2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/206516We show that due to entanglement, quantum fluctuations may differ significantly from statistical fluctuations. We calculate quantum fluctuations of the particle number and of the energy in a sub-volume of a system of bosons in a pure state, and briefly discuss the possibility of measuring them. We find that energy fluctuations have a non-extensive nature.Replaced with published version. Added calculations, explanations and clarifications, results unchangedHigh Energy Physics - TheoryOther Condensed MatterQuantum Physicstext