arXiv subjects

Nadia Bouloufa-Maafa

Publications and source records attributed to Nadia Bouloufa-Maafa.

At least 19 recordsLinked to original sources

arXiv2026

Rotational laser spectroscopy of the $X^1Σ_g^+\rightarrow B^1Π_u$ transition of $\text{Rb}_2$ molecule in a supersonic beam: As good as it gets

High-resolution laser spectroscopy of the $^{85}\mathrm{Rb}_2$, $^{85}\mathrm{Rb}^{87}\mathrm{Rb}$, and $^{87}\mathrm{Rb}_2$ isotopologues has been performed in a supersonic molecular beam using a continuous-wave (cw) tunable diode laser. A total of 958 rovibronic transitions were recorded up to $7~\mathrm{cm}^{-1}$ below the vibrational band heads of the $X^1Σ_g^+(v''=0)\rightarrow B^1Π_u(v'=1,2)$ and $X^1Σ_g^+(v''=1)\rightarrow B^1Π_u(v'=1)$ bands, with a spectral resolution of $3.3\times10^{-4}$~cm$^{-1}$. Although restricted to the $v'=1$ and $v'=2$ vibrational levels of the excited $B^1Π_u$ state, the measurements extend previous work by Amiot and Vergès [Chemical Physics Letters 274, 91 (1997)] through substantially higher resolution and dense low-$J'$ rotational data for all three isotopologues. A global least-squares analysis combining the new and published data, yields improved Dunham coefficients for the excited $B^1Π_u$ state, significantly refines rotational and rovibrational coupling constants. In addition, the $Λ$-doubling constants of $B^1Π_u$ state were determined for the three isotopologues.

physics.atom-ph↗

arXiv2026

Quantum study of ultracold atom-ion excitation exchange

The quantum dynamics of ultracold collisions between rubidium atoms and excited metastable strontium ions is treated in the laboratory frame, enlightening the importance of the coupling between internal angular momenta of the particles and their mutual rotation. The study reveals a subtle competition between electronic excitation exchange and fine structure quenching, with no charge exchange, which is found to be very sensitive to the details of ion-atom interactions. The rate constant for electronic excitation exchange is found in agreement with the experimental results of Ben-Shlomi \textit{et al.} (Phys. Rev. A \textbf{102}, 031301(R) (2020)), while the rate for fine structure quenching is predicted to strongly depend on the initial polarization of the reactants.

physics.atom-ph↗

arXiv2026

An Alternate Pathway for H$_2$ Formation in the Early Universe: A physical process to account for the presence and coevolution of the luminous galaxies and supermassive black holes at the high redshifts

Molecular hydrogen (H$_2$) and hydrogen deuteride (HD) are key coolants in primordial gas and regulate the formation of the first stars and proto-galaxies. Recent results from the James Webb Space Telescope provide striking insights into galaxies detected at high redshifts, which are found to be significantly more abundant and luminous than expected from galaxy formation models, thus suggesting a gap in our understanding of the early Universe. Standard pathways for H$_2$ formation in the early Universe proceed through the H$^-$ and H$_2^+$ intermediates, both of which are strongly suppressed at high redshift by the cosmic microwave background. We propose an additional pathway for H2 and HD formation that could be active as early as the end of the epoch of recombination and could enable the formation of the first stars earlier than the current prediction at redshift z ~ 30 - 20. The proposed pathway relies on the manifestation of Jahn-Teller dynamical coupling between electronic states of H$_3^+$. This coupling induces transient three-body recombination in H$^+$, H and H, and charge exchange within the charged atom-dimer complex that directly creates ground-state H$_2$ (and HD), bypassing the fragile intermediates that limit the standard primordial pathways. Our analysis shows that this mechanism could occur under the thermodynamic conditions of the post-recombination epoch, also suggesting that it might be playing a role in the active galactic nuclei feedback processes, regulating the formation rates of the first stars and the accretion rates of the first black holes. Though the global impact on galaxy formation and black-hole growth is not yet determined and will require quantitative assessment in future modeling, the mechanism offers an additional chemical route for H$_2$ and HD formation, with substantial cosmological relevance for primordial chemistry and early structure formation.

