Partial time-reversal invariance violation in a flat, superconducting microwave cavity with the shape of a chaotic Africa billiard

TL;DR

This study demonstrates partial violation of time-reversal symmetry in a superconducting microwave billiard with chaotic geometry, enabling precise measurement of T invariance violation through resonance analysis.

Contribution

It presents the first experimental realization of a superconducting microwave billiard with controlled partial T invariance violation and derives an analytical expression for resonance strength distribution.

Findings

Partial T invariance violation detected via resonance properties.

Superconductivity enabled accurate resonance frequency and width measurements.

Analytical model for resonance strength distribution across T violation levels.

Abstract

We report on the experimental realization of a flat, superconducting microwave resonator, a microwave billiard, with partially violated time-reversal (T ) invariance, induced by inserting a ferrite into the cavity and magnetizing it with an external magnetic field perpendicular to the resonator plane. In order to prevent its expulsion caused by the Meissner-Ochsenfeld effect we used a cavity of which the top and bottom plate were made from niobium, a superconductor of type II, and cooled it down to liquid-helium temperature T LHe ' 4 K. The Cavity had the shape of a chaotic Afrivca billiard. Superconductivity rendered possible the accurate determination of complete sequences of the resonance frequencies and of the widths and strengths of the resonances, an indispensable prerequisite for the unambiguous detection of T invariance violation, especially when it is only partially violated. This allows for the first time the precise specification of the size of T invariance violation from the fluctuation properties of the resonance frequencies and from the strength distribution, which actually depends sensitively on it and thus provides a most suitable measure. For this purpose we derived an analytical expression for the latter which is valid for isolated resonances in the range from no T invariance violation to complete violation.