Decoherence resilience of the non-Hermitian skin effect

Decoherence and dissipation, arising from interactions with the environment, can exert a dual influence on transport in physical systems, suppressing coherent propagation while inducing diffusion and mitigating localization in disordered systems. Non-Hermitian physics offers a distinct scenario, where structured dissipation induces directional bulk-to-boundary transport, known as the non-Hermitian skin effect. Whether such transport can persist, be enhanced, or hindered under decoherence remains a largely open question. Here we experimentally address this question using photonic quantum walks with two tunable prototypical decoherence channels, dephasing and amplitude damping. Under dephasing, the non-Hermitian skin effect survives up to the fully incoherent regime and is observed to even be enhanced by dephasing, yielding drift velocities that exceed those of coherent dynamics. By contrast, amplitude damping shows a pronounced order dependence: applied before the non-Hermitian loss operator, it suppresses and ultimately eliminates the non-Hermitian skin effect in the fully incoherent limit; applied afterward, the non-Hermitian skin effect persists and can be enhanced at sufficiently large loss strengths. Our work bridges quantum and classical non-Hermitian dynamics, demonstrates the resilience of the non-Hermitian skin effect to decoherence, and opens avenues for harnessing decoherence to enhance directional transport in noisy, nonequilibrium systems. Decoherence, often viewed as detrimental to coherent transport, can instead enhance the non-Hermitian skin effect, which persists into the fully incoherent regime. Its effect can be tuned by the type and implementation of decoherence.