We determine the exact strong converse exponent for entanglement-assisted classical communication of a quantum channel. Our main contribution is the derivation of an upper bound for the strong converse exponent which is characterized by the sandwiched R\'enyi divergence. It turns out that this upper bound coincides with the lower bound of Gupta and Wilde (Commun. Math. Phys. 334:867-887, 2015). Thus, the strong converse exponent follows from the combination of these two bounds. Our result has two implications. Firstly, it implies that the exponential bound for the strong converse property of quantum-feedback-assisted classical communication, derived by Cooney, Mosonyi and Wilde (Commun. Math. Phys. 344:797-829, 2016), is optimal. This answers their open question in the affirmative. Hence, we have determined the exact strong converse exponent for this problem as well. Secondly, due to an observation of Leung and Matthews, it can be easily extended to deal with the transmission of quantum information under the assistance of entanglement or quantum feedback, yielding similar results. The above findings provide, for the first time, a complete operational interpretation to the channel's sandwiched R\'enyi information of order $\alpha > 1$.

翻译：我们确定了量子信道纠缠辅助经典通信的精确强逆指数。我们的主要贡献是推导了强逆指数的上界，该上界由夹层R\'enyi散度刻画。结果表明，该上界与Gupta和Wilde（Commun. Math. Phys. 334:867-887, 2015）给出的下界完全一致。因此，强逆指数由这两个界共同确定。我们的结果具有两方面意义。首先，它表明Cooney、Mosonyi和Wilde（Commun. Math. Phys. 344:797-829, 2016）推导的量子反馈辅助经典通信强逆性质的指数界是最优的，这肯定地回答了他们的开放性问题。因此，我们也确定了该问题的精确强逆指数。其次，根据Leung和Matthews的观察，该结果可轻松推广至纠缠或量子反馈辅助下的量子信息传输问题，并得到类似结论。上述发现首次为$\alpha > 1$阶信道夹层R\'enyi信息提供了完整的操作解释。