by its laws are only capable of being aware of the foundations via the most indirect kind of inference. In any case, this experiment shows some of the power of "entanglement" vs "collapse" as an account of measurement. If "collapse" is a short-hand for measurements that involve "entanglement with a heat bath" then it is possible perform a measurement that involves entangling part of a wavefunction with a coherent signal (the local oscillator in a homodyne detector) without doing to it what we would call "collapse". That appears (to me at least) to be what is happening in the present case. No magic involved.
- gpvos 12y agoI apparently need to read up a lot on this, because I understand very little of what you write.