High-Fidelity Ternary Quantum Logic for Near-Term Algorithms

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Quantum information science (QIS) is entering the noisy intermediate-scale (NISQ) era, where executing algorithms that reach beyond classical computational capability becomes realistic. Applications impacting several fields, ranging from pharmaceutical design to resource allocation optimization, have been proposed for NISQ-era quantum computers. Vital towards this effort is an exploration of the fundamental physics determining the characteristics and dynamics of QIS implementations, and how this understanding can be utilized for improved quantum control. This project focuses on extending the resource efficiency of modern processors, by leveraging the naturally rich structure of superconducting circuits to develop a ternary quantum logic processor. With QIS experiencing such growth, it is essential to recruit and train an engaged and diverse workforce of scientists. Research for this project will be conducted by graduate students, with mentorship from senior personnel, gaining the skills required for future careers in academic and industrial research. Developing the field is not limited to graduate students already involved in academia. In a summer internship program, students from local East Bay Area high schools will be introduced to the topics and skills involved in QIS research, as well as engaging in hands-on experience.The central challenge here is development of high-fidelity two-qutrit (quantum trit) gates, an essential ingredient for generating entanglement and universal quantum computation. To accomplish this, the processor utilizes a tunable coupling scheme to generate strong interaction for fast gates, while allowing for suppression of unwanted interactions. To verify these gate techniques, scalable qutrit processor benchmarking is developed and employed, measuring state-of-the-art fidelities compatible with a multi-qutrit processor. Finally, the processor is used to execute hybrid quantum-classical algorithms, such as the quantum approximate optimization algorithm (QAOA), well suited to ternary quantum logic. NISQ-era algorithms specifically utilizing ternary logic demonstrate the power of such a processor, while adapting and developing necessary error mitigation techniques vital to accuracy in the presence of noise.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.