Observation of the ground-state-geometric phase in a Heisenberg XY model

Abstract

Geometric phases play a central role in a variety of quantum phenomena, especially in condensed matter physics. Recently, it was shown that this fundamental concept exhibits a connection to quantum phase transitions where the system undergoes a qualitative change in the ground state when a control parameter in its Hamiltonian is varied. Here we report the first experimental study using the geometric phase as a topological test of quantum transitions of the ground state in a Heisenberg XY spin model. Using NMR interferometry, we measure the geometric phase for different adiabatic circuits that do not pass through points of degeneracy.

manuscript (4 pages, 3 figures) + supporting online material (6 pages + 7 figures), to be published in Phys. Rev. Lett. (2010)