Topological Photonics Enables Long-Lived Coherence in Quantum Emitter Networks.

The pursuit of stable quantum states, essential for advancements in quantum computing and sensing, frequently encounters the problem of decoherence, where quantum systems lose their coherence due to interactions with the environment. Researchers are now demonstrating novel methods to sustain coherence in quasiparticles, entities that emerge from complex interactions within materials, by manipulating their environment using topologically protected photonic structures. Fatemeh Davoodi, affiliated with both the Institute of Materials Science and Kiel Nano, Surface and Interface Science (KiNSIS) at Christian-Albrechts University, leads a study published detailing this approach. The work, entitled “Beyond Decoherence: Control the Collective Quantum Dynamics of Quasi Particles in Topological Interface”, demonstrates how a specifically engineered plasmonic interface acts as a chiral reservoir, preserving the phase information of spatially separated emitters and enabling long-range correlations that surpass conventional expectations within waveguide quantum electrodynamics. The team utilises the third Stokes parameter, S3, to trace far-field polarization patterns, revealing signatures of superradiance and subradiance correlated with spatial interference, and confirming coherent many-body dynamics.

Researchers demonstrate a pathway to maintain coherence within systems comprised of otherwise incoherent light sources, establishing a robust chiral reservoir that preserves phase information and facilitates long-range correlations. This suggests topological chiral photonic environments offer a novel approach to controlling light-matter interactions and advancing quantum technologies. The study meticulously investigates the manipulation of light using structures inspired by topological materials, traditionally studied in condensed matter physics, with the goal of creating robust and unconventional light propagation pathways that offer potential advantages in areas requiring maintained coherence, such as quantum technologies and optical communications.

Topological photonics explores the control of spatially separated emitters through a topological waveguide, functioning as a chiral reservoir that preserves phase information, addressing the challenge of decoherence arising from finite emitter lifetimes. Decoherence, the loss of quantum information due to interaction with the environment, is a significant obstacle in quantum technologies. Scientists couple incoherently positioned emitters to a mutual topological interface mode, tracing far-field polarization patterns using the third Stokes parameter (S3) to reveal signatures of emitter coherence and spin-momentum locking. The Stokes parameters are a set of values that describe the polarization state of light, with S3 indicating the degree of circular polarization. Spin-momentum locking is a phenomenon where the spin of a photon links to its momentum, a characteristic of topological systems.

Analysis of far-field polarization patterns, utilising the S3 Stokes parameter, reveals a clear correlation between emitter coherence and spin-momentum locking, confirming that the coherence arises from genuine many-body dynamics rather than simple classical interference effects. The study establishes a mechanism whereby a perturbed honeycomb plasmonic interface, functioning as a chiral reservoir, mitigates decoherence typically caused by finite emitter lifetimes, coupling these emitters to a topological interface mode. Plasmonics involves the study of the interaction between light and free electrons at the interface between a metal and a dielectric.

Time-domain dynamics reveal signatures of both superradiance, where emitters radiate collectively and intensely, and subradiance, where emission is suppressed and slowed down, correlating with spatial interference observed in the S3 parameter. These temporal features provide additional evidence supporting the coherent nature of the observed emission and the role of the topological waveguide in mediating long-range correlations, highlighting the potential of topological waveguides to engineer complex light-matter interactions.

Researchers actively demonstrate that topological waveguides effectively preserve the coherence of spatially separated, incoherent emitters. They also demonstrate that topological chiral photonic environments facilitate correlations not readily achievable in conventional waveguide systems, extending beyond the established framework of waveguide quantum electrodynamics (QED). QED is the quantum theory of the interaction between light and matter.

Future research will focus on optimising the design of topological waveguides to enhance coherence and explore their potential applications in quantum information processing and other advanced photonic technologies. Scientists plan to investigate different materials and structures to further improve the performance of these devices and develop new functionalities, ultimately aiming to unlock the full potential of topological photonics for revolutionising quantum technologies.