Non-commutative Harmonic Oscillators

This is a survey on the non-commutative harmonic oscillator, which is a generalization of usual (scalar) harmonic oscillators to the system introduced by Parmeggiani and Wakayama. With the definitions and the basic properties, we summarize the positivity of several related operators with \(\mathfrak{sl}_{2}\) interpretations. We also mention some unsolved questions, in order to clarify the current status of the problems and expected further development.