arXiv subjects

Piotr Wcisło

Publications and source records attributed to Piotr Wcisło.

18 recordsLinked to original sources

arXiv2026

Density effects in precision laser spectroscopy of exotic helium atoms

Exotic helium atoms act as unique atomic traps for heavy, negatively charged particles, protecting them from nuclear annihilation and nuclear capture on timescales long enough to enable high-precision laser spectroscopy. Such measurements serve as stringent tests of three-body quantum electrodynamics and offer a direct route to determining fundamental particle masses. Motivated by upcoming spectroscopic efforts targeting pionic ($π^{-\,4}\mathrm{He}^+$) and kaonic ($K^{-\,4}\mathrm{He}^+$) helium, we present a rigorous theoretical evaluation of the collisional and density effects governing these systems. Using an ab initio potential energy surface and coupled-channel quantum scattering calculations, we study the collisional stability of the candidate metastable states against inelastic quenching in a cryogenic helium buffer gas. Furthermore, we provide theoretical reference values for the pressure broadening and pressure shift coefficients of the targeted transitions. These results establish an essential benchmark for future experiments, paving the way for refined determinations of the pion and kaon masses.

physics.atom-ph↗

arXiv2026

Full-dimensional quantum scattering calculations of rovibrationally excited HD+HD collisions

Full-dimensional quantum scattering calculations are reported for ro-vibrational transitions in HD+HD collisions using a highly accurate interaction potential for the H$_2$-H$_2$ system. Several near-resonant ro-vibrational transitions are identified that conserve the overall rotational angular momentum and nearly conserve the internal energy of the collision partners. Key anisotropic terms that drive the rotational transitions and angular momentum partial waves that contribute to low energy resonant features in the energy dependence of the cross sections are identified. The computed results are in agreement with total cross sections reported in previous experimental results, including resonant features in the energy dependence of the cross section. In particular, low-energy cross sections show a strong resonant feature associated with an $l=3$ partial wave in the incident channel. Rate coefficients for several inelastic rotational and ro-vibrational transitions are reported for temperatures ranging from $0.1$ K to $200$ K and they display a maximum between $1$ K-$10$ K reflecting the important contributions from the $l=3$ shape resonance that occurs around 2.5 K.

physics.atom-ph↗

arXiv2025

Letokhov-Chebotayev intracavity trapping spectroscopy of H$_2$

In the early days of laser spectroscopy Letokhov and Chebotayev proposed a scheme for measuring narrow spectral lines where the resolution is not restricted to Doppler effects because the molecules are entrained in a standing-wave light field. Now, such one-dimensional trapping in the intensity maxima of an intracavity field, slightly detuned from resonance, is experimentally demonstrated in the measurement of the very weak S(0) (2-0) quadrupole overtone transition in H$_2$ at 1189 nm. The trapping manifests as an extremely narrow absorption feature at the predicted zero-recoil position, a 70 kHz shift from the blue-recoil component observed in Lamb-dip spectroscopy. A quantitative analysis of the saturation and trapping conditions supports the findings.

physics.atom-ph↗

arXiv2025

Quantum calculation of the collision-induced line-shape effects in antiprotonic helium and the new accurate ab initio $\bar{p}$He$^{+}$-He potential energy surface

We present the first fully ab initio calculations of collision-induced broadening and shift of spectral lines in antiprotonic helium ($\bar{p}$He$^{+}$) perturbed by atomic helium. To overcome critical limitations of previous studies, we construct a new highly accurate potential energy surface (PES) that spans a wide range of $\bar{p}$He$^{+}$-He geometries relevant to all metastable states of the exotic helium atom. Rigorous quantum scattering calculations performed using the new PES yield scattering $S$-matrices from which we extract pressure broadening and shift coefficients for 50 transitions in antiprotonic helium-4 ($\bar{p}^{4}$He$^{+}$). This dataset provides the first rigorous benchmark for earlier semiclassical calculations and establishes a robust theoretical reference for high-precision spectroscopy of antiprotonic helium, which is used to test the fundamental charge, parity, and time reversal (CPT) symmetry. The results extend to temperatures relevant to non-gaseous phases of helium, supporting a new class of precision measurements. This study introduces a methodological framework for future investigations of other exotic systems, such as pionic or kaonic helium atoms, enabling the development of reference data for high-precision spectroscopy of these species - an essential component for improving the determination of the pion and kaon masses.

