  Quantum Data Centers (QDCs) could overcome the scalability challenges of
modern quantum computers. Single-processor monolithic quantum computers are
affected by increased cross talk and difficulty of implementing gates when the
number of qubits is increased. In a QDC, multiple quantum processing units
(QPUs) are linked together over short distances, allowing the total number of
computational qubits to be increased without increasing the number of qubits on
any one processor. In doing so, the error incurred by operations at each QPU
can be kept small, however additional noise will be added to the system due to
the latency cost and errors incurred during inter-QPU entanglement
distribution. We investigate the relative impact of these different types of
noise using a classically simulated QDC with two QPUs and compare the
robustness to noise of the two main ways of implementing remote gates, cat-comm
and TP-comm. We find that considering the quantity of gates or inter-QPU
entangled links is often inadequate to predict the output fidelity from a
quantum circuit and infer that an improved understanding of error propagation
during distributed quantum circuits may represent a significant optimisation
opportunity for compilation.
