When following the laws of quantum mechanics, systems made of many interacting particles can display behavior so complex that they cannot be quantitatively described by even the most powerful computers. In 1981, visionary physicist Richard Feynman argued that such complex behavior could be simulated using a “quantum simulator” — an artificial device governed by the same quantum laws as the system being studied. Physicists at École Polytechnique Fédérale de Lausanne (EPFL) have proposed a new quantum simulator — a laser-based device that could be used to study a range of quantum systems. The simulator could help scientists better understand the properties of complex materials under extreme conditions. Riccardo Rota and Vincenzo Savona, the two EPFL physicists leading the study, working on the design of their quantum simulator. Courtesy of R. Ravasio/EPFL. The researchers built their simulator using superconducting circuits coupled to laser fields to cause an effective interaction among photons. They modeled the behavior of their simulator using traditional computer simulations. One example of a complex quantum system that could be studied using such a quantum simulator are magnets placed at extremely low temperatures. At near-absolute zero (−273.15 °C), magnetic materials can undergo a quantum phase transition. Like a conventional phase transition, the system still switches between two states; however, when near the transition point, the system manifests quantum entanglement. Studying this phenomenon in real materials would be an extremely challenging task, the researchers said. The EPFL simulator could address this problem, according to the team. “The simulator is a simple photonic device that can easily be built and run with current experimental techniques,” said researcher Riccardo Rota. “But more importantly, it can simulate the complex behavior of real, interacting magnets at very low temperatures. “When we studied the simulator, we found that the photons behaved in the same way as magnetic dipoles across the quantum phase transition in real materials,” Rota said. “In short, we can now use photons to run a virtual experiment on quantum magnets instead of having to set up the experiment itself.” “Our findings prove that the quantum simulator we propose is viable, and we are now in talks with experimental groups who would like to actually build and use it,” said professor Vincenzo Savona. Rota believes that the simulator could be applied to a broad class of quantum systems, allowing it to be used to study several complex quantum phenomena. The research was published in Physical Review Letters (https://doi.org/10.1103/PhysRevLett.122.110405).