physics.atom-ph↗

arXiv2025

Experimental and theoretical investigation on N2 pressure-induced coefficients of the lowest rotational transitions of HCN

We present the first experimental determination of room-temperature N2 pressure broadening, speed dependent broadening, and pressure shift coefficients of the three lowest rotational lines of HCN. The experimental results served to assess the accuracy of a low-cost yet accurate computational strategy, which relies on a simplified characterization of the HCN-N2 interaction potential, and employs a novel approximate method of solving the quantum scattering problem. Building on the validation of this computational approach, the dataset was extended to higher rotational transitions, up to J(HCN)=5-4. For these transitions, we provide the temperature dependence of the pressure broadening coefficient, its speed dependence parameter, and the Dicke narrowing parameter. This new dataset can support and refine the modeling of HCN in both the terrestrial and Titan's atmospheres. This work constitutes an important step towards populating spectroscopic databases with accurate HCN line-shape parameters.

physics.chem-ph↗

arXiv2025

Leveraging resonant frequencies of an optical cavity for spectroscopic measurement of gas temperature and concentration

We introduce a spectroscopic approach to primary gas thermometry, harnessing precise optical cavity resonance frequencies and ab initio molecular line intensity calculations. By utilizing CO (3-0) vibrational band lines and cavity mode dispersion spectroscopy, we achieve an uncertainty of 82 ppm (24 mK at 296 K) in line-intensity-ratio thermometry (LRT) - over an order of magnitude lower than any previously reported spectroscopic thermometry at gas pressures above 1.2 kPa. This method extends high-precision spectroscopic thermometry across a pressure range an order of magnitude larger than prior techniques, enabling a fully optical, non-contact, and molecule-selective primary amount-of-substance measurement. We further demonstrate sub-permille uncertainty in gas concentration measurements across pressures from 50 Pa to 20 kPa, significantly enhancing the precision and versatility of spectroscopic gas metrology.

physics.optics↗

arXiv2025

Cavity-enhanced spectroscopy in the deep cryogenic regime -- new hydrogen technologies for quantum sensing

Spectrometers based on high-finesse optical cavities have proven to be powerful tools for applied and fundamental studies. Extending this technology to the deep cryogenic regime is beneficial in many ways: Doppler broadening is reduced, peak absorption is enhanced, the Boltzmann distribution of rotational states is narrowed, all unwanted molecular species disturbing the spectra are frozen out, and dense spectra of complex polyatomic molecules become easier to assign. We demonstrate a cavity-enhanced spectrometer fully operating in the deep cryogenic regime down to 4 K. We solved several technological challenges that allowed us to uniformly cool not only the sample but also the entire cavity, including the mirrors and cavity length actuator, which ensures the thermodynamic equilibrium of a gas sample. Our technology well isolates the cavity from external noise and cryocooler vibrations. This instrument enables a variety of fundamental and practical applications. We demonstrate a few examples based on accurate spectroscopy of cryogenic hydrogen molecules: accurate test of the quantum electrodynamics for molecules; realization of the primary SI standards for temperature, concentration and pressure in the deep cryogenic regime; measurement of the H$_{2}$ phase diagram; and determination of the ortho-para spin isomer conversion rate.

physics.atom-ph↗

arXiv2025

Intensities of all fine-structure resolved rovibrational electric quadrupole absorption lines in $^{16}$O$_2$($X^{3}Σ^{-}_{g}$) calculated with a new $\textit{ab initio}$ quadrupole moment curve

