Quasars at z~7 hosting highly accreting black holes are unique probes for the early Universe, including the growth of the earliest supermassive black holes (SMBHs), the assembly of their massive host galaxies, and cosmic reionization. I have been leading a distant quasar survey, which yielded the largest sample of luminous quasars at z~6.5-7.6. Pre-JWST, studies using this sample have placed stringent constraints on early SMBH growth and the intergalactic medium (IGM) evolution. The launch of JWST opens up a new era. I will introduce my recent effort to conduct high-resolution observations of a sample of ~30 luminous z~7 quasars using JWST and ALMA, in synergy with observations in other wavelengths. This dataset allows us to delve into a comprehensive study of the interactions between early SMBHs and their host galaxies at multiple scales and phases, and enables new methods to constrain the reionization physics. I will present early results, covering early SMBHs, AGN feedback, host galaxy stellar emission, and IGM evolution. These new discoveries mark the beginning of a new era towards understanding the formation of early SMBHs, the assembly of massive host galaxies, and reionization history. With the upcoming next-generation surveys and facilities, our understanding of these key questions will be revolutionized in the next decade.
