Cross Coupling of a Solid-State Qubit to an Input Signal due to Multiplexed Dispersive Readout

Abstract

The integration, scale-up, and multiplexing arrays of superconducting qubits in quantum circuits are the main challenges of superconducting quantum technology. Here we experimentally investigate the solid-state qubit multiplexing readout scheme, containing coplanar quarter-wavelength resonators coupled with a planar Xmon-type qubit, connected to a common coplanar transmission line. We find that the qubit energy spectrum is modified in the presence of an additional exciting signal at the fundamental frequency of the neighboring resonators. We attribute the origin of this effect to the electromagnetic field propagating through the common ground plane, which changes the qubit's characteristics. Our finding may be useful for the development of scalable superconducting quantum integrated circuits with arrays of multiplexed or coupled qubits for applications in superconducting quantum processing and computing.