Nb-based Josephson parametric amplifier for superconducting qubit measurement

We report a fabrication process and characterization of the Josephson parametric amplifier (JPA) for the single-shot quantum state measurement of superconducting multiqubit system. The device is prepared using Nb film as its base layer, which is convenient in the sample patterning process like e-beam lithography and film etching. Our results show that the JPA has a bandwidth up to 600 MHz with gain above 15 dB and noise temperature approaching the quantum limit. The qubit state differentiation measurements demonstrate the signal-to-noise ratio around 3 and the readout fidelity above 97% and 91% for the ground and first-excited states, respectively. (paper)