## Understanding Quantum Simulation

Trying to fully understand the quantum mechanical properties of real materials is an extremely complex challenge that requires the development of innovative new techniques and approaches. Even the most powerful conventional computers do not operate using quantum mechanical principles, and so trying to formulate quantum mechanical problems on a classical computer requires enormous effort. Because of this computational difficulty, it is not generally possible to obtain exact solutions for properties of quantum systems with more than a few tens of particles, even on powerful supercomputers. Quantum simulators are an alternative way of solving this complex problem. Rather than trying to model the quantum mechanical behaviour of particles on a regular classical computer, quantum simulators are fundamentally quantum mechanical from the ground up. They are designed to directly realise models of interest, and construct them piece-by-piece by manipulating individual atoms in a highly controllable, programmable way.

The key idea is to use a highly controlled quantum system to directly simulate another quantum system that we want to learn more about, but which may be less controllable or even impossible to experimentally investigate. For example, quantum simulators can be used to probe properties relevant to materials science, condensed matter physics, quantum chemistry and even high-energy physics.

In developing and using quantum simulators, we are making use of a fundamentally quantum mechanical device to explore the properties of another quantum mechanical system. This approach is also known as analog quantum simulation, and promises to be much more efficient than trying to accomplish the same task using classical supercomputers. Another possibility is the use of quantum computers as digital quantum simulators, which can have more flexibility at the cost of being more complex and difficult to control.