Capacities of Quantum Amplifier Channels

TL;DR

This paper analyzes the communication capacities of quantum amplifier channels, revealing their potential for enhanced quantum and classical information transfer and demonstrating advantages over classical strategies.

Contribution

It determines the capacities of quantum-limited amplifier channels across multiple scenarios using a new entropy theorem, highlighting their superior performance.

Findings

Capacities for classical, quantum, and entanglement trade-offs are established.

Capacities for public, private, and secret key communication are derived.

Quantum strategies outperform classical coherent detection methods.

Abstract

Quantum amplifier channels are at the core of several physical processes. Not only do they model the optical process of spontaneous parametric down-conversion, but the transformation corresponding to an amplifier channel also describes the physics of the dynamical Casimir effect in superconducting circuits, the Unruh effect, and Hawking radiation. Here we study the communication capabilities of quantum amplifier channels. Invoking a recently established minimum output-entropy theorem for single-mode phase-insensitive Gaussian channels, we determine capacities of quantum-limited amplifier channels in three different scenarios. First, we establish the capacities of quantum-limited amplifier channels for one of the most general communication tasks, characterized by the trade-off between classical communication, quantum communication, and entanglement generation or consumption. Second, we establish capacities of quantum-limited amplifier channels for the trade-off between public classical communication, private classical communication, and secret key generation. Third, we determine the capacity region for a broadcast channel induced by the quantum-limited amplifier channel, and we also show that a fully quantum strategy outperforms those achieved by classical coherent detection strategies. In all three scenarios, we find that the capacities significantly outperform communication rates achieved with a naive time-sharing strategy.