The basic principle for Rydberg mediated gates is called the Rydberg blockade. Consider two neutral atoms in their respective ground states. When they are close to each other, their interaction potential is dominated by van Der Waals force V q q ≈ ≈ μ μ B 2 R 6 where μ μ B is the Bohr Magneton and R is the distance between the atoms. This interaction is very weak, around 10 − − 5 Hz for R = 10 μ μ m . When one of the atoms is put into a Rydberg state (state with very high principal quantum number), the interaction between the two atoms is dominated by second order dipole-dipole interaction which is also weak. When both of the atoms are excited to a Rydberg state, than the resonant dipole-dipole interaction becomes V r r = ( n 2 e a 0 ) 2 R 3 where a 0 is the Bohr radius. This interaction is around 100 MHz at R = 10 μ μ m , around twelve orders of magnitude larger. This interaction potential induces a blockade, where-in, if one atom is excited to a Rydberg state, the other nearby atoms cannot be excited to a Rydberg state because the two-atom Rydberg state is far detuned. This phenomena is called the Rydberg blockade. Rydberg mediated gates make use of this blockade as a control mechanism to implement two qubit controlled gates.