Cross coupling of a solid-state qubit to an input signal due to multiplexed dispersive readout

The integration, scale up and multiplexing arrays of superconducting qubits in quantum circuits are one of 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 planar Xmon-type qubit, connected to a common coplanar transmission line. We find that the qubit energy spectrum modifies in the presence of an additional exciting signal at the neighbour resonators fundamental frequency. We attribute the origin of this effect to electromagnetic field propagating through the common ground plane, which changes the qubits characteristics. Our finding may be useful for the development of scalable superconducting quantum integrated circuits with arrays of multiplexed/coupled qubits for applications in superconducting quantum processing and computing