17th of September 2019 (Paris) – PhD defense of Mengzi Huang

Mengzi HUANG will defend his thesis on 17th of September 2019 at 2:00 pm on the subject “Spin squeezing and spin dynamics in a trapped-atom clock”, realized at SYRTE and LKB under the supervision of Carlos Garrido Alzar and Jakob Reichel.

The defense will take place in the amphitheater of the Institut d’Astrophysique de Paris (IAP).

The defense will be in English, in front of a jury composed of Monika Schleier-Smith, Morgan Mitchell, Ludovic Pricoupenko and Rodolphe Boudot.


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 (QPN), 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 (QED) 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 cavity-QED 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 6E-13 at 1 s. We demonstrate spin squeezing by cavity QND measurement, reaching 8 (1) dB for 1.7E4 atoms, currently limited by decoherence due to technical noise. Applying these spin-squeezed states in the clock measurement is within reach.

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.