arXiv subjects

Prerna Paliwal

Publications and source records attributed to Prerna Paliwal.

5 recordsLinked to original sources

arXiv2025

Control of chemical reactions in radiofrequency ion traps

Over the past years, radiofrequency ion traps have become an attractive platform for studying chemical reactions as they enable a high degree of control over ion-molecule dynamics. In this review, we summarize techniques for the trapping and cooling of atomic and molecular ions in radiofrequency traps including Doppler and resolved-sideband laser cooling, sympathetic cooling, and cryogenic buffer-gas methods. We discuss strategies for controlling key reaction parameters: the preparation of specific internal quantum states by internal cooling, optical pumping, state-selective photoionization and quantum-logic spectroscopy; the manipulation of collision energies through micromotion control, dynamic trapping and combination with molecular beams; and the selection of molecular structure via isotopic substitution, conformational separation and isomer-specific ion generation. We illustrate applications of these approaches by discussing studies on quantum-state-dependent kinetics, quantum-resonance effects and structure-sensitive reactivity in ion-neutral collisions. We conclude by outlining future challenges, including full state-to-state reaction mapping, reaching the ultracold quantum regime free of micromotion, and the exploration of complex and chiral systems.

physics.chem-ph↗

arXiv2022

Observation of the P-wave Shape Resonance

Partial wave resonances are quasi-bound states that are formed by tunneling through the centrifugal barrier. Such states are important to collisions that deviate from the Langevin limit where direct collision path is suppressed due to quantum symmetry or a potential barrier. In such a case, quantum resonances play a major role in the dynamics at low temperatures where scattering process can be described mainly by the resonance contribution. Here we present the first observation of the lowest-lying partial wave resonance in the Penning ionization collisions between metastable neon and rovibrationally ground state HD molecules. We observe the resonance at an energy of $k_B\times$22mK taking advantage of the phase space correlation similar to atomic delta kick cooling. We show that the $p$-wave resonance position is particularly sensitive to the leading term of the van der Waals interaction. We also measure shape resonance at a higher angular momentum state, $l=6$, allowing us to disentangle and probe the short and the long parts of the intermolecular interaction.

physics.atom-ph↗

arXiv2021

Fano interference in quantum resonances from angle-resolved elastic scattering

Asymmetric spectral line shapes are a hallmark of interference of a quasi-bound state with a continuum of states. Such line shapes are well known for multichannel systems, for example, in photoionization or Feshbach resonances in molecular scattering. On the other hand, in resonant single channel scattering, the signature of such interference may disappear due to the orthogonality of partial waves. Here, we show that probing the angular dependence of the cross section allows us to unveil asymmetric Fano profiles also in a single channel shape resonance. We observe a shift in the peak of the resonance profile in the elastic collisions between metastable helium and deuterium molecules with detection angle, in excellent agreement with theoretical predictions from full quantum scattering calculations. Using a model description for the partial wave interference, we can disentangle the resonant and background contributions and extract the relative phase responsible for the characteristic Fano-like profiles from our experimental measurements.

quant-ph↗

arXiv2020

Determining the nature of quantum resonances by probing elastic and reactive scattering in cold collisions

Scattering resonances play a central role in collision processes in physics and chemistry. They help building an intuitive understanding of the collision dynamics due to the spatial localization of the scattering wavefunctions. For resonances that are localized in the reaction region, located at short separation behind the centrifugal barrier, sharp peaks in the reaction rates are the characteristic signature, observed recently with state-of-the-art experiments in low energy collisions. If, however, the localization occurs outside of the reaction region, mostly the elastic scattering is modified. This may occur due to above barrier resonances, the quantum analogue of classical orbiting. By probing both elastic and inelastic scattering of metastable helium with deuterium molecules in merged beam experiments, we differentiate between the nature of quantum resonances -- tunneling vs above barrier -- and corroborate our findings by calculating the corresponding scattering wavefunctions.

physics.chem-ph↗

arXiv2019

Phase protection of Fano-Feshbach resonances

Decay of bound states due to coupling with free particle states is a general phenomenon occurring at energy scales from MeV in nuclear physics to peV in ultracold atomic gases. Such a coupling gives rise to Fano-Feshbach resonances (FFR) that have become key to understanding and controlling interactions - in ultracold atomic gases, but also between quasiparticles such as microcavity polaritons. The energy positions of FFR were shown to follow quantum chaotic statistics. In contrast, lifetimes which are the fundamental property of a decaying state, have so far escaped a similarly comprehensive understanding. Here we show that a bound state, despite being resonantly coupled to a scattering state, becomes protected from decay whenever the relative phase is a multiple of $π$. We observe this phenomenon by measuring lifetimes spanning four orders of magnitude for FFR of spin-orbit excited molecular ions with merged beam and electrostatic trap experiments. Our results provide a blueprint for identifying naturally long-lived states in a decaying quantum system.

physics.atom-ph↗