A quantum simulator can be thought of as a special purpose quantum computer. The machine exploits quantum properties to answer practical questions about models that describe complex materials. These models are usually beyond the reach of a classical computer. A working quantum simulator could help scientists understand high-temperature superconductor for efficient energy transport, designing new materials, and improving drug discovery process. Experimental progress over the past 30 years have made it possible to control and manipulate individual quantum systems, transiting quantum simulation from a theoretical dream to the realm of reality
Simulating physical systems on a classical computer has been a crucial tool in the development of science and technology. For example, in the drug design process, instead of relying on trial and error experiments which can be time-consuming and costly, one can predict the outcome of those experiments on a computer by simulating models that appropriately describe the molecular system. Simulation is also needed when performing experiments on the real system is not possible such as the climate system and the financial market.
Materials consist of atoms and electrons that are described by quantum mechanics. However, simulating such quantum materials on a classical computer generally, require computational resources that grow exponentially with the number of constituting particles. Even the largest supercomputers may struggle to simulate a system as small as 50 electrons, as opposed to ~10^23 electrons in real materials.
Recognizing this problem, in 1981 Richard Feynman proposes a new type of computing devices to fight fire with fire, in a manner of speaking. The machine for exploiting quantum coherence to do
YES! Although a universal quantum simulator, as originally envisioned by Feynman, has not been realized, quantum simulator for certain classes of models has already been demonstrated. In the past 15 years, several techniques have been developed to control and manipulate individual quantum systems with unprecedented precision. These techniques include cold neutral atoms in optical lattices, trapped ions, nuclear magnetic resonance, interacting photons, quantum dots, superconducting circuits, and nitrogen-vacancy centers. For example, recent cold atoms experiment have been used to predict the breakdown of the thermodynamic description of interacting quantum gas in the presence of disorder . Predicting such a transition is currently not possible with a classical computer. A programmable quantum simulator with 51-atoms trapped in optical tweezers  and 53 trapped-ions  have also been built to study the dynamics of complex quantum systems. Trapped ions have also recently been used to realize the sought-after time-crystal phase . A nine-site superconducting circuit has been fabricated to demonstrate a many-body spectroscopy technique to study quantum phases of matter . A semiconductor quantum dot array has also been fabricated to simulate electrons in solid state . The latter could provide insights into high-temperature superconductivity.
A quantum simulator promises a revolutionary tool for the development of science and technology. Experimental progress over the past 15 years have been impressive and pushed the field beyond a proof-of-principle. However, controllability and scalability of quantum simulators in all platforms still need to be improved to be able to efficiently
simulate any models on-demand before commercialization.