Southwest Quantum Information and Technology

Spin squeezing and magnetometry with magnetic field-sensitive states

Presenting Author: Daniel Hemmer, University of Arizona
Contributing Author(s): Senthilnathan Lingasamy, David Melchior, Ezad Shojaee, Ivan Deutsch, Poul Jessen

Collective spin squeezing can be produced through quantum backaction from a quantum non-demolition measurement. In our experiment we start with the collective angular momentum of a million spin-4 Cs atoms prepared in a spin coherent state (SCS), and generate upwards of 4 dB of metrologically relevant spin squeezing though measurement backaction. By introducing real-time feedback in the form of a radio-frequency (RF) magnetic field we can generate deterministic spin squeezing and use the atomic ensemble as a RF magnetometer. Moving forward, we plan to use internal state control to further increase the amount of spin squeezing. Preliminary results show that up to 8 dB of metrologically relevant squeezing can be produced by preparing the internal atomic spins in a “cat” state before performing the QND measurement. To be metrologically useful, squeezing in the “cat” state basis must be coherently mapped to the SCS basis. So far fluctuating background magnetic fields at frequencies up to tens of kHz have prevented us from doing this reliably. To mitigate the problem we designed and installed a triple-layered magnetic shield which suppresses these fields by more than a factor of 10,000, and have now rebuilt the experiment inside it. We will discuss progress using composite pulses to diagnose and correct for control errors due to residual fields and other experimental imperfections.

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