Imaging topological edge states in silicon photonics (1302.2153v2)

Abstract: Topological features - global properties not discernible locally - emerge in systems from liquid crystals to magnets to fractional quantum Hall systems. Deeper understanding of the role of topology in physics has led to a new class of matter: topologically - ordered systems. The best known examples are quantum Hall effects, where insensitivity to local properties manifests itself as conductance through edge states that is insensitive to defects and disorder. Current research in engineering topological order primarily focuses on analogies to quantum Hall systems, where the required magnetic field is synthesized in non-magnetic systems. Here, we realize synthetic magnetic fields for photons at room temperature, using linear Silicon photonics. We observe, for the first time, topological edge states of light in a two - dimensional system and show their robustness against intrinsic and introduced disorder. Our experiment demonstrates the feasibility of using photonics to realize topological order in both the non-interacting and many-body regimes.

• The paper demonstrates direct imaging of topological edge states in a silicon photonic system via synthetic magnetic fields.
• Experimental measurements reveal that the edge states maintain robust propagation, even amid structural disorder.
• Results benchmarked against simulations validate the spectral robustness of the photonic topological bands for resilient device applications.

Imaging Topological Edge States in Silicon Photonics

The paper "Imaging topological edge states in silicon photonics" by M. Hafezi et al. presents a significant advancement in the paper of topological order in photonic systems. The authors successfully implement and observe topological edge states in a two-dimensional photonic system using silicon photonics, revealing new avenues for exploring topological properties without the complication of electronic impurities.

Overview

This work capitalizes on the concept of synthetic magnetic fields in linear and room-temperature silicon photonic systems to replicate the effects of traditional magnetic fields, usually applied to charged particles. The research builds upon the quantum Hall effect's key idea by exploiting topological properties, here translated into photonics, a field where photons are advantaged by the absence of mass and charge. The authors utilized high-Q ring resonators formed in a silicon-on-insulator platform to demonstrate this capability.

Key Results

The paper establishes several noteworthy results with robust experimental data. Key achievements include:

1. Observation of Robust Topological Edge States: The authors report the direct observation of robust edge states. These states propagate along predefined boundaries of magnetic domains rather than physical edges, indicative of the topological nature of the phenomenon.
2. Demonstration of Disorder Invariance: The edge states retain their propagation characteristics despite the introduction of disorder. For instance, even when a resonator was omitted from the path, the edge states were observed to bypass this defect, maintaining stable transmission. This disorder tolerance is a haLLMark of topological systems.
3. Spectral Measurements and Topological Bands: Spectral transmission measurements were thoroughly benchmarked against simulations, showing the alignment of predicted and observed dispersions. The edge states demonstrated spectral robustness over a broad bandwidth.

Implications and Future Directions

The implications of this research are multifaceted:

• Photonic Devices: The demonstrated topological robustness can be directly employed in the design of new photonics-based devices such as resilient optical filters and delay lines. Such devices require the stability provided by topological protection to maintain performance in varying conditions.
• Quantum Simulation: By extending these concepts to include non-linear interactions or integrating with quantum-dot technologies, this platform could lead to new methods for simulating many-body quantum systems. Observing many-body phenomena in photonic systems remains an exciting and open frontier.
• Development of Non-Magnetic Materials: The ability to create synthetic magnetic fields at room temperature through design, rather than physical magnetic fields, opens possibilities for optomechanical and nonlinear optical applications.

Conclusion

The paper signifies a crucial step in photonic topological systems' experimental feasibility and usability. The capacity to harness topological states in silicon photonics provides both a testbed for fundamental physics and an underpinning for new device architectures. As advancements continue in creating stronger interactions through photonic resonators, further exploration into the non-interacting regime and possible transition into interacting systems is anticipated to yield enriching insights and applications in the broader context of quantum technologies.