Squeezed atomic clock below the standard quantum limit
The performance of the best atomic clocks and other precision atom interferometers is limited by the quantum noise in the final readout measurement, a situation referred to as the standard quantum limit. This limit arises from the projection postulate when applied to an ensemble of independent particles. I will discuss how quantum mechanically correlated (entangled) states of the many-body system can be used to overcome the standard quantum limit, and how to generate such states in an ensemble of distant atoms using light. We demonstrate a clock operated with a phase-squeezed input state that achieves a given precision almost three times faster than a clock operating at the standard quantum limit.