A quantum scattering interferometer

Abstract

The collision of two ultracold atoms results in a quantum mechanical superposition of the two possible outcomes: each atom continues without scattering, and each atom scatters as an outgoing spherical wave with an s-wave phase shift. The magnitude of the s-wave phase shift depends very sensitively on the interaction between the atoms. Quantum scattering and the underlying phase shifts are vitally important in many areas of contemporary atomic physics, including Bose-Einstein condensates, degenerate Fermi gases, frequency shifts in atomic clocks and magnetically tuned Feshbach resonances. Precise experimental measurements of quantum scattering phase shifts have not been possible because the number of scattered atoms depends on the s-wave phase shifts as well as the atomic density, which cannot be measured precisely. Here we demonstrate a scattering experiment in which the quantum scattering phase shifts of individual atoms are detected using a novel atom interferometer. By performing an atomic clock measurement using only the scattered part of each atom's wavefunction, we precisely measure the difference of the s-wave phase shifts for the two clock states in a density-independent manner. Our method will enable direct and precise measurements of ultracold atom-atom interactions, and may be used to place stringent limits on the time variations of fundamental constants.

Sensitivity of ultracold-atom scattering experiments to variation of the fine-structure constant

“…[22], this enhancement near narrow Feshbach resonances (e.g., near g-wave resonance in Cs 2 ) may reach 10 9 − 10 12 . Recently, a method for measurement of the scattering length to the accuracy 10 −6 was proposed [29]. A combination of these two ideas makes the repeating measurements of the scattering length a promising method to study the variation of the fundamental constants in the laboratory.…”

Avoided crossings between bound states of ultracold cesium dimers

“…It may be seen that a calculation including only the g͑4,5͒ intermediate states captures most of the crossing strength but does not reproduce the level shifts well. Conversely, a calcu- g (6) g (3) d (4,5) g (3) g (6) d ( 4g (3) 6g (6) FIG. 4.…”

Quantum Scattering in an Optical Collider for Ultracold Atoms

“…In an early example, Gibble et al [5] used a cesium fountain to launch cold clouds of atoms in an upward direction, where they would collide -a technique that was later refined to measure the p-wave threshold of cesium [6]. The atomic fountain experiments also subsequently introduced an interferometric method that considered the effect of collisions on atoms in a superposition of internal clock states [7] and this was used to locate Feshbach resonances and measure their shift with magnetic field [8]. However, as this technique measures the relative scattering phase shift between two clock states in cesium, it cannot be readily extended to arbitrary species of atoms in arbitrary internal quantum states.…”