Southwest Quantum Information and Technology

Spin squeezing and closed-loop magnetometry with magnetic field-sensitive states

Presenting Author: Ian Marsh, University of Arizona
Contributing Author(s): David Melchior, Poul Jessen

Measurements with quantum limited resolution have important applications in metrology and sensing, including atomic clocks, atom interferometry, and magnetometry. In our work we perform a quantum-non-demolition measurement on the collective angular momentum of a million spin-4 Cs atoms. Through quantum backaction this measurement generates upwards of 5 dB of metrologically relevant spin-squeezing. By introducing real-time feedback, we can use the collective spin to perform precision magnetometry with resolution below the standard quantum limit. In the past our ability to leverage squeezing and quantum feedback has been limited by a noisy field environment. We have reduced these background fields by a factor >10,000 at frequencies up to tens of kHz by rebuilding our experiment inside a multi-layered magnetic shield of mu-metal and aluminum. In this quiet field environment, we use radio-frequency (RF) composite pulse sequences to correct remaining classical control errors such as noisy rotations of the collective spin, allowing us to reliably prepare the atoms in the desired initial states. We report progress in implementing closed-loop RF feedback control to generate deterministic squeezing and use the atomic ensemble as an RF magnetometer.

(Session 5 : Thursday from 5:00 pm - 7:00 pm)