Vibrational ground state cooling of a neutral atom in a tightly focused optical dipole trap

Abstract

It was recently shown that a single atom can efficiently scatter photons out of a focused coherent light beam [1, 2, 3]. The scattering probability is strongly dependent on a thermal motion of the atom and can be maximized if the atom is well localized at a focus. To achieve that, we implement a Raman sideband cooling technique that is commonly used in ion traps [4]. Our trap, formed by focused Gaussian light beam at 980nm, has characteristic frequencies of ντ = 55 kHz and l = 7 kHz corresponding to transverse and longitudinal confinements. A single 87Rb atom is loaded into the trap from an optical molasses. Two Raman beams couple the motional states of F = 2 and F = 1 manifolds with a Lamb-Dicke parameter = 0.084 (Figure 1). The Raman beams are oriented such that momentum transfer occurs only along the strong confinement of the trap with ντ = 55 kHz. The cooling sequence consists of following steps: (1) initial preparation of the atom in F = 2,mF = 2 Zeeman state, (2) Raman transfer between the motional states F = 2,mF = 2,N and F = 1,mF = 1,N 1. (3) recycling the atomic population back to F = 2,mF = 2 state via an optical pulse resonant to 5P3/2, F = 2 state thus removing a phonon via spontaneous emission. © 2011 IEEE.