Narrow Linewidth Laser Cooling (SWAP)

Spatial setup of the atom standing-wave configuration. b) Two-level state structure. c) Top: Laser frequency as a function of time. The approximate resonance frequencies for an atom with velocity v are labeled. Bottom: The ideal excited state fraction over time. d) Transfer of average momentum to zero over several sweeps.

SWAP (Sawtooth Wave Adiabatic Passage) cooling is a new laser cooling mechanism that offers significant advantages over traditional cooling techniques for particles with narrow linewidth transitions. The particles interact with counter-propagating laser beams that are repeatedly, linearly swept over the transition frequency. Compared to Doppler cooling, SWAP cooling's reduced reliance on spontaneous emission allows for larger slowing forces per scattering event, i.e., a higher quantum efficiency. Using simulation techniques such as quantum Monte Carlo wavefunction and c-number Langevin equation methods, we characterize the parameters necessary to achieve significant phase space compression with minimal scattering events. We also investigate other quantities of interest, such as minimum temperatures, conservative forces and capture range. SWAP cooling's ability to promote significant coherent transfer suggests its applicability to systems lacking closed cycling transitions, such as molecules.

Cooling of a particle to the recoil limit after 5 sweep-wait cycles. Top inset: A snapshot of the momentum distribution halfway through the 7th sweep. Bottom inset: A closer look at the cooling trajectory once it has equilibrated. The recoil limit is included as a green line.