The research focuses on enhancing the spontaneous emission rate of quantum dots (QDs) for advancements in photonic quantum technologies. Purcell's work established that an emitter's environment modifies its spontaneous emission rate. Enhancement has been achieved using various structures like micro/nano-cavities, nanoantennas, and plasmonic nanostructures, leading to efficient single-photon sources. Integrating QDs into photonic-crystal waveguides (PCWs) offers benefits for chip-based platforms, enabling efficient photon extraction. The Purcell enhancement factor in a waveguide is proportional to the group index, which is significantly increased in the slow-light region near the photonic band edge. Previous studies reported emission rates up to 6.28 ns⁻¹ (9-fold Purcell factor) in W1 waveguides and up to 12-fold enhancement in topological slow-light valley PCWs. Waveguide geometry also offers chiral coupling between the quantum emitter's spin and the waveguide mode's helicity, leading to directional coupling. However, achieving both strong chiral coupling and high Purcell enhancement simultaneously remains a challenge, as maximal spin-dependent directionality often occurs in low-field intensity regions, resulting in poor emitter-waveguide coupling. Glide-plane symmetry PCWs are proposed to address this, but experimental realizations have been limited. This paper aims to demonstrate record-high Purcell factors for both non-chirally and chirally coupled QDs emitting in the slow-light region of a glide-plane line defect PCW, achieved through careful QD frequency tuning using electric and magnetic fields and quasi-resonant phonon-sideband excitation to eliminate slow internal relaxation.

The literature review extensively covers previous research on Purcell enhancement and chiral coupling in various nanophotonic structures. It highlights the advancements in achieving high Purcell factors using different waveguide designs, including W1 waveguides and topological slow-light valley PCWs. The review also discusses the importance of chiral coupling for applications in quantum information processing and the challenges in achieving both high Purcell enhancement and strong chiral coupling simultaneously. The authors cite numerous studies demonstrating Purcell enhancement in various waveguide systems and chiral coupling in nanobeams, glide-plane PCWs, and topological PCWs. The review sets the stage for the current work by highlighting the limitations of previous approaches and the potential advantages of the proposed glide-plane PCW design.

The study employed a glide-plane PCW design fabricated on a gallium arsenide (GaAs) wafer with self-assembled InGaAs QDs embedded in the center of the GaAs membrane. The slow-light section of the waveguide was connected to standard nanobeam waveguides through adaptors, and grating outcouplers enabled off-chip coupling. Electrical contacts allowed spectral tuning of the QDs, and a magnetic field enabled Zeeman splitting measurements. The sample was held at 4.2 K. Waveguide design utilized up-down glide-plane symmetry for enhanced slow-light and chiral coupling. Simulations using finite-element modeling determined the Purcell factor spatial profile, revealing large enhancements near air holes. Experimentally, QDs were identified based on emission frequency relative to the photonic band edge. Lifetime measurements used a mode-locked Ti:sapphire laser and time-resolved photon counting. Two excitation schemes were used: above-band non-resonant (808 nm) and quasi-resonant (phonon-sideband) excitation. The quasi-resonant method was crucial for measuring fast decay rates. Hanbury Brown-Twiss (HBT) measurements confirmed single-photon emission. Chirality was assessed using Stokes parameters, with simulations guiding the identification of chiral regions. Electric field tuning and magnetic field manipulation were used to tune the QD emission wavelength with respect to the photonic band edge of the waveguide.

The key findings demonstrate record-high Purcell factors for both non-chirally and chirally coupled quantum dots. For non-chirally coupled QDs, a record radiative decay rate of 17 ± 2 ns⁻¹ (60 ± 6 ps lifetime) was observed, corresponding to a 20 ± 2-fold Purcell enhancement. This was achieved by tuning the QD to the slow-light region and using quasi-resonant phonon-sideband excitation to eliminate slow internal relaxation processes. For chirally coupled QDs, a 5 ± 1-fold Purcell enhancement was achieved, significantly surpassing previous measurements. The high degree of chiral coupling was confirmed through measurements of the oppositely polarized Zeeman components of the QD emission, showing directional emission along opposite propagation directions. The single-photon nature of the QD emission was confirmed using Hanbury Brown-Twiss (HBT) measurements. The results show that it is possible to achieve both a high degree of chirality and a large Purcell factor simultaneously using the glide-plane waveguide platform, as predicted by simulations. The measured values are substantially better than those reported for other chiral waveguide geometries including nanobeams, W1 waveguides, and topological waveguides.

The results demonstrate the effectiveness of the glide-plane PCW platform in achieving both high Purcell enhancement and strong chiral coupling. The record-high Purcell factors achieved, especially the 20-fold enhancement for non-chirally coupled dots and 5-fold for chirally coupled dots, significantly advance the capabilities of on-chip quantum optical devices. The use of quasi-resonant phonon-sideband excitation was crucial in revealing the true radiative lifetime of the QDs, eliminating the effects of slow internal relaxation processes. The ability to achieve both strong chiral coupling and high Purcell enhancement in the same region opens up possibilities for building scalable spin-photon networks for quantum information processing. The significantly improved performance compared to other waveguide systems confirms the suitability of the glide-plane platform for applications in chiral quantum optics.

This research demonstrates record-high Purcell enhancement factors for both non-chirally and chirally coupled quantum dots embedded in a glide-plane photonic crystal waveguide. The achieved 20-fold (non-chiral) and 5-fold (chiral) enhancements represent significant advancements for on-chip quantum optical technologies. Future research could focus on optimizing waveguide designs to achieve even higher enhancement factors and exploring the use of these devices in building complex quantum networks.

The study's limitations include the random positioning of QDs, leading to variations in their coupling to the waveguide modes. The number of QDs studied is also limited, and further investigation is needed to explore the reproducibility and scalability of the results. The spectral tuning range available with the current device may limit the level of Purcell enhancement that can be achieved for chirally coupled QDs.