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的纠缠辅助经典通信的确切强逆指数。主要贡献在于推导了由夹层Rényi散度表征的强逆指数上界。该上界恰好与Gupta和Wilde（Commun Math Phys 334:867–887, 2015）的下界一致。因此，强逆指数由这两个界的组合得出。该结果有两方面意义：其一，表明Cooney、Mosonyi和Wilde（Commun Math Phys 344:797–829, 2016）为量子反馈辅助经典通信推导的强逆性质指数界是最优的，从而肯定地回答了他们的开放问题——据此我们也确定了该问题的确切强逆指数；其二，基于Leung和Matthews的观察，该结果可轻松推广至处理纠缠或量子反馈辅助下的量子信息传输问题，并得到相似结论。上述发现首次为信道在阶数$\alpha > 1$时的夹层Rényi信息提供了完整的操作诠释。