Entanglement and nonlocality in quantum theory

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In 2018 we have concluded our two main research projects. We have written the results we have obtained in two papers: “Reversing unknown quantum transformations: A universal protocol for inverting general unitary operations”, (submitted to Physical Review Letters) and “Implementing positive maps with multiple copies of an input state” (submitted to Physical Review A).Regarding the problem of quantum unitary operations, we made a deeper analysis into our quantum algorithms that transform multiple uses of a unitary into its inverse. We have found a systematic method to obtain quantum algorithms for transforming multiple copies of quantum unitary operations. This systematic method admits a robust numerical approach based in semi-definite programming which can find optimal protocols in in three classes: parallel - where the input copies can be used at the same time - sequential - where the use of the input copies are made in a causally ordered way - and general - where the use of the input operations may not respect a definite causal order. With this method, we have shown that there exists a strict hierarchy between these three classes and we could understand better the power and limitations of processes with indefinite causal order.