Another fun trick for quantum communications: retroactively enabling or disabling them. This is a real experiment, not just neat math:
http://arstechnica.com/science/news/2012/04/decision-to-entangle-effects...
http://arxiv.org/abs/1203.4834
http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys2294.html
Essentially, Alice and Bob receive photons. Victor can, a while later, decide whether they were actually entangled or not (which would allow or disallow using them for quantum encrypted communication). He cannot send information this way, since the only thing he can steer is whether Alice's and Bob's photons are correlated or not. The authors point out:
So either you believe in free will or an unchangeable past (or, like me, you become a compatibilist and ignore the whole business). This is an experiment that can be done with fairly standard farcasters in EP (no need for those expensive QE comms qubits). I wonder how players might exploit it. Note that in a conspiratorial fashion, Victor’s choice might not be free but always such that he chooses a separable-state measurement whenever Alice and Bob’s pair is in a separable-state, and he chooses a Bell-state measurement whenever their pair is in an entangled state.
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