Fig. 1: Variational experiment principle.
From: Variational quantum algorithm for enhanced continuous variable optical phase sensing
A probe state is prepared as a squeezed, displaced state. The free parameters of our system are the measurement basis angle, ϕHD, and the displacement angle, ϕα, both relative to the squeezing angle ϕr. After interacting with the environment, the state is detected in a homodyne detector. The cost function is estimated by varying the measurement basis of the detector. Subsequently, the experiment either estimates the gradient of the cost function to determine the next set of initial parameters or employs a Gaussian Process (GP) in a Bayesian gradient-free optimization algorithm for parameter selection.
