Coherent quantum dynamics: Exploiting the wave-like nature of quantum particles for computation.
Quantum interference: Utilizing the interference patterns of quantum waves for certain algorithms.
To achieve true computronium, these quantum effects would need to be harnessed at the highest possible density and efficiency allowed by physics. This would likely involve:
Maximizing information density: Storing and processing information at the smallest possible scale, potentially at the Planck scale.
Minimizing energy use: Operating at or near the Landauer limit for energy consumption per bit operation.