Consider classical and quantum harmonic oscillators. When the classical harmonic oscillator is in the ground state, i. e., at rest, it sits still at the equilibrium position. This would correspond to the limit of the oscillatory solutions with po = 0 and Xo = 0, for which the total energy E is zero. The corresponding case for the quantum harmonic oscillator would have the expectation values of momentum and position zero as well:
= 0