Soft Matter and Complex Systems Seminar

A general model of frequency estimation in presence of Markovian noise is considered, where the parameter to be estimated is associated with the Hamiltonian part of the dynamics. In absence of noise, unitary parameter can be estimated with precision scaling as T^-1, where T is the total probing time. We provide a simple algebraic condition involving solely the operators appearing in the quantum Master equation, implying at most T^-1/2 scaling of precision under the most general adaptive quantum estimation strategies. A construction of a quantum error-correction like protocol is presented that provides 1/T precision scaling in case the above mentioned algebraic condition is not satisfied.