Which method is primarily used to achieve zero-energy state

Laser cooling uses photons to slow down atoms or ions. When an atom absorbs a photon, it recoils, and if the photon's frequency is slightly below an atomic resonance frequency (a red-detuned laser), the atom will absorb photons more effectively when it is moving towards the laser. This absorption and subsequent re-emission of photons reduces the atom's kinetic energy, effectively cooling it down. By carefully tuning the lasers, atoms can be cooled to extremely low temperatures, approaching absolute zero, which is a state of minimal energy.