  As quantum computers increase in size, the total energy used by a quantum
data center, including the cooling, will become a greater concern. The cooling
requirements of quantum computers, which must operate at temperatures near
absolute zero, are determined by computing system parameters, including the
number and type of physical qubits, the operating temperature, the packaging
efficiency of the system, and the split between circuits operating at cryogenic
temperatures and those operating at room temperature. When combined with
thermal system parameters such as cooling efficiency and cryostat heat
transfer, the total energy use can be determined. Using a first-principles
energy model, this paper reports the impact of computer architecture and
thermal parameters on the overall energy requirements. The results also show
that power use and quantum volume can be analytically correlated. Approaches
are identified for minimizing energy use in integrated quantum systems relative
to computational power. The results show that the energy required for cooling
is significantly larger than that required for computation, a reversal from
energy usage patterns seen in conventional computing. Designing a sustainable
quantum computer will require both efficient cooling and system design that
minimizes cooling requirements.
