Flux-based superconducting quantum computing

Terry P. Orlando, Seth Lloyd, Leonid S Levitov +6 more

Nobuyuki Yoshikawa

The recent rapid increase in the scale of superconducting quantum computing systems greatly increases the demand for qubit control by digital circuits operating at qubit temperatures. In this paper, superconducting digital circuits, such as single-flux quantum and adiabatic quantum flux parametron circuits are described, that are promising candidates for this purpose. After estimating their energy consumption and speed, a conceptual overview of the superconducting electronics for controlling a multiple-qubit system is provided, as well as some of its component circuits.

Michael Wulf, Thomas Ohki, M. J. Feldman

We present and demonstrate experimentally a persistent-current bias loop that is intended to provide an on-chip stable dc magnetic field to flux-bias the flux qubits in a superconducting quantum computer. The bias loop is initialized to approximately the desired persistent current and then the external source is disengaged; this procedure prevents the fluctuations in the bias sources from causing decoherence in the qubit.

Nakamura Yasunobu

Chuck Easttom

Estefani Marchiori, L. Ceccarelli, N. Rossi +6 more

We use a scanning superconducting quantum interference device (SQUID) to image the magnetic flux produced by a superconducting device designed for quantum computing. The nanometer-scale SQUID-on-tip probe reveals the flow of superconducting current through the circuit as well as the locations of trapped magnetic flux. In particular, maps of current flowing out of a flux-control line in the vicinity of a qubit show how these elements are coupled, providing insight on how to optimize qubit control.