Huang, Mengzi

Date:   Thursday, February 20, 2020
Time:   15:30
Place:   ETH Zurich, Hönggerberg, HPF G 6
Host:    Tilman Esslinger

Spin squeezing and spin dynamics in a trapped-atom clock

Mengzi Huang
LKB, École Normale Supérieure, France

Atomic sensors that utilise uncorrelated particles are ultimately limited by quantum projection noise, as is already the case for state-of-the-art atomic clocks. This so-called standard quantum limit (SQL) can be overcome by employing entanglement, a prime example being the spin-squeezed states. Spin squeezing can be created in a quantum non-demolition (QND) measurement of the collective spin, particularly with cavity-quantum electrodynamical (QED) interactions. Despite the exceptional progress in achieving higher levels of squeezing, applications at a metrological level of precision remain challenging. Here we combine a metrology-grade compact clock based on magnetically-trapped ultracold 87Rb atoms with a miniature cavity-QED platform to test quantum protocols in a metrological context, namely at a stability level of 6E-13 at 1 s. We demonstrate spin squeezing by cavity QND measurement, reaching 8 dB for 2E4 atoms. In addition, cold collisions between atoms play an important role at this level of precision. We find that the interplay between cavity measurements and spin-exchange collisions manifests itself in an amplication effect of the cavity measurement. New experiments in this direction may shed light on the many-body physics of interacting cold atoms.