Bandwidth Enhancement of Weakly Coupled Josephson Parametric Amplifiers with Bandwidth Expanding circuit by Resonance Detuning

In superconducting qubit-based quantum computing circuits, multiplexed readout is used to measure several qubits via a single transmission channel. Achieving optimal measurement performance in this framework requires a broadband quantum amplifier that covers the frequency range of the qubits. The Josephson Traveling Wave Parametric Amplifier (JTWPA) is widely utilized, providing the necessary broadband amplification. To minimize the complexity of optimizing thousands of Josephson junctions, the band amplification of a JPA has been explored by employing an auxiliary resonator[1] of which resonant frequency matches the JPA's effective resonance. In practical implementations, achieving precise frequency matching between these components faces significant challenges so that it is crucial to understand the tolerance for detuning. In this study, we investigate the effects of resonance detuning on bandwidth enhancement and signal gain. In addition, we optimize JPA performance based on this context.