# Novel thermal phases of topological quantum matter in the lab

April 17, 2018For the first time in the lab, a group of researchers from Universidad Complutense de Madrid, IBM, ETH Zurich, MIT and Harvard University have observed topological phases of matter of quantum states under the action of temperature or certain types of experimental imperfections. The experiment has been carried out in a platform of superconducting qubits at IBM, also known as quantum simulator.

Quantum simulators were first conjectured by the Nobel Prize in Physics, Richard Feynman, in 1982 since ordinary classical computers that we use nowadays were proved to be inefficient to simulate systems of interacting quantum particles.

These new simulators are genuinely quantum and can be controlled very precisely (for instance, systems of cold atoms trapped with lasers, or superconducting materials coupled to microwave radiation). They replicate other quantum systems that are harder to manipulate and whose physical properties remain very much unknown.

In an article published in the journal

*Quantum Information*of the Nature Publishing Group, these researchers explain how using a quantum simulator with superconducting qubits at IBM, they were able to replicate materials known as topological insulators at finite temperature, and measure for the first time their topological quantum phases.

Topological phase of matter represent a very exciting and active field of research that is revolutionising our understanding of nature and material science. The study of these novel phases of matter has given rise to new materials such as topological insulators, which behave as regular insulators in the bulk and as metals at the boundaries. These boundary electronic currents have the spin (intrinsic magnetic moment) polarised, thus they are expected to play a very important role in spintronics, a novel alternative to conventional electronic technology.

**Thermal topological phases**

Since the discovery of topological matter, researchers have looked for innovative ways to maintain their properties at finite temperature. Previous theoretical works of the researchers at Universidad Complutense proposed a new topologial quantum phase, known as Uhmann phase, to characterise these phases of matter in thermal systems. The Uhlmann phase allows to generalise the topological phases of matter to systems with temperature.

The results found in this experiment with quantum simulators represent the first measurement of topological quantum phases with temperature, and advance the synthesis and control of topological matter using quantum technologies. Among other applications, the topological quantum matter could be used as hardware for future quantum computers due to its intrinsic robustness against errors. The experimental results presented in this work show how these topological quantum phases can also be robust against temperature effects.

-end-

**Reference**

Observation of topological Uhlmann phases with superconducting qubits, O. Viyuela, A. Rivas, S. Gasparinetti, A. Wallraff, S. Filipp, M.A. Martin-Delgado, NPJ

*Quantum Information*, Volume 4, Article number: 10 (2018). DOI:10.1038/s41534-017-0056-9

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