Carrier-free Raman manipulation of trapped neutral atoms

Abstract

We experimentally realize an enhanced Raman control scheme for neutral atoms that features an intrinsic suppression of the two-photon carrier transition, but retains the sidebands which couple to the external degrees of freedom of the trapped atoms. This is achieved by trapping the atom at the node of a blue detuned standing wave dipole trap, that acts as one field for the two-photon Raman coupling. The improved ratio between cooling and heating processes in this configuration enables a five times lower fundamental temperature limit for resolved sideband cooling. We apply this method to perform Raman cooling to the two-dimensional vibrational ground state and to coherently manipulate the atomic motion. The presented scheme requires minimal additional resources and can be applied to experiments with challenging optical access, as we demonstrate by our implementation for atoms strongly coupled to an optical cavity.

Increased dimensionality of Raman cooling in a slightly nonorthogonal optical lattice

“…Reference [8] overcame this problem by driving a second-order red sideband with ∆n 1 = ∆n 2 = −1. The corresponding two-photon Rabi frequency is suppressed by the square of the Lamb-Dicke parameter, which reduces the cooling rate.…”

“…Hence, the mean excitation number in the direction which is difficult to cool was experimentally limited to 0.3(2) in Ref. [8]. The goal of our work is to use cross-dimensional mixing with ϕ ≪ 1 and ω 1 ≈ ω 2 to overcome this problem, achieve 2D cooling without resorting to second-order sidebands, and thus reach lower mean excitation number.…”

“…5(a) show the results of a fit of ω + /2π and ω − /2π to the data, using Eqs. (7), (8), and where P 0 is the value of P z at which the avoided crossing occurs. The fit is performed for the red and blue data points simultaneously.…”

“…5(b) using Eqs. (7), (8), (10), (13), and (19)-(22). The duration t = 0.3 ms of the spectroscopy pulse is known prior to fitting.…”

“…To circumvent this problem, Ref. [8] drove second-order sideband transitions that are suppressed by the square of the Lamb-Dicke parameter, which makes these transitions quite weak. Hence, the mean number of vibrational excitations was experimentally limited to 0.3 (2) along the direction which is difficult to cool.…”