Precision timing is essential in the GPS navigation system, for financial markets and for fundamental science. The ultimate timekeepers are atoms, as microwave and optical transitions within a collection of isolated and most importantly identical single atoms form the ultimate accurate and precise frequency reference. Atomic clocks using the same atoms cooled down 10⁸ times lower than room temperature atoms can yield 10⁴ times better sensitivity simply because they are 10⁴ times slower and we can measure their transitions correspondingly longer.

Our cold atom clock experiments are aided by our expertise in grating magneto-optical traps (GMOTs). The general principle is illustrated below, and highlighted in these news items: Nature Nanotech paper, May 2013 cover + News and Views. The GMOT arose as a planar geometry extension of our shadow-free 4-beam pyramidal magneto-optical trap. Diffraction gratings are used to split and steer a single incoming beam into e.g. a tripod of diffracted beams, allowing trapping in the four-beam overlap volume. Using the technique with our micro-fabricated gratings we trap and subsequently sub-Doppler cool ₈₇Rb atoms to a recent record of 3$\mu$K. Our latest paper on the use of GMOTs for an atomic clock, is available here.

This work is part of the continuing UK Quantum Technology Hub in Sensing and Metrology.

• EPSRC grants EP/M013294/1 and EP/T001046/1
• ESA 4000110231/13/NL/PA
• DSTL DSTLX-100095636R
• InnovateUK EP/M50824X/1