A quantum gas clock is an advanced version of atomic clocks, the most accurate time keepers. Each of the thousands of “ticking” atoms in atomic clocks behave and work largely independently. In contrast, the quantum gas clock uses a globally interacting collection of atoms to constrain collisions and improve measurements. At its heart is an unusual state of matter called a degenerate Fermi gas (a quantum gas for Fermi particles), first created in 1999. All prior atomic clocks have used thermal gases. The use of a quantum gas enables all of the atoms' properties to be quantised, or restricted to specific values, for the first time.