Abstract: Superconducting quantum processers often rely on strong drives acting on qubits or couplers to implement off-resonant processes we refer to as parametric interactions. In some cases, these can be utilized to actuate gates such as the “subharmonic” single-qubit gate or an iSWAP gate between two qubits mutually connected to a coupler. However, these drives can also induce spurious excitations, setting an upper limit on the rate, and hence fidelity, of these operations. When the applied drive is well below the resonance frequency of the qubit or coupler, these unwanted excitations arise due to strong hybridization of many energy levels both inside and outside the potential well which eventually subsumes the ground state. For transmons, we show that this effect is captured in both numerical simulations of the full driven Hamiltonian and the Floquet spectrum, and that we can use the ac-Stark shift and subharmonic gate speed as benchmarks for the rate of four-wave parametric interactions. The excellent correspondence between simulation and experiment for transmons with similar frequency and varying anharmonicity gives insight to which designs are most resilient against unwanted excitations and allows us to predict and design devices that are optimal for different parametric processes.
Bio: Jake received his PhD from The Ohio State University where he studied surface magnetic textures using STM. He joined the Hatlab in August of 2022 and has worked on various cQED experiments across the lab, especially improving coherence in tantalum transmons and the effects of strong drives on transmons and parametric couplers. Outside of the lab, Jake is an avid golfer and enjoys experimenting on the best methods for brewing a cup of coffee.