Contents

22 February 2019
Vol 363, Issue 6429

About The Cover

Cover image expansion

COVER Molecules produced at just a few billionths of a degree above absolute zero display exotic quantum properties. A classical gas of potassium-rubidium molecules is chemically reactive (top); when the gas is cooled to low temperatures, collective quantum effects govern how molecules move and collide, suppressing reactivity and enabling formation of a stable, degenerate molecular gas (bottom). See pages 820 and 853.
Illustration: V. Altounian/Science