Quantum information processing is a promising way that deals with the aspects of superposition, entanglement, computation using coherence, communication, and sensing. This review is an analysis of how alkali Rydberg atoms can be used in quantum information processing. The leading candidates are the alkali atoms, as they have a simple electronic structure, transitions that are well characterized, and which can be laser-cooled and trapped. Important mechanisms, such as EIT, dipole-dipole interactions, and Rydberg blockade, are necessary to achieve high-fidelity quantum gates, photon-photon interactions, and long-lived quantum memories. Experimental devices such as magneto-optical traps, optical tweezers, optical lattices, and warm vapor cells have made it possible to use a controllable atom-photon interface and scalable architecture. In the recent development of laser and microwave control methods, the time of coherence, state-transfer, and single-atom addressability have been enhanced. Such challenges include decoherence due to spontaneous emission, motional dephasing, and technical issues in trapping stability and laser linewidth. This review concludes that alkali Rydberg atoms, especially rubidium and cesium, are of relevance in scalable fault-tolerant quantum computing and quantum simulation, and represent the meeting of basic quantum science with new technology uses.

Modulation of adsorption and diffusion of alkali atoms on armchair graphene nanoribbons by edge passivation

Excitation Spectra of Alkali Atoms under Spatially Confined Core Potentials

Real-time observation of molten droplet-driven crystal growth provides an unprecedented in situ window into the formation of atomically thin transition metal dichalcogenides (TMDCs). Materials such as MoS2 and WS2 exhibit remarkable optoelectronic properties arising from their monolayer structures, enabling advanced applications that exploit valley degrees of freedom. Among various synthetic approaches, vapor-liquid-solid (VLS) growth from a low-melting molten source containing alkali, transition metal, halide, and oxygen atoms has proven highly effective for producing large single-crystal monolayer TMDCs, while also yielding distinct growth regimes including molten particle-driven nanoribbon formation. A chemical vapor deposition method is recently developed that integrates VLS growth with the spatial confinement provided by a substrate-stacked microreactor; however, the precise role of confinement and droplet dynamics remains unclear. Here, in situ the VLS growth of TMDCs inside such microreactors is directly captured using an infrared heating furnace. The microreactor, formed by sealing a transparent sapphire substrate with a Na2WO4-coated SiO2/Si wafer, enables continuous observation of growth mode transitions governed by the balance of sulfur and Na2WO4 supply. The findings demonstrate that fine control over precursor supply rates is essential for engineering the size, morphology, and crystallinity of monolayer TMDCs in the VLS regime.

First-principles study of the adsorption of alkali atoms in PbC monolayers and their potential applications

Coherent low-energy electrons have been demonstrated as a practical tool for imaging individual macromolecules and two-dimensional (2D) crystals. Low-energy electrons exhibit unique properties: low radiation damage to biological molecules and high sensitivity to the local potentials. In this study, we outline the conditions at which single isolated charge-free atoms can be imaged by low-energy electron holography. A single atom produces an interference pattern consisting of concentric fringes of finite diameter and of very weak intensity. The diffraction angle θ, determined as the first minimum of the concentric rings interference pattern, exhibits similar dependency on the source-to-sample distance zs as sinθ ∼ 0.3/zs1/2 for electrons of different energies (50, 100 and 200 eV) and scattered off different elements (Li, C, and Cs). The results are compared to the recently reported experimental holograms of alkali atoms intercalated into bilayer graphene and adsorbed on top of graphene.

In this study, an Artificial Neural Network (ANN) model was suggested and trained to predict the quantum defect values of alkali atoms. The dataset was divided into training and testing subsets with a % 60 – % 40, respectively. To prevent overfitting, the number of training epochs was limited to 250, and the learning rate was set to 0.25. The training process employed the Gradient Descent optimization algorithm for updating the network weights. Two different activation functions, ReLU and Swish, were utilized to evaluate their impact on prediction accuracy. The predicted quantum defect values obtained from the ANN were compared with corresponding experimental results to assess the model’s performance.

