Superradiance for atoms trapped along a photonic crystal waveguide (1503.04503v1)

Abstract: We report observations of superradiance for atoms trapped in the near field of a photonic crystal waveguide (PCW). By fabricating the PCW with a band edge near the D$1$ transition of atomic cesium, strong interaction is achieved between trapped atoms and guided-mode photons. Following short-pulse excitation, we record the decay of guided-mode emission and find a superradiant emission rate scaling as $\bar{\Gamma}{\rm SR}\propto\bar{N}\cdot\Gamma_{\rm 1D}$ for average atom number $0.19 \lesssim \bar{N} \lesssim 2.6$ atoms, where $\Gamma_{\rm 1D}/\Gamma_0 =1.1\pm0.1$ is the peak single-atom radiative decay rate into the PCW guided mode and $\Gamma_{0}$ is the Einstein-$A$ coefficient for free space. These advances provide new tools for investigations of photon-mediated atom-atom interactions in the many-body regime.

• The paper experimentally demonstrates superradiance, showing that decay rates scale linearly with the number of trapped cesium atoms.
• It employs photonic crystal waveguides that align the band edge frequency with the Cs D1 line to enhance atom-light interaction strength.
• The findings highlight potential advances in quantum optics and waveguide QED, paving the way for improved quantum state control and devices.

Superradiance in Photonic Crystal Waveguides

This paper presents a paper of atom-light interactions using photonic crystal waveguides (PCWs), focusing specifically on the phenomenon of superradiance. The paper investigates how trapped atoms along a nanophotonic waveguide exhibit enhanced radiative decay rates due to collective effects when coupled to the guided modes of the waveguide. Here, atoms are optically trapped in the vicinity of a photonic crystal, providing a robust platform for controlling and observing light-matter interactions in a controlled setting.

Key Findings

At the core of the research lies the successful trapping and coupling of cesium atoms within an array oriented along a PCW. The researchers experimentally demonstrate a superradiant emission with decay rates surpassing the typical single-atom rates. The experimental setup leverages a photonic crystal structure fabricated to align its band edge frequency closely with the cesium D$_1$ line, thereby enhancing the interaction strength due to the well-known van-Hove singularity in photonic structures. Notably, the measured single-atom decay rate into the waveguide, $\Gamma_{\rm 1D}$, achieves a value slightly exceeding the free-space rate $\Gamma_0$, indicating strong coupling efficiency.

Moreover, by varying the mean number of trapped atoms, $\bar{N}$, in the PCW, the paper observes a superradiant decay rate $\bar{\Gamma}_{\rm SR}$ scaling linearly with $\bar{N}$, as $$\bar{\Gamma}_{\rm SR} = \eta \bar{N} \cdot \Gamma_{\rm 1D}$$ where the coupling efficiency $\eta$ is characterized. The findings extend to both temporal and spectroscopic domains, where enhanced decay rates and line broadening effects are observed, supporting their results through detailed modeling and numerical simulations.

Technical Implications

From a theoretical perspective, the research explores frontier areas within waveguide quantum electrodynamics (waveguide QED), offering potential advances in coherent optical networks and quantum information processing. The ability to control atom-photon interactions at such fine scales suggests that photonic crystals could serve as an elemental block for future quantum devices. By demonstrating enhanced emission rates and cooperative effects, the paper reaffirms the importance of photonic structures engineered at near-resonance conditions to maximize interaction effects.

The capability to dynamically tune these structures signifies a robust route to explore novel many-body physics, atom-cavity coupling in strong interaction regimes, and long-range quantum correlations in dense atomic systems. With potential applications in quantum memories and enhanced photon sources, the implications of the described research broaden to foundational studies in quantum transport phenomena.

Future Directions

This research opens several pathways for future work. Optimizing atom trapping and cooling techniques within these photonic structures could achieve even higher coupling efficiencies. Further exploration, such as aligning atomic transitions within the bandgap, might lead to compelling investigations into atomic mirrors and self-organizing atom-photon structures. Additionally, integrating multiple coupled waveguides could facilitate networked quantum systems, extending the scope of PCWs as universal platforms for quantum state engineering.

Conclusion

Overall, the paper provides a refined examination of superradiance using PCWs, bringing to light significant experimental observations that underscore the utility of photonic crystal technologies in advancing quantum optics. Bridging theoretical models with experimental proof, this work consolidates PCWs as a powerful tool for exploring quantum phenomena at the intersection of optics and atomic physics, paving the way for both applied and fundamental advancements in the field.