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 paper, we report the experimental reversal 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 $F=0.9767\pm 0.0048$, in close agreement with the theoretical prediction.

中文翻译：

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实验性地撤销未知的单量子位unit

取消unit运算，即反转其作用，是消除a演化对量子系统的影响的任务，当the已知时，可以轻松实现。然而，给定单一运算而没有任何具体描述，实现逆运算是一项艰巨而具有挑战性的任务。最近，提出了一种通用量子电路[ Phys。牧师 123，210502（2019）]来撤消一个任意未知$d$维unit $ü$通过以一定的概率实现其逆。在本文中，我们报告了三个单量子位unit的实验逆转$（d=2）$通过线性光学元件。实验结果证明了该逆方案的可行性，表明逆in的平均保真度为$F=0.9767\pm 0.0048$，与理论预测非常吻合。