# Unconstrained Capacities of Quantum Key Distribution and Entanglement Distillation for Pure-Loss Bosonic Broadcast Channels

## TL;DR

This paper establishes the maximum achievable rates for quantum key distribution and entanglement sharing over pure-loss bosonic broadcast channels, significantly surpassing traditional time-sharing methods and advancing quantum network communication.

## Contribution

It determines the unconstrained capacity region for QKD and entanglement distillation in broadcast channels, providing a new framework for quantum communication networks.

## Key findings

- Capacity region exceeds naive time-sharing strategies
- Demonstrates a broadcast QKD protocol surpassing point-to-point limits
- Advances towards network-based quantum communication technology

## Abstract

We consider quantum key distribution (QKD) and entanglement distribution using a single-sender multiple-receiver pure-loss bosonic broadcast channel. We determine the unconstrained capacity region for the distillation of bipartite entanglement and secret key between the sender and each receiver, whenever they are allowed arbitrary public classical communication. A practical implication of our result is that the capacity region demonstrated drastically improves upon rates achievable using a naive time-sharing strategy, which has been employed in previously demonstrated network QKD systems. We show a simple example of the broadcast QKD protocol overcoming the limit of the point-to-point strategy. Our result is thus an important step toward opening a new framework of network channel-based quantum communication technology.