The intensities of all rovibrational electric quadrupole absorption lines in $^{16}$O$_2$($X^{3}Σ^{-}_{g}$), for which the vibrational quantum number is $v \leq 35$ and the total angular momentum quantum number is $J \leq 40$, are calculated in the intermediate coupling using a new $\textit{ab initio}$ quadrupole moment curve of the ground electronic state of O$_2$. The calculated values agree with those available in the HITRAN database, which at present includes only the $1$-$0$ fundamental vibrational band of $^{16}$O$_2$($X^{3}Σ^{-}_{g}$). We therefore recommend using the intensities of the vibrational overtones and hot bands reported here in updating the HITRAN database for O$_2$ in the upcoming 2024 edition.

physics.atom-ph↗

arXiv2024

Spectral line shape in the limit of frequent velocity-changing collisions

The speed-dependent spectral line profiles collapse into a simple Lorentz profile in the regime dominated by the velocity-changing collisions. We derive general formulas for the effective width and shift of the Lorentzian for arbitrary speed-dependent collisional broadening and shift and velocity-changing collision operators. For a quadratic speed dependence of collisional broadening and shift, and the billiard ball model of velocity-changing collisions, we provide simple analytical expressions for the effective Lorentzian width and shift. We show that the effective Lorentzian width and shift split into components originating from the: well-known Dicke-narrowed Doppler width, speed-averaged collisional broadening and shift, their speed dependencies, and a product term that mixes the contributions of the broadening and shift speed dependencies. We show how the components depend on rates of speed-changing and velocity-changing collisions related to the perturber/absorber mass ratio. We validate analytical formulas numerically on example of H$_{2}$ transition perturbed by He.

cond-mat.stat-mech↗

arXiv2024

Heterodyne dispersive cavity ring-down spectroscopy exploiting eigenmode frequencies for high-fidelity measurements

Measuring low light absorption with combined uncertainty < 1 permille is crucial in a wide range of applications. Popular cavity ring-down spectroscopy can provide ultra-high precision, below 0.01 permille, but its accuracy is strongly dependent on the measurement capabilities of the detection system and typically is about 10 permille. Here, we exploit the optical frequency information carried by the ring-down cavity electromagnetic field, not explored in conventional CRDS, for high-fidelity spectroscopy. Instead of measuring only the decaying light intensity, we perform heterodyne detection of ring-downs followed by Fourier analysis to provide exact frequencies of optical cavity modes and a dispersive spectrum of a gas sample from them. This approach is insensitive to inaccuracies in light intensity measurements and eliminates the problem of detector band nonlinearity, the main cause of measurement error in traditional CRDS. Using the CO and HD line intensities as examples, we demonstrate the sub-permille accuracy of our method, confirmed by the best ab initio results, and the long-term repeatability of our dispersion measurements at 10^(-4) level. Such results have not been achieved in optical spectroscopy before. The high accuracy of the presented method indicates its potential in atmospheric studies, isotope ratio metrology, thermometry, and the establishment of primary gas standards.

physics.optics↗

arXiv2024

Hyperfine and Zeeman interactions in ultracold collisions of molecular hydrogen with atomic lithium

We present a rigorous quantum scattering study of the effects of hyperfine and Zeeman interactions on cold Li - H$_{2}$ collisions in the presence of an external magnetic field using a recent ab initio potential energy surface. We find that the low-field-seeking states of H$_{2}$ predominantly undergo elastic collisions: the ratio of elastic-to-inelastic collisions exceeds 100 for collision energies below 1.5 K. Furthermore, we demonstrate that most inelastic collisions conserve the space-fixed projection of the nuclear spin. We show that the anisotropic hyperfine interaction between the nuclear spin of H$_{2}$ and the electron spin of Li can have a significant effect on inelastic scattering in the ultracold regime, as it mediates two processes: the electron spin relaxation in lithium, and the nuclear spin - electron spin exchange. Given the predominance of elastic collisions and the propensity of inelastic collisions to retain H$_{2}$ in its low-field-seeking states, our results open up the possibility of sympathetic cooling of molecular hydrogen by atomic lithium, paving the way for future exploration of ultracold collisions and high-precision spectroscopy of H$_{2}$ molecules.

