Models of light-matter interaction with natural atoms typically invoke the dipole approximation, wherein atoms are treated as point-like objects compared with the wavelength of their resonant driving fields. In this talk, William D. Oliver of MIT will present a demonstration of “giant artificial atoms” realized with superconducting qubits in a waveguide QED architecture. The superconducting qubits couple to the waveguide at multiple, well-separated locations. In this configuration, the dipole approximation no longer holds, and the giant atom may quantum mechanically self-interfere.

This system enables tunable qubit-waveguide couplings with large on-off ratios and a coupling spectrum that can be engineered by design. Multiple, interleaved qubits in this architecture can be switched between protected and emissive configurations, while retaining qubit-qubit interactions mediated by the waveguide. Using this architecture, we generate a Bell state with 94% fidelity, despite both qubits being strongly coupled to the waveguide.

Time permitting, Oliver will also discuss recent advances in 3D integration of superconducting quantum circuits.