Sato et al. showed that this macroscopic state occurs when recombining a helium plasma with a neutral gas, and Furukane (“foo-roo-KAH-nay”) et al. predicted that this state only occurs when three-body recombinations dominate. Velocity coherence and this state are needed for Dicke superradiance to occur. One kind of frequency standard induces this state in hydrogen by using 21-centimeter photons to flip electron spin from antiparallel to parallel. Since systems in this state experience a decrease in entropy when increasing internal energy, this state causes amplification of radiation and is an example of negative temperature. An yttrium aluminum garnet acts as a gain medium for this state to occur in neodymium ions via pumping. For 10 points, more particles are in an excited state than the ground state in what state that causes stimulated emission in lasers? ■END■
ANSWER: population inversion [prompt on pumping; prompt on masing or masers or lasing or lasers (until read) by asking “what statistical mechanical process governs them?”; prompt on negative temperature; prompt on excitations by asking “what macroscopic state does that correspond to?”]
<Physics>
= Average correct buzz position