  Fixed-frequency transmon quantum computers (QCs) have advanced in coherence
times, addressability, and gate fidelities. Unfortunately, these devices are
restricted by the number of on-chip qubits, capping processing power and
slowing progress toward fault-tolerance. Although emerging transmon devices
feature over 100 qubits, building QCs large enough for meaningful
demonstrations of quantum advantage requires overcoming many design challenges.
For example, today's transmon qubits suffer from significant variation due to
limited precision in fabrication. As a result, barring significant improvements
in current fabrication techniques, scaling QCs by building ever larger
individual chips with more qubits is hampered by device variation. Severe
device variation that degrades QC performance is referred to as a defect. Here,
we focus on a specific defect known as a frequency collision.
  When transmon frequencies collide, their difference falls within a range that
limits two-qubit gate fidelity. Frequency collisions occur with greater
probability on larger QCs, causing collision-free yields to decline as the
number of on-chip qubits increases. As a solution, we propose exploiting the
higher yields associated with smaller QCs by integrating quantum chiplets
within quantum multi-chip modules (MCMs). Yield, gate performance, and
application-based analysis show the feasibility of QC scaling through
modularity.
