The most accurate timekeepers in the universe, atomic clocks are unsurprisingly reliant on quantum principles. Magnetic fields and blue laser light are used to cool individual atoms of beryllium, caesium or strontium to extremely low temperatures at which the atoms are hardly moving. A red laser is then shone onto the atoms, its wavelength specifically attuned to the amount of energy required for their electrons to make a quantum jump to a higher energy level.
Once the electrons have absorbed a photon and jumped, they immediately emit a microwave photon and drop back down. As long as the atoms remain illuminated by the red laser, the electrons keep jumping up and down within a precise period, like a pendulum ticking off the seconds. Pulses of emitted microwaves create a measurable signal with an accuracy of one lost second every 300 million years. Even more accurate are ‘quantum clocks’ that measure the vibrational states of cooled ions of beryllium or aluminium. These clocks only lose a second every 3.86 billion years.
The Future in Minutes – Keith Mansfield
1: See this article on Atom Energy Levels (Electron Shells)
A Fermi-degenerate three-dimensional optical lattice clock (Science Journal Entry)
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