*Atomic clocks* are the world’s most precise timekeepers. Instead of using a swinging pendulum or an electronic circuit, they measure time by closely monitoring the natural ‘ticks’ inside atoms— often cesium or rubidium. These ‘ticks’ are caused by probing the ultra-steady transitions between [[Energy Level|energy levels]] of an atom. ![[atomic_clock.excalidraw.light.svg]] In order to find the transition, cesium atoms are vaporized in an oven. These atoms are floating through a microwave resonator that tries to excite all atoms in the ground state (blue) to the first excited state (orange). The correct frequency is found if as many atoms as possible are detected in the excited state on the detector. The feedback cycle (on the top) adapts the frequency of the microwave resonator to maximize the count on the detector. Because those transitions are incredibly stable, atomic clocks can keep time so accurately that they would be off by less than one second over millions of years. This accuracy makes them vital for navigation systems like GPS, global communications, and all kinds of scientific research. >[!read]- Further Reading >- [[SI Units]] >- [[Quantum Metrology]] >[!ref]- References