D. Z. Rossatto

Two-photon quantum Rabi model with superconducting circuits

  1. S. Felicetti,
  2. D. Z. Rossatto,
  3. E. Rico,
  4. E. Solano,
  5. and P. Forn-Díaz
We propose a superconducting circuit to implement a two-photon quantum Rabi model in a solid-state device, where a qubit and a resonator are coupled by a two-photon interaction. We
analyze the input-output relations for this circuit in the strong coupling regime and find that fundamental quantum optical phenomena are qualitatively modified. For instance, two-photon interactions are shown to yield single- or two-photon blockade when a pumping field is either applied to the cavity mode or to the qubit, respectively. In addition, we derive an effective Hamiltonian for perturbative ultrastrong two-photon couplings in the dispersive regime, where two- photon interactions introduce a qubit-state-dependent Kerr term. Finally, we analyze the spectral collapse of the multi-qubit two-photon quantum Rabi model and find a scaling of the critical coupling with the number of qubits. Using realistic parameters with the circuit proposed, three qubits are sufficient to reach the collapse point.
arxiv pdf

Entangling polaritons via dynamical Casimir effect in circuit quantum electrodynamics

  1. D. Z. Rossatto,
  2. S. Felicetti,
  3. H. Eneriz,
  4. E. Rico,
  5. M. Sanz,
  6. and E. Solano
We investigate how the dynamical Casimir effect (DCE) can entangle quantum systems in different coupling regimes of circuit quantum electrodynamics, and show the robustness of such
entanglement generation against dissipative effects with current technology. We consider two qubit-resonator systems, which are coupled by a SQUID driven with an external magnetic field, and explore the entire range of coupling regimes between each qubit and its respective resonator. In this scheme, we derive a semianalytic explanation for the entanglement generation between both superconducting qubits when they are coupled to their resonators in the strong coupling (SC) regime. For the ultrastrong (USC) and deep strong coupling (DSC) regimes, we design feasible protocols to generate maximally-entangled polaritonic states.
arxiv pdf