"Analogue" Hamiltonian simulation involves engineering a Hamiltonian of interest
in the laboratory and studying its properties experimentally. Large-scale
Hamiltonian simulation experiments have been carried out in optical lattices,
ion traps and other systems for two decades. This is often touted as the most
promising near-term application of quantum computing technology, as it is argued
it does not require a scalable, fault-tolerant quantum computer.
Despite this, the theoretical basis for Hamiltonian simulation is surprisingly
sparse. Even a precise definition of what it means to simulate a Hamiltonian was
lacking. In my talk, I will explain how we put analogue Hamiltonian simulation
on a rigorous theoretical footing, by drawing on techniques from Hamiltonian
complexity theory in computer science, and Jordan and C* algebra results in
mathematics.
I will then explain how this proved to be far more fruitful than a mere
mathematical tidying-up exercise. It led to the discovery of universal quantum
Hamiltonians [Science, 351:6 278, p.1180 (2016); Proc. Natl. Acad. Sci. 115:38
p.9497, (2018); J. Stat. Phys. 176:1 p228\u2013261 (2019);
[[[01]
https://link.springer.com/article/10.1007/s00023-021-01111-7][Annales
Henri Poincar?, 23 p.223 (2021)], later shown to have a deep connection back to
quantum complexity theory [PRX Quantum 3:010308 (2022)]. The theory has also
found applications in developing new and more efficient fermionic encodings for
quantum computing [Phys. Rev. B 104:035118 (2021)], leading to dramatic
reductions in the resource requirements for Hamiltonian simulation on near-term
quantum computers [Nature Commun. 12:1, 4929 (2021)]. It has even found
applications in quantum gravity, leading to the first toy models of AdS/CFT to
encompass energy scales, dynamics, and (toy models of) black hole formation [J.
High Energy Phys. 2019:17 (2019); J. High Energy Phys. 2022:52 (2022)].