Researchers under the direction of Peter Zoller have created a novel instrument for measuring entanglement in many-body systems and have experimentally proven its efficacy. The technique makes it possible to investigate physical phenomena that were previously unreachable and could improve the understanding of quantum materials. Nature has published the study.
A quantum phenomenon known as entanglement occurs when the characteristics of two or more particles entangle to the point where it is no longer possible to identify the precise state of each individual particle. Instead, one must take into account every particle at once that shares a particular condition. The characteristics of a material are ultimately determined by the particle entanglement.
Entanglement of many particles is the feature that makes the difference. At the same time, however, it is very difficult to determine.
Christian Kokail, Study First Author, University of Innsbruck
A new method that could significantly improve the investigation and comprehension of entanglement in quantum materials is currently offered by researchers under the direction of Peter Zoller at the University of Innsbruck and the Institute of Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences (ÖAW). One would naively need to perform an unimaginably enormous number of measurements to describe massive quantum systems and extract information about the existing entanglement from them.
We have developed a more efficient description, that allows us to extract entanglement information from the system with drastically fewer measurements.
Rick van Bijnen. Theoretical Physicist, University of Innsbruck
Scientists have replicated a real material, particle by particle, in an ion trap quantum simulator with 51 particles, allowing them to analyze the substance in a controlled laboratory setting. Few research teams in the world possess the required control over as many particles as the experimental physicists led by Christian Roos and Rainer Blatt at Innsbruck.
The main technical challenge we face here is how to maintain low error rates while controlling 51 ions trapped in our trap and ensuring the feasibility of individual qubit control and readout.
Manoj Joshi, Experimentalist, University of Innsbruck
During this procedure, the experiment's effects—which had hitherto only been theoretically described—were seen by the scientists for the first time.
Kokail added, “Here we have combined knowledge and methods that we have painstakingly worked out together over the past years. It is impressive to see that you can do these things with the resources available today.”
Shortcut via Temperature Profiles
Particles in a quantum material can have varying degrees of entanglement. Results from measurements on a tightly entangled particle are purely random. Scientists refer to a situation as “hot” if the measurement findings are highly variable or entirely random. It is a “cold” quantum item if the likelihood of a particular outcome rises. The precise state can only be determined by measuring each and every entangled object.
In systems with a large number of particles, the measurement effort rises significantly. It is predicted by quantum field theory that a system of many entangled particles can have a temperature profile ascribed to its subregions. The degree of particle entanglement can be ascertained using these profiles.
These temperature profiles in the Innsbruck quantum simulator are obtained through a feedback loop in which the quantum system and a computer work together to generate new profiles that are then compared to the experiment’s real observations.
The researchers’ temperature profiles demonstrate that “hot” particles are those that interact with the environment intensely, while “cold” particles interact with it less.
“This is exactly in line with expectations that entanglement is particularly large where the interaction between particles is strong,” Kokail added.
Opening Doors to New Areas of Physics
The methods we have developed provide a powerful tool for studying large-scale entanglement in correlated quantum matter. This opens the door to the study of a new class of physical phenomena with quantum simulators that already are available today. With classical computers, such simulations can no longer be computed with reasonable effort.
Peter Zoller, Professor, Theoretical Physics, University of Innsbruck
New theories on such platforms will also be tested using the techniques used at Innsbruck.
The findings were published in the journal Nature. The European Union, the Federation of Austrian Industries Tyrol, the Austrian Science Fund (FWF), the Austrian Research Promotion Agency (FFG), and other organizations contributed funds to the study.
Joshi, M. K., et. al. (2023) Exploring large-scale entanglement in quantum simulation. Nature. doi:10.1038/s41586-023-06768-0