The entanglement-assisted transmission capacity is a strong converse bound for identification

• URL: http://arxiv.org/abs/2608.11000v1
• Date: Tue, 11 Aug 2026 14:48:53 GMT
• Title: The entanglement-assisted transmission capacity is a strong converse bound for identification
• Abstract summary: We prove that the entanglement-assisted transmission capacity $C_E$ is a strong converse bound for this task.<n>We also obtain the first example of strict superadditivity of the identification capacity $C_mathrmIDC_E$.
• Score: 2.0305676256390934
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Classical identification via a noisy channel is a communication task in which the receiver is not required to reconstruct the full transmitted message, but only to decide whether it coincides with a message of interest. This relaxation allows the number of identifiable messages to grow doubly exponentially with the blocklength. For quantum channels, the resulting (doubly exponential) identification capacity $C_{\mathrm{ID}}$ can strictly exceed the ordinary (exponential) transmission capacity $C$. In this paper, we prove that the entanglement-assisted transmission capacity $C_E$ is a strong converse bound for this task: $C_{\mathrm{ID}}\leq C_E$. For sufficiently low-noise channels, this bound can also be achieved via the Hayden-Winter (quantum) identification + fingerprinting codes. This yields an exact characterization $C_{\mathrm{ID}}=C_E$ of identification capacity for such channels. However, for general channels, we prove that this upper bound can be strict. We exhibit an explicit family of transpose-depolarizing channels for which $C_{\mathrm{ID}}<C_E$. As a consequence, we also obtain the first example of strict superadditivity of the identification capacity $C_{\mathrm{ID}}$.

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