Does Stim support the Mølmer–Sørensen gate?

Question

The Mølmer–Sørensen gate is a common ion trap gate. Does Stim support it? I tried MS 0 1 but it didn't work.

Answer 1

Stim does support the Molmer–Sorensen gate, but it's not called MS. It's called SQRT_XX.

The name comes from the fact that the Molmer–Sorensen gate is equal to $\sqrt{X \otimes X}$, the principle square root of applying a bit flip to both qubits. The Molmer–Sorensen gate phases the $-1$ eigenspace of $X \otimes X$ by $i$ instead of by $-1$, relative to the +1 eigenspace. Stim also has the inverse gate SQRT_XX_DAG, as well as variants such as SQRT_ZZ.