Periodic Reporting for period 1 - QUTEMAG (Quantum-Enhanced Optical Magnetometers)
Reporting period: 2016-04-01 to 2018-03-31
The overall objective of the project Quantum-Enhanced Optical Magnetometers QUTEMAG was to combine QND and squeezed light to magnetometry at large atomic densities in a regime where spin-exchange collisions dominate the spin dynamics. This regime is of particular interest for the implementation of high-sensitivity, miniaturized, and high-bandwidth magnetometers as described above. The tools developed during QUTEMAG will find application to enhance current technology most suitable to address challenges in the real world.
In a follow up experiment we used the developed dynamical models to study causal waveform estimation (tracking) of time-varying signals coupled to atomic spins. We used Kalman filtering techniques, which optimally track known linear Gaussian stochastic processes, to estimate stochastic input signals that we generated by optical pumping. Comparing the known input to the estimates, we confirmed the accuracy of the atomic statistical model and the reliability of the Kalman filter, allowing recovery of waveform details far briefer than the sensor’s intrinsic time resolution. With proper filter choice, we obtained similar benefits when tracking partially known and non-Gaussian signal processes, as are found in most practical sensing applications. This work not only demonstrated a technique to evade the trade-off between sensitivity and time resolution in coherent sensing but also how to track waveforms with dynamics unknown prior to the measurement. The results are of particular interest for employing Kalman filtering techniques in a wide range of atomic sensing applications.
Finally a unique and fascinating aspect of our work has been the analysis of QND measurements on atomic spins in the SERF regime using Kalman filtering techniques, a powerful Bayesian inference technique to perform optimal state estimation in real time. In our experiments the optimality of KF has been key in extracting all relevant information from QND measurements with minimum uncertainty, generating entanglement-type correlations among the probed spins. This particular work has shown that the unique properties of SERF-regime ensembles are extremely attractive for QND-based quantum technologies, with potential applications in quantum memories, quantum sensing, and quantum simulation.