Quantum entanglement assistance is known to improve the Shannon capacity of classical communication networks but the largest gains noted thus far are rather modest (less than 6%), motivating the question: are large capacity gains ever possible? It is shown in this work that in the presence of causal channel state information at the transmitters, quantum entanglement assistance provides a multiplicative capacity advantage that grows exponentially with the number of users K for certain classical K-user multiple access channels with fixed size (binary) alphabet for inputs, outputs and states. Similarly, in the presence of causal channel state information at the transmitters, quantum entanglement assistance is shown to provide a multiplicative capacity advantage that is unbounded as the size of the state alphabet grows, while the number of users (K=3) and the input and output alphabet (binary) are held fixed. Even with only a few users and small alphabet sizes, substantial multiplicative gains in capacity are found, e.g., with binary inputs, outputs and states, multiplicative gains by factors exceeding 21 and 88 are noted with K=5 and K=7 users, respectively. The gains are robust in the sense that they persist even with noisy quantum resources, e.g., an exponential (in K) capacity advantage from quantum entanglement assistance remains available even if each entangled qubit independently depolarizes completely with probability $\approx$ 30%. The gains are based on quantum entanglement assistance provided only to the transmitters.

翻译：量子纠缠辅助已知可提升经典通信网络的香农容量，但迄今观测到的最大增益相当有限（低于6%），这引发了疑问：是否可能存在大规模容量增益？本文表明，在发射端具备因果信道状态信息的情形下，量子纠缠辅助可为某些输入、输出与状态均采用固定大小（二进制）字母表的经典K用户多址接入信道，提供随用户数K呈指数增长的多倍容量优势。类似地，在发射端具备因果信道状态信息的情形下，若用户数（K=3）及输入输出字母表（二进制）固定不变，量子纠缠辅助可提供随状态字母表规模增长而趋于无界的多倍容量优势。即便仅有少量用户与小字母表，仍可观测到显著的容量倍数增益：例如，在二进制输入、输出与状态下，K=5与K=7用户分别可实现超过21倍与88倍的增益。该增益具有鲁棒性——即使量子资源存在噪声仍能保持，例如：即使每个纠缠量子比特以约30%的概率独立完全退极化，量子纠缠辅助仍能提供关于K的指数级容量优势。此类增益仅基于向发射端提供的量子纠缠辅助。