Quantum Noise Limited Nondegenerate Josephson Parametric Amplifier with Nb/AlOx/Nb Junctions for Qubit Readout

Over the last two decades, the superconducting qubits have become a promising and rapidly growing area of research. However, there are specific challenges when working with such a delicate system. One of them is the qubit state readout. Since a very small signal (of the order of 1 photon) is used for the readout, its detection is challenging and it requires low-noise cryogenic amplifiers working in the 3–12 GHz frequency range. Josephson parametric amplifiers (JPAs) are one of the most studied and developed candidates. Currently, several JPA designs offer low noise performance and instantaneous bandwidth from tens of MHz to several GHz; they are also becoming an integral part of circuit quantum electrodynamics (cQED) setups. In the current work, results are presented of the measurements of a JPA made of a coplanar waveguide with an array of three SQUIDs. Nondegenerate amplification and an amplifier added noise being close to the quantum limit are demonstrated.