Quantum simulation

Quantum simulation uses a controllable quantum system to reproduce selected properties or dynamics of another quantum system. The motivation is that the Hilbert space of many interacting particles grows rapidly, making a full classical representation expensive.

In an analog simulation, an engineered Hamiltonian approximates the target interactions directly. In a digital simulation, a sequence of quantum gates approximates the target unitary time evolution. For example, interacting spins can model a XXZ spin chain, with measured correlations compared to the target theory. A useful result requires identifying what is reproduced, controlling preparation and measurement errors, and estimating the effect of imperfect interactions. Reproducing a few observables can be valuable even when the simulator does not reproduce every microscopic degree of freedom.