Practical, high dynamic range parametric amplification with RF SQUID arrays

High-fidelity qubit readout, which is critical for error correction in large-scale quantum computers, requires a short and strong pulse transiting the qubit’s measurement mode which is then processed by a necessarily high bandwidth, high saturation power, quantum-limited amplifier. Larger quantum processors additionally employ frequency multiplexing, expanding the required bandwidth by the number of channels to be amplified. Resonant Josephson parametric amplifiers (JPAs), weakly nonlinear harmonic oscillators that use Josephson junctions as nonlinear inductors, have been workhorses in enabling scaling to this point, but they suffer from limitations in dynamic range, bandwidth, and operation with commercial circulators or isolators that are straining their ability to further support scaling readout in ever-larger processors. This thesis shows several methods to combat these shortcomings in resonant JPAs. First, we show data from high saturation-power JPAs that utilize radio frequency superconducting quantum interference device (rf SQUID) arrays to carefully control the nonlinearity of the amplifier, increasing the saturation power while still maintaining their lauded quantum efficiency. With the success of this collaboration with scientists at the Advanced Microwave Photonics group at NIST Boulder, we discuss time-domain qubit measurement with these devices. Here we detail the nanosecond-to-nanosecond dynamics of a qubit measurement, exploring how discrete samples of a qubit readout signal processed by a parametric amplifier can best be weighted and integrated to extract the maximum amount of information possible, especially in the context of high-power qubit readout. Lastly, we address another limitation of reflection Josephson parametric amplifiers: their instantaneous bandwidth. Using similar rf SQUID designs, we show how to tune the equations of motion of a multi-pole device to create a broadband response, allowing for an increase in bandwidth from the 10 MHz scale to the 100 MHz or even 1 GHz scale. Additionally, we will discuss how the simulation methods used for the design of high saturation power devices can extend to these broadened devices. Following this design process, we will detail the fabrication of more devices at NIST as well as measurements of a similar broadband Josephson parametric amplifier.