| Description |
I shall introduce the notion of the Loschmidt echo using the central spin model in which a central spin (qubit) is globally coupled to a spin chain. I shall indicate how does the Loschmidt echo behave close to a quantum critical point and how it is also related to the decoherence of the central spin which was initially in a pure state. Finally, I shall discuss at some length the behavior of the echo when the spin chain is driven across a quantum critical point suddenly or slowly. |