Observation of the ⁸⁷Rb 5S_1/2 to 4D_3/2 electric quadrupole transition at 516.6 nm mediated via an optical nanofibre

Abstract

Light guided by an optical nanofibre can have a very steep evanescent field gradient extending from the fibre surface. This can be exploited to drive electric quadrupole transitions in nearby quantum emitters. In this paper, we report on the observation of the 5S 1/2 → 4D 3/2 electric quadrupole transition at 516.6 nm (in vacuum) in laser-cooled 87 Rb atoms using only a few µW of laser power propagating through an optical nanofibre embedded in the atom cloud. This work extends the range of applications for optical nanofibres in atomic physics to include more fundamental tests.

Quadrupole absorption rate and orbital angular momentum transfer for atoms in optical vortices

“…Research has also dealt with the study of the mechanical forces on atoms due to the coupling of optical vortices, such as the Laguerre-Gaussian (LG) and Bessel-Gaussian modes, to quadrupole-active atomic transitions [6,10,19] and the results displayed a considerable enhancement in the case of twisted beams due to the gradient coupling, which increases with increasing winding number. Quadrupole transitions have also been observed in the case of Rb atoms by evanescent light when Rb is localized in the vicinity of an optical nanofiber [9].…”

“…where a μ = 4πǫ 0h 2 μe 2 = a 0 m e μ is the reduced Bohr radius, L 2L+1 n−L−1 (ρ(r)) are the associated Laguerre polynomials, and ρ(r) = 2Z a r na μ . The valence electron of the Cs atom sees an effective nuclear charge of Z a = 8.56 [9,[31][32][33][34][35]. Using Eq.…”

“…The absorption or emission of any type of light by atoms is accompanied by the transfer of linear momentum between the light and the atoms, and this effect has been exploited in the cooling and trapping of atoms [4][5][6]. It has also been established that the application of vortex light to atoms affects the center-of-mass motion [6,7] via the dipole force, but the quadrupole force too can influence atomic motion attracting the atoms to high-or low-intensity regions of the light field [8][9][10].…”

Rubidium atom spectral lineshapes in high intensity electric fields near an optical nanofibre

“…We focus our discussion on optical nanofibres, which provide tight confinement of light beyond the Rayleigh range and also serve as an ideal channel for light propagation. Optical nanofibres have been used to efficiently probe, manipulate and trap cold, alkali atoms [6,7,8,9,10] with recent works extending atom and ONF studies to the observation of a quadrupole transition in 87 Rb atoms [11], the demonstration of quadrature squeezing of nanofibreguided light [12], and a determination of the polarization dependency of spin selection in laser-cooled atoms [13].…”

Spin selection in single-frequency two-photon excitation of alkali-metal atoms

“…In one of the more popular systems, neutral atoms are coupled to the evanescent field of a vacuum-clad optical nanofiber (ONF) [17][18][19][20][21][22][23][24]. Strong confinement of light around the ultrathin ONF waist region has led to demonstrations of two-photon and nonlinear atomic processes at ultralow excitation powers [25][26][27][28], including an electric quadrupole transition driven by a few microwatts [29]. Owing to the recent achievements of full polarization control for light guided in single-mode nanofibers [30][31][32], spin selection for two-photon excitation in ONF-coupled atoms can finally be explored experimentally.…”