Nuclear Winds Drive Cold Gas Outflows on Kiloparsec Scales in Reionization-Era Quasars

Accreting supermassive black holes (SMBHs) are thought to influence the evolution of their host galaxies through multi-phase feedback driven by powerful nuclear outflows. Although this mechanism is central to theoretical models of SMBH-galaxy co-evolution across cosmic time, direct observational evidence connecting nuclear winds to large-scale cold gas outflows remains limited, especially in the early universe. Here we report statistical evidence for such a connection in a sample of luminous quasars at z ~ 5.5. We compare stacked [C\,{ ii}] 158 $μ$m emission profiles from ALMA observations, which trace galactic-scale neutral gas, for quasars with and without broad absorption lines (BALs) that indicate powerful nuclear winds on sub-kiloparsec scales. The BAL quasar stack exhibits a significant (S/N = 4.45) blueshifted broad component in the [C\,{ ii}] line profile, with a velocity offset of Δvb = -2.1 × 10²\, km\,s⁻¹ and a full width at half maximum of 1.18 × 10³\, km\,s⁻¹, whereas the non-BAL stack shows no such feature. We estimate that a few percent to one-quarter of the nuclear wind energy may be transferred to cold neutral gas on kiloparsec scales. These results suggest that BAL winds can couple to the host galaxy's interstellar medium, providing empirical support for models of multi-phase AGN feedback. This mechanism may also contribute to the observed divers ity in MBH/M_* among luminous quasars recently identified by JWST.