Flux noise in a magnetic field

Abstract

Quantum computers promise to speedup certain problems that conventional computers take too long to solve. These problems include nitrogen fixation, quantum chemistry and prime factorization. One promising platform for the implementation of a practical quantum computer are superconducting qubits in combination with circuit quantum electrodynamics (CQED). However, preventing the large scale application of quantum computers is noise and decoherence, limiting the size and depth of a quantum algorithm. Particularly flux noise plagues tunable qubits, limiting their flexibility and fidelity.
One of the most used and advanced qubits is the transmon, a LC oscillator with a capacitor in parallel with a non-linear inductive element called a Josephson junction. Conventionally, the Josephson junction is formed with an Al-AlO-Al tunnel barrier. Contrastingly, here we use a InAs nanowire covered with a thin layer of Al forming a S-N-S Josephson junction. Crucially, this junction is magnetic field compatible, allowing us to do experiments with cQED in a magnetic field. Additionally this junction is voltage-tunable, opening the path towards lower distortion voltage gates. This thesis focusses on measuring the flux noise in a magnetic field using the nanowire Josephson junction. To that end, the chapters address the necessary conditions to achieve this goal....