Toolbox for Quantum Computing with Spin Qubits

Overall aims and objectives: The objective of the project is to further develop the toolbox for quantum information processing using real-time signal processing based on field-programmable gate arrays (FPGA) in a collaboration between University College London (UCL) and industry partner Zurich Instruments (ZI). New functionalities will be added to the toolbox which will be both software (regression) tested at ZI and in a lab environment at UCL using quantum hardware that consists of spin qubits defined in carbon nanotube quantum dots. The ultimate aim of the project is to demonstrate measurement-based entanglement of two spin qubits using the developed functionalities.

Outline of the Project: Months 0-10: The student will start the studentship at UCL. During the first four months the student will receive training on relevant experimental techniques - such as radio-frequency reflectometry - and physical concepts important for the project such as quantum science and technologies. This will be followed by a placement at Zurich Instruments for a period of approximately 6 months. During this time the student will receive training in the FPGA-based measurement and control systems of ZI and work within a team to test a new regression test setup for quantum computing applications. The basic idea of the quantum computing regression setup is to combine a number of instruments (HDAWG, UHF-QA and PQSC) in a fixed test setup designed to mimic how they are employed in a lab setup. The setup will be used for running tests that are not feasible on our regular regression setup due to their unique cross-instrument requirements. The tests envisaged will utilize all the instruments and their capabilities, operating the instruments in a similar fashion as will be done doing actual experiments. The student will also verify signal integrity to a level that is not possible using a normal regression setup. Finally, the tests will be run over very long time in order to verify the stability of the system.

Months 10-24: Following, the placement at ZI, the student will use the developed measurement functionalities for the readout and control of spin qubits defined in carbon nanotube double quantum dots at UCL. This requires the student to familiarize themselves with radio-frequency and microwave readout techniques in the UCL lab as well as the operation of a dilution refrigerator to measure devices at mK temperatures. This will be in close collaboration with other PhD students and PDRAs in the Quantum Devices group at UCL who will be responsible for device fabrication and provide assistance in the lab. The outcomes expected from the lab work will be benchmarks for charge and spin coherence of the nanotube qubits (for different carbon isotope ratios) as well as establishing fidelities of qubit control and readout using the tools provided by/developed at ZI.

Months 24-48. The last 24 months of the PhD project will focus on the generation of entanglement between spatially separated qubits using a measurement-based approach. This requires fast qubit readout and real-time feedback for deterministic entanglement generation. This will involve work both at ZI and UCL (with all lab measurements taking place at UCL). It is expected that the measurements will inform on the software requirements; and that the measurement in the lab will benefit from the ongoing improvements in quantum readout developed at ZI (such as the new ultrahigh frequency quantum analyser toolkit). The work is also expected to provide the academic and industry partner with annual 'application notes' that will be used to showcase the work on the ZI websites as well as in peer-reviewed articles. It is expected that the last 6 months of the PhD will be large devoted to writing of manuscripts and the student's thesis.