Asia Pacific Physics Week 2024 (APPW2024)

Wednesday, Nov. 6, 2024 

4:00 PM - 4:30 PM  C. N. Yang Award Talk  Yong-Chun Liu (Tsinghua University) 

Quantum control of macroscopic systems and precision measurement

Yong-Chun Liu

Tsinghua University

Quantum control of macroscopic systems holds significant importance in both fundamental studies and applications. This report details our research progress in manipulating macroscopic quantum systems with a large number of atoms and precision measurement applications. We propose dynamic interaction control methods that utilize specially designed coupling pulse sequences to achieve artificially constructed interactions, effectively controlling the evolution dynamics of the system. Based on these methods, we provide schemes for preparing various quantum states such as atomic Schrödinger's cat states and spin squeezed states with a large number of atoms. We have synthesized a collective-spin XYZ model with three-body interactions, which can rapidly prepare GHZ-like states containing a substantial number of atoms. The prepared states not only exhibit Heisenberg-limited scaling in precision measurement, but also preserve entanglement properties even when multiple particles are lost. Moreover, we propose new methods for controlling the interactions in thermal atomic ensembles, which are crucial for enhancing the measurement sensitivity of magnetic field. Employing high-sensitivity atomic magnetometers, we have established an upper limit for the coupling parameter of the spin-dependent "fifth force" beyond the standard model. We have also developed high-sensitivity cavity optomechanical magnetometers capable of operating at room temperature and in the Earth's magnetic field environment.