Abstract
Undoing a unitary operation, . 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 -dimensional unitary by implementing its inverse with a certain probability. In this letter, we report the experimental reversing of three single-qubit unitaries by linear optical elements. The experimental results prove the feasibility of the reversing scheme, showing that the average fidelity of inverse unitaries is , in close agreement with the theoretical prediction.