A quantum simulator reveals information about an abstract mathematical function
relating to a physical model.

T. H. Johnson, S. R. Clark, D. Jaksch
Quantum simulators are devices that actively use quantum effects to answer questions about model systems and, through them, real systems. Here we expand on this definition by answering several fundamental questions about the nature and use of quantum simulators. Our answers address two important areas. First, the difference between an operation termed simulation and another termed computation. This distinction is related to the purpose of an operation, as well as our confidence in and expectation of its accuracy. Second, the threshold between quantum and classical simulations. Throughout, we provide a perspective on the achievements and directions of the field of quantum simulation…
… Read more at http://arxiv.org/pdf/1405.2831v1.pdf