The strong observed clustering of z > 3.5 quasars indicates they are hosted by massive ( M _ { halo } \gtrsim 10 ^ { 12 } h ^ { -1 } { M _ { \odot } } ) dark matter halos .
Assuming quasars and galaxies trace the same large-scale structures , this should also manifest as strong clustering of galaxies around quasars .
Previous work on high-redshift quasar environments , mostly focused at z > 5 , have failed to find convincing evidence for these overdensities .
Here we conduct a survey for Lyman alpha emitters ( LAEs ) in the environs of 17 quasars at z \sim 4 probing scales of R \lesssim 7 h ^ { -1 } { Mpc } .
We measure an average LAE overdensity around quasars of 1.4 for our full sample , which we quantify by fitting the quasar-LAE cross-correlation function .
We find consistency with a power-law shape with correlation length of r ^ { QG } _ { 0 } = 2.78 ^ { +1.16 } _ { -1.05 } h ^ { -1 } { cMpc } for a fixed slope of \gamma = 1.8 .
We also measure the LAE auto-correlation length and find r ^ { GG } _ { 0 } = 9.12 ^ { +1.32 } _ { -1.31 } h ^ { -1 } cMpc ( \gamma = 1.8 ) , which is 3.3 times higher than the value measured in blank fields .
Taken together our results clearly indicate that LAEs are significantly clustered around z \sim 4 quasars .
We compare the observed clustering with the expectation from a deterministic bias model , whereby LAEs and quasars probe the same underlying dark matter overdensities , and find that our measurements fall short of the predicted overdensities by a factor of 2.1 .
We discuss possible explanations for this discrepancy including large-scale quenching or the presence of excess dust in galaxies near quasars .
Finally , the large cosmic variance from field-to-field observed in our sample ( 10/17 fields are actually underdense ) cautions one from over-interpreting studies of z \sim 6 quasar environments based on a single or handful of quasar fields .