Fabrication of high-impedance Josephson junction chains for novel quantum devices

High-impedance superconducting transmission lines and high-inductance lumped circuit elements are useful for a range of quantum information experiments, from improving the coherence of superconducting qubits to simulating exotic many-body Hamiltonians. Conventional electromagnetic structures are generally limited by the vacuum impedance with a relatively low value of 377.0 Ohm. By contrast, wires made of Josephson tunnel junction chains have a large kinetic inductance associated with Cooper pair tunneling and thus are not limited by the properties of the low-impedance vacuum. Here we present fabrication of compact linear chains involving up to 30,000+ Al/AlOx/Al tunnel junctions utilizing the Dolan bridge technique and double-angle shadow evaporation. Shorter chains are used to create conventional fluxonium qubits with coherence times exceeding 100 microseconds. Longer chains demonstrate propagating microwaves with a wave impedance exceeding the value of von Klitzing resistance, 26.5 kOhm. Ultra-tight junction packing is demonstrated to achieve inductances above 1 uH with high self-resonance frequencies, useful for exploring protected qubit designs.