The paper presents a novel approach to coupling a single semiconductor quantum dot (QD) deterministically to a second-order topological corner state in a photonic crystal cavity. This setup leverages the inherent topological robustness of the corner state to enhance the light-matter interaction, leading to significant Purcell enhancement and polarization control of emitted photons. Key findings include: 1. **Purcell Enhancement**: The experimental Purcell factor (F_p) is measured to be 3.7, significantly higher than typical values in cQED systems. 2. **On-Demand Polarized Single Photon Emission**: The system demonstrates on-demand emission of polarized single photons with a second-order autocorrelation function (g^(2)(0)) as low as 0.024 ± 0.103, indicating strong antibunching behavior. 3. **Design and Fabrication**: The topological cavity is designed based on a 0D corner state in a second-order topological photonic crystal (PhC) structure. The cavity features a high Q factor (13192) and a small mode volume (0.309(λ/nGaAs)^3), which are crucial for achieving strong light-matter coupling. 4. **Coupling and Characterization**: The QD is precisely positioned near the corner state, and the coupling strength is tuned using temperature control. The Purcell factor is observed to peak at 28 K, with a maximum enhancement of 3.2 in PL intensity. 5. **Polarization Control**: The cavity exhibits efficient polarization modulation, with a linear polarizability of 96% for circularly polarized light. Simulations show that the cavity enhances emission from dipoles oriented at 45°, while suppressing those at 135°. This work opens new avenues for advanced quantum photonics applications, particularly in the development of topological quantum optics interfaces and single-photon sources with enhanced performance.The paper presents a novel approach to coupling a single semiconductor quantum dot (QD) deterministically to a second-order topological corner state in a photonic crystal cavity. This setup leverages the inherent topological robustness of the corner state to enhance the light-matter interaction, leading to significant Purcell enhancement and polarization control of emitted photons. Key findings include: 1. **Purcell Enhancement**: The experimental Purcell factor (F_p) is measured to be 3.7, significantly higher than typical values in cQED systems. 2. **On-Demand Polarized Single Photon Emission**: The system demonstrates on-demand emission of polarized single photons with a second-order autocorrelation function (g^(2)(0)) as low as 0.024 ± 0.103, indicating strong antibunching behavior. 3. **Design and Fabrication**: The topological cavity is designed based on a 0D corner state in a second-order topological photonic crystal (PhC) structure. The cavity features a high Q factor (13192) and a small mode volume (0.309(λ/nGaAs)^3), which are crucial for achieving strong light-matter coupling. 4. **Coupling and Characterization**: The QD is precisely positioned near the corner state, and the coupling strength is tuned using temperature control. The Purcell factor is observed to peak at 28 K, with a maximum enhancement of 3.2 in PL intensity. 5. **Polarization Control**: The cavity exhibits efficient polarization modulation, with a linear polarizability of 96% for circularly polarized light. Simulations show that the cavity enhances emission from dipoles oriented at 45°, while suppressing those at 135°. This work opens new avenues for advanced quantum photonics applications, particularly in the development of topological quantum optics interfaces and single-photon sources with enhanced performance.