lowering the temperature (direct cooling) to get high enough polarization

1.4.5 Cooling methods
The form of dependence of the bias on the particular variables described in Equation
(1.1) suggests two obvious approaches to increase the bias, with equally obvious
limitations. The first approach is lowering the temperature (direct cooling) of both
system and environment, but there are practical limits on how low the temperature
can be, especially considering how small these temperatures have to be to get
high enough polarization. The second approach would be to engineer the system
to have bigger gaps between the ground state and the other energy eigenstates.
This is obviously technology dependent.