Would the Existence of CTCs Allow for Nonlocal Signaling?

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Dunlap, Lucas
conference paper description
A recent paper from Brun et al. has argued that access to a closed timelike curve (CTC) would allow for the possibility of perfectly distinguishing nonorthogonal quantum states. I show how this result can be used to develop a protocol for instantaneous nonlocal signaling, and detail the debate surround- ing these results. Several commenters have argued that nonlocal signaling must fail in this and in similar cases, for various reasons. I argue that each of these objections fails to rule out nonlocal signaling in the presence of a CTC. I argue that the reason these authors are motivated to exclude the prediction of nonlocal signaling is because the No Signaling principle is considered to a fundamental part of the formulation of the quantum information approach. I draw out the relationship between nonlocal signaling, quantum information, and relativity, and argue that the principle theory formulation of quantum mechanics, which is at the foundation of the quantum information approach, is inconsistent with Deutsch's D-CTC model, on which this protocol is based.