Have they made even a single working logic gate? The video only shows flipping bits back and forth by direct manipulation.
Edit: I am happy to report yes:
"Last, we explore the metastructure as simple mechanical logic gates. Figure 8 (C and D) demonstrates the achievement of both “OR” and “AND” logic gate operations by using independent bistability in local elements."
They do in the full paper (not open source & at this time no one's put it on archive):
"Mechanical logic gates
Last, we explore the metastructure as simple mechanical logic gates. Figure 8 (C and D) demonstrates the achievement of both “OR” and “AND” logic gate operations by using independent bistability in local elements. To facilitate the reading of output information (see more details in fig. S17A and the Supplementary Materials), we use a supported height-adjustable flat plate on the top to cover a small region of the platform. Its initial state is set as an output of “0.” When the plate is even and elevated, it outputs "1," otherwise "0" for the cases of either being tilted or lowered. The configurations of the top plate are determined by the pop-up ("1") or pop-down ("0") motions of three supports bonded to the bistable elements as inputs. A pyramid support denoted as P1 is placed in the center with two other neighboring supports surrounded, e.g., cuboids of S1 and S2 and pyramids of P2 and P3 for the OR and AND logic gate, respectively.
Figure 8C and fig. S17B show that when P1 is popped up and fixed, popping-up either S1 or S2 or combined as inputs leads to a stable and evenly elevated plate on the top as an output of "1" for an OR operation, because one point contact at P1 alongside one plane contact at S1 or S2 will render a stable and even surface. For the case of AND logic gate shown in Fig. 8D and fig. S17C, three pyramid that supports Pi are free to pop up or down, providing the point contacts to support the top plate. Only when the plate is supported by three pop-up point contacts, i.e., P1 = P2 = P3 = 1, it will generate a stable and evenly elevated plate as an output of "1" for an AND operation.
We note that most previous mechanical logic metastructures are limited to 1D and 2D structural forms (1–3, 11, 19, 20, 26, 29, 41). Our design extends the structural form of the mechanical binary logic computation to a 3D structural form. In Fig. 8 (D and E), we demonstrate the logic operation in only one zone. In particular, given the independent bistability of each local elements, such design principles can be readily applied to multiple zones for conducting a myriad of parallel mechanical binary operations on the same metastructure platform (see details in fig. S18). Moreover, by altering the structural components as schematically illustrated in fig. S19, we can also conduct “NOR” and “NAND” binary logic computations in our designed platform.
I believe a NAND gate is required as the base on which all other possible circuits can be built, so they need just to add an inverter for potential turing completeness.
It's not, we just use NAND everywhere because they're easier to make with transistors. You can get functional completeness with a NOR instead, or alternatively with some different combinations of other logical operators.
We even implement AND gates with NANDs in electronics (because they're way simpler), but we might not have to limit ourselves to a single base gate with mechanical computers.
> Where do you think the N in NOR and NAND come from?
That makes it sound like you could also do a NOT with XNOR, which is only the case if you can use a constant 0. But that would similarly also be the case for a XOR, but with the requirement of a 1.
Edit: I am happy to report yes:
"Last, we explore the metastructure as simple mechanical logic gates. Figure 8 (C and D) demonstrates the achievement of both “OR” and “AND” logic gate operations by using independent bistability in local elements."