Entanglement in time

Question

Quantum entanglement links particles through time, according to this study that received some publicity last year:

• New Type Of Entanglement Allows 'Teleportation in Time,' Say Physicists at The Physics arXiv Blog - Technology Review
• S.J. Olson, T.C. Ralph, Extraction of timelike entanglement from the quantum vacuum, arXiv:1101.25650
• S.J. Olson, T.C. Ralph, Entanglement between the Future and the Past in the Quantum Vacuum, Phys. Rev. Lett. 106, 110404 (2011)

  Timelike entanglement may be regarded as a non-classical resource in a manner analogous to the spacelike entanglement that is often studied in the Minkowski vacuum, since any quantum information theoretic protocol may utilize conversion of timelike entanglement to spacelike entanglement as a step in the protocol.

I have read all the reviews in the popular press, most of the "time-travel-discovered" type, but I am looking for more sober comments, written by physicists who have studied the paper. What does this result really mean? I would appreciate pointers to reviews, comments etc. This post has been migrated from (A51.SE)

Comments

What does "this result" in _What does this result really mean?_ mean? Do you mean the concept of "timelike entanglement" or sth else?

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Piotr - yes, by "this result" I mean the general concept of timeline entanglement (particles at different times can be entangled just like particles at different locations at a given time), and the specific conclusion of Olson and Ralph:"timelike entanglement may be regarded as a non-classical resource in a manner analogous to the spacelike entanglement that is often studied in the Minkowski vacuum, since any quantum information theoretic protocol may utilize conversion of timelike entanglement to spacelike entanglement as a step in the protocol."

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Answer 1

I would venture that the paper is less significant than it seems, since in a universe with special relativity, what looks like a successful experimental proof of spatial entanglement to one observer will always look like a mix of space and time entanglement to another one.

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Comments

Thanks Terry. If "a successful experimental proof of spatial entanglement" is defined as experimental confirmation of entanglement between two particles out of each other's light cone (in other words, if there is not enough time for the particles to have exchanged signals at the speed of light), which is an invariant, then a successful experimental proof of spatial entanglement will look the same to all observers.

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[on the road] Well stated Giulio; nice clean fallacy capture, and mea culpa for creating the fallacy. I'll try again when I get a moment. SR should still have geometric implications even for this spacelike separation, but not the way I just said. (Anyone?)

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Giulio: I need a diagram for this, but here goes: An entangled event has two classical terminators that within a single light cone that radiates from the point of entanglement. Both origin-to-terminator paths must remain causally isolated from the rest of the universe. One short path and one long path gives time-like separation; same-length paths gives space-like separation. _Neither case differs_ when defining the consistency relationship between the terminus points. However, to classical observers the cases are different, with time-like akin to capturing half a Stern-Gerlach population.

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