The frequency Ω = | r | / ℏ = β 2 + γ 2 + δ 2 / ℏ = | Ω R | 2 + Δ 2 {\displaystyle \Omega =|\mathbf {r} |/\hbar ={\sqrt {\beta ^{2}+\gamma ^{2}+\delta ^{2}}}/\hbar ={\sqrt {|\Omega _{R}|^{2}+\Delta ^{2}}}} is called the generalised Rabi frequency, Ω R = ( β + i γ ) / ℏ {\displaystyle \Omega _{R}=(\beta +i\gamma )/\hbar } is called the Rabi frequency, and Δ = δ / ℏ {\displaystyle \Delta =\delta /\hbar } is called the detuning. At zero detuning, P 1 ( t ) = cos 2 ⁡ ( | Ω R | t ) {\displaystyle P_{1}(t)=\cos ^{2}(|\Omega _{R}|t)} , i.e. there is Rabi flopping from guaranteed occupation of state 1, to guaranteed occupation of state 2, and back to state 1 etc with frequency | Ω R | {\displaystyle |\Omega _{R}|} . As the detuning is increased away from zero, the frequency of the flopping increases (to Ω {\displaystyle \Omega } ) and the amplitude decreases to 1 − Δ 2 / Ω 2 {\displaystyle 1-\Delta ^{2}/\Omega ^{2}} .