  We present measurements of silicon nitride nonlinear microresonators and
frequency comb generation at cryogenic temperatures as low as 7~K. The
resulting two orders of magnitude reduction in the thermo-refractive
coefficient relative to room-temperature enables direct access to single bright
Kerr soliton states through adiabatic frequency tuning of the pump laser while
remaining in thermal equilibrium. Our experimental results, supported by
theoretical modeling, show that single solitons are easily accessible at
temperatures below 60~K for the microresonator device under study. We further
demonstrate that the cryogenic temperature primarily impacts the
thermo-refractive coefficient. Other parameters critical to the generation of
solitons, such as quality factor, dispersion, and effective nonlinearity, are
unaltered. Finally, we discuss the potential improvement in thermo-refractive
noise resulting from cryogenic operation. The results of this study open up new
directions in advancing chip-scale frequency comb optical clocks and metrology
at cryogenic temperatures.