We present simulation and analysis of the magnetic field evolution generated by human-sized copper coils when extrinsic metallic objects are introduced in their proximity. The magnetic field variation can be effectively detected by leveraging the Zeeman effect, when light interacts resonantly with alkali atoms confined in nanometric or micrometric thin cells. To precisely quantify these changes, we analyse spectra of light-atom interaction in the presence of a magnetic field and introduce an algorithm capable of measuring magnetic field variations induced by a relatively small iron sphere. The key strength of our approach lies in its robustness, as it can extract meaningful information from experimental spectra without requiring a direct reference spectrum.

Abstract Excitons, i.e., the bound states of an electron and a positively charged hole, are the solid-state analog of the hydrogen atom. As such, they exhibit a Rydberg series, which in cuprous oxide has been observed up to high principal quantum numbers by Kazimierczuk et al. (Nature 514:343–347, 2014. https://doi.org/10.1038/nature13832 ). In this energy regime, the quantum mechanical properties of the system can be understood in terms of classical orbits by the application of semiclassical techniques. In fact, the first theoretical explanation of the spectrum of the hydrogen atom within Bohr’s atomic model was a semiclassical one using classical orbits and a quantization condition for the angular momentum. Contrary to the hydrogen atom, the degeneracy of states with the same principal quantum number n is lifted in exciton spectra. This is similar to the situation in alkali atoms, where these splittings are caused by the interaction of the excited electron with the ionic core. For excitons in cuprous oxide, these splittings occur due to the influence of the complex band structure of the crystal. Using an adiabatic approach and analytically derived energy surfaces, we develop a semiclassical spherical model and determine, via semiclassical torus quantization, the quantum defects of various angular momentum states.

We design and implement a low-impedance, high-current radio-frequency (RF) circuit, enabling fast coherent coupling between magnetic levels in cold alkali atomic samples. It is based on a compact, shape-optimized coil that maximizes the RF field coupling with the atomic magnetic dipole, and on coaxial transmission-line transformers that step up the field-generating current flowing in the coil by a factor ∼4 to about 7.5A for 100W of RF driving. This allows us to obtain a RF coupling field of about 0.035G/W at the atomic sample location. The system is robust and versatile, as it generates a large RF field without compromising the available optical access, and its central resonant frequency can be adjusted in situ. Our approach provides a cost-effective, reliable solution, featuring a negligible level of interference with surrounding electronic equipment thanks to its symmetric layout. We test the circuit performance using a maximum RF power of 80W at a frequency around 82 MHz, which corresponds to a measured Rabi frequency ΩR/2π ≃ 18.5 kHz, that is, a π-pulse duration of about 27μs, between two of the lowest states of 6Li at an offset magnetic field of 770G. Our solution can be readily adapted to other atomic species and vacuum chamber designs, in view of an increasing modularity of cold atom experiments.

We developed a fiber-laser-pumped Ti:sapphire laser system designed for quantum precision measurement applications. By employing a 35 W single-frequency 532 nm fiber laser as the pump source, the system delivered continuous-wave output powers of 4.12 W at 770.108 nm (D1 line, K), 4.72 W at 780.244 nm (D2 line, Rb), and 5.29 W at 794.982 nm (D1 line, Rb), thereby fulfilling the requirements for optical pumping and probing of alkali atoms. To enhance frequency stability, saturated absorption spectroscopy was used to lock the laser frequency, resulting in frequency drifts below 1 MHz over two hours. Furthermore, since low-frequency intensity noise (DC-100 Hz) critically affects spin-relaxation-free quantum sensing, we carried out a theoretical analysis which identified the pump laser as the dominant noise source. By implementing feedback control to the pump source as well as an external noise suppression, both methods achieved over 30 dB of intensity noise suppression within the DC-4kHz frequency range. In addition, improved beam pointing stability further reduced noise below 3 Hz. These results collectively demonstrate the system's strong potential for quantum sensing applications.

