 Resolved sideband cooling

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 $|g,1⟩$ to $-i|e,0⟩$; the same interaction can send it back. An ideal dissipative reset instead takes $|e,0⟩$ to $|g,0⟩$, 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 $|g,0⟩$; neither is included in the ideal pulse below.

Resolved sideband cooling is a technique used primarily in the context of quantum physics and atom optics to cool an oscillator, such as a trapped ion or an atom in an optical lattice, down to its quantum ground state. This method exploits the interaction between the oscillatory motion of the particle and a laser field to reduce the energy of the particle's motion. The concept arises from the observation that an oscillator can absorb or emit energy in discrete packets (quanta) when interacting with light.