Broadband Parametric Amplification Using Impedance Engineering*

Josephson junction based parametric amplifiers have become a crucial component of cryogenic quantum measurement circuitry and have enabled recent studies of quantum jumps, squeezed microwave radiation, qubit state tracking, quantum feedback, quantum error detection, and more. This has been possible because these amplifiers provide sufficient gain (~ 20 dB) and operate close to the quantum noise limit for amplification, resulting in excellent signal to noise ratio in various experiments. Typically, devices which use one or two oscillator modes provide 5 – 50 MHz of instantaneous bandwidth, while those based on non-linear transmission lines can provide few GHz of bandwidth. Recently, we demonstrated a simple impedance engineering technique to enhance the bandwidth of a single mode Josephson Parametric Amplifier (JPA) beyond the standard gain-bandwidth product. In this talk, I will first describe this technique and present results on a device where we obtained 640 MHz of bandwidth with 20 dB gain and near quantum limited noise performance. I will then discuss how to generalize this technique to other parametric amplifier designs with a particular focus on Josephson Parametric Converter (JPC) based amplifiers. I will present theoretical and experimental results on bandwidth enhanced JPC based amplifiers, working not only in the standard reflection mode but also in the transmission mode with non-reciprocal gain. Finally, I will discuss possible methods to improve saturation properties of such devices in order to make a practical amplifier useful for quantum measurements.