Simple high-saturation-power quantum-limited rf-SQUID-array-based Josephson parametric amplifiers
Ryan Kaufman, Chenxu Liu, Katarina Cicak, Boris Mesits, Mingkang Xia, Chao Zhou, Maria Nowicki, José Aumentado, David Pekker, Michael Hatridge · Physical Review Applied · 2025
High-fidelity quantum nondemolition qubit measurement is critical to error correction and rapid qubit feedback in large-scale quantum computing. Maximizing high-fidelity dispersive readout in superconducting qubits commonly requires passing a short and strong pulse through the qubit's readout resonator, which is then processed by a sufficiently high bandwidth, high saturation power, and quantum-limited amplifier. We have developed an amplifier design pipeline that combines time-domain simulation of the untruncated device Hamiltonian, fabrication constraints, and maximization of saturation power. We have realized an amplifier based on a modified trilayer (Nb-Al-${\mathrm{Al}\mathrm{O}}_{x}$-Nb) fabrication suite at NIST, which utilizes an array of 25 rf superconducting quantum interference devices embedded within a low-$Q$ resonator powered by a high-power voltage pump delivered via a diplexer on the signal port. We show that, despite the intensity of the pump, the device is quantum efficient and capable of high-fidelity measurement limited by state transitions in the transmon. We present experimental data demonstrating up to $\ensuremath{-}91.2\phantom{\rule{0.2em}{0ex}}\mathrm{dBm}$ input saturation power with 20-$dB$ gain, up to 28-MHz instantaneous bandwidth, and phase-preserving qubit measurements with $62\mathrm{%}$ quantum efficiency.