van der Waals interaction of an atom near a fiber tip

Herschel S. Pilloff

Antoine Browaeys

Haruhiko Ito, Akifumi Takamizawa, H. Tanioka +1 more

We present a new scheme of atom manipulation by means of a sharpened optical fiber with near-field light. In particular, we discuss the feasibility of deflecting and trapping Rb atoms. The optical potential produced by the dipole force is estimated from numerical calculations based on the Yukawa-type intensity distribution. We show that a slow Rb atom can be deflected at a large deflection angle. A static atom trap can be made near the tip of a sharpened fiber. A cold Rb atom is captured at the minimum of the trap potential composed of the repulsive optical potential and the attractive van der Waals potential. A spatial intensity distribution of an optical near-field produced near the tip of a protrusion-type fiber is measured in the fiber-to-probe configuration with a shear-force technique. We also describe an atom funnel to form a cold atomic beam required for the near-field light manipulation.

Burkley D. Patterson

We present measurements of the transmission spectra of 87Rb atoms at 780 nm in the vicinity of a nanofiber. A uniform distribution of fixed atoms around a nanofiber should produce a spectrum that is broadened towards the red due to shifts from the van der Waals potential. If the atoms are free, this also produces an attractive force that accelerates them until they collide with the fiber which depletes the steady-state density of near-surface atoms. It is for this reason that measurements of the van der Waals interaction are sparse. We confirm this by measuring the spectrum cold atoms from a magneto-optical trap around the fiber, revealing a symmetric line shape with nearly the natural linewidth of the transition. When we use an auxiliary 750 nm laser we are able to controllably desorb a steady flux of atoms from the fiber that reside near the surface (less than 50 nm) long enough to feel the van der Walls interaction and produce an asymmetric spectrum. We quantify the spectral asymmetry as a function of 750 nm laser power and find a maximum. Our model, which that takes into account the change in the density distribution, qualitatively explains the observations. In the future this can be used as a tool to more comprehensively study atom-surface interactions.

Aleksandr A. Kamenski, Nikolai L. Manakov, Sergey N. Mokhnenko +2 more

Fam Le Kien, D F Kornovan, S Sahar S Hejazi +4 more

We study the force of light on a two-level atom near an ultrathin optical fiber using the mode function method and the Green tensor technique. We show that the total force consists of the driving-field force, the spontaneous-emission recoil force, and the fiber-induced van der Waals potential force. Due to the existence of a nonzero axial component of the field in a guided mode, the Rabi frequency and, hence, the magnitude of the force of the guided driving field may depend on the propagation direction. When the atomic dipole rotates in the meridional plane, the spontaneous-emission recoil force may arise as a result of the asymmetric spontaneous emission with respect to opposite propagation directions. The van der Waals potential for the atom in the ground state is off-resonant and opposite to the off-resonant part of the van der Waals potential for the atom in the excited state. Unlike the potential for the ground state, the potential for the excited state may oscillate depending on the distance from the atom to the fiber surface.