The most accurate clock of all time

Katori uses six laser beams to create a pattern of standing electromagnetic waves. This creates a series of energy wells, each of which supports one strontium atom, in much the same way as each dimple in an egg box holds an egg. This prevents the electromagnetic fields of individual atoms interfering with those of their neighbours, and allows the oscillating signals of many atoms to be measured at once.
Previous attempts to make clocks this way failed because the trapping lasers themselves interfered with the atoms' oscillation frequency. Katori's group has got round this by tuning the frequencies of the lasers so they alter the upper and lower transition energy levels of strontium by exactly the same amount, so the oscillation frequency remains unaltered. Katori claims that this "optical lattice clock" will keep time with an accuracy of 1 part in 10¹⁸.
[An accuracy to 1 second for 30 billion years.]