Editing Ensemble (mathematical physics) (section)

=== Quantum statistical mechanics ===
{{unsourced section|date=November 2023}}
In [[quantum statistical mechanics]], for a quantum system in thermal equilibrium with its environment, the weighted average takes the form of a sum over [[Energy eigenvalues|quantum energy states]], rather than a continuous integral:{{clarify|reason=This is true only for discrete spectrum (bound states); continuous spectrum still involves continuous integration.|date=November 2023}}
<math display="block">\bar{A} = \frac{\sum_i A_ie^{-\beta E_i}}{\sum_i e^{-\beta E_i}}.</math>