A chip scale atomic clock (CSAC) includes a temperature stabilized physics system and a temperature stabilized electronics circuitry electrically coupled to the temperature stabilized physics system. Atomic clocks utilize an optical signal having a frequency component. The temperature stabilization increases frequency stability. The temperature stabilized physics system includes a vapor cell and a magnetic field coil, and is enclosed in a magnetic shield. When an ambient temperature of a chip scale atomic clock increases, fluid is extended away, due to thermal expansion, from at least one reservoir towards or away from a thermally isolated subsystem in at least one of the temperature stabilized electronics circuitry and the temperature stabilized physics system.