Two‐dimensional black phosphorus (BP or phosphorene) has drawn significant interest in alkali metal ion storage due to its capacity to adsorb alkali atoms and high theoretical prediction of specific capacity. But the problem persists in large‐scale production of the nanoscale BP, low electronic conductivity, considerable volume change (≈300%), and polyphosphide‐induced shuttle effect. To solve this problem, a single‐step lasing method is employed to prepare nanoscale BP covalently bound to the sp2 bonded carbon framework through a P─O─C/P─C bond. The sp2 bonded carbon provides exceptional electrical conductivity, while BP offers high theoretical capacity. The possible bond formation between carbon, oxygen, and phosphorus atoms was studied using synchrotron‐based X‐ray photoelectron spectroscopy and near‐edge X‐ray absorption fine structure spectroscopy. The experimental findings were supported by the ab‐initio density functional theory modelling and REAX FF molecular dynamics simulations. By adopting such structure, an ultrastable lithium‐ion battery (LIB) cell was developed with ≈100 % coulombic efficiency till 700 cycles at 2 A g−1 current density. Theoretical computation reveals that interlayer covalent bonding is a crucial mechanism for this stable device performance during Li+ intercalation/deintercalation process. This study provides valuable insights into the customized fabrication of nanoscale 2D heterostructure using laser techniques, focusing on long‐lasting LIBs.

ABSTRACTWe present a derivation of an ab initio model potential (AIMP) based on the Van Vleck Perturbation theory. We applied the derivation to the specific case of a molecular system made of one alkali atom interacting with rare gas atoms. Our approach provides a formal background for the empirical potential often used to study this kind of molecular system and allows us to discuss their intrinsic limitations and some possible improvements. In particular, the use of AIMP, which keeps the nodal structure of the orbitals, allows us to take into account accurately the spin‐orbit relativistic correction. Its application to alkali‐rare gas diatomic molecules allows us to reproduce rather well the known experimental results and the best ab initio calculations at a lower computational cost.

Chip-integrated optical frequency combs (OFCs) based on Kerr nonlinear resonators are of great significance given their scalability and wide range of applications. Broadband on-chip OFCs reaching visible wavelengths are especially valuable as they address atomic clock transitions that play an important role in position, navigation, and timing infrastructure. Silicon nitride (SiN) deposited via low-pressure chemical vapor deposition (LPCVD) is the usual platform for chip-integrated OFCs, due to its low absorption and repeatable dispersion, and such fabrication is now standard at wafer sizes up to 200 mm. However, the LPCVD high temperature and film stress pose challenges in scaling to larger wafers and integrating with electronic and photonic devices. Here, we report the linear performance and broadband frequency comb generation from microring resonators fabricated on 300 mm wafers at AIM Photonics, using a lower temperature, lower stress plasma-enhanced chemical vapor deposition process suitable for thick (≈700 nm) SiN films and compatible with electronic and photonic integration. The platform exhibits consistent insertion loss, high intrinsic quality factor, and thickness variation of ±2% across the whole 300 mm wafer. We demonstrate broadband soliton microcomb generation with a lithographically tunable dispersion profile extending to wavelengths of common alkali atom transitions. These results are a step towards more highly integrated and mass-manufacturable devices, enabling advanced applications including optical clocks, LiDAR, and beyond.

Qubits are the fundamental units in quantum computing, quantum communication, and sensing. In current platforms, such as cold atoms, superconducting circuits, point defects, and semiconductor quantum dots, each qubit requires individual preparation, making identical replication a challenging task. Constructing and maintaining stable, scalable qubits remains a formidable challenge. The race to identify the best one remains inconclusive. Our Letter introduces twisted bilayer materials as a promising platform for qubits due to their tunability, natural patterns, and extensive materials library. Our large-scale first-principles calculations reveal that the moiré superlattices have identical and localized states, akin to the discrete energy levels of an alkali atom. Existing experimental techniques allow for individual initialization, manipulation, and readout. The vast array of 2D materials provides a multitude of potential candidates for qubit exploration. Because of their inherent scalability and uniformity, our proposed qubits present significant advantages over conventional solid-state qubit systems.

