Gyrators, quantum wormholes, and exceptional points

The symbiosis of ideas between the communities of high energy and condensed matter physics has a long and fruitful tradition, be it the elusive Majorana fermion, BCS theory serving as the blueprint for the Higgs mechanism, or the plethora of relativistic effects in graphene and Weyl semimetals. The condensed matter viewpoint helped in particular to elucidate some of the more obscure features of Hawking radiation, most prominently in ultra-cold atoms. However, in order to generate apparent event horizons, it seemed up until now indispensable to keep the system in a continuously driven state – rendering black holes only meaningful for open systems. We here propose for the first time a pure circuit-QED realization of a quantum wormhole, with gyrators and Josephson junctions as the main protagonists. While the emerging Hawking radiation is similar to other previously studied systems, the circuit realization adds one important new ingredient: quantum fields that are compact due to charge quantization. This allows for creating the necessary "overtilt" of the light cone by using a single quantum quench, but otherwise letting the system evolve autonomously. In addition, we are able to understand the generation of the radiation in terms of exceptional points, which here emerge somewhat unexpectedly, to describe the transient dynamics of a closed system instead of the usual open system. We thus aim to show that superconducting circuits provide a novel and highly accessible testbed for quantum gravitational effects.