Palestrante: Dr. Saulo Moreira (IMECC - UNICAMP)

Abstract:Quantum measurement invasiveness is a feature of quantum phenomena, i.e. associated with the fact that measurements can affect quantum systems in a manner which cannot be described by classical physics. In this presentation, I will focus on the Leggett-Garg inequality, the violation of which is a witness of measurement invasiveness. After a short introduction of this inequality, I will present a model for its violation which allows us to provide an operational characterization of measurement invasiveness through a parameter associated with the detection efficiency of the measurement apparatus. This parameter controls the violation of the Leggett-Garg inequality and may be associated with experimental tests, helping one to understand and interpret them. By using spin systems, I will also discuss, through the aforementioned model, the relationship between measurement invasiveness and a specific definition of macroscopicity, related to a notion of “size” of these systems. Finally, I will explore the application of measurement invasiveness in the context of protocols for parameter estimation in quantum metrology. A relationship between the Fisher information and temporal quantum correlations will be presented, allowing one to characterize the robustness of metrological scenarios against the presence of noise. As we will see, this relationship also serves as a guideline for a connection between measurement invasiveness and metrological performance.