Geometric phases induced by quantum and classical fields in superconducting qubits

9 10/2015

Friday, 09 Oct. 2015, 14:00 - 15:00

Presenter: Stefan Filipp; IBM Research Zurich
Host: I. Fuentes
Where: `Schrödingerroom, 4th Floor, Boltzmanngasse 5, 1090 Wien

Berry’s geometric phase naturally appears as a quantum system is driven by an external field whose parameters are slowly and cyclically changed in time. Using a superconducting qubit, we experimentally show that noise in the external field causes dephasing that has both dynamic and geometric origins. It is found that geometric dephasing, which is present even in the adiabatic limit and when no geometric phase is acquired, can either reduce or restore coherence depending on the orientation of the path the qubit traces out in its projective Hilbert space. Furthermore, by coupling the superconducting qubit to a single mode of a microwave cavity we demonstrate that a geometric phase is acquired even when the driving field is in a quantum state such as a Fock state or the vacuum state. These experiments provide the basis for robust geometric control of atom-cavity systems.