Robust Smoothing for Estimating Optical Phase Varying as a Continuous Resonant Process
For quantum optics and metrology, this work provides a robust estimation method that handles parameter uncertainties in continuous phase estimation.
The paper develops a robust fixed-interval smoother for homodyne phase estimation of coherent and squeezed states of light under second-order resonant noise, demonstrating improved worst-case performance over optimal smoothers and robust filters.
Continuous phase estimation is known to be superior in accuracy as compared to static estimation. The estimation process is, however, desired to be made robust to uncertainties in the underlying parameters. Here, homodyne phase estimation of coherent and squeezed states of light, evolving continuously under the influence of a second-order resonant noise process, are made robust to parameter uncertainties using a robust fixed-interval smoother, designed for uncertain systems satisfying a certain integral quadratic constraint. We observe that such a robust smoother provides improved worst-case performance over the optimal smoother and also performs better than a robust filter for the uncertain system.