Engineering Non-Hermitian Quantum Evolution Using a Hermitian Bath Environment

TL;DR

This paper presents a systematic method to engineer non-Hermitian quantum dynamics within Hermitian photonic systems, enabling controlled quantum evolution and bath engineering without actual absorption loss, thus advancing quantum information processing.

Contribution

The authors introduce a framework for constructing non-Hermitian subsystems in Hermitian photonic platforms, demonstrating controlled decay and parity-time symmetry in experiments.

Findings

Successfully realize controlled exponential decay in waveguide chains.

Experimentally demonstrate parity-time symmetric quantum systems.

Show that non-Hermitian dynamics can be simulated with Hermitian baths.

Abstract

Engineering quantum bath networks through non-Hermitian subsystem Hamiltonians has recently emerged as a promising strategy for qubit cooling, state stabilization, and fault-tolerant quantum computation. However, scaling these systems while maintaining precise control over their complex interconnections, especially in the optical domain, poses significant challenges in both theoretical modeling and physical implementation. In this work, drawing on principles from quantum and mathematical physics, we introduce a systematic framework for constructing non-Hermitian subsystems within entirely Hermitian photonic platforms. In particular, controlled exponential decay without actual absorption loss is realized in finite 1-D waveguide chains through discrete-to-continuum coupling and Lanczos transformations. Using this new methodology, we implement parity-time symmetric quantum systems and experimentally demonstrate that these artificial bath environments accurately replicate the dynamics of non-Hermitian arrangements in both single- and multi-photon excitation regimes. Since the non-Hermitian subsystem response deterministically arises from an artificially built Hermitian bath, the quantum evolution can be monitored via post-selection in this fully conservative configuration. This approach bridges the gap between theoretical models and experimental realizations, thus paving the way for exploiting quantum bath engineering in advanced information processing and emerging quantum technologies.