Undoing a unitary operation, i.e. reversing its action, is the task of canceling the effects of a unitary evolution on a quantum system, and it may be easily achieved when the unitary is known. Given a unitary operation without any specific description, however, it is a hard and challenging task to realize the inverse operation. Recently, a universal quantum circuit has been proposed [Phys.Rev.Lett. 123, 210502 (2019)] to undo an arbitrary unknown d-dimensional unitary U by implementing its inverse with a certain probability. In this letter, we report the experimental reversing of three single-qubit unitaries (d=2) by linear optical elements. The experimental results prove the feasibility of the reversing scheme, showing that the average fidelity of inverse unitaries is F=0.9767±0.0048, in close agreement with the theoretical prediction.
Cite
@article{arxiv.2007.03440,
title = {Experimentally undoing an unknown single-qubit unitary},
author = {Qin Feng and Tianfeng Feng and Yuling Tian and Maolin Luo and Xiaoqi Zhou},
journal= {arXiv preprint arXiv:2007.03440},
year = {2020}
}