High Fidelity Measurement of Single and Multi-qubit Superconducting Quantum Circuits*

Fast, high fidelity measurements of multi-qubit devices are crucial for quantum error correction and fault tolerant quantum computation. In superconducting qubits, dispersive circuit-QED readout using a Josephson parametric amplifier (JPA) has been the common approach to obtain high-fidelity QND measurement. A standard way to improve speed and/or measurement fidelity is to use higher measurement power. However, that often leads to unwanted transitions both within and outside of the computational subspace, resulting in reduced fidelity. Moreover, this problem can get exacerbated when performing joint readout of multiple qubits. Using the 3D circuit-QED architecture, we explore the optimization of various parameters like measurement power, qubit-cavity coupling, qubit-cavity detuning to enhance measurement fidelity in both single and multi-qubit circuits. We will also discuss the optimization of the JPA so that it can handle the larger measurement signals needed for high fidelity.