We investigate the photoassociation dynamics of exactly two laser-cooled ^{85}Rb atoms in an optical tweezer and reveal fundamentally different behavior to photoassociation in many-atom ensembles. We observe nonexponential decay in our two-atom experiment that cannot be described by a single rate coefficient and find its origin in our system's pair correlation. This is in stark contrast to many-atom photoassociation dynamics, which are governed by decay with a single rate coefficient. We also investigate photoassociation in a three-atom system, thereby probing the transition from two-atom dynamics to many-atom dynamics. Our experiments reveal additional reaction dynamics that are only accessible through the control of single atoms and suggest photoassociation could measure pair correlations in few-atom systems. It further showcases our complete control over the quantum state of individual atoms and molecules, which provides information unobtainable from many-atom experiments.
We investigate the photoassociation dynamics of exactly two laser-cooled ^{85}Rb atoms in an optical tweezer and reveal fundamentally different behavior to photoassociation in many-atom ensembles. We observe nonexponential decay in our two-atom experiment that cannot be described by a single rate coefficient and find its origin in our system's pair correlation. This is in stark contrast to many-atom photoassociation dynamics, which are governed by decay with a single rate coefficient. We also investigate photoassociation in a three-atom system, thereby probing the transition from two-atom dynamics to many-atom dynamics. Our experiments reveal additional reaction dynamics that are only accessible through the control of single atoms and suggest photoassociation could measure pair correlations in few-atom systems. It further showcases our complete control over the quantum state of individual atoms and molecules, which provides information unobtainable from many-atom experiments.
In this thesis, we present experimental methods and results for direct measurements of the photoassociation of two individual ultra-cold rubidium-85 atoms, each prepared in the |F = 2,m_F = −2⟩ ground state. From there two individual rubidium-85 atoms are loaded into separate far-off resonance optical tweezers which are near-deterministically prepared into |F = 2,m_F = −2⟩. The two optical tweezers are then merged and the atoms are exposed to photoassociation light. To ensure the correct frequency of photoassociation light is used a dual cavity locking scheme, capable of generating frequencies with a stability of ±425.7 kHz over a large wavelength range for use in photoassociation spectroscopy, was developed. From there, a light modulation technique is implemented to isolate the photoassociation event from unwanted far-off resonance trap effects, such as the AC Stark shift. By controlling the intensity, frequency, and duration parameters of the photoassociation pulses applied to the rubidium atoms, frequency-dependent, and time-dependent atom loss is observed for a single band of the 0^{+}_{u} series; located at 377.00067±0.00006 THz. The resonance and linewidth data exhibits the same behaviour as photoassociation performed on large atom ensembles within the many-body regime. However, two distinct fast and slow photoassociation rates are observed in contrast to the many-body regime where only a single photoassociation rate constant, K_{PA}, has been reported. This marks a novel physical process which heretofore has not been reported in the field of atomic or molecular physics.
The quantum statistics of atoms is typically observed in the behavior of an ensemble via macroscopic observables. However, quantum statistics modifies the behavior of even two particles. Here, we demonstrate near-complete control over all the internal and external degrees of freedom of two laser-cooled (87)Rb atoms trapped in two optical tweezers. This controllability allows us to observe signatures of indistinguishability via two-particle interference. Our work establishes laser-cooled atoms in optical tweezers as a promising route to bottom-up engineering of scalable, low-entropy quantum systems.
We present a new approach to investigating Rydberg molecules by demonstrating the formation and characterization of individual Rb^{*}Cs Rydberg molecules using optical tweezers. By employing single-atom detection of Rb and Cs, we observe molecule formation via correlated loss of both species and study the formation dynamics with single-particle resolution. We control the interatomic distances by manipulating the relative wave function of atom pairs using the tweezer intensity, optimizing the coupling to molecular states and exploring the effect of the tweezer on these states. Additionally, we demonstrate molecule association with atoms trapped in separate tweezers, paving the way for state-selective assembly of polyatomic molecules. The observed binding energies, molecular alignment, and bond lengths are in good agreement with theory. Our approach is broadly applicable to Rydberg tweezer platforms, expanding the range of available molecular systems and enabling the integration of Rydberg molecules into existing quantum science platforms.
Chemical reactions typically proceed via stochastic encounters between reactants. Going beyond this paradigm, we combined exactly two atoms in a single, controlled reaction. The experimental apparatus traps two individual laser-cooled atoms [one sodium (Na) and one cesium (Cs)] 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.
This thesis presents experimental methods and results for comparative measurements of the photoassociation dynamics of two individual ultracold rubidium-85 atoms when geometry of the trapping potential is changed. An asymmetric trap geometry is hypothesized to change the dynamics of two-atom photoassociation, as the asymmetry increases the probability of the two-atom wavefunction forming as a peaked state. Two atoms in an optical trap, of which the symmetry is controlled via a mechanical iris, are exposed to photoassociation light. The results from the asymmetric trap are compared to the photoassociation dynamics of atoms in a symmetric trap. A paired sample t-test determines a statistically significant difference in the two measurements. This t-test yields a p-value no higher than p = 7 × 10−3 , thus it is likely that the two measurements do not come from the same distribution. This aligns with our hypothesis, and is a new, enlightening piece of research done in the field of few-atom physics.
Abstract The complex collisional properties of atoms fundamentally limit investigations into a range of processes in many-atom ensembles. In contrast, the bottom-up assembly of few- and many-body systems from individual atoms offers a controlled approach to isolating and studying such collisional processes. Here, we use optical tweezers to individually assemble pairs of trapped 85Rb atoms, and study the spin dynamics of the two-body system in a thermal state. The spin-2 atoms show strong pair correlation between magnetic sublevels on timescales exceeding one second, with measured relative number fluctuations 11.9 ± 0.3 dB below quantum shot noise, limited only by detection efficiency. Spin populations display relaxation dynamics consistent with simulations and theoretical predictions for 85Rb spin interactions, and contrary to the coherent spin waves witnessed in finite-temperature many-body experiments and zero-temperature two-body experiments. Our experimental approach offers a versatile platform for studying two-body quantum dynamics and may provide a route to thermally robust entanglement generation.