Kirkwood-Dirac quasiprobability
The Kirkwood–Dirac quasiprobability distribution (often abbreviated KD distribution) is a complex-valued generalization of a classical joint probability distribution. It was first introduced independently by John G. Kirkwood and later by Paul Dirac as an attempt to describe quantum states in phase space using a joint distribution for noncommuting observables (like position and momentum).
Source: Wikipedia — Kirkwood-Dirac quasiprobability (CC BY-SA 4.0)