Spin squeezing and spin dynamics in a trapped-atom clock

Atomic sensors are among the best devices for precision measurements of time, electric and magnetic fields, and inertial forces. However, all 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 produced in a quantum non-demolition (QND) measurement of the collective spin, particularly with cavity quantum electrodynamical (cQED) interactions. In this thesis, I present the second-generation trapped-atom clock on a chip (TACC) experiment, where we combine a metrology-grade compact clock with a miniature cQED platform to test quantum metrology protocols at a metrologically-relevant precision level. In a standard Ramsey spectroscopy, the stability of the apparatus is confirmed by a fractional frequency Allan deviation of 6×10^-13 at 1 s. We demonstrate spin squeezing by QND measurement, reaching 8(1) dB for 1.7×10⁴ atoms, currently limited by decoherence due to technical noise. Cold collisions between atoms play an important role at this level of precision, leading to rich spin dynamics. Here we find that the interplay between cavity measurements and collisional spin dynamics manifests itself in a quantum amplification effect of the cavity measurement. A simple model is proposed, and is confirmed by initial measurements. New experiments in this direction may shed light on the surprising many-body physics in this sytem of interacting cold atoms.

atom chip, Atomic clock, spin-squeezed states, cavity quantum electrodynamics, spin dynamics, quantum metrology

Full document : https://tel.archives-ouvertes.fr/tel-02356949