We examine mixedness and entanglement of the chronology-respecting (CR) system assuming that quantum mechanical closed timelike curves (CTCs) exist in nature. In order to discuss these two issues analytically, we introduce the qubit system and apply the general controlled operations between CR and CTC systems. We use the magnitude of Bloch vector as a measure of mixedness. While Deutschian-CTC (D-CTC) either preserves or decreases the magnitude, postselected-CTC (P-CTC) can increase it. Non-intuitively, even the completely mixed CR qubit can be converted into a pure state after CTC qubit travels around the P-CTC. It is also shown that while D-CTC cannot increase the entanglement of CR system, P-CTC can increase it. This means that any partially entangled state can be maximally entangled pure state if P-CTC exists. Thus, distillation of P-CTC-assisted entanglement can be easily achieved without preparing the multiple copies of the partially entangled state.
Quantum Information Processing – Springer Journals
Published: Mar 30, 2016
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