One example of a complex quantum system is that of magnets placed at really low temperatures. Close to absolute zero (-273.15 degrees Celsius), magnetic materials may undergo what is known as a "quantum phase transition". Like a conventional phase transition (e.g. ice melting into water, or water evaporating into steam), the system still switches between two states, except that close to the transition point the system manifests quantum entanglement - the most profound feature predicted by quantum mechanics. Studying this phenomenon in real materials is an astoundingly challenging task for experimental physicists.
But physicists led by Vincenzo Savona at EPFL have now come up with a quantum simulator that promises to solve the problem. "The simulator is a simple photonic device that can easily be built and run with current experimental techniques", stated Riccardo Rota, the postdoc at Vincenzo Savona's lab who led the study. "But more importantly, it can simulate the complex behavior of real, interacting magnets at very low temperatures."
The simulator may be built using superconducting circuits - the same technological platform used in modern quantum computers. The circuits are coupled to laser fields in such a way that it causes an effective interaction among light particles (photons). "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", stated Riccardo Rota. In short, we can now use photons to run a virtual experiment on quantum magnets instead of having to set up the experiment itself.
"We are theorists", stated Vincenzo Savona. "We came up with the idea for this particular quantum simulator and modelled its behaviour using traditional computer simulations, which can be done when the quantum simulator addresses a small enough system. 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."
Understandably, Riccardo Rota is excited: "Our simulator can be applied to a broad class of quantum systems, allowing physicists to study several complex quantum phenomena. It is a truly remarkable advance in the development of quantum technologies."
Riccardo Rota, Fabrizio Minganti, Cristiano Ciuti, and Vincenzo Savona are the authors of the paper titled " Quantum critical regime in a quadratically-driven nonlinear photonic lattice ". This paper appeared inPhysical Review Letters122, 110405 on 21 March 2019 - DOI: 10.1103/PhysRevLett.122.110405.