Quantum Cramér–Rao bound
The quantum Cramér–Rao bound is the quantum analogue of the classical Cramér–Rao bound. It bounds the achievable precision in parameter estimation with a quantum system:
where is the quantum Fisher information.
Here, is the state of the system and is the Hamiltonian of the system. We consider a unitary dynamics of the type
where is the initial state of the system. Here, is the parameter to be estimated based on measurements on
