^{87} Rb87Rb
atoms are known to have long-lived Rydberg excited states with
controllable excitation amplitude (detuning) and strong repulsive van
der Waals interaction V_{{r} {r'}}Vrr′
between excited atoms at sites {r}r
and {r'}r′.
Here we study such atoms in a two-leg ladder geometry in the presence of
both staggered and uniform detuning with amplitudes
\DeltaΔ
and \lambdaλ
respectively. We show that when V_{{r r'}} \gg(\ll) \Delta, \lambdaVrr′≫(≪)Δ,λ
for |{r}-{r'}|=1(>1)|r−r′|=1(>1),
these ladders host a plateau for a wide range of
\lambda/\Deltaλ/Δ
where the ground states are selected by a quantum order-by-disorder
mechanism from a macroscopically degenerate manifold of Fock states with
fixed Rydberg excitation density 1/41/4.
Our study further unravels the presence of an emergent Ising transition
stabilized via the order-by-disorder mechanism inside the plateau. We
identify the competing terms responsible for the transition and estimate
a critical detuning \lambda_c/\Delta=1/3λc/Δ=1/3
which agrees well with exact-diagonalization based numerical studies. We
also study the fate of this transition for a realistic interaction
potential V_{{r} {r'}} = V_0 /|{r}-{r'}|^6Vrr′=V0/|r−r′|6,
demonstrate that it survives for a wide range of
V_0V0,
and provide analytic estimate of \lambda_cλc
as a function of V_0V0.
This allows for the possibility of a direct verification of this
transition in standard experiments which we discuss.