How many qubits to simulate the chips inside quantum computers?

Quantum dots — the nanoscale structures at the heart of spin-qubit processors and solar cells — are surprisingly hard to model once more than two electrons are involved. Mapping out the algorithms needed to run these simulations on near-future fault-tolerant hardware, this work finds that a ground-state energy calculation for a four-electron double quantum dot would take about 24 hours on a 226,000-physical-qubit machine. That's a concrete, time-stamped benchmark for when early quantum computers might start designing the very hardware they're built from.