Buckminsterfullerene (C60) has extensively been studied due to its various exotic electronic and magnetic properties which range semiconductor in the pristine phase to metals or Mott insulators and even superconductors when C60 is doped by alkali atoms [1]. Ultrathin films of endohedral fullerenes encapsulating metal ions on highly ordered substrates further widen the range of complex and exotic electronic states [1]. While the fullerene thin film deposition on metal and insulating substrates has been explored, there are not many studies focusing on fullerene thin film deposition on topologically protected surfaces [2]. Here, we study the electronic structure of a highly ordered ultrathin fullerene film (1ML C60) deposited on the topological insulator Bi4Te3 using ARPES, Raman, and DFT methods [3]. In addition to hexagonal ordering of C60 film on Bi4Te3, the LEED analysis confirms a (4X4) reconstruction of the C60 on a (9X9) supercell of the Bi4Te3 surface. The ARPES and Fermi-surface mapping of the topologically protected surface state confirms a strong hexagonal warping deviating from the typical linearly dispersive Dirac bands [4,5]. While we observe a hole doping to the TI with C60 deposition at room temperature as rigid shifting of the Dirac point, no charge transfer at low temperature is observed. The estimated hole doping to the TI surface at room temperature is ~ 0.03 holes per C60 molecule. Due to excellent long-range ordering of C60 molecules on TI substrate, both HOMO and HOMO-1 molecular bands of C60 show a clear electron and weakly hole like band dispersions with p- and s-polarized lights, respectively. Clearly, both the molecular bands of C60 on TI surface are further splitted into at least two degenrate states due to long range hexagonal ordering. Comparison of the momentum distribution curves at C60 bands shows a rigid shift of the bands towards Fermi level with cooling consistent with observed changes in the TI surface band. Temperature dependence resonance Raman spectroscopy of the C60 pentagon pinch reveals a molecular ordering of the C60 thin film below 250 K that is reminiscent to the structural transition in bulk C60. Significant change in the Photoluminescence of C60 film at low temperature further confirms the molecular ordering at low temperature. Ab initio calculations of the reconstructed heterostructure suggest electron-doping of the C60 molecules due to tri-vacancy of the Te-terminated surface. Simulations performed for different molecular ordering suggest low electron affinity in the ground state comparison to the 300 K affecting the charge transfer at low temperatures. Our work highlights that TI surfaces are excellent substrates for the growth of highly ordered layers of fullerenes. The work shown here also paves the way for further experiments using magnetic fullerenes and superconducting C60 films grown on TI.[1] László Forró and László Mihály, Rep. Prog. Phys. 64, 649-699 (2021).[2] X.-Q. Shi et. al., J Mater Sci. 47, 7341-7355 (2012); A. N. Mihalyuk et al., J. Chem. Phys. 154, 104703(2021).[3] Pandeya, R. P., et al. arXiv preprint arXiv:2405.09119 (2024).[4] T. Chagas et. al., Electron. Struct. 2, 015002 (2020); T. Chagas et. al., Phys. Rev. B 105, L081409 (2022).[5] L. Fu, Phys. Rev. Lett. 103, 266801 (2009); K. Kuroda et. al., Phys. Rev. Lett. 105, 076802 (2010).[6] Takabayashi, Y., and Kosmas, P. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 374.2076 (2016): 20150320. Figure 1

