In analogue quantum simulation, highly controllable quantum systems directly realise specific model Hamiltonians using the quantum resources available on potentially scalable physical platforms; digital quantum simulation, by contrast, is difficult to scale up but can tackle more complex models. Here, Peter Zoller and collaborators take a third route: they combine quantum-classical variational techniques with a programmable analogue quantum simulator based on a 1D array of up to 20 trapped calcium ions to simulate the ground state of the lattice Schwinger model. An additional feature of this realisation is the ability to provide algorithmic error bars on the obtained approximate ground-state energies – a notable step towards the verification of quantum simulations. The authors expect their strategy to be applicable to a broader class of lattice models of importance to condensed matter and high-energy physics.
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