Experimental investigation of distributions of the off-diagonal elements of the scattering and the Wigner's $\hat K$ matrices for networks with broken time reversal invariance

TL;DR

This paper experimentally investigates the distributions of off-diagonal elements of scattering and Wigner's K matrices in microwave networks with broken time-reversal symmetry, confirming theoretical predictions from random matrix theory.

Contribution

The study provides the first experimental verification of the distributions of off-diagonal elements of the Wigner's K matrix in systems with broken time-reversal invariance, aligning with recent RMT predictions.

Findings

Experimental distributions match theoretical RMT predictions

Good agreement observed for both scattering and Wigner's K matrices

Losses included as tunable parameters in the models

Abstract

We present an extensive experimental study of the distributions of the real and imaginary parts of the off-diagonal elements of the scattering matrix $\hat S$ and the Wigner's reaction $\hat K$-matrix for open microwave networks with broken time ($T$) reversal invariance. Microwave Faraday circulators were applied in order to break $T$-invariance. The experimental distributions of the real and imaginary parts of the off-diagonal entries of the scattering matrix $\hat S$ are compared with the theoretical predictions from the supersymmetry random matrix theory [A. Nock, S. Kumar, H.-J. Sommers, and T. Guhr, Annals of Physics {\bf 342}, 103-132 (2014)]. Furthermore, we show that the experimental results are in very good agreement with the recent predictions for the distributions of the real and imaginary parts of the off-diagonal elements of the Wigner's reaction $\hat K$-matrix obtained within the framework of the Gaussian unitary ensemble of random matrix theory (RMT) [S. B. Fedeli and Y. V. Fyodorov, J. Phys. A: Math. Theor. {\bf 53}, 165701 (2020)]. Both theories include losses as tunable parameters and are therefore well adapted to the experimental verification.