Seminarium Fizyki Materii Skondensowanej

Quantum states of a microscopic two-level system are subject to decoherence due to the interaction of the system with its environment. In many cases one can assume that the environment is in fact a source of classical noise. I will attempt to describe how the measurement of qubit's decoherence can be used in order to gain information about statistical properties of the environmental noise. Specifically, I will describe how one can reconstruct the spectral density of noise from measurements of coherence dynamics of a qubit driven by a sequence of fast rotations (so-called dynamical decoupling from the environmental influence. Simple theoretical ideas will be illustrated with examples of measurements on semiconductor spin qubits, superconducting qubits, and trapped ions.