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Center for Nonlinear Studies |
In the last decade, variational algorithms have been the tool of choice for researchers and practitioners of quantum computing to tackle ground state problems on pre-fault-tolerant quantum processors. Currently, several practical and theoretical issues prevent scalability of variational algorithms to large system sizes. In this talk, I will discuss three quantum diagonalization methods, based on subspaces obtained from quantum computers, which overcome the scaling limitations of variational algorithms. First, the Krylov quantum diagonalization, which allowed us to perform quantum ground state calculations for lattice models of up to 50 spins, and the sample-based quantum diagonalization, which enabled realistic chemistry computations of up to 77 qubits on a quantum centric supercomputing architecture, using a Heron quantum processor and the supercomputer Fugaku. Finally, merging these two ideas together leads to a ground state algorithm with convergence similar to phase estimation, combined with robustness against noise, leading to an experimental demonstration obtained with IBM quantum computers and the supercomputer Frontier.
Bio: Dr. Mezzacapo is a Principal Research Scientist at IBM Quantum, leading IBM Quantum’s efforts around quantum-centric supercomputing and the applied quantum sciences. One of his areas of interest is quantum simulations of chemistry and materials science, where he contributed with advancements on quantum algorithms for computing molecular energies, more efficient encodings for fermionic simulations, and experiments that have pushed the frontier of quantum simulations with quantum processors. He is interested in understanding how quantum computers can be optimally coupled with classical high-performance computers, and what are the best algorithms and workflows for quantum-centric supercomputing architectures. More broadly, he is interested in how one can use quantum computers to deliver value in quantum-classical computational workflows. In the past, he has worked on the characterization of superconducting quantum processors, modeling of quantum gates, and quantum software, with some foundational contributions to the Qiskit software stack.
Host: Cincio Lukasz (T-4) and Akram Touil (T-4)