Design of realistic switches for coupling superconducting solid-state qubits

TL;DR

This paper evaluates various coupling mechanisms for superconducting flux qubits, analyzing their strengths and decoherence effects, and proposes promising options like Josephson field effect transistors for improved quantum coherence.

Contribution

It provides a comparative analysis of coupling methods for flux qubits, highlighting the impact on decoherence and suggesting practical implementations with existing technology.

Findings

Subgap conductance induces additional decoherence.

Josephson field effect transistors are promising for coupling.

Magnetic junctions severely limit coherence.

Abstract

Superconducting flux qubits are a promising candidate for solid-state quantum computation. One of the reasons is that implementing a controlled coupling between the qubits appears to be relatively easy, if one uses tunable Josephson junctions. We evaluate possible coupling strengths and show, how much extra decoherence is induced by the subgap conductance of a tunable junction. In the light of these results, we evaluate several options of using intrinsically shunted junctions and show that based on available technology, Josephson field effect transistors and high-Tc junctions used as pi-shifters would be a good option, whereas the use of magnetic junctions as pi-shifters severely limits quantum coherence.