### Quantum Phase Transition Enables Deterministic Preparation of Multi-Particle Entangled States: A Breakthrough by Tsinghua University On February 27, 2018, the Department of Basic Research and the Basic Research Management Center of the Ministry of Science and Technology jointly organized the "Expert Interpretation Meeting for the Top Ten Scientific Advances in China 2017," where they officially announced the top scientific achievements of the year. Among these, the project "Deterministic Preparation of Multi-Particle Entangled States Using Quantum Phase Transitions," conducted by Professors You Li and Zheng Mengkun from the Department of Physics at Tsinghua University, was notably recognized. #### Core Events and Findings The research team, led by Professors You Li and Zheng Mengkun, achieved a significant breakthrough by manipulating the spin mixing process in a Bose-Einstein condensate (BEC) of rubidium-87 atoms. They induced two consecutive quantum phase transitions, resulting in the deterministic preparation of a multi-particle entangled state containing approximately 11,000 atoms. This state, known as a double Fock state, was characterized by observing the fluctuations in the atom number difference between different internal states, which were found to be 10.7 ± 0.6 decibels below the classical limit. Additionally, the normalized length of the collective spin was measured to be nearly perfect at 0.99 ± 0.01. These metrics indicate that the multi-particle entangled state can enhance phase measurement sensitivity by about 6 decibels beyond the standard quantum limit and involves at least 910 entangled atoms, setting a new world record for the number of particles that can be deterministically entangled. #### Methodology and Implications The team's approach of using quantum phase transitions to generate entangled states is a novel and innovative method. Despite the small energy gap at the quantum phase transition point, which can lead to significant excitations, the researchers demonstrated that the distinct multi-particle energy level structures on either side of the transition point can still facilitate the creation of high-quality multi-particle entangled states. This new understanding and technique could pave the way for the deterministic preparation of other multi-particle entangled states, which are crucial for various applications in quantum technology. The deterministic preparation of the double Fock state has significant implications for precision measurement technologies. It offers a potential pathway to achieving measurements that surpass the standard quantum limit, such as those required for atomic clocks and atomic interferometers, which could operate with Heisenberg-limited precision. This advancement is particularly important for fields that rely on ultra-precise measurements, such as metrology and fundamental physics. #### Publication and Recognition The research findings were published in the prestigious journal *Science* on February 10, 2017, in the article titled "Deterministic Preparation of Multi-Particle Entangled States Using Quantum Phase Transitions" (Science, 355(6318):620—623). The recognition of this work in the "Top Ten Scientific Advances in China 2017" underscores its significance and the impact it has on the field of quantum physics. #### Additional Recognition: First Detection of Doubly Charmed Baryons Another notable achievement highlighted in the same announcement was the first detection of doubly charmed baryons. This groundbreaking discovery was made by the LHCb (Large Hadron Collider beauty) international collaboration, which includes over 1,000 scientists from 16 countries. Tsinghua University, along with Central China Normal University, University of the Chinese Academy of Sciences, and Wuhan University, is a member of this collaboration. Professor Gao Yuanning, who previously worked in the Department of Physics at Tsinghua University and now serves as the Director of the Tsinghua University Center for High Energy Physics and the Institute of Modern Physics at the Department of Engineering Physics, led the Chinese research team that played a crucial role in the physical analysis and discovery of the doubly charmed baryon. #### Selection Process for the Top Ten Scientific Advances The "Top Ten Scientific Advances in China" selection process is organized by the High Technology Research and Development Center of the Ministry of Science and Technology. As of 2018, this annual event has been held for 13 consecutive years. The research progress is recommended by the editorial boards of *China Basic Science*, *Science & Technology Review*, *Bulletin of the Chinese Academy of Sciences*, *China Science Fund*, and *Chinese Science Bulletin*. A panel of experts, including members of the Chinese Academy of Sciences and Engineering, advisors and consultants from the 973 Program, chief scientists of 973 Program projects, and directors of key national laboratories, then conducts two rounds of voting to select the top ten advances. This recognition by the "Top Ten Scientific Advances in China 2017" not only highlights the pioneering work of Professors You Li and Zheng Mengkun but also underscores the collaborative efforts and international significance of scientific research conducted at Tsinghua University and its partner institutions. The achievements in both quantum physics and particle physics demonstrate the university's commitment to advancing fundamental science and its potential applications in technology and industry.