astro-ph.GA↗

arXiv2026

Two-photon-assisted collisions in ultracold gases of polar molecules II : Optical shielding of ultracold polar molecular collisions

We theoretically investigate the collisions between ultracold polar molecules in the presence of two lasers ensuring a Raman resonant transition on individual molecules to suppress photon scattering, taking the example of bosonic $^{23}$Na$^{39}$K molecules. By varying laser detunings and intensities, we enable a repulsive long-range interaction potential between molecules. After solving a set of coupled Schrödinger equations with the Hamiltonian written in the basis of laser-dressed states of the molecule pair at infinite distance, we identify quasi-resonant conditions under which elastic collisions are favored over inelastic and reactive ones, by a factor of about 2, thus demonstrating a promising pathway for efficient two-photon optical shielding of ultracold molecular collisions. The results are analyzed in terms of scattering length of the colliding laser-dressed molecules, which exhibit prominent resonances assigned to the interaction of the entrance channel with other specific channels, consistent with the existence of a quasi-bound level of the long-range molecular pair induced by the lasers.

cond-mat.quant-gas↗

arXiv2025

Two-photon-assisted collisions in ultracold gases of polar molecules

We present a theoretical formalism to treat the ultracold dynamics of a pair of colliding polar molecules submitted to two laser fields. We express the dressed Hamiltonian including the dipole-dipole interaction of the colliding molecular pair, both in their ground and electronic excited states, as well as their interaction with the two laser fields. We apply adiabatic elimination of the electronic excited state to reduce the size of the dressed-state basis in which the dressed Hamiltoninan is expressed. In an application, we investigate the feasibility of two-photon collisional shielding between two \NaK molecules, which could be favored by the Raman resonance condition suppressing unwanted spontaneous emission and photon scattering. We demonstrate the influence of the laser Rabi frequencies on the dynamics through the computation of elastic, inelastic, and reactive collision rates.

cond-mat.quant-gas↗

arXiv2025

Ionization Energy of Rb$_2$ by electric field-ionization of molecular Rydberg states

We report the measurement of the ionization energy of the $^{85}\text{Rb}_2$ molecule through resonantly enhanced 2-photon ionization in a supersonic beam. The first photon excites the $X^1Σ_g^+ (v_X = 0)\rightarrow B^1Π_u (v_B = 2)$ transition, while the second photon wavenumber is scanned over the 16720 cm$^{-1}$-16750 cm$^{-1}$ range, thus yielding a structured spectrum of Rb$_2^+$ ions extracted by an electric field and recorded by mass spectrometry. We modeled the onset of the ionization signal as a function of the electric field strength between $18 V/cm$ and $180 V/cm$, leading to the Rb$_2$ ionization energy $E_i = 31497.3 \pm 0.6 $cm$^{-1}$, and to the dissociation energy of the Rb$_2^+$ ground state $D_0 = 6158.2 \pm 0.6$ cm$^{-1}$. Our measured value $E_i$ is found to be $149.3$ cm$^{-1}$ larger than the one reported in the experiment by Bellos et al. [Phys. Rev. A 87, 012508 (2013)]. Our value of $D_0$ agrees with our theoretical determination using a quantum chemistry approach. Using a simple theoretical model, we assign unevenly spaced structures of the ionization spectrum to molecular Rydberg levels belonging to several series that converge to the lowest vibrational levels of Rb$_2^+$.

physics.atom-ph↗

arXiv2024

Ultracold charged atom-dimer collisions: state-selective charge exchange and three-body recombination

Based on an accurate determination of the potential energy surfaces of Rb$_3^+$ correlated to its first asymptotic limit Rb$^+$$+$Rb($5s$)$+$Rb($5s$), we identify the presence of intersections of a pair of singlet and triplet surfaces over all interparticle distances, leading to Jahn-Teller couplings. We elaborate scenarios for charge exchange between ultracold charged atom-dimer complex (Rb$+$Rb$_2^+$ or Rb$^+$$+$Rb$_2$), predicting a strong selectivity on the preparation of the initial state of the dimer. We also demonstrate that the JT couplings must drive the three-body recombination (TBR) of Rb$^+$, Rb, and Rb at ultracold energies. Using the current analysis, we provide a consistent picture of the TBR experiments performed in ion-atom hybrid Rb samples \cite{dieterle2020inelastic,harter2012single}. We also demonstrate the presence of JT coupling as a general phenomenon in the singly-charged homonuclear alkali triatomic systems.

