“…For example, the quantum Augustin and Rényi information determine the error exponent of communications over a classical-quantum channel using certain random codebooks and that of composite quantum hypothesis testing [DW17, CHT19, CGH18, MO17, MO21, HT16]. The quantum conditional Rényi entropies have profound applications to quantum cryptographic protocols, such as bounding the convergence rate of privacy amplification [Dup21], analyzing the security of quantum key distributions [Ren05, KRS09,Tom12], and bounding the error exponent of source coding with quantum side information [CHDH18,CHDH21]. The above-mentioned quantities share a common feature-they require optimizing some order-α quantum Rényi divergence over the set of all quantum states.…”