Quantum simulation uses one controllable quantum system — trapped ions, superconducting circuits, neutral atoms, or others — to reproduce the dynamics of a different quantum system that is harder to access or control directly, such as a material’s electrons or a chemical reaction’s coupled nuclear and electronic motion. This is distinct from digital gate-based quantum computing: rather than compiling a problem into a sequence of universal logic gates, a simulator’s own physical Hamiltonian is engineered to match the physics being studied, and its natural time evolution stands in for the target system’s.

Because the simulator is itself a real quantum system, it inherits real quantum systems’ constraints — including which physical conditions, such as temperature, are practical to reach and control — and part of the field’s progress is in extending which of the target system’s properties a simulator can actually reproduce.