Estimation of Phase and Diffusion: Combining Quantum Statistics and Classical Noise

Understand

Coherent ensembles of $N$ qubits present an advantage in quantum phase estimation over separable mixtures, but coherence decay due to classical phase diffusion reduces overall precision.

• In some contexts, the strength of diffusion may be the parameter of interest.
• We examine estimation of both phase and diffusion in large spin systems using a novel mathematical formulation.
• For the first time, we show a closed form expression for the quantum Fisher information for estimation of a unitary parameter in a noisy environment.