Entanglement of Two Superconducting Qubits in a Waveguide Cavity via Monochromatic Two-Photon Excitation

S. Poletto; Jay M. Gambetta; Seth T. Merkel; John A. Smolin; Jerry M. Chow; A. D. Córcoles; George A. Keefe; Mary B. Rothwell; J. R. Rozen; D. W. Abraham; Chad Rigetti; M. Steffen

doi:10.1103/PhysRevLett.109.240505

Entanglement of Two Superconducting Qubits in a Waveguide Cavity via Monochromatic Two-Photon Excitation

S. Poletto, Jay M. Gambetta, Seth T. Merkel, John A. Smolin, Jerry M. Chow, A. D. Córcoles, George A. Keefe, Mary B. Rothwell, J. R. Rozen, D. W. Abraham, Chad Rigetti, M. Steffen

DOI 10.1103/PhysRevLett.109.240505 · Physical Review Letters

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Abstract

We report a system where fixed interactions between noncomputational levels make bright the otherwise forbidden two-photon |00⟩→|11⟩ transition. The system is formed by hand selection and assembly of two discrete component transmon-style superconducting qubits inside a rectangular microwave cavity. The application of a monochromatic drive tuned to this transition induces two-photon Rabi-like oscillations between the ground and doubly excited states via the Bell basis. The system therefore allows all-microwave two-qubit universal control with the same techniques and hardware required for single qubit control. We report Ramsey-like and spin echo sequences with the generated Bell states, and measure a two-qubit gate fidelity of Fg=90% (unconstrained) and 86% (maximum likelihood estimator).