# Can closed timelike curves or nonlinear quantum mechanics improve quantum state discrimination or help solve hard problems - Quantum Physics

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Abstract: We study the power of closed timelike curves CTCs and other nonlinearextensions of quantum mechanics for distinguishing nonorthogonal states andspeeding up hard computations. If a CTC-assisted computer is presented with alabeled mixture of states to be distinguished-the most natural formulation-weshow that the CTC is of no use. The apparent contradiction with recent claimsthat CTC-assisted computers can perfectly distinguish nonorthogonal states isresolved by noting that CTC-assisted evolution is nonlinear, so the output ofsuch a computer on a mixture of inputs is not a convex combination of itsoutput on the mixture-s pure components. Similarly, it is not clear that CTCassistance or nonlinear evolution help solve hard problems if computation isdefined as we recommend, as correctly evaluating a function on a labeledmixture of orthogonal inputs.

Author: ** Charles H. Bennett, Debbie Leung, Graeme Smith, John A. Smolin**

Source: https://arxiv.org/