Building one molecule from a reservoir of two atoms (1804.04752v2)

Abstract: Chemical reactions typically proceed via stochastic encounters between reactants. Going beyond this paradigm, we combine exactly two atoms into a single, controlled reaction. The experimental apparatus traps two individual laser-cooled atoms (one sodium and one cesium) in separate optical tweezers and then merges them into one optical dipole trap. Subsequently, photoassociation forms an excited-state NaCs molecule. The discovery of previously unseen resonances near the molecular dissociation threshold and measurement of collision rates are enabled by the tightly trapped ultracold sample of atoms. As laser-cooling and trapping capabilities are extended to more elements, the technique will enable the study of more diverse, and eventually more complex, molecules in an isolated environment, as well as synthesis of designer molecules for qubits.

Precision Synthesis of Molecular Entities Using Ultracold Atom Trapping Techniques

The paper Building one molecule from a reservoir of two atoms presents a method for synthesizing individual molecules by manipulating ultracold atoms with optical tweezers. This approach is focused on achieving precise control over the fundamental process of chemical reactions by isolating exactly two atoms and inducing their combination. The experiment uses single sodium (Na) and cesium (Cs) atoms confined in separate optical tweezers, which are subsequently merged into a single optical dipole trap to form an excited-state NaCs molecule via photoassociation.

Methodological Overview

The experimental setup involves trapping individual laser-cooled Na and Cs atoms in optical tweezers, followed by merging them into a singular optical dipole trap. This setup allows the formation of an excited-state NaCs molecule, demonstrating controlled reaction dynamics at the atomic scale. The initial ultracold environment, maintained below 1 μK, ensures that quantum motional characteristics significantly influence the reaction, aligning with quantum degenerate gas behavior. The precise control afforded by this method facilitates the observation of previously unseen resonances near the molecular dissociation threshold and enables measurement of collision rates. The use of tunable optical tweezers is crucial to independently manipulate Na and Cs, achieving a typical trap depth of 1 mK.

Experimental Results

Several key results are highlighted in the paper:

1. Atom Trapping and Merging: Cs atoms remain effectively trapped throughout the experimental sequence, while Na atoms are successfully retained when tweezers are optimally merged. The survival probability of Na reaches 94%, near the re-imaging survival probability of 96%.
2. Collision Dynamics: The paper reports rapid 2-body loss for mixed hyperfine states with a loss rate constant β = 5×10⁻¹¹ cm³/s. The hyperfine-spin-changing collisions prove exothermic enough to eject atoms from the trap, leading to rapid loss when Na and Cs are not optically pumped to their lowest energy hyperfine states.
3. Photoassociation Spectroscopy: The authors conduct spectroscopy to observe NaCs* vibrational levels near the dissociation threshold. The paper identifies three potential progressions beside the dissociation threshold, with vibrational levels fitted using the LeRoy-Bernstein dispersion model, yielding C₆ dispersion coefficients that correspond closely with theoretical predictions.

Implications and Future Prospects

This research represents an advancement in understanding individual chemical reactions by manipulating atom interactions at quantum mechanical levels. The ability to realize chemistry in minimal atomic regimes aids in probing elementary reaction processes with enhanced specificity and precision.

In terms of practical applications, the synthesis of molecules with defined quantum states has significant implications for quantum computing, specifically for creating molecular qubits. The demonstrated technique potentially extends to more complex molecules beyond simple bialkali atoms, including those deeply bound.

The methodology also opens avenues for exploring and utilizing quantum states in condensed systems, suggesting applications in quantum information processing and investigating quantum phases.

The demonstrated feasibility of precisely controlling atom interactions heralds a promising future for developing controlled molecular synthesis methods relevant for technological advancements in quantum applications and molecular engineering. The implications for manipulating a range of chemical species offer intriguing possibilities for expanded experimental and theoretical frameworks within the realms of ultracold chemistry and quantum physics.