0
0.5
1
1.5
2
2.5
3
0
0.5
1
1.5
2
2.5
3
0 0.5 1 1.5 20 0.5 1 1.5 2
ab
Nat (×10^11 )Nat (×10^11 )
[Var(S
)y
SN-1]
2Extended Data Fig. 3 | Spin noise versus atom number. a, Effective coupling
constant ∼κ^2 as a function of the number of atoms. The values of ∼κ^2 are derived
from the spin noise of the thermal state. b, Spin noise of prepared CSS versus
the number of atoms. The observed linear dependence proves that technical
noise is mostly suppressed and the measured spin noise is at the projection
noise limit (PNL).