Prof. Ashley Montanaro
University of Bristol, UK
25th April 2022, 5:00pm - 6:00pm (GST)
Observing ground-state properties of the Fermi-Hubbard model using a scalable algorithm on a quantum computer
The famous, yet unsolved, Fermi-Hubbard model for strongly-correlated electronic systems is a prominent target for quantum computers. It may underpin the theory of high-temperature superconductivity and is a simplified form of models for solid-state systems whose solution would have important practical applications, such as to the design of new materials for batteries and solar cells. In this talk I will discuss recent results showing experimentally that an efficient, low-depth variational quantum algorithm with few parameters can reproduce important qualitative features of medium-size instances of the Fermi-Hubbard model. We address 1x8 and 2x4 instances on 16 qubits on a superconducting quantum processor, substantially larger than previous work based on less scalable compression techniques, and going beyond the family of 1D Fermi-Hubbard instances, which are solvable classically. Consistent with predictions for the ground state, we observe the onset of the metal-insulator transition and Friedel oscillations in 1D, and antiferromagnetic order in both 1D and 2D. Our results rest on a variety of error-mitigation techniques and a new variational optimisation algorithm based on iterative Bayesian updates of a local surrogate model. Our scalable approach is a first step to using near-term quantum computers to determine low-energy properties of strongly-correlated electronic systems that cannot be solved exactly by classical computers.
Ashley Montanaro is a co-founder of the quantum software startup Phasecraft and is Professor of Quantum Computation at the University of Bristol. He has worked in the field of quantum computing for 18 years, specializing in quantum algorithms and quantum computational complexity, and has published over 50 papers on this topic. He holds an ERC Consolidator grant and was awarded a Whitehead Prize by the London Mathematical Society.