Geometric phase with nonunitary evolution in presence of a quantum critical bath

F. M. CUCCHIETTI, J.-F. ZHANG, F. C. LOMBARDO, P. I. VILLAR AND R. LAFLAMME

PHYSICAL REVIEW LETTERS

AMER PHYSICAL SOC

Año: 2010 vol. 105 p. 240406 - 240410

0031-9007

Geometric phases, arising from cyclic evolutions in a curved parameter space, appear in a wealth of physical settings. Recently, and largely motivated by the need of an experimentally realistic definition for quantum computing applications, the quantum geometric phase was generalized to open systems. The definition takes a kinematical approach, with an initial state that is evolved cyclically but coupled to an environment—leading to a correction of the geometric phase with respect to the uncoupled case. We obtain this correction by measuring the nonunitary evolution of the reduced density matrix of a spin one-half coupled to an environment. In particular we are interested in baths near a quantum phase transition, which are known to induce strong decoherence. The experiments are done with a NMR quantum simulator, where we emulate qualitatively the influence of a critical environment using a simple one-qubit model.