Amplification of quantum signals by the non-Hermitian skin effect

TL;DR

This paper demonstrates that the non-Hermitian skin effect (NHSE) can be harnessed in quantum systems with boson nonconserving processes to achieve exponential photon amplification and directional quantum signal enhancement.

Contribution

It introduces the application of NHSE in quantum nonlinear resonator lattices for quantum amplification, a novel extension from classical to quantum regimes.

Findings

One-dimensional NHSE lattices enable exponential photon amplification.

Two-dimensional NHSE lattices facilitate directional photon amplification.

NHSE-based quantum amplifiers outperform non-NHSE configurations.

Abstract

The non-Hermitian skin effect (NHSE) is a phenomenon whereby certain non-Hermitian lattice Hamiltonians, particularly those with nonreciprocal couplings, can host an extensive number of eigenmodes condensed to the boundary, called skin modes. Although the NHSE has mostly been studied in the classical regime, we show that it can also manifest in quantum systems containing boson number nonconserving processes arising from uniform parametric driving. We study lattices of coupled nonlinear resonators that can function as reciprocal quantum amplifiers. A one-dimensional chain exhibiting NHSE can perform strong photon amplification, aided by the skin modes, that scales exponentially with the chain length and outperforms alternative lattice configurations that lack the NHSE. We show also that two-dimensional nonlinear lattices can perform directional photon amplification between different lattice corners, due to the two-dimensional NHSE.