China University of Science and Technology has completed the first conclusive experimental test of dark energy theory

Du Jiangfeng, an academician at the Key Laboratory of Micromagnetic Resonance of the Chinese Academy of Sciences at the University of Science and Technology of China, and a joint research team from Nanjing University have made significant progress in the field of dark energy detection. They have tested an important dark energy theory, the chameleon theory, using maglev mechanics system in a laboratory environment, and have not found the "fifth force" predicted by the theory. Which rules it out as dark energy. This is the first definitive experimental test of any dark energy theory. The research results, titled "Experiments with levitated force sensor challenge theories of dark energy," were published online in the international academic journal Nature Physics on August 25.

On a list of the 125 most challenging scientific questions published by the journal Science, "What is the universe made of?" was ranked No. 1. Some observational facts from cosmology and astronomy suggest that our universe is in an accelerating expansion, and dark energy is thought to be driving the expansion. However, the nature of dark energy and how it interacts with our world is still unknown. In order to explore the mysterious dark energy field, the international layout of a variety of experimental research programs, the traditional means mainly by astronomical observation or large physical devices, such as space telescopes, underground laboratories and large high-energy particle accelerators. In recent years, the Key Laboratory of Micromagnetic Resonance of the Chinese Academy of Sciences has innovated and developed experimental systems and technologies that can be explored at the Lab scale based on solid spin, gaseous atoms, micromechanical systems, etc., providing a new way to expand human understanding of the universe. A series of important experimental studies have been completed [Nat.Commun. 9, 739 (2018); PRL 121, 080402 (2018); PRL 127, 010501 (2021); Nat.Phys. 17, 1402 (2021); Adv. 7, eabi9535 (2021); PRL 129, 051801 (2022)].

The study tested an important dark energy theory, the chameleon theory. Chameleon theory is a theoretical model used to explain the accelerating expansion of the universe, and one of the biggest features of the theory is the prediction of a "fifth force" in addition to the known four fundamental interactions, which can be formally written as a small deviation from the action of gravity, which provides the possibility for experimental research. In this work, the researchers used the maglev mechanical system as a force detector, and constructed a submillimeter scale "desktop" force detection platform with ultra-high sensitivity to detect the fifth force predicted by the chameleon theory. In the study, the chameleon field was simulated and designed based on the first principles, and a thin film structure was adopted for the mass source and force detector, which effectively solved the difficulty of double shielding of the chameleon field at the mass source and force detector end (FIG. 1 left). In addition, a fifth force drive with very long coherence time is generated to improve the accuracy of force detection. The above techniques greatly improve the detection efficiency of the fifth force, achieving the highest international detection accuracy of the chameleon theory to date (Figure 1 right), limiting the upper limit of the chameleon force predicted by the theory to 6 x 10-17 N. Combined with other previous experiments, the study finally completed a full-parameter spatial test of the underlying chameleon theory, finding no "fifth force" predicted by the theory, conclusively ruling out the dark energy theory (see Figure 2).

Figure 1: Experimental system of maglev mechanical system (left); The upper limit of the chameleon's fifth force given by experimental detection (right)

Figure 2: The dark energy detection results of the study: the coupling limits of the basic chameleon field with ordinary matter (left), the coupling limits of the different order chameleon field with ordinary matter (middle), and the coupling limits of the basic chameleon field with photons (right). Where the stained region is the region that has been tested experimentally and excluded, the region examined by the current work is in red, which, together with the previously reported experiments, completely excludes the chameleon model.

The maglev mechanical system used in this study is an ultra-sensitive mechanical sensor developed in recent years. The Key Laboratory of Micromagnetic resonance of Chinese Academy of Sciences, China University of Science and Technology is one of the earliest laboratories in the world to carry out research on this cutting-edge technology. Ten years ago, the laboratory laid out the experimental research direction of precise measurement of weak force signals. Academician Du Jiangfeng led his graduate students Huang Pu and Yin Peiran (now professors and postdocs of Nanjing University respectively, co-corresponding author and co-first author of this paper) to build an experimental platform from scratch. A series of experimental techniques for precision measurement of high-precision force signals have been successfully developed [PRL 110, 227202 (2013); PRL 117, 017701 (2016); Nat. Commun. 7, 11517 (2016)], including taking the lead in developing precision measurement technology based on maglev mechanical systems [Physical Review Applied 12, 044017 (2019)]. The above work has laid the core experimental foundation for the research of this paper.

The reviewer spoke highly of the work: "In my opinion this is a very important result... this represents a significant step forward in this field. "(It seems to me a very important result... Represents a significant advance in the field). This work fully demonstrates the cross-fusion of precision force detection and cosmological research, and is expected to stimulate a wide range of basic science fields such as cosmic astronomy, particle physics, and atomic and molecular physics.

Rui Li, PhD candidate, Key Laboratory of Micromagnetic resonance, CAS, Peiran Yin, postdoctoral fellow, and Chengjiang Yin, Master candidate, Nanjing University, are co-first authors of the paper. Academician Du Jiangfeng and Professor Huang Pu and Associate Professor He Jianhua, Nanjing University, are co-corresponding authors. The research was funded by the Chinese Academy of Sciences, the Ministry of Science and Technology, the National Natural Science Foundation of China, Anhui Province and the city of Hefei.

Paper link

：https://www.nature.com/articles/s41567-022-01706-9

(Key Laboratory of Micromagnetic Resonance, School of Physics, Academy of Quantum Information and Quantum Technology Innovation, Department of Scientific Research, Chinese Academy of Sciences)