Efficient vibrational state coupling in an optical tilted-washboard potential via multiple spatial translations and application to pulse echo

TL;DR

This study demonstrates that using multiple spatial translations in an optical lattice enhances vibrational state coupling and pulse-echo coherence in ultracold atoms, outperforming traditional single-step and Gaussian pulses.

Contribution

It introduces a novel pulse sequence with multiple spatial translations that improves vibrational state coupling and coherence in a tilted-washboard potential.

Findings

Square pulses outperform Gaussian and single-step pulses in coupling efficiency.

Enhanced pulse-echo signals allow probing of longer coherence times.

Shallow lattices exhibit more efficient vibrational state coupling.

Abstract

We measure the application of simple and compound pulses consisting of time-dependent spatial translations to coupling vibrational states of ultracold 85Rb atoms in a far-detuned 1D optical lattice. The lattice wells are so shallow as to support only two bound states, and we prepare the atoms in the ground state. The lattice is oriented vertically, leading to a tilted-washboard potential analogous to those encountered in condensed-matter systems. Experimentally, we find that a square pulse consisting of lattice displacements and a delay is more efficient than single-step and Gaussian pulses. This is described as an example of coherent control. It is striking that contrary to the intuition that soft pulses minimize loss, the Gaussian pulse is outperformed by the square pulse. Numerical calculations are in strong agreement with our experimental results and show the superiority of the square pulse to the single-step pulse for all lattice depths and to the Gaussian pulse for lattice depths greater than 7 lattice recoil energies. We also compare the effectiveness of these pulses for reviving oscillations of atoms in vibrational superposition states using the pulse-echo technique. We find that the square and Gaussian pulses result in higher echo amplitudes than the single-step pulse. These improved echo pulses allow us to probe coherence at longer times than in the past, measuring a plateau which has yet to be explained. In addition, we show numerically that the vibrational state coupling due to such lattice manipulations is more efficient in shallow lattices than in deep lattices.