Tangled Circuits: Characterizing Errors in Experimental Superconducting Quantum Processors

Abstract

As progress is made towards the first generation of error-corrected quantum computers based on physical quantum bits (qubits), researchers require robust techniques for designing, operating, and characterizing coupled multi-qubit systems in the laboratory, and for understanding the errors which arise in such systems. This doctoral thesis is structured around three interconnected bodies of technical work which span the field of superconducting quantum information science. In Part II, we consider the design, simulation, and measurement of high coherence quantum bits mediated by tunable coupler elements, a fundamental building block of extensible quantum processors based on superconducting Josephson circuits. In Part III, we consider the calibration of high fidelity single- and two-qubit gate operations, and we show how these operations were harnessed to perform a demonstration of Density Matrix Exponentiation, a deep Trotter-like quantum algorithm. In Part IV, we consider an array of techniques for the characterization, verification, and validation of quantum computing hardware, and we put forth a novel quantum characterization technique for reconstructing the dynamic loss channels of multi-qubit systems, known as Lindblad tomography. Framing the dissertation on each end, Parts I and V offer a complementary account of quantum computing grounded in feminist science and technology studies, situating quantum computing as a historical, social, and material-semiotic enterprise, complicating the narrative of progress which animates our work in the laboratory.