The current definition of 1 second depends upon the accuracy of the Cesium¹³³ atomic clock. An atomic clock uses the atomic resonance frequency (depends on the time it takes for an electron to jump from excited state to ground state in the outer layers of the atom) as its counter. Since this frequency is a function of the fundamental properties of the atom, it is extremely accurate (small fluctuations can and do exist, due to quantum fluctuations). The Cesium clock is accurate upto 1 part in 10¹⁵, and currently defines the second. However, this atomic clock is hard to stabilize, and this has imposed an inherent upper limit to the accuracy.

Vacuum Chamber to cool atoms using a laser (Courtesy: PhysicsWeb)
Now researchers in Japan have demonstrated a way to trap neutral atoms that could herald a new era in timekeeping. The team believes that an optical clock based on Strontium atoms trapped in an optical lattice could lead to clocks that are accurate to one part in 10¹⁸, and thus a 1000 fold better than the Cesium clocks:):).
The Japanese team first trapped a cloud of 10,000 Strontium atoms at a temperature of just 2 microkelvin in a one-dimensional optical lattice (a very narrow wire). A blue laser cools down the atoms to that temperature. When a light is shined upon the atoms, the atoms get trapped in the crests and troughs of the light wave! So by measuring the number of atoms in a fixed length of wire, the scientists can find the frequency of the light used, and thus set a new standard for the measurement of time:):).