Quantum channels with entangled inputs boost classical communication rates
Explicit channels with unbounded gains in classical communication using entangled inputs
Information Theory
Summary
This work shows a special kind of quantum communication channel where using entangled inputs—meaning pairs of connected quantum bits—can send a lot more classical information than sending bits separately. Normally, sending information without such connections limits how much you can communicate, but here the authors build explicit examples where entanglement makes a big difference. They use clever quantum operations and measurements combined with classical feedback to make these channels work better than previous random constructions. Their result demonstrates how entanglement can unlock much higher communication efficiency in such channels.
What this means in practice
- •For quantum communication engineers: Design quantum communication protocols that use entangled inputs to greatly increase classical data rates over specific quantum channels.
- •For quantum hardware developers: Develop quantum devices implementing Clifford operations with measurement and feedforward to test enhanced communication capabilities identified in this work.
Authors
Hao-Chung Cheng, Peixue Wu
Abstract
We construct an explicit family of finite-dimensional quantum channels for which the optimal classical communication rate achievable with product-state codewords and collective decoding tends to zero, while rates achievable using entanglement only within pairs of channel inputs grow without bound. Our construction combines deterministic qudit Clifford unitaries with a binary measurement and classical feedforward, providing a derandomization to Hastings' probabilistic construction. The key ingredient is a careful design of measurement and feedforward process that yields the required one-copy and two-copy output entropy bounds from moment estimates alone, without requiring strong convergence of the underlying unitary family.