Design and fabrication of a high frequency superconducting microwave cavity

Pascal Febvre

Thomas J. Clark

This thesis describes the design, fabrication, and characterization of 3D superconducting microwave cavities for two applications. It first describes a cryogenically compatible microwave filter that is able to tune its resonant frequency by an unprecedented 5 GHz via deformation caused by a a helium pressure vessel. Then, it describes a novel microwave optomechanics device where such a cavity is coupled to an aluminized SiN membrane. It demonstrates that this device can be back-action cooled from the 450 mK base temperature of the cryostat down to 160 mK.

E. Carlsson

Chan U Lei, Lev Krayzman, Suhas Ganjam +2 more

Low-loss cavities are important in building high-coherence superconducting quantum computers. Generating high-quality joints between parts is crucial for the realization of a scalable quantum computer using the circuit quantum electrodynamics (cQED) framework. In this paper, we adapt the technique of indium bump bonding to cQED to realize high-quality superconducting microwave joints between chips. We use this technique to fabricate compact superconducting cavities in the multilayer microwave integrated quantum circuit (MMIQC) architecture and achieve single photon quality factors over 300 × 106 or single-photon lifetimes approaching 5 ms. To quantify the performance of the resulting seam, we fabricate microwave stripline resonators in multiple sections connected by different numbers of bonds, resulting in a wide range of seam admittances. The measured quality factors combined with the designed seam admittances allow us to bound the conductance of the seam at gseam≥2×1010/(Ω m). Such a conductance should enable the construction of micromachined superconducting cavities with a quality factor of at least a billion. These results demonstrate the capability to construct very high-quality microwave structures within the MMIQC architecture.

C.J. Ballard, Rangga P. Budoyo, Kristen Voigt +4 more

Eric T. Holland, Yaniv Jacob Rosen, Nicholas Materise +7 more

Investigations into the microwave surface impedance of superconducting resonators have led to the development of single photon counters that rely on kinetic inductance for their operation, while concurrent progress in additive manufacturing, “3D printing,” opens up a previously inaccessible design space for waveguide resonators. In this manuscript, we present results from the synthesis of these two technologies in a titanium, aluminum, vanadium (Ti-6Al-4V) superconducting radio frequency resonator which exploits a design unattainable through conventional fabrication means. We find that Ti-6Al-4V has two distinct superconducting transition temperatures observable in heat capacity measurements. The higher transition temperature is in agreement with DC resistance measurements, while the lower transition temperature, not previously known in the literature, is consistent with the observed temperature dependence of the superconducting microwave surface impedance. From the surface reactance, we extract a London penetration depth of 8 ± 3 μm—roughly an order of magnitude larger than other titanium alloys and several orders of magnitude larger than other conventional elemental superconductors.