Witnessing topological Weyl semimetal phase in a minimal circuit-QED lattice

We present an experimentally feasible protocol to mimic topological Weyl semimetal phase in a small one-dimensional circuit-QED lattice. By modulating the photon hopping rates and on-site photon frequencies in parametric spaces, we demonstrate that the momentum space of this one-dimensional lattice model can be artificially mapped to three dimensions accompanied by the emergence of topological Weyl semimetal phase. Furthermore, via a lattice-based cavity input-output process, we show that all the essential topological features of Weyl semimetal phase, including the topological charges associated with Weyl points and the photonic surface states connecting the Weyl points as open arcs, can be unambiguously detected in a circuit with four dissipative resonators by measuring the reflection spectra. These remarkable features may open up a new prospect for simulating topological phases with well-controlled small quantum artificial lattices.