  Quantum parameter estimation is central to many fields such as quantum
computation, communications and metrology. Optimal estimation theory has been
instrumental in achieving the best accuracy in quantum parameter estimation,
which is possible when we have very precise knowledge of and control over the
model. However, uncertainties in key parameters underlying the system are
unavoidable and may impact the quality of the estimate. We show here how
quantum optical phase estimation of a squeezed state of light exhibits
improvement when using a robust fixed-interval smoother designed with
uncertainties explicitly introduced in parameters underlying the phase noise.
