Each cell here is a nanoscale quantum-dot cellular automaton: four tunnel-coupled quantum dots at the corners of a square, shared by exactly two electrons. Coulomb repulsion forces the pair onto one of the two diagonals — call them 0 (top-left / bottom-right, blue) and 1 (top-right / bottom-left, amber). That diagonal choice, the cell's polarization, is the bit.
Place two cells edge to edge and their electrons repel each other too. This simulator computes the actual Coulomb energy, Σ 1/r over every electron pair, for both possible polarizations of a cell given its already-settled neighbor, and the cell relaxes into the lower-energy one. Run that rule down a line of cells and the input polarization propagates to the far end — a working logic wire — without a single electron ever leaving its own cell. No current, no resistive dissipation in the wire itself.
E(state) = Σ k·e² / r_ij over all neighbor electron pairs
cell settles to argmin E(state)
- Binary wire — flip the driver and watch the polarization cascade cell-by-cell to the output.
- Majority gate — a device cell with three neighbors settles to whatever polarization the majority of them share; this is the universal QCA logic primitive, and fixing one input turns it into AND or OR.
Real QCA cells have been built from metal islands at millikelvin temperatures and, in principle, from molecules at room temperature — the appeal is that switching energy scales with the (tiny) Coulomb energy between a handful of electrons, not with charging a wire's capacitance the way CMOS logic does.