Digital Control of Superconducting Fluxonium Qubits

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Two of the main challenges facing the development of superconducting quantum computers in the coming years will be (i) their limited coherence time and (ii) their scalability. This PhD aims to combine two state-of-the-art technologies to realise an architecture that mitigates both of these problems. The first problem of coherence time is addressed by utilising the fluxonium qubit (quantum bit). These qubits have been shown to provide much longer coherence times than the superconducting qubits that currently dominate the industry. The second issue, scalability, is a problem for superconducting qubits because, currently, each qubit requires significant experimental overhead to control, measure and readout the quantum information. This cannot be applied to the quantum computers that utilise thousands or millions of qubits. The problem of scalability is addressed by utilising digital single flux quantum (SFQ) control of superconducting qubits. This technology, being worked on by companies such as SEEQC, provides a promising path to control and measure qubits in the cryogenic environment in which superconducting qubits operate. This removes the significant overhead needed to use room temperature electronics to control cryogenic qubits. The project will involve the design and fabrication of a fluxonium qubit using readily available fabrication techniques. Upon successful fabrication, the aim is to couple this fluxonium qubit to an SFQ control chip provided by SEEQC to demonstrate the coherent control of a single fluxonium qubit. The successful combination of these technologies provides the building blocks for a high coherence and very scalable superconducting quantum computer.