The team of academician Guangcan Guo at the University of Science and Technology of China has made new progress in precision measurements based on phase transitions. In collaboration with Prof. Klaus Mølmer of Aarhus University in Denmark and Prof. Charles S. Adams of Durham University in the UK, the group of Shi Baosen and Ding Dongsheng has improved the precision and sensitivity of microwave electric field measurements of Rydberg atoms using phase transitions of strongly correlated systems, and the related results were published as “Enhanced metrology at the The related results were published in the internationally recognized academic journal Nature Physics under the title of “Enhanced metrology at the criTIcal point of a many-body Rydberg atomic system”.
The development of a modern advanced quantum measurement system has important research significance, which meets the needs of the times and the international development trend, while facing the international frontier and national major needs. Since Riedberg atoms have a large electric dipole moment and can produce a strong response to weak electric fields, they have become a very promising quantum system for microwave measurements. On the other hand, because of the long-range strong interactions between Riedberg atoms, they are often used in simulations to study strongly correlated systems as well as phase transitions. Strongly correlated systems are more sensitive to external perturbations near the critical point and can be applied to the field of quantum precision measurements. Although there are a large number of theoretical reports using the critical states of strongly correlated systems to do quantum sensing, more than a decade since the theory was proposed, it has not been successfully implemented experimentally. The main reasons are: the difficulty to prepare the phase transition process of the multi-body system, the lack of external field regulation technology of the critical point, etc.
In recent years, the scientific research team led by Baosen Shi and Dongsheng Ding has made important progress by focusing on quantum simulation and quantum precision measurement scientific research using the Riedberg atomic system. In the present work, the team has developed the technique of coupling the critical point of Ridderberg atoms with microwave electric field. Based on the room temperature rubidium atomic system, the accuracy and sensitivity of measuring microwaves are significantly improved by taking advantage of the more sensitive characteristics of the phase change point of the many-body system to microwave perturbations. As shown in Figure 1, the atomic transmission spectrum in the multibody system becomes steeper near the phase change point, which is equivalent to a ruler with a finer scale in the frequency domain and therefore has higher accuracy for microwave measurements. The steeper spectrum is produced by the abrupt change process that jumps the system from one state to another as the phase transition occurs.
From theFigure 1, the first row shows the energy level diagram (a) and the electromagnetically induced transparent transmission spectrum curve (b) in the case of few-body without phase transition, and the second row shows the energy level diagram and the transmission spectrum curve in the case of many-body. The many-body has a broadening in the upper energy level distribution relative to the few-body, and the transmission spectrum is steeper near the critical point, which is equivalent to a ruler with a finer scale in the frequency domain, thus allowing a higher precision measurement of the microwave electric field.
The team used Fisher informaTIon to measure the accuracy, as shown in Figure 2. The experiments show that the Fisher informaTIon at the critical point of the multi-body system has a significant improvement of three orders of magnitude compared to the case of few-body no phase transition. This corresponds to an improvement in measurement accuracy of at least one order of magnitude, and increases exponentially with the increase in measurement time. In the single-body case, the system sensitivity is about 3.1 μV/cm/Hz^0.5, while in the multi-body case, the system has a measurement sensitivity of 49 nV/cm/Hz^0.5 for microwave electric fields, an improvement of more than 60 times.
From Fig. 2, comparison of the many-body and few-body transmission spectra at different measurement times in the experiment. The slope of the multi-body transmission spectrum near the critical point grows significantly with measurement time, faster than linearly, while in the case of few-body, the spectral lines do not change significantly. The work received high praise from the reviewers: This experiment is truly groundbreaking with significant potenTIal impact as it opens the gate for developing a new generation of quantum sensors based on strongly interacting many-body systems. The stated sensitivity of 49 nV/cm/sqrt(Hz) is very impressive, and is a good indication of the potential applications of this method for metrology. Dong-Sheng Ding and Zong-Kai Liu, PhD students at the Key Laboratory of Quantum Information, Chinese Academy of Sciences, are co-first authors of this paper. Prof. Charles S. Adams of Durham University, UK, is the co-corresponding author of this paper. The results were supported by grants from the Ministry of Science and Technology, the Foundation Committee, the Chinese Academy of Sciences, the Major Science and Technology Project of Anhui Province, the Hefei National Laboratory, and the University of Science and Technology of China.
