Measurement of a Vacuum-Induced Geometric Phase

Berry's geometric phase naturally appears when a quantum system is driven by an external field whose parameters are slowly and cyclically changed. A variation in the coupling between the system and the external field can also give rise to a geometric phase, even when the field is in the vacuum state or any other Fock state. Here we demonstrate the appearance of a vacuum-induced Berry phase in an artificial atom, a superconducting transmon, interacting with a single mode of a microwave cavity. As we vary the phase of the interaction, the artificial atom acquires a geometric phase determined by the path traced out in the combined Hilbert space of the atom and the quantum field. Our ability to control this phase opens new possibilities for the geometric manipulation of atom-cavity systems also in the context of quantum information processing.Comment: 5 + 6 page

Autosoliton in Ablowitz-Ladik chain with linear damping and nonlinear amplification

The existence of discrete autosolitons in a nonlinear lattice is studied. The Ablowitz–Ladik (AL) model with linear damping, nonlinear cubic amplification and quintic damping and complex second difference representing the discrete analog of the filter is investigated. The parameters of the autosoliton are calculated using the perturbation theory for the AL model. Analytical predictions are confirmed by numerical simulations of the AL model with nonconservative perturbations

Vacuum Rabi splitting due to strong coupling of a flux qubit and a coplanar-waveguide resonator

We have experimentally studied a superconducting flux qubit strongly coupled to a single mode of a high-quality transmission-type coplanar-waveguide resonator. The qubit-resonator coupling is revealed in the resonator transmission spectrum as a vacuum Rabi splitting. In the dispersive regime the qubit energy levels are spectroscopically probed. We observe a shift in the qubit transition frequency that linearly depends on the number of photons in the resonator, which is attributed to the ac-Zeeman shift. The observations are in agreement with the theoretical predictions

Measurement of geometric dephasing using a superconducting qubit

A quantum system interacting with its environment is subject to dephasing, which ultimately destroys the information it holds. Here we use a superconducting qubit to experimentally show that this dephasing 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. It accompanies the evolution of any system in Hilbert space subjected to noise.ISSN:2041-172