Superconducting Quarter-Wave Resonator for Quantum Information Systems

Computers based on quantum-mechanical phenomena, if realized, could disrupt many computationally intense fields of science, including high-energy physics.Complex physical problems require powerful machines consisting of many qubits arrayed in a high-speed network.High quality factor superconducting RF resonators coupled to Josephson junctions are one of the most promising solutions.Niobium resonators used in particle accelerators can reach Q-factors of the level of 1011.However, their designs were not optimized for hosting qubits.In response to this problem, RadiaBeam has designed an SRF cavity for quantum computers based on a quarter-wave resonator (QWR) with optimized shape, operating at the 6 GHz.A QWR is an attractive choice for the simplicity of its integration with the Josephson junction, which can be placed near the central conductor to allow higher coupling strength, and the feasibility of scaling it to multi-qubit system.In Phase I, we optimized the shape of the QWR and improved its geometric factor (proportional to Q-factor) by at least a factor of two.We designed and fabricated two resonators out of high purity niobium, with optimized and non-optimized shapes, and the test stand, including electrical and thermal couplers and magnetic shielding.The resonators were chemically etched at Argonne National Laboratory and delivered to the University of Chicago, where they were tested at 10 mK temperature and with single photon power levels.The Q-factor measured with several methods demonstrated clear advantage of the optimized shape.In Phase II of the project we will increase the absolute values of the Q-factor by improving magnetic and IR shielding, vacuum performance, surface finish, as well as by applying chemical and electrical polishing and baking.We will explore different materials and frequencies, and finally build and test the resonator with an integrated Josephson junction.The emerging discipline of quantum computing, although presently in its infancy, is rapidly growing and has an explosive commercial potential.Upon successful completion of the Phase II work, RadiaBeam would be in an excellent position to establish its presence as a supplier of components for this growing field by leveraging the SRF technology developed in this project.