Nonlinear superconducting metamaterials

Superconducting circuits are among the most suitable and successful candidates for the realization of a qubit. These circuits include one specific nonlinear superconducting element, the Josephson tunnel junction. While the Josephson junction has been meticulously researched leading to several breakthroughs and realizations, its dual counterpart the ‘quantum-phase slip (QPS) center’ remains poorly understood. In this superconducting center, the superconducting phase fluctuates (it 'slips') and gives rise to different energy states. Moreover, by tuning the QPS-rate different energy states can be coupled, creating a two-level system or qubit. Mooij and Harmans suggested in 2005 that a small nanowire embedded in a superconducting loop could be used as a phase-slip qubit. However, a quantitative description of how different macroscopic variables determine the QPS-rate, and therefore the behavior of the qubit, is lacking. In this proposal, I aim to realize a Molybdenum Germanium phase-slip qubit and determine the QPS-rate from the qubit energy splitting. This I will achieve using nondestructive high frequency measurements at cryogenic temperatures. As such I will be able to gain new insights on the effect of macroscopic parameters on the QPS-rate. Moreover, the quality of the qubit (e.g. lifetimes) will be determined. These combined experiments will pave the road for QPS-based devices.