Superconducting qubits are a leading platform for scalable quantum computing and quantum error correction. One feature of this platform is the ability to perform projective measurements orders of magnitude more quickly than qubit decoherence times. Such measurements are enabled by the use of quantum-limited parametric amplifiers in conjunction with ferrite circulators - magnetic devices which provide isolation from noise and decoherence due to amplifier backaction. Because these non-reciprocal elements have limited performance and are not easily integrated on-chip, it has been a longstanding goal to replace them with a scalable alternative. Here, we demonstrate a solution to this problem by using a superconducting switch to control the coupling between a qubit and amplifier. Doing so, we measure a transmon qubit using a single, chip-scale device to provide both parametric amplification and isolation from the bulk of amplifier backaction. This measurement is also fast, high fidelity, and has 70% efficiency, comparable to the best that has been reported in any superconducting qubit measurement. As such, this work constitutes a high-quality platform for the scalable measurement of superconducting qubits.

Eric I. Rosenthal is a Ph.D. student at the University of Colorado, Boulder, under the advisement of Professor Konrad Lehnert at JILA. He received his B.A. and M.S. in physics from the University of Pennsylvania in 2015 and is expected to receive his Ph.D. in physics in the spring of 2021. His research interest is in the advancement of quantum information technology using superconducting systems. In particular, his research has involved the development of superconducting switches, amplifiers, and non-reciprocal devices to improve the measurement of superconducting qubits.