Crosstalk between transmons during multiqubit readout.

High-fidelity readout of the state of a qubit is an indispensable part of a quantum computer. Progress in implementation of controllable large-scale quantum computers calls for implementation of a scalable high fidelity multi- qubit readout scheme. In a typical transmon superconducting qubit, measurement is implemented by applying a microwave drive to a readout resonator dispersively coupled to the qubit. Recent experiments demonstrated that despite detuning between the drive and qubit frequencies, measurement renormalizes the spectrum of the combined qubit-resonator system and induces cross-talk between nearby qubits resulting in reduced fidelity. A starting point is to develop an optimized readout scheme for a two-qubit system. With both numerical and approximate analytical analysis, we were able to identify the source of spurious transitions and explore qubit parameters optimal for scalable multi-qubit readout scheme.