physics.chem-ph↗

arXiv2023

Rovibrational (de-)excitation of H$_{2}$ by He revisited

Collisional (de-)excitation of H$_{2}$ by helium plays an important role in the thermal balance and chemistry of various astrophysical environments, making accurate rate coefficients essential for the interpretation of observations of the interstellar medium. Our goal is to utilize a state-of-the-art potential energy surface (PES) to provide comprehensive state-to-state rate coefficients for He-induced transitions among rovibrational levels of H$_{2}$. We perform quantum scattering calculations for the H$_{2}$-He system and provide state-to-state rate coefficients for 1 089 transitions between rovibrational levels of H$_{2}$ with internal energies up to 15 000 cm$^{-1}$ for temperatures ranging from 20 to 8 000 K. Our results show good agreement with previous calculations for pure rotational transitions between low-lying rotational levels, but we find significant discrepancies for rovibrational processes involving highly-excited rotational and vibrational states. We attribute these differences to two key factors: the broader range of intramolecular distances covered by ab initio points, and the superior accuracy of the PES, resulting from the utilization of the state-of-the-art quantum chemistry methods, compared to the previous lower-level calculations. Radiative transfer calculations performed with the new collisional data indicate that the population of rotational levels in excited vibrational states experiences significant modifications, highlighting the critical need for this updated dataset in models of high-temperature astrophysical environments.

astro-ph.GA↗

arXiv2023

Ab initio quantum scattering calculations and a new potential energy surface for the HCl($X^1Σ^+$)-O$_{2}$($X^3Σ^-_g$) system: collision-induced line-shape parameters for O$_{2}$-perturbed R(0) 0-0 line in H$^{35}$Cl

The remote sensing of abundance and properties of HCl -- the main atmospheric reservoir of Cl atoms which directly participate in ozone depletion -- are important for monitoring the partitioning of chlorine between "ozone-depleting" and "reservoir" species. Such remote studies require knowledge of the shapes of molecular resonances of HCl, which are perturbed by collisions with the molecules of the surrounding air. In this work, we report the first fully quantum calculations of collisional perturbations of the shape of a pure rotational line in H$^{35}$Cl perturbed by an air-relevant molecule (as the first model system we choose the R(0) line in HCl perturbed by O$_2$). The calculations are performed on our new highly-accurate HCl($X^1Σ^+$)-O$_2$($X^3Σ^-_g$) potential energy surface. In addition to pressure broadening and shift, we determine also their speed dependencies and the complex Dicke parameter. This gives important input to the community discussion on the physical meaning of the complex Dicke parameter and its relevance for atmospheric spectra (previously, the complex Dicke parameter for such systems was mainly determined from phenomenological fits to experimental spectra and the physical meaning of its value in that context is questionable). We also calculate the temperature dependence of the line-shape parameters and obtain agreement with the available experimental data. We estimate the total combined uncertainties of our calculations at 2% relative RMSE residuals in the simulated line shape at 296~K. This result constitutes an important step towards computational population of spectroscopic databases with accurate ab initio line-shape parameters for molecular systems of terrestrial atmospheric importance.

physics.chem-ph↗

arXiv2023

Engineering the sensitivity of macroscopic physical systems to variations in the fine-structure constant

Experiments aimed at searching for variations in the fine-structure constant $α$ are based on spectroscopy of transitions in microscopic bound systems, such as atoms and ions, or resonances in optical cavities. The sensitivities of these systems to variations in $α$ are typically on the order of unity and are fixed for a given system. For heavy atoms, highly charged ions and nuclear transitions, the sensitivity can be increased by benefiting from the relativistic effects and favorable arrangement of quantum states. This article proposes a new method for controlling the sensitivity factor of macroscopic physical systems. Specific concepts of optical cavities with tunable sensitivity to $α$ are described. These systems show qualitatively different properties from those of previous studies of the sensitivity of macroscopic systems to variations in $α$, in which the sensitivity was found to be fixed and fundamentally limited to an order of unity. Although possible experimental constraints attainable with the specific optical cavity arrangements proposed in this article do not yet exceed the present best constraints on $α$ variations, this work paves the way for developing new approaches to searching for variations in the fundamental constants of physics.

