Will (near-term) quantum computers deliver real advantage? (45' + 15')

• Bálint Koczor (University of Oxford)

**Abstract**: Quantum computers are becoming a reality and current generations of machines are already well beyond the 50-qubit frontier. However, hardware imperfections still overwhelm these devices and it is generally believed the fault-tolerant, error-corrected systems will not be within reach in the near term: a single logical qubit needs to be encoded into potentially thousands of physical qubits which is prohibitive. Due to limited resources, in the near term, we need to resort to quantum error mitigation techniques. I will explain the basic concepts and then discuss breakthrough results on exponentially effective error mitigation [PRX 11, 031057 (2021)], including an architecture of multiple quantum processors that perform the same quantum computation in parallel [PR Applied 18, 044064 (2022)]; using their outputs to verify each other results in an exponential suppression of errors. I will then explain that hybrid quantum-classical protocols are the most promising candidates for achieving early quantum advantage. These have the potential to solve real-world problems – including optimisation or ground-state search – but they suffer from a large number of circuit repetitions required to extract information from the quantum state. I will explain recent breakthroughs as hybrid quantum algorithms that exploit extremely powerful classical shadows in order to extract and post-process a large amount of information from the quantum computer [PRX 12, 041022 (2022)] and [arXiv:2212.11036]. I will finally identify the most likely areas where quantum computers may deliver a true advantage in the near term. **Short bio**: Dr. Bálint Koczor is an early career independent research fellow in the Department of Materials of the University of Oxford. He has authored several breakthrough contributions and is internationally recognised for his works on quantum error mitigation and near-term quantum computing. His current research focuses on improving the practicality of quantum computers by developing advanced, error-robust quantum algorithms and error handling protocols -- in a sole-author publication he proposed the most advanced error mitigation technique to date.