Purification of mixed states with closed timelike curve is not possible

@article{Pati2011PurificationOM,
title={Purification of mixed states with closed timelike curve is not possible},
author={A. Pati and I. Chakrabarty and P. Agrawal},
journal={Physical Review A},
year={2011},
volume={84},
pages={062325}
}

In ordinary quantum theory, any mixed state can be purified in an enlarged Hilbert space by adding an ancillary system. The purified state does not depend on the state of any extraneous system with which the mixed state is going to interact or on the physical interaction. Here, we prove that it is not possible to purify a mixed state that traverses a closed timelike curve (CTC) and is allowed to interact in a consistent way with a causality-respecting (CR) quantum system in the same manner. In… Expand