Experimental Aspects of Indefinite Causal Order in Quantum Mechanics

Lee A. Rozema, Teodor Strömberg, Huan Cao, Yu Guo, Bi-Heng Liu, Philip Walther

Published 2024-05-01Version 1

In the past decade, the toolkit of quantum information has been expanded to include processes in which the basic operations do not have definite causal relations. Originally considered in the context of the unification of quantum mechanics and general relativity, these causally indefinite processes have been shown to offer advantages in a wide variety of quantum information processing tasks, ranging from quantum computation to quantum metrology. Here we overview these advantages and the experimental efforts to realise them. We survey both the different experimental techniques employed, as well as theoretical methods developed in support of the experiments, before discussing the interpretations of current experimental results and giving an outlook on the future of the field.