# How is a Rydberg Blockade Radius defined?

Rydberg blockade is a phenomena in 3 or more level systems of Rydberg dressed atoms.

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The wikipedia artilce on Rydberg atoms cites several papers from 2007 and 2008 that have "Rydberg blockage" in their titles. –  dmckee Mar 9 '13 at 16:35

## 1 Answer

In zero electric field, the interactions energy between two Rydberg atoms is $U=C_6 r^{-6}$. If the Rydberg transition is driven with an (effective) Rabi frequency $\Omega$, then the blockade radius is $$R_b = \left( \frac{\hbar\Omega}{C_6} \right)^{-1/6}$$ If one atom is excited to the Rydberg state, a second atom will be detuned by just enough to prevent a complete transition.

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