Spin Squeezing in an Atomic Clock:
Suppressing Projection Noise Using Cavity-Mediated Interactions

The phase noise of an atomic clock is limited by the discreteness of the
read-out signal---imposed by quantum mechanics---which gives rise to
projection noise.  This projection noise can be suppressed by engineering
correlations (entanglement) between the atoms in the clock to produce squeezed spin states.  By using an optical resonator to introduce such correlations in a dilute atomic gas, a prototype atomic clock has demonstrated an Allan variance nearly three times below the standard quantum limit, with scope for substantial further improvement.  I'll present the basic concepts and
techniques underlying this achievement and, time permitting, briefly discuss
its relevance for state-of-the-art precision measurements as well as some more
recent theoretical developments.