physics.atom-ph↗

arXiv2024

Competing excitation quenching and charge exchange in ultracold Li-Ba$^+$ collisions

Hybrid atom-ion systems are a rich and powerful platform for studying chemical reactions, as they feature both excellent control over the electronic state preparation and readout as well as a versatile tunability over the scattering energy, ranging from the few-partial wave regime to the quantum regime. In this work, we make use of these excellent control knobs, and present a joint experimental and theoretical study of the collisions of a single $^{138}$Ba$^+$ ion prepared in the $5d\,^2D_{3/2,5/2}$ metastable states with a ground state $^6$Li gas near quantum degeneracy. We show that in contrast to previously reported atom-ion mixtures, several non-radiative processes, including charge exchange, excitation exchange and quenching, compete with each other due to the inherent complexity of the ion-atom molecular structure. We present a full quantum model based on high-level electronic structure calculations involving spin-orbit couplings. Results are in excellent agreement with observations, highlighting the strong coupling between the internal angular momenta and the mechanical rotation of the colliding pair, which is relevant in any other hybrid system composed of an alkali-metal atom and an alkaline-earth ion.

quant-ph↗

arXiv2023

Two-photon optical shielding of collisions between ultracold polar molecules

We propose a method to engineer repulsive long-range interactions between ultracold ground-state molecules using optical fields, thus preventing short-range collisional losses. It maps the microwave coupling recently used for collisional shielding onto a two-photon transition, and takes advantage of optical control techniques. In contrast to one-photon optical shielding [Phys. Rev. Lett. 125, 153202 (2020)], this scheme avoids heating of the molecular gas due to photon scattering. The proposed protocol, exemplified for 23Na39K, should be applicable to a large class of polar diatomic molecules.

quant-ph↗

arXiv2022

Ion loss events in a cold Rb-Ca$^+$ hybrid trap: photodissociation, black-body radiation and non-radiative charge exchange

We theoretically investigate the collisional dynamics of laser-cooled $^{87}$Rb ground-state atoms and $^{40}$Ca$^+$ ground-state ions in the context of the hybrid trap experiment of Ref. [Phys. Rev. Lett. 107, 243202 (2011)], leading to ion losses. Cold $^{87}$Rb$^{40}$Ca$^+$ ground-state molecular ions are created by radiative association, and we demonstrate that they are protected against photodissociation by black-body radiation and by the $^{40}$Ca$^+$ cooling laser at 397~nm. This study yields an interpretation of the direct observation of $^{87}$Rb$^{40}$Ca$^+$ ions in the experiment, in contrast to other hybrid trap experiments using other species. Based on novel molecular data for the spin-orbit interaction, we also confirm that the non-radiative charge-exchange is the dominant loss process for Ca$^+$ and obtain rates in agreement with experimental observations and a previous calculation.

physics.chem-ph↗

arXiv2022

Study of excited electronic states of the $^{39}$KCs molecule correlated with the K($4^2$S)+Cs($5^2$D) asymptote: experiment and theory

Using the polarisation labelling spectroscopy, we performed the detailed analysis of the level structure of excited electronic states of the $^{39}$KCs molecule in the excitation energy interval between 17500~cm$^{-1}$ and 18600~cm$^{-1}$ above the $v=0$ level of the $X^1Σ^+$ ground state. We prove that the observed states are strongly coupled by spin-orbit interaction above 18200~cm$^{-1}$, as manifested by numerous perturbations in the recorded spectra. The spectra are interpreted with the guidance of accurate electronic structure calculations on KCs, including potential energy curves, transition electric dipole moments, and representation of the spin-orbit interaction with a quasi-diabatic effective Hamiltonian approach. The agreement between theory and experiment is found remarkable, clearly discriminating among the available theoretical data. This study confirms the accuracy of the polarisation labelling spectroscopy to analyse highly-excited electronic molecular states which present a dense level structure.

