Simulation and Measurement of Simultaneous Gain and Isolation in Kinetic Inductance Traveling Wave Parametric Amplifiers

Parametric amplifiers (PAs) permit near-quantum-limited (nQL) noise levels but lack the directionality of semiconducting amplifiers (HEMTs). Without circulators at the PA output, backacting noise from higher temperatures spoils realization of nQL amplification. Commercial ferrite circulators are bulky, lossy, and magnetic – mandating a need for compact and non-magnetic solutions in scaled quantum systems.

Isolation via frequency conversion in PAs is a viable solution. The intrinsic wideband and nonreciprocal nature of traveling wave PAs (TWPAs) enables both nQL amplification and isolation over gigahertz bandwidths. Indeed, Josephson TWPAs have achieved over 30 dB of isolation over nearly 1 GHz [1]. However, JTWPAs are magnetically-sensitive and struggle to achieve dynamic ranges sufficient for high multiplexing factors. Alternatively, kinetic inductance TWPAs (KTWPAs) are resilient to Tesla-scale fields [2] and feature higher dynamic ranges.

We present directional amplification in a KTWPA by measuring isolation of more than 20 dB over bandwidths of 1–2 GHz. Devices are modeled using a multi-mode coupled mode equation solver, twpasolver [3], which supports simultaneous amplification and frequency conversion for forward and backward propagating modes – as well as loss and phase-mismatch-induced gain ripple. Coupled with demonstrations of added noise below 1.5 quanta in circulator-laden amplifier chains [4] directional KTWPAs are promising candidates for demanding readout systems.