Realization of Gapped Flat Band Models in Circuit QED

Alicia J. Kollár, Mattias Fitzpatrick, Andrew Houck

Won Chan Lee, Ali Fahimniya, Kellen O'Brien +5 more

Circuit QED systems provide an ideal platform for exploring the strong-coupling regime of multimode cavity QED. Here we present two new phenomena from multimode strong coupling: a circuit Lagrangian analysis which captures beyond tight-binding effects of strong photon-photon coupling and experimental observation of strong wave-mixing resonances in the qubit response. Our circuit analysis reveals qualitatively new features such as emergent band gaps, lifted degeneracies, broadened flat bands, and frequency-dependent hopping. Within the multimode photon environment, strong qubit-photon coupling in turn gives rise to multiphoton processes involving multiple normal modes. We demonstrate a strong four-wave-mixing process involving excitation of a qubit and simultaneous frequency conversion between modes. Notably, this wave-mixing process is dominated by localized flat-band modes of the photonic lattice, which exhibit the strongest coupling to the transmon qubit.

Matteo Biondi, Evert van Nieuwenburg, G. Blatter +2 more

We study the interplay of geometric frustration and interactions in a nonequilibrium photonic lattice system exhibiting a polariton flat band as described by a variant of the Jaynes-Cummings-Hubbard model. We show how to engineer strong photonic correlations in such a driven, dissipative system by quenching the kinetic energy through frustration. This produces an incompressible state of photons characterized by short-ranged crystalline order with period doubling. The latter manifests itself in strong spatial correlations, i.e., on-site and nearest-neighbor antibunching combined with extended density-wave oscillations at larger distances. We propose a state-of-the-art circuit QED realization of our system, which is tunable in situ.

Alicia J. Kollár, Mattias Fitzpatrick, Peter Sarnak +1 more

Frank Deppe, M. Mariantoni, Shiro Saito +4 more

Gui‐Lei Zhu, Xin-You Lü, Hamidreza Ramezani

We show the superradiant phase transition (SPT) can control the existence of flat band in an extended Dicke-Hubbard lattice [1].