What term describes a collection of bosons all occupying the same quantum state?

A collection of bosons all occupying the same quantum state is called a Bose–Einstein condensate. It is a special state of matter in which quantum behavior becomes visible on a macroscopic scale.

Bosons have integer spin and are not restricted by the Pauli exclusion principle, so many identical bosons can share one state. When a sufficiently dilute bosonic gas is cooled extremely close to absolute zero, a large fraction of its particles can settle into the lowest available energy state. Their matter waves then overlap, allowing the group to behave coherently like one quantum object.

The idea grew from Satyendra Nath Bose’s 1924 work on quantum statistics. Albert Einstein extended it to material particles in 1924–1925 and predicted the condensation phenomenon. The first dilute-gas condensates were created in 1995 using rubidium and sodium atoms. A Bose gas is simply a gas of bosons, not necessarily a condensate; ideal gas and Fermi gas describe different physical models or particle statistics.