Abstract: A Traveling Wave Parametric Amplifier (TWPA) transmission line with improved bandwidth includes one or more unit cell. Each unit cell includes a capacitor to a ground and a Josephson junction in series configured to provide inductance and non-linearity. One or more dispersion resonator is coupled to the transmission line. The dispersion resonator is configured to (i) use a first harmonic mode of the resonator for resonant phase matching in the transmission line and (ii) prevent a second mode of the resonator from interacting with an intermodulation product of the transmission line.

Abstract: A system resets leakage states of a superconducting qubit to a qubit subspace by using a dedicated electrical circuit on a timescale faster than a natural decay process. One system comprises a qubit including a qubit transition frequency and multiple qubit leakage transition frequencies; and a filter circuit coupled to the qubit for leakage mitigation based on the qubit frequency and the multiple qubit leakage transition frequencies, wherein the filter circuit causes dissipation at the leakage transition frequencies while isolating the qubit transition frequency. Another system comprises a qubit including a qubit transition frequency and multiple qubit leakage transition frequencies; and a tunable dissipative cavity circuit coupled to the qubit for leakage mitigation based on the qubit frequency and the multiple qubit leakage transition frequencies, wherein the tunable dissipative cavity circuit causes the leakage transition frequencies to dissipate while isolating the qubit transition frequency.