A quantum harmonic oscillator is something used in physics to explain the behavior of particles in certain situations. It helps us to understand how the behavior of particles changes if something changes around them, like their temperature or the amount of light. To explain the quantum harmonic oscillator, think about a see-saw. When the see-saw is balanced in the middle, it just stays there. That's like a particle in a quantum harmonic oscillator when it's at its "normal" energy level. But when the see-saw is tipped to one side, it tries to go back to the middle. That's like a particle in a quantum harmonic oscillator - it wants to go back to its "normal" energy level, but it can't because its energy is either too high or too low. It needs some kind of help, usually in the form of energy, in order to go back to its normal energy level. That's why physicists look at quantum harmonic oscillators to understand how particles act in different situations.