Clock transition
= Clock transition
{title2=$\partial\omega_{21}/\partial B=0$}
A transition whose <frequency> is stationary to first order in a specified perturbation at an operating point. For magnetic sensitivity, the derivative shown vanishes, but second and higher derivatives can remain nonzero. A <clock transition> need not have zero individual <energy> slopes: equal slopes suffice. Optical light shifts and other perturbations require their own sensitivity analysis.