= Resolved sideband cooling
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Resolved sideband cooling removes motional quanta by selectively driving a red <motional sideband> and then resetting the internal <quantum state> through <spontaneous emission> or <optical pumping>. Spectral resolution requires the effective cooling-transition width smaller than the motional <angular frequency> in the same units. A narrow <Raman transition> can meet that requirement even when the optical transition used for <Doppler cooling> is broad.
The reset is essential: the coherent red <motional sideband> merely exchanges internal and motional excitation reversibly. To see the distinction, an ideal pulse sends $|g,1\rangle$ to $-i|e,0\rangle$; the same interaction can send it back. An ideal dissipative reset instead takes $|e,0\rangle$ to $|g,0\rangle$, with information and <energy> carried into the environment. Repeating this cycle accumulates population near the motional <ground state>. Recoil during the reset can add motion, and off-resonant excitation can disturb $|g,0\rangle$; neither is included in the ideal pulse below.
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