5 June 2023
Thouless Pumps: Unveiling the Remarkable Role of Topology in Quantum Systems
A recent review article by Roberta Citro from the University of Salerno, Italy, and Monika Aidelsburger from LMU Munich and MCQST RU-G co-coordinator dives deep into the rich properties and experimental realizations of topological pumps. The study was published in Nature Review Physics and shedds light on future directions and opens up new questions.
A key concept in slowly-driven quantum systems, thouless pumping has emerged as an ideal model system for understanding the profound influence of topology on quantum systems. Introduced by David Thouless and Qian Niu in the early 1980s, this phenomenon has sparked tremendous theoretical and experimental interest.
Thouless pumping involves the coherent transport of particles induced by cyclic variations in system parameters, eliminating the need for an external bias. The pivotal breakthrough lies in the quantization of the pumped charge, following the topological invariant known as the Chern number. Remarkably, this quantization remains robust against weak disorder or perturbations, as long as the fundamental topology of the pump remains unaltered. However, understanding the localization properties of relevant states and the breakdown of quantized transport in the presence of interactions or deviations from the adiabatic approximation remain subjects of current research.
Illustration of a classical Archimede’s screw, where a directional motion of water is generated by slow and periodic movement of the handle. The topological Thouless pump can be thought of as its quantum version, with the key difference that the amount that is pumped is quantized and therefore extremely robust to perturbations.
Thouless pumping has not only provided insights into quantized transport but also opened the door to comprehending topological phases in periodically-driven systems, which can exhibit exotic topological behavior without any static analogue. In a recent review article by Roberta Citro from the University of Salerno, Italy, and Monika Aidelsburger from LMU Munich, the rich properties and experimental realizations of topological pumps are summarized, shedding light on future directions and open questions. Monika Aidelsburger states, "Our review aims to serve as a foundation for understanding the resilience of topology in these systems and highlights the diverse range of applications of topological pumps."
The experimental exploration of Thouless pumping has spanned various platforms, including cold atoms, photonics and condensed-matter systems. These studies not only deepen our understanding of the quantized transport properties but also pave the way for advancements based on the concept of synthetic dimensions. By treating time as an additional spatial dimension, researchers can for instance realize higher-dimensional systems, such as the 4D quantum Hall effect.
The fascinating properties of Thouless pumps are driving advancements in the field of topological quantum matter and raising hopes for further breakthroughs in unraveling the intricate connections between topology and quantum physics, as well as potential applications.
Synthetic Quantum Matter Group
Faculty of Physics, LMU Munich