The properties of basic electronic components can be simulated with ultracold atoms that flow through structures made of laser light. This is the result of work in which scientists at ETH Zurich, Switzerland, use a new generation of quantum experiments to explore the behaviour of electronic currents in a regime where predictions are often difficult to make.
The building blocks of modern electronics reach such small dimensions that quantum effects start to have a role. For further development and miniaturization of these devices, it is increasingly important to understand ensembles composed of many quantum particles, such as electrons. With current theoretical and computational methods, it is often impossible to predict the behaviour of such quantum many-body systems. Finding alternative methods is therefore the subject of intense research. The group of Tilman Esslinger of the Institute of Quantum Electronics at ETH Zurich has now developed an experimental platform that enables simulating the flow of electrons through tiny channels. The results of this work have been published in two papers in the journals Science and Nature.
In the face of the continuing miniaturization of electronic components, it becomes increasingly important to take quantum effects into consideration when designing new devices. The emergence of quantum-mechanical effects brings new technological opportunities, together with new potential obstacles. But the additional flexibility also means that it is much harder to make theoretical predictions regarding the behaviour of electrons. With additional quantum particles, the computational cost essentially doubles. Even today’s most powerful computers reach their limits when more than a few dozen particles are involved.
An alternative to the theoretical or numerical treatment of a quantum-many-body problem is to emulate the system of interest using another quantum system that can be well controlled experimentally. This is similar to early astronomical instruments, which made it possible to predict the positions of celestial bodies using mechanical devices. Quantum-mechanical simulators were first proposed in 1981 by the American physicist Richard Feynman. Especially in the last ten years, significant experimental progress has been made towards isolating, manipulating, and measuring individual quantum particles. Today, first ’quantum technologies’ emerge from the laboratories.
The researchers at ETH Zurich now put cold lithium atoms in the role of the electrons, and channel them through tiny restrictions formed by laser light. "With our work, we extend the concept of quantum simulation towards transport phenomena", explains Jean-Philippe Brantut, one of the senior staff members involved in the project. In their setup, the physicists can control a number of parameters, including the geometry of the channels and the interactions between the atoms. Furthermore, the system of atoms and light is literally without flaw, enabling a direct comparison between experiments and theoretical models — which is a decisive advantage over a system with electrons and wires, where imperfections never can be completely avoided.
But even in such an ideal system, the flowing particles meet resistance. In an initial experiment Esslinger and his team have confirmed theoretical results which predicted that electrical resistance arises purely because the electrons flow through a thin wire, which can be absolutely flawless. A much stranger behaviour came to light, however, when In this case, the particles began to flow without any resistance, even if there were obstacles. "It is as if you are standing in a river and so don’t feel, in any way, the water flowing around you", says Tilman Esslinger.
The phenomenon of flow without any resistance is known as superfluidity, and it is of great interest with a view to future electronic components. New generations of electronic devices may be a long way off, but works like that of the researchers at ETH Zurich make important contributions to a fundamental understanding of the physical properties that are the basis of these electronic elements, and allow to test theories and new approaches.
