Purification of mixed states with closed timelike curve is not possible

Physical cosmic strings do not generate closed timelike curves.

Closed Timelike Curves

In this paper, we explore the possibility that closed timelike curves might be allowed by the laws of physics. A closed timelike curve is perhaps the closest thing to time travel that general relativity allows. We will begin our discussing just what closed timelike curves are, and in what kinds of contexts they were first shown to appear. We then explore how one might actually travel on a close...

Stability of Closed Timelike Geodesics

The existence and stability under linear perturbations of closed timelike geodesics (CTG) in Bonnor-Ward spacetime is studied in some detail. Regions where the CTG exist and are linearly stable are exhibited. In 1949 Gödel found a solution to the Einstein field equation with nonzero cosmological constant that admits closed timelike curves (CTC) [1]. It could be argued that the Gödel solution is...

Purification of two-qubit mixed states

is a frequent choice. However, in practical situations decoherence makes pure states evolve into mixed states and reduces its entanglement. Therefore, in the last years much work has been devoted to understand under which conditions the entanglement that has been lost can be recovered using local operations and classical communication (LOCC). In general there are two frameworks under which the ...

Computability Theory of Closed Timelike Curves

We ask, and answer, the question of what’s computable by Turing machines equipped with time travel into the past: that is, closed timelike curves or CTCs (with no bound on their size). We focus on a model for CTCs due to Deutsch, which imposes a probabilistic consistency condition to avoid grandfather paradoxes. Our main result is that computers with CTCs can solve exactly the problems that are...