the qubit is cooled. As the diamond narrows to the point $A = A^*$, the narrowest qubit step is observed. This is the universal cooling condition: only one of the two side avoided crossings ($\Delta_{0,1}$ or $\Delta_{1,0}$) is reached and, thereby, strong transitions with relaxation to the ground state result for all $\delta f_{\rm dc}$. In contrast, for $A > A^*$, both side avoided crossings ($\Delta_{0,1}$ and $\Delta_{1,0}$) are reached simultaneously for $|\delta f_{\rm{dc}}| < A-A^*$, leading once again to a large population transfer between $|0R\rangle$ and $|0L\rangle$, and opening the second diamond feature (see Fig. \[fig:5\]).

The cooling exhibits a rich structure as a function of driving frequency and detuning, resulting from the manner in which state $|1R\rangle$ is accessed (Fig. \[fig:4\]C). Transitions occur via a (multiphoton) resonant or adiabatic passage process when the driving frequency is high or low enough, respectively [@Berns06a; @Valenzuela06a]. At high frequencies (800 and 400 MHz in Fig. \[fig:4\]E) well-resolved resonances of n-photon transitions are observed and cooling is thus maximized near resonances. At intermediate frequencies (400 and 200 MHz), Mach-Zehnder interference at the side avoided crossing $\Delta_{01}$ becomes more prominent and modulates the intensity of the n-photon resonances [@Oliver05a; @Berns06a]. Below $\nu=200\,{\rm MHz}$, 