Topological framework for directional amplification in driven-dissipative cavity arrays

TL;DR

This paper introduces a topological framework to understand and design directional amplifiers in driven-dissipative cavity arrays, linking topological invariants to non-reciprocal signal amplification.

Contribution

It establishes a unifying topological approach that correlates spectral invariants with directional amplification regimes, aiding the design of quantum amplifiers.

Findings

Topological invariant determines regimes of exponential gain.

Explicit formulas for scattering matrix and gain depend on topology.

Parameter space can be visualized as a topological phase diagram.

Abstract

Directional amplification, in which signals are selectively amplified depending on their propagation direction, has attracted much attention as key resource for applications, including quantum information processing. Recently, several, physically very different, directional amplifiers have been proposed and realized in the lab. In this work, we present a unifying framework based on topology to understand non-reciprocity and directional amplification in driven-dissipative cavity arrays. Specifically, we unveil a one-to-one correspondence between a non-zero topological invariant defined on the spectrum of the dynamic matrix and regimes of directional amplification, in which the end-to-end gain grows exponentially with the number of cavities. We compute analytically the scattering matrix, the gain and reverse gain, showing their explicit dependence on the value of the topological invariant. Parameter regimes achieving directional amplification can be elegantly obtained from a topological `phase diagram', which provides a guiding principle for the design of both phase-preserving and phase-sensitive multimode directional amplifiers.