This lecture delves into the quantum harmonic oscillator, focusing on its applications in coupling quantum dot circuits to microwave cavities. The instructor discusses the LC oscillator, explaining its components such as inductance and capacitance, and how they form a resonator. The lecture covers the Hamiltonian of the LC circuit, canonical variables, and the creation and annihilation operators. The instructor illustrates the concept of coherent states and their significance in quantum mechanics, particularly in relation to the distribution of photons. The discussion includes examples of resonators on chips and the importance of maintaining low temperatures for superconducting applications. The lecture concludes with exercises on Hamiltonians and the coupling of identical LC resonators, emphasizing the mathematical representation of these concepts. Overall, the lecture provides a comprehensive overview of the harmonic oscillator's role in quantum science and its practical implications in modern technology.