Theory to Enable Practical Quantum Advantage

Quantum computers have already reached a scale that they can fundamentally outperform any conventional supercomputer (often referred to as classical computers) on artificial benchmarking tasks. However, the ultimate goal of the field is to reach practical quantum advantage (PQA), i.e., the point where quantum computers perform otherwise-infeasible useful functions for users beyond the immediate community. For example, a materials scientist or chemist who would calculate properties of novel materials/drugs for screening purposes to forgo expensive laboratory research. Most hardware companies aim to ultimately build error-corrected quantum computers, however, the implied engineering complexity is so vast that it is generally believed that large-scale, fully quantum-error-corrected machines will not be feasible within a decade or more. Unfortunately, every operation current and near-future machines will perform are substantially flawed, i.e., noisy and thus the most pressing issue currently is: how can we make use of quantum computers that are expected to emerge in the near future and in the early-fault tolerant era? The overarching objective of this project is to understand and overcome the challenges posed by noisy quantum computers and will deliver key innovations in exploiting early quantum computers that we expect will emerge in the period we call (late) NISQ and early fault tolerant. The project has three distinct but closely interlinked targets that will all play a key role in lowering barriers for practical quantum advantage. First, the project aims to exploit powerful classical supercomputers in order to enhance the capabilities of noisy quantum computers. In particular, recent developments in classical shadow tomography will be exploited in order to efficiently extract large amounts of information from a quantum computer that is post-processed classically. Second, error mitigation techniques will be developed that make tradeoffs between accuracy and measurement overhead thereby improving the practicality of noisy quantum computers -- this includes error mitigated classical shadows. Furthermore, one of the goals of this project is to better understand the fundamental limitations of noisy quantum computers with an emphasis on tradeoffs between accuracy and measurement overhead. Finally, in order to achieve an optimal hardware implementation of quantum algorithms, hardware-level protocols will be developed for improved control of the quantum computer as well as protocols will be tailored to specific hardware architectures. Ultimately, this project aims to reduce the barriers for achieving practical quantum advantage thereby leading to useful applications of early quantum computers. These applications include, simulating chemical systems for discovering novel drugs, atomistic modelling in materials science to develop novel materials, batteries, solar cells, or performing binary optimisation in logistics. The project is supported by an impressive range of both quantum hardware and software companies.