# Experimental simulation of closed timelike curves

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Fri., Jan. 27, 2017 12:00 p.m.
- Fri., Jan. 27, 2017 1:00 p.m.
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Location: LB 237
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Contact: Lowell Peltier

**Subject: Experimental simulation of closed timelike curves**

Closed timelike curves are among the most controversial features of modern physics. As legitimate solutions to Einstein’s field equations, they allow for time travel, which instinctively

seems paradoxical. However, in the quantum regime these paradoxes can be resolved, leaving closed timelike curves consistent with relativity. The study of these systems therefore

provides valuable insight into nonlinearities and the emergence of causal structures in quantum mechanics—essential for any formulation of a quantum theory of gravity. Here we

experimentally simulate the nonlinear behaviour of a qubit interacting unitarily with an older version of itself, addressing some of the fascinating effects that arise in systems traversing a closed timelike curve. These include perfect discrimination of non-orthogonal states and, most intriguingly, the ability to distinguish nominally equivalent ways of preparing pure

quantum states. Finally, we examine the dependence of these effects on the initial qubit state, the form of the unitary interaction and the influence of decoherence.

The full paper can be found here: http://www.nature.com/articles/ncomms5145 And I have attached it for your convenience as well.

A helpful supplemental resource is a Scientific American article that can be found here:

https://www.scientificamerican.com/article/time-travel-simulation-resolves-grandfather-paradox/

The paper itself covers in great detail the exact experimental setup, but glosses over the interesting implications of such a system.

The Scientific American article does a much better job of explaining why this is all interesting.