Source-linked AI summary
Direct and Reverse Secret-Key Capacities of a Quantum Channel
Stefano Pirandola, Raul Garcia-Patron, Samuel L. Braunstein, Seth Lloyd
TL;DR
The paper studies secret-key extraction from memoryless quantum channels using one-way forward or feedback classical communication. It defines direct and reverse capacities, analyzes arbitrary one-mode Gaussian channels, and shows reverse reconciliation can remain secure for antidegradable channels, with a protocol that can outperform the reverse coherent information bound.
Problem
The paper addresses how secret-key capacities behave under single forward or feedback classical communication, especially when the channel is antidegradable and no forward strategy is known to be secure.
Method
The authors formulate entanglement-based direct and reverse protocols, restrict key-distillation to product input states for achievable bounds, and use the canonical classification of arbitrary one-mode Gaussian channels.
Results
Reverse secret-key capacity can be positive for antidegradable one-mode Gaussian channels, and an explicit reverse key-distillation protocol establishes a tighter lower bound than reverse coherent information.
Takeaways & Limitations
Antidegradability does not necessarily preclude secret-key extraction, and reverse reconciliation can outperform the reverse coherent information bound in the considered Gaussian setting.
Abstract
from arXiv · showhide
We define the direct and reverse secret-key capacities of a memoryless quantum channel as the optimal rates that entanglement-based quantum key distribution protocols can reach by using a single forward classical communication (direct reconciliation) or a single feedback classical communication (reverse reconciliation). In particular, the reverse secret-key capacity can be positive for antidegradable channels, where no forward strategy is known to be secure. This property is explicitly shown in the continuous variable framework by considering arbitrary one-mode Gaussian channels.