China News Service, Hefei, February 8 (Reporter Wu Lan) Chinese scientists have achieved a new breakthrough in the field of quantum simulation-for the first time, they have observed a pseudogap generated by many-body pairing. This research takes an important step towards understanding the mechanism of high-temperature superconductivity and is an example of using quantum simulation to solve important physical problems.
On February 8, relevant research results were published in the international academic journal Nature. This result was first observed by Pan Jianwei, Yao Xingcan, Chen Yuao and others from the University of Science and Technology of China based on the uniform Fermi gas with strong interaction.
The two carps with jade beads on their heads in the picture symbolize a pair of fermions with opposite spins; the dragon gate represents superfluid phase transition and pseudo-energy gap. The carp jumped over the gantry, indicating that pairing occurs above the superfluid phase transition temperature. This pairing phenomenon in turn leads to the emergence of pseudoenergy gaps. Chen Lei/Drawing.
The generation of energy gap is the iconic phenomenon of superconductivity. In conventional superconductors, the energy gap exists below the superconducting phase transition temperature. With the discovery of cuprate high-temperature superconductors, energy gaps can still be observed even above the superconducting phase transition temperature. This phenomenon is called a pseudogap. The origin and properties of the pseudogap can provide key clues to answer the mechanism of high-temperature superconductivity.
The ultracold Fermi gas in the strong interaction (unitary) limit provides an ideal quantum simulation platform for the study of the mechanism of pseudogaps due to its purity and controllability. After years of research, the research team established an ultracold lithium-dysprosium atomic quantum simulation platform and achieved the world's leading preparation of uniform Fermi gas. The research team has also developed stabilization technology for large magnetic fields. Under a magnetic field of about 700 G (Gauss), its short-term fluctuation is better than 25 μG (micro-Gauss). The relative magnetic field stability is close to 10 to the minus 8th power, which is better than previous international ones. The optimal results are improved by more than an order of magnitude.
Single particle spectrum representation. The connected and independent balls represent Cooper pairs and single particles respectively, and the surface gap is the pseudo energy gap. Chen Lei/Drawing.
Based on the above research, the research team systematically measured the single-particle spectral function of unitary Fermi gas at different temperatures and successfully observed the existence of a pseudogap, which provided support for the electron pre-pairing hypothesis.
The ultracold atom quantum control technology developed in this work lays a technical foundation for the next step of studying other important condensed matter physics phenomena. The reviewers of Nature magazine unanimously agreed: "This work solves an important long-standing physical problem and is a milestone in quantum simulation research."
Professor Yao Xingcan (right) and Professor Chen Yuao (left) of the University of Science and Technology of China discuss the topic in the laboratory. (Photo courtesy of University of Science and Technology of China)
According to reports, relevant research teams at the University of Science and Technology of China have carried out fruitful work in quantum simulations based on ultracold atoms in recent years, and have published 10 papers in Nature and Science. Based on the accumulation of previous technologies, ultracold atom quantum simulation has begun to show significant effectiveness in revealing the laws of complex physical systems including high-temperature superconducting mechanisms, paving the way for the construction of a dedicated quantum simulator capable of solving practical problems in the near future. the road. (over)