Fractional Josephson effect induced by weak measurement

The fractional Josephson effect is commonly directly linked to the presence of Majorana- and parafermions, which are important candidates to implement (universally) protected quantum gates in superconducting quantum hardware. However, these exotic particles still seem notoriously challenging to realize in experiment, and difficult to unambiguously identify via transport measurements. Moreover, a proper understanding of the topological transport properties requires a generalization to an open quantum system context.

Here, we study a standard quantum dot in proximity to two conventional superconducting contacts, including a weak transport measurement and a nonequilibrium quasiparticle source. The non-hermitian system dynamics are analysed by means of exceptional points, leading to a braiding of the complex eigenspectrum. Based on this analysis, we show that this system exhibits an open system version of a fractional Josephson effect, in spite of using only conventional materials.