Context. Potassium was first detected in spectra of the sungrazer comet C/1965 S1 Ikeya-Seki at the heliocentric distance rh = 0.15 au and, 48 years later, in comets C/2011 L4 PanSTARRS and C/2012 S1 ISON at rh = 0.46 au. The alkali tail photoionization model provides a Na/K ratio close to the solar value in comets C/1965 S1 and C/2011 L4. No lithium was detected in any comet: the lower limit of the Na/Li ratio was almost one order of magnitude greater than the solar ratio. Aims. Here we searched for the emissions of the alkali NaI, KI, and LiI in Comets C/2020 F3 NEOWISE and C/2024 G3 ATLAS. Methods. High-resolution spectra of the comets were taken with the 0.84 m telescope at the Schiaparelli Observatory at rh = 0.36 and rh = 0.15 au, respectively, the observations closest to the Sun since C/1965 S1. To model the data, we assumed that alkali phenoxides are present in the aromatic fraction of organic dust at the nucleus surface where they react with carbon dioxide ejecting alkali atoms. Results. NaI and KI were detected in emission lines of exceptional intensity in both comets, with no evidence of LiI emission. The NaI/KI ratios were determined: 31 ± 5 and 26 ± 8 in comets C/2020 F3 and C/2024 G3, respectively, whereas solar Na/K ≈ 15. This excess and its observed trend with the heliocentric distance are consistent with chemistry between CO2 and alkali phenoxides at the nucleus surface. The Li upper limit for comet C/2020 F3 is very stringent at Na/Li > 3.4 × 104, a factor of 34 greater than the solar value. This Li depletion is consistent with the reaction rate of lithium phenoxides, which is a factor of 104 slower than sodium phenoxides. Conclusions. The widespread chemistry of carbon dioxide with organic dust may provide a significant energy and mass sink of carbon dioxide in all comets also at rh > 1 au, reconciling recent models of cometary activity with Rosetta CO2 measurements. At rh < 0.5 au potassium was observed in all comets, so that we predict the formation of a KI tail spatially resolved from the NaI tail.

Abstract Jupiter’s icy moon Europa is enveloped in gaseous sodium and potassium that resonantly scatter sunlight as optical emission lines. The High Resolution Echelle Spectrograph on the Keck I telescope has spatially mapped these alkalis contemporaneously with Juno’s PJ45 flyby. Beyond 3 Europa radii, where emission becomes separable from bright surface reflectance, their extended radial profiles indicate atmospheric escape. This suggests that alkalis are ejected from the ice by a high-energy process—likely ion sputtering—into an exosphere where initial energies are not appreciably dampened through collisions with the cold O2 atmosphere and icy surface. The neutral sodium cloud exhibits remarkable symmetry east–west and north–south, a sign that incident plasma has access to the majority of Europa’s surface, and the effects of centrifugal latitude may be negligible at the time of observations. However, sodium is more extended east–west, suggesting an oval-shaped cloud. The Na column density is a few × 1010 atoms cm−2, and the Na/K ratio is 28 ± 8 at 10 Europa radii, consistent with prior estimates. However, this ratio decreases with distance despite sodium’s lower mass and lifetime against ionization. Doppler broadening in the resolved Na line profiles grows with tangent altitude from a few thousand kelvins to >15,000 K by 25 Europa radii. Considering the more than twofold increase in Io’s Na loss at this time, brightness levels in good agreement with past data reinforce an interpretation that Europa is a net source of alkali atoms that ultimately derive from its subsurface brines or saline ocean.

In this paper, we review the various origins of the logarithmic Schrödinger equation: quantum informational and thermodynamic (based on quantum information entropy), statistical (pertinent to strongly correlated and interacting systems), hydrodynamic (ideal fluid), empirical (acoustics and scattering inside liquid helium and Bose–Einstein condensates of alkali atoms), gravitational (long range of induced gravity in superfluid vacuum theory and its compatibility with relativity), cosmological (accelerated expansion of the universe), and others. We argue that the statistical origin is the most fundamental one from an axiomatic point of view, because it is based on assumptions which are universally valid for a large class of materials. In fact, it can lay the foundations of a nonperturbative approach to strongly correlated and interacting systems. The empirical origin is instrumental in establishing the role of logarithmic nonlinearity in the standard theory of quantum Bose liquids and in placing experimental constraints upon its parameters. We also discuss the origins of the Lorentz-covariant version of the model, the logarithmic Klein–Gordon equation, which occurs in dilatation-covariant local relativistic scalar field models, non-Abelian gauge theories with radiative corrections in dimensional regularization and quantum astrophysics.

Alkali Atomic Density Detection With Arbitrarily Polarized Light