What does this equation mean?

That experiment has nothing to say about $t_G$ . Its seven qubits carry no conserved charge playing the role $\hat J$ plays above, no compass was thrown in, and no alignment problem of the kind Bartlett, Rudolph, and Spekkens formalize was ever posed to the circuit [ 9 ] . The honest parameter range this construction can claim, then, is narrow and asymmetric on purpose: the mechanism behind $t_L$ has a laboratory analogue at the scale of a handful of trapped ions, verified by an actual measured teleportation fidelity; the mechanism behind $t_G$ has none. Every number attached to $t_G$ in this article — the toy accumulation law, the per-quantum Fisher information $f_1$ , the crossover tolerance $\delta^\ast$ — is a phenomenological construction consistent with a rigorous symmetry result, not a measured or simulated quantity, and it should be read that way.