physics.atom-ph↗

arXiv2019

Direct observation of bimolecular reactions of ultracold KRb molecules

Femtochemistry techniques have been instrumental in accessing the short time scales necessary to probe transient intermediates in chemical reactions. Here we take the contrasting approach of prolonging the lifetime of an intermediate by preparing reactant molecules in their lowest ro-vibronic quantum state at ultralow temperatures, thereby drastically reducing the number of exit channels accessible upon their mutual collision. Using ionization spectroscopy and velocity-map imaging of a trapped gas of potassium-rubidium molecules at a temperature of 500~nK, we directly observe reactants, intermediates, and products of the reaction $^{40}$K$^{87}$Rb + $^{40}$K$^{87}$Rb $\rightarrow$ K$_2$Rb$^*_2$ $\rightarrow$ K$_2$ + Rb$_2$. Beyond observation of a long-lived energy-rich intermediate complex, this technique opens the door to further studies of quantum-state resolved reaction dynamics in the ultracold regime.

physics.atom-ph↗

arXiv2018

Coherent multidimensional spectroscopy of dilute gas-phase nanosystems

Two-dimensional electronic spectroscopy (2DES) is one of the most powerful spectroscopic techniques, capable of attaining a nearly complete picture of a quantum system including its couplings, quantum coherence properties and its real-time dynamics. While successfully applied to a variety of condensed phase samples, high precision experiments on isolated quantum systems in the gas phase have been so far precluded by insufficient sensitivity. However, such experiments are essential for a precise understanding of fundamental mechanisms and to avoid misinterpretations, e.g. as for the nature of quantum coherences in energy trans-port. Here, we solve this issue by extending 2DES to isolated nanosystems in the gas phase prepared by helium nanodroplet isolation in a molecular beam-type experiment. This approach uniquely provides high flexibility in synthesizing tailored, quantum state-selected model systems of single and many-body properties. For demonstration, we deduce a precise and conclusive picture of the ultrafast coherent dynamics in isolated high-spin Rb2 molecules and present for the first time a dynamics study of the system-bath interaction between a single molecule (here Rb3) and a superfluid helium environment. The results demonstrate the unique capacity to elucidate prototypical interactions and dynamics in tailored quantum systems and bridges the gap to experiments in ultracold quantum science.

physics.chem-ph↗

arXiv2017

High Resolution Molecular Spectroscopy for Producing Ultracold Absolute Ground-State $^{23}$Na$^{87}$Rb Molecules

We report a detailed molecular spectroscopy study on the lowest excited electronic states of $^{23}\rm{Na}^{87}\rm{Rb}$ for producing ultracold $^{23}\rm{Na}^{87}\rm{Rb}$ molecules in the electronic, rovibrational and hyperfine ground state. Starting from weakly-bound Feshbach molecules, a series of vibrational levels of the $A^{1}Σ^{+}-b^{3}Π$ coupled excited states were investigated. After resolving, modeling and interpreting the hyperfine structure of several lines, we successfully identified a long-lived level resulting from the accidental hyperfine coupling between the $0^+$ and $0^-$ components of the $b^3Π$ state, satisfying all the requirements for the population transfer toward the lowest rovibrational level of the X$^1Σ^+$ state. Using two-photon spectroscopy, its binding energy was measured to be 4977.308(3) cm$^{-1}$, the most precise value to date. We calibrated all the transition strengths carefully and also demonstrated Raman transfer of Feshbach molecules to the absolute ground state.

cond-mat.quant-gas↗

arXiv2016

Polarizability of ultracold $\textrm{Rb}_2$ molecules in the rovibrational ground state of $\mathrm{a}^3Σ_u^+$

