Unitary Fermi gases offer an unparalleled platform for quantum simulation, facilitating investigations into the existence and attributes of a pairing pseudogap. Their remarkable controllability, purity, and the presence of known short-range attractive interactions make them ideal candidates for such studies. Moreover, the absence of a lattice structure in bulk Fermi gases eliminates the influence of competing quantum orders.
Previous experiments have attempted to measure the trap-averaged single-particle spectral function of strongly interacting Fermi gases. However, these efforts often fell short of providing convincing evidence of a pseudogap due to trap inhomogeneity and challenges posed by final-state interactions in conventional rf spectroscopy techniques.
After years of dedicated research, the USTC research team has established a cutting-edge quantum simulation platform utilizing ultracold lithium and dysprosium atoms, achieving exceptional preparation of homogeneous Fermi gases. Notably, the team devised innovative methods to stabilize magnetic fields crucial for their experiments.
By maintaining short-term fluctuations below 25 μG at a magnetic field of approximately 700 G, the team achieved record-high relative magnetic field stability. This breakthrough enabled the utilization of microwave pulses to excite atoms to high-lying energy states devoid of interactions with initial states, facilitating momentum-resolved photoemission spectroscopy.
With these pivotal technical advancements, the research team systematically investigated the single-particle spectral function of unitary Fermi gases across various temperatures, successfully identifying the presence of the pairing pseudogap. This discovery provides compelling evidence for the role of preformed pairing as a precursor to superfluidity.
Moreover, the team derived essential quantities such as the pairing gap, pair lifetime, and single-particle scattering rate from the measured spectral function. These parameters are crucial for characterizing the behavior of strongly interacting quantum systems, furthering our understanding of such complex phenomena.
These groundbreaking findings not only propel the study of strongly correlated systems forward but also offer invaluable insights for the development of comprehensive many-body theories.
The techniques developed in this groundbreaking research lay a solid foundation for future explorations into other significant low-temperature quantum phases, including single-band superfluidity, stripe phases, and Fulde–Ferrell–Larkin–Ovchinnikov superfluidity.