The lottery, drawn twice
A robot's correct action is often a set, not a point. Representing that set is what an energy landscape does for free and what a regression policy structurally cannot do. The question this instrument answers is not which is smarter. It is what each one costs on the substrate underneath it, and the answer changes depending on which substrate you are standing on.
Predict first
A robot can go around an obstacle to the left or to the right. Both routes appear in the human demonstrations, equally often. The policy is trained by minimising mean squared error against those demonstrations. At run time, what does it do?
The task
One way is a unique answer. Two or more is a set, and the set is what a squared-error loss cannot hold.
Substrate A — von Neumann
Diffusion Policy samples its action by running Langevin steps on a learned gradient
field. Each step is one network forward pass, and the steps are serial. Published range is
10–100 NFE per action.
Substrate B — a fabric that settles
The fabric holds the landscape and relaxes into it. Cost does not grow with the number of modes or the number of steps, because there are no steps. What it costs instead is imposing the new state each tick. 100 ms is a measured figure, not an assumption.
The deadline
Visuomotor policies commonly run near 10 Hz with action chunking, and the pressure is upward. Every rung here is reachable by some setting of the two substrate controls, so if a rung is failing, it is failing for a reason you can go and change.
Where these numbers come from
| Quantity | Value | Status |
|---|---|---|
| Denoising steps per action | 10–100 NFE | published range |
| Network forward pass | 3 ms | stated assumption |
| Embedded Ising machine, end to end | ~100 ms | measured |
| Ising fabric size | 2,048 spins | measured |
| Coupling-matrix compression | 32x | measured |
Diffusion Policy, arXiv:2303.04137 and its literature, which names the
10–100 NFE cost as the key barrier to real-time deployment. The 100 ms is Toshiba's
measured system-wide latency, independent of problem size, on an FPGA simulated-bifurcation
machine (arXiv:2503.23966). The 3 ms forward pass is an assumption of this instrument and the quantity a reader is most
likely to have better information about. Change it and the crossing point moves proportionally.