We study, both theoretically and experimentally, the dynamical polarizability $α(ω)$ of $\textrm{Rb}_2$ molecules in the rovibrational ground state of $\mathrm{a}^3Σ_u^+$. Taking all relevant excited molecular bound states into account, we compute the complex-valued polarizability $α(ω)$ for wave numbers up to $20000\:\textrm{cm}^{-1}$. Our calculations are compared to experimental results at $1064.5\:\textrm{nm}$ ($\sim9400\:\textrm{cm}^{-1}$) as well as at $830.4\:\textrm{nm}$ ($\sim12000\:\textrm{cm}^{-1}$). Here, we discuss the measurements at $1064.5\:\textrm{nm}$. The ultracold $\textrm{Rb}_2$ molecules are trapped in the lowest Bloch band of a 3D optical lattice. Their polarizability is determined by lattice modulation spectroscopy which measures the potential depth for a given light intensity. Moreover, we investigate the decay of molecules in the optical lattice, where lifetimes of more than $2\:\textrm{s}$ are observed. In addition, the dynamical polarizability for the $\mathrm{X}^1Σ_g^+$ state is calculated. We provide simple analytical expressions that reproduce the numerical results for $α(ω)$ for all vibrational levels of $\mathrm{a}^3Σ_u^+$ as well as $\mathrm{X}^1Σ_g^+$. Precise knowledge of the molecular polarizability is essential for designing experiments with ultracold molecules as lifetimes and lattice depths are key parameters. Specifically the wavelength at $\sim1064\:\textrm{nm}$ is of interest, since here, ultrastable high power lasers are available.

physics.atom-ph↗

arXiv2016

Creation of an ultracold gas of ground-state $^{23}\rm{Na}^{87}\rm{Rb}$ molecules

We report the successful production of an ultracold sample of absolute ground-state $^{23}$Na$^{87}$Rb molecules. Starting from weakly-bound Feshbach molecules formed via magneto-association, the lowest rovibrational and hyperfine level of the electronic ground state is populated following a high efficiency and high resolution two-photon Raman process. The high purity absolute ground-state samples have up to 8000 molecules and densities of over $10^{11}$ cm$^{-3}$. By measuring the Stark shifts induced by external electric fields, we determined the permanent electric dipole moment of the absolute ground-state $^{23}$Na$^{87}$Rb and demonstrated the capability of inducing an effective dipole moment over one Debye. Bimolecular reaction between ground-state $^{23}$Na$^{87}$Rb molecules is endothermic, but we still observed a rather fast decay of the molecular sample. Our results pave the way toward investigation of ultracold molecular collisions in a fully controlled manner, and possibly to quantum gases of ultracold bosonic molecules with strong dipolar interactions.

cond-mat.quant-gas↗

arXiv2016

Long-range states of the NaRb molecule near the Na($3^2S_{1/2}$)+Rb($5^2P_{3/2}$) asymptote

We report a high-resolution spectroscopic investigation of the long-range states of the $^{23}$Na$^{87}$Rb molecule near its Na($3^2S_{1/2}$)+Rb($5^2P_{3/2}$) asymptote. This study was performed with weakly bound ultracold molecules produced via magneto-association with an inter-species Feshbach resonance. We observed several regular vibrational series, which are assigned to the 5 attractive long-range states correlated with this asymptote. The vibrational levels of two of these states have sharp but complex structures due to hyperfine and Zeeman interactions. For the other states, we observed significant linewidth broadenings due to strong predissociation caused by spin-orbit couplings with states correlated to the lower Na($3^2S_{1/2}$)+Rb($5^2P_{1/2}$) asymptote. The long-range $C_6$ van der Waals coefficients extracted from our spectrum are in good agreement with theoretical values.

physics.atom-ph↗

arXiv2013

Long-range interactions between polar alkali-metal diatoms in external electric fields

We computed the long-range interactions between two identical polar bialkali molecules in their rovibronic ground level, for all ten species involving Li, Na, K, Rb and Cs, using accurate quantum chemistry results combined with available spectroscopic data. Huge van der Waals interaction is found for eight species in free space. The competition of the van der Waals interaction with the dipole-dipole interaction induced by an external electric field parallel or perpendicular to the intermolecular axis is investigated by varying the electric field magnitude and the intermolecular distance. Our calculations predict a regime with the mutual orientation of the two molecules but with no preferential direction in the laboratory frame. A mechanism for the stimulated one-photon radiative association of a pair of ultracold polar molecules into ultracold tetramers is proposed, which would open the way towards the optical manipulation of ultracold polyatomic molecules.

physics.atom-ph↗