演講者：李彥奇教授 ( 國立中央大學數學系 )

日   期：2025 年 11 月 05 日（星期三）13:30

地   點：國立高雄大學理學院 408 室

講   題：Quantum Channel Capacities in the Low-Noise Regime: From Fundamentals to Superadditivity

摘   要：

Quantum information science aims to understand how information can be stored, transmitted, and processed according to the principles of quantum mechanics. At the heart of this field lies the concept of a quantum channel—a mathematical model that captures how quantum states evolve under noise and decoherence. Just as Shannon’s classical theory defines the ultimate limits of reliable communication, quantum information theory seeks to characterize these limits in the quantum domain.

This talk will begin with an overview of classical and quantum Shannon theory, emphasizing how channel capacity quantifies the fundamental limits of information transmission. I will then introduce different types of quantum channel capacities—classical, private, and quantum—and discuss why their evaluation remains a central open problem due to the phenomenon of superadditivity.

In the second part of the talk, I will focus on our recent study of quantum channels in the low-noise regime, where the channel behavior closely approximates the identity map. By employing the framework of approximately degradable channels, we develop a method to bound and quantify the degree of superadditivity in some near-perfect channels. In particular, we demonstrate that a family of modified Landau–Streater channels achieves O(p²)-degradability, providing new insights into how this particular channel structure governs the emergence of superadditive quantum-capacity effects.