  We present a microscopic model of a bridge connecting two large
Anti-de-Sitter Universes. The Universes admit a holographic description as
three-dimensional ${\cal N}=4$ supersymmetric gauge theories based on large
linear quivers, and the bridge is a small rank-$n$ gauge group that acts as a
messenger. On the gravity side, the bridge is a piece of a highly-curved
AdS$_5\times$S$_5$ throat carrying $n$ units of five-form flux. We derive a
universal expression for the mixing of the two massless gravitons: $M^2 \simeq
3n^2 (\kappa_4^2 + \kappa_4^{\prime\,2})/16\pi^2$, where $M$ is the mass
splitting of the gravitons, $\kappa_4^2, \kappa_4^{\prime\,2}$ are the
effective gravitational couplings of the AdS$_4$ Universes, and $n$ is the
quantized charge of the gate. This agrees with earlier results based on
double-trace deformations, with the important difference that the effective
coupling is here quantized. We argue that the apparent non-localities of
holographic double-trace models are resolved by integrating-in the (scarce)
degrees of freedom of the gate.
