High-energy-resolution measurements of an ultracold-atom--ion collisional cross section

Editors' Suggestion

High-energy-resolution measurements of an ultracold-atom–ion collisional cross section

Ruti Ben-shlomi, Meirav Pinkas, Ziv Meir, Tomas Sikorsky, Or Katz, Nitzan Akerman, and Roee Ozeri

Phys. Rev. A 103, 032805 – Published 5 March 2021

Abstract

The cross section of a given process fundamentally quantifies the probability for that process to occur. In the quantum regime of low energies, the cross section can greatly vary with collision energy due to quantum effects. Here, we report on a method to directly measure the atom-ion collisional cross section in the energy range of 0.2– $12 mK \times k_{B}$ , by shuttling ultracold atoms trapped in an optical-lattice across a radio-frequency trapped ion. Using this method, the average number of atom-ion collisions per experiment is below one, such that the energy resolution is not limited by the broad (power-law) steady-state atom-ion energy distribution. Here, we estimate that the energy resolution is below $200 μ K \times k_{B}$ , limited by drifts in the ion's excess micromotion compensation and can be reduced to the tens of $μ K \times k_{B}$ regime. This resolution is one order-of-magnitude better than previous experiments measuring cold atom-ion collisional cross-section energy dependence. We used our method to measure the energy dependence of the inelastic collision cross sections of a nonadiabatic electronic-excitation-exchange (EEE) and spin-orbit change (SOC) processes. We found that, in the measured energy range, the EEE and SOC cross sections statistically agree with the classical Langevin cross section. This method allows for measuring the cross sections of various inelastic processes and opens the possibility to search for atom-ion quantum signatures such as shape resonances.

Received 19 October 2020
Accepted 9 February 2021

DOI:https://doi.org/10.1103/PhysRevA.103.032805

Physics Subject Headings (PhySH)

Atomic & molecular collisions Chemical reactions Electronic excitation & ionization Electronic structure of atoms & molecules Electronic transitions Fine & hyperfine structure Interatomic & molecular potentials Potential energy surfaces Ultracold collisions

Atomic, Molecular & Optical

Authors & Affiliations

Ruti Ben-shlomi ^*, Meirav Pinkas, Ziv Meir ^†, Tomas Sikorsky ^‡, Or Katz, Nitzan Akerman, and Roee Ozeri

Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 7610001, Israel

^*ruti.ben-shlomi@weizmann.ac.il
^†Present address: Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel, Switzerland.
^‡Present address: Atominstitut - E141, Technische Universitt Wien, Stadionallee 2, 1020 Vienna, Austria.

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 103, Iss. 3 — March 2021

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
An illustration of the atom-ion system and the velocity profiles of the transport. (a) The experimental setup. Rb atoms are held in a ${CO}_{2}$ dipole trap, loaded onto the 1D optical lattice made of two counterpropagating beams. The atoms occupy $\approx 40$ lattice sites. The distance between the loading position of the atoms in the upper chamber and the ion in the lower chamber is 248 cm, as indicated by the dotted black curve. The figure is not to scale. (b) The atoms' position as a function of their velocity, for five different collision energies: 0, 0.1, 1, 5, and $10 k_{B} \times mK$ (from black to blue and from left to right). The background represents the different stages of transport: acceleration (top, pale blue), movement in a constant velocity (middle, yellow) and deceleration to the desired collision velocity (bottom, pink). The atoms continued to be transported by the lattice at a constant velocity, even after colliding with the ion. (c) The atoms' velocity profile. The right $y$ axis, $Δ f$ , is the frequency difference between the two lattice AOMs. The diamond indicates the times for which the atoms collide with the ion for each velocity profile.
Reuse & Permissions
Figure 2
Quench cross section as a function of the collision energy. (a) The total quench probability (top, green) and for the (b) EEE (middle, blue) and (c) SOC (bottom, red) channels, separately. Error bars are $1 σ$ standard deviation of a binomial distribution and also include systematic noise, as explained in the body of the text. Smaller error bars indicate areas over which more repetitions were performed. The solid black curve is an exponential fit to $A E^{α}$ , where the exponents given by the fits are $α = - 0.51$ (3), $- 0.53 (4)$ , and $- 0.48 (6)$ , respectively. The dashed black lines indicate the Langevin cross section given by Eq. (8).
Reuse & Permissions
Figure 3
(a) The distribution of the ion's energy $E_{ion}$ after a single collision with an atom in the moving optical lattice, for different lattice velocities, $E_{col}$ , ranging from 0.2 to 11 mK (from left to right). The distributions are calculated by a molecular-dynamics simulation that takes into account the Paul trap potential and the EMM of the ion.
Reuse & Permissions
Figure 4
Maximum likelihood estimation for a semiclassical cross section for the non-normalized, EEE channel (up) and SOC channel (down), with and without a Gaussian resonance, green (gray) and black, respectively. The $p$ values are 0.091 and 0.0088, which correspond to $1.7 σ$ and $2.6 σ$ for the EEE and SOC channels, respectively.
Reuse & Permissions
Figure 5
The frequency profiles of the two AOMs controlling the frequency of the lattice laser beams. The solid (dotted-dashed) curve refers to the frequency set by the function-generator of the upper (and lower) lattice beam.
Reuse & Permissions

Physical Review A

covering atomic, molecular, and optical physics and quantum information