Breakthrough for the quantum simulator: When ultra-cold atoms can be anything

The theoretical physicists around Hendrik Weimer and Hans Peter Büchler from Stuttgart and Peter Zoller from Innsbruck present their results in Nature Physics.

The work goes back to a famous idea of Nobel laureate Richard Feynman. He realized that conventional computers lack the processing power to calculate the behavior of complex quantum systems. For the general description of a quantum spin system with 300 particles a computer would need more memory than there is available in the world; even if all the observable matter in the universe is processed into storage media. Therefore Feynman proposed to use a different quantum system as a quantum simulator. For this idea to work, the building blocks of the quantum simulator need to be controlled in a precise way in order to mimic the behavior of the simulated system.

The scientists led by Hans Peter Büchler and Peter Zoller have now been able to show that this level of control can be achieved using ultra-cold atoms in a highly excited Rydberg states. The team used the strong interactions between spatially close Rydberg atoms to tune the desired properties of the quantum simulator. "This method is a huge step towards the dream of a universal quantum simulator, which allows us to study the behavior of any other quantum system" says Büchler about the versatility of the Rydberg atoms.

Furthermore, the scientists were able show that the approach can also be used for a novel cooling technique. This allows for the creation of exotic states of matter such as a spin liquid, where magnetic order is absent even at very low temperatures. From their study physicists hope to gain novel insights about quantum many-body systems, having direct applications in condensed matter physics.

The work was conducted with in the transregional research center SFB/TRR 21 (Control of quantum correlations in tailored matter) and was supported by the German research foundation DFG and the Austrian science fund FWF.