A Traveling-Wave Parametric Amplifier and Converter

Abstract: High-fidelity qubit measurement is a critical element of all quantum computing architectures. In superconducting systems, qubits are typically measured by probing a readout resonator with a weak microwave tone which must be amplified before reaching the room temperature electronics. Superconducting parametric amplifiers have been widely adopted as the first amplifier in the chain, primarily because of their low noise performance, approaching the quantum limit. However, they require isolators and circulators to route signals up the measurement chain, as well as to protect qubits from amplified noise. While these commercial components are wideband and very simple to use, their intrinsic loss, size, and magnetic shielding requirements impact the overall measurement efficiency while also limiting prospects for scalable readout in large-scale superconducting quantum computers. Here we demonstrate a parametric amplifier that achieves both broadband forward amplification and backward isolation in a single, compact, non-magnetic circuit that could be integrated on chip with superconducting qubits. It relies on a nonlinear transmission line which supports traveling-wave parametric amplification of forward propagating signals, and isolation via frequency conversion of backward propagating signals. This kind of traveling-wave parametric amplifier and converter is poised to reduce the readout hardware overhead when scaling up the size of superconducting quantum computers.