Laser-noise-immune pulsed optically pumped atomic clock by means of differential detection

The accurate measurement of frequency is of great importance in many fields. One of the main limiting factors affecting the frequency stability of atomic clocks is laser noise. To achieve optimal frequency stability, it is essential to find an effective way to simultaneously eliminate laser noise effects. We propose a differential atomic clock using two atomic sensors whose laser noise is common-mode while the signal responses are opposite. We experimentally demonstrate this approach in two 87Rb atomic vapor cells. Compared with a conventional atomic clock using a single cell, the optical signal achieves an enhancement factor of 1.81, while the laser noise is reduced by approximately 20 dB, thus significantly improving the signal-to-noise ratio and short-term frequency stability of atomic clocks, with a frequency stability of 6.54×10-13/τ using the low-noise, well-operated laser. Notably, when subjected to deteriorated laser noise conditions, a 30-fold improvement in clock stability can be achieved. The results demonstrate that the current differential atomic clock is immune to laser noise. This protocol can be applied to a wide range of atomic clocks and interferometers that use the Ramsey method.