Non-reciprocal devices such as circulators, which route signals in a preferred direction, are important components of quantum technology. Chen-How Huang and Tero Heikkilä of QMAT's Condensed Matter Theory group at the University of Jyväskylä present a symmetry-based framework that classifies the non-reciprocal responses of multiterminal ring devices.

Modelling the device as a ring with a preferred direction of flow on each bond, they show for a three-terminal ring that non-reciprocity requires breaking both time-reversal and inversion symmetry, and that the remaining geometric symmetry decides which responses can be observed: in an isosceles triangle, only two types of circulation are allowed. A toy model of three quantum dots coupled to superconductors confirms the predictions and behaves as a reactive quantum circulator.

The preprint has not yet been peer reviewed.

Image: QMAT