Experimental width shift distribution: a test of nonorthogonality for local and global perturbations

Abstract : The change of resonance widths in an open system under a perturbation of its interior was recently introduced by Fyodorov and Savin [PRL 108, 184101 (2012)] as a sensitive indicator of the nonorthogonality of resonance states. We experimentally study universal statistics of this quantity in weakly open two-dimensional microwave cavities and reverberation chambers realizing scalar and electromagnetic vector fields, respectively. We consider global as well as local perturbations, and also extend the theory to treat the latter case. The impact of the perturbation type on the width shift distribution is increasing with the number of open channels. We compare the theory to experimental results for one and two attached channels and to numerical simulations with higher channel numbers, observing a good agreement in all cases.