This paper presents the demonstration of high-fidelity silica-on-silicon integrated optical circuits for quantum photonic applications. The circuits include two-photon quantum interference with 94.8% visibility, a controlled-NOT (CNOT) gate with 94.3% fidelity, and a path-entangled two-photon state with >92% fidelity. These results show the potential of silica-on-silicon waveguides for quantum information processing, as they enable stable, scalable, and high-performance photonic circuits. Silica-on-silicon waveguides are fabricated on a silicon substrate, with a low-loss silica core and cladding. The waveguides are designed to support single-mode operation at 800 nm, enabling efficient coupling with single-photon sources and detectors. The devices are fabricated using standard optical lithography techniques, and the waveguides are designed to minimize mode mismatch and ensure sub-wavelength stability. The circuits are implemented using directional couplers and Mach-Zender interferometers, which are essential for achieving high visibility quantum interference. The results show that the monolithic nature of these devices allows for stable phase control, which is crucial for quantum operations. The devices are fabricated on a single wafer, with performance that is robust, repeatable, and well understood. The paper also demonstrates the implementation of a CNOT gate, which is a fundamental quantum logic gate. The gate is implemented using a combination of directional couplers and interferometers, and the results show that the devices are in close agreement with the theoretical design. The fidelity of the CNOT gate is 94.3%, which is the highest reported for any entangling logic gate. The paper also demonstrates the generation of a path-entangled two-photon state with >92% fidelity, which is a key resource for quantum information processing. The results show that the devices are capable of generating high-fidelity quantum states, which is essential for quantum metrology and other quantum applications. Overall, the paper demonstrates the potential of silica-on-silicon waveguides for quantum photonic circuits, showing that they can be used to implement high-fidelity quantum operations with high stability and scalability. The results open the way for the miniaturization and improvement of photonic quantum circuits for future quantum technologies and fundamental quantum optics studies.This paper presents the demonstration of high-fidelity silica-on-silicon integrated optical circuits for quantum photonic applications. The circuits include two-photon quantum interference with 94.8% visibility, a controlled-NOT (CNOT) gate with 94.3% fidelity, and a path-entangled two-photon state with >92% fidelity. These results show the potential of silica-on-silicon waveguides for quantum information processing, as they enable stable, scalable, and high-performance photonic circuits. Silica-on-silicon waveguides are fabricated on a silicon substrate, with a low-loss silica core and cladding. The waveguides are designed to support single-mode operation at 800 nm, enabling efficient coupling with single-photon sources and detectors. The devices are fabricated using standard optical lithography techniques, and the waveguides are designed to minimize mode mismatch and ensure sub-wavelength stability. The circuits are implemented using directional couplers and Mach-Zender interferometers, which are essential for achieving high visibility quantum interference. The results show that the monolithic nature of these devices allows for stable phase control, which is crucial for quantum operations. The devices are fabricated on a single wafer, with performance that is robust, repeatable, and well understood. The paper also demonstrates the implementation of a CNOT gate, which is a fundamental quantum logic gate. The gate is implemented using a combination of directional couplers and interferometers, and the results show that the devices are in close agreement with the theoretical design. The fidelity of the CNOT gate is 94.3%, which is the highest reported for any entangling logic gate. The paper also demonstrates the generation of a path-entangled two-photon state with >92% fidelity, which is a key resource for quantum information processing. The results show that the devices are capable of generating high-fidelity quantum states, which is essential for quantum metrology and other quantum applications. Overall, the paper demonstrates the potential of silica-on-silicon waveguides for quantum photonic circuits, showing that they can be used to implement high-fidelity quantum operations with high stability and scalability. The results open the way for the miniaturization and improvement of photonic quantum circuits for future quantum technologies and fundamental quantum optics studies.