The NextPlatform article hints at their approach:
“We have got this scheme for the mask ROM recall fabric – the hard-wired part – where we can store four bits away and do the multiply related to it – everything – with a SINGLE TRANSISTOR. So the density is basically insane. And this is not nuclear physics – it is fully digital. It is just a clever trick that we don’t want to broadcast. But once you hardwire everything, you get this opportunity to stuff very differently than if you have to deal with changing things. The important thing is that we can put a weight and do the multiply associated with it all in one transistor. And you know the multipliers are kind of the big boy piece of the computer.“
One transistor doing 4-bit multiplication? A plausible way to get “4-bit weight plus multiply in one transistor” in a 6 nm FinFET mask-ROM fabric is to make the ROM cell a single device whose drive strength is the stored value. At tapeout you pick one of about 16 discrete strengths (for example by choosing fin count and possibly Vt), so that transistor itself encodes a 4-bit weight. Then you do the multiply in the charge/time domain by encoding the input activation as a discrete pulse width or pulse count and letting the cell source or sink a weight-proportional current onto a precharged bitline for that duration. The resulting bitline voltage change (or time-to-threshold) is proportional to current times time, so it behaves like weight times input and can be accumulated along a column before a simple comparator or time-to-digital readout. It’s “digital” in the sense that both weight and input are quantized, but it relies on device physics; the hard parts are keeping 16 levels separable across PVT, mismatch, and aging, plus managing bitline noise and coupling and ensuring the device stays in a predictable operating region.
VLSI design produces digital outputs, but in the quantum silicon domain, it’s all about the analog…