physics.atom-ph↗

arXiv2020

Propagation of optically tunable coherent radiation in a gas of polar molecules

Coherent, optically dressed media composed of two-level molecular systems without inversion symmetry are considered as all-optically tunable sources of coherent radiation in the microwave domain. A theoretical model and a numerical toolbox are developed to confirm the main finding: the generation of a low-frequency radiation, and the buildup and propagation dynamics of such low-frequency signals in a medium of polar molecules in a gas phase. The physical mechanism of the signal generation relies on the permanent dipole moment characterizing systems without inversion symmetry. The molecules are polarized with a DC electric field yielding a permanent electric dipole moment in the laboratory frame; the direction and magnitude of the moment depend on the molecular state. As the system is resonantly driven, the dipole moment oscillates at the Rabi frequency and, hence, generates microwave radiation. We demonstrate the tuning capability of the output signal frequency with the drive amplitude and detuning. We find that even though decoherence mechanisms such as spontaneous emission may damp the output field, a scenario based on pulsed illumination yields a coherent, pulsed output of tunable temporal width. Finally, we discuss experimental scenarios exploiting rotational levels of gaseous ensembles of heteronuclear diatomic molecules.

quant-ph↗

arXiv2020

Hyperfine components of all rovibrational quadrupole transitions in the H$_{2}$ and D$_{2}$ molecules

We report results of a theoretical investigation of hyperfine interactions in two homonuclear isotopologues of the hydrogen molecule: H$_{2}$ and D$_{2}$. We present a set of hyperfine coupling constants: spin-rotation, spin-spin dipole and, in the case of the D$_{2}$ molecule, electric quadrupole coupling constants for all bound states of the two isotopologues in their ground electronic $X^{1}Σ^{+}_{g}$ state. We provide a list of positions and intensities of 220 997 hyperfine components of 16 079 rovibrational quadrupole transitions of the O, Q and S branches. The positions and intensities of the hyperfine components are necessary for a reliable interpretation of accurate measurements of rovibrational transition frequencies in H$_{2}$ and D$_{2}$, which are used for tests of the quantum electrodynamics of molecules and searches for new physics beyond the Standard Model.

physics.atom-ph↗

arXiv2020

Beyond the Limits of Conventional Stark Deceleration

Stark deceleration enables the production of cold and dense molecular beams with applications in trapping, collisional studies, and precision measurement. Improving the efficiency of Stark deceleration, and hence the achievable molecular densities, is central to unlock the full potential of such studies. One of the chief limitations arises from the transverse focusing properties of Stark decelerators. We introduce a new operation strategy that circumvents this limit without any hardware modifications, and experimentally verify our results for hydroxyl radicals. Notably, improved focusing results in significant gains in molecule yield with increased operating voltage, formerly limited by transverse-longitudinal coupling. At final velocities sufficiently small for trapping, molecule flux improves by a factor of four, and potentially more with increased voltage. The improvement is more significant for less readily polarized species, thereby expanding the class of candidate molecules for Stark deceleration.

physics.chem-ph↗

arXiv2019

Nonlinear magneto-optical rotation with parametric resonance

We report on investigations of nonlinear magneto-optical rotation (NMOR) in rubidium vapor subjected to a modulated magnetic field and continuous-wave (CW) laser-light illumination. By superimposing modulation and a static (DC) magnetic field, we demonstrate the appearance of resonances at both small and large (compared to the ground-state relaxation rate) values of the static field. Since in conventional NMOR, there is no rotation at high fields, this suggests an existence of a novel mechanism generating anisotropy in the considered case, which we identify as parametric resonance. The experiments are performed using light of small ellipticity and rotation signals are significantly enhanced by combining atom-induced polarization rotation with a passive rotation induced with a wave plate. All the observations are supported with theoretical simulations. The density-matrix formalism and angular-momentum probability surfaces are used to provide intuitive explanation of the observed signals.

physics.atom-ph↗