High Principal Quantum Number Research Articles

Photo-induced loss of H2 from H2S, CH4, H2O and SiH4, when and why is it possible

We have explored the possibility of forming H⋅ and H2 from H2S, CH4, H2O and SiH4 in a series of ab initio calculations. The key finding is that H2S can give rise to direct photolytic ultrafast formation of H2 This finding is in agreement with the available experimental data and is a result of a directed pathway that leads toward H2 formation at easily accessible wavelengths. It arises at the (conical) intersection between the two lowest-lying electronic states. This intersection is a result of the valence orbital interaction of the two hydrogen atoms. This interaction is becoming more favorable as the S-H bonds simultaneously becomes longer. The H-S σ-σ∗ bonding interaction cannot compete with the bond formation that takes place between the hydrogens as two bonds stretch simultaneously. For oxygen this interaction it predominant. The reason is that sulfur has a higher principal quantum number and the interaction with the 1s of hydrogen therefore is less favorable. The excited states that are involved in the H2 formation from H2S could be populated by, for example, a two-photon 400 nm excitation. The other hydrides have a more entangled potential energy landscape close to the Franck-Condon region in the direction of the reaction coordinate that leads to H2 loss and as a result the direct loss of a hydrogen atom is favored. A two-photon excitation could be induced by femtosecond laser pulses that at the same time is proposed as a future platform for sensing the H2S molecules with the backward transient absorption scheme. The implication would be that both sensing and photoinduced H2 formation could be in place at the same time which justifies the use of expensive femtosecond light sources getting “two for the price of one”.

Stark Effects of Rydberg Excitons in a Monolayer WSe2 P-N Junction.

The enhanced Coulomb interaction in two-dimensional semiconductors leads to tightly bound electron-hole pairs known as excitons. The large binding energy of excitons enables the formation of Rydberg excitons with high principal quantum numbers (n), analogous to Rydberg atoms. Rydberg excitons possess strong interactions among themselves as well as sensitive responses to external stimuli. Here, we probe Rydberg exciton resonances through photocurrent spectroscopy in a monolayer WSe2 p-n junction formed by a split-gate geometry. We show that an external in-plane electric field not only induces a large Stark shift of Rydberg excitons up to quantum principal number 3 but also mixes different orbitals and brightens otherwise dark states such as 3p and 3d. Our study provides an exciting platform for engineering Rydberg excitons for new quantum states and quantum sensing.

Nonlinear Rydberg exciton-polaritons in Cu2O microcavities

Rydberg excitons (analogues of Rydberg atoms in condensed matter systems) are highly excited bound electron-hole states with large Bohr radii. The interaction between them as well as exciton coupling to light may lead to strong optical nonlinearity, with applications in sensing and quantum information processing. Here, we achieve strong effective photon–photon interactions (Kerr-like optical nonlinearity) via the Rydberg blockade phenomenon and the hybridisation of excitons and photons forming polaritons in a Cu2O-filled microresonator. Under pulsed resonant excitation polariton resonance frequencies are renormalised due to the reduction of the photon-exciton coupling with increasing exciton density. Theoretical analysis shows that the Rydberg blockade plays a major role in the experimentally observed scaling of the polariton nonlinearity coefficient as ∝ n4.4±1.8 for principal quantum numbers up to n = 7. Such high principal quantum numbers studied in a polariton system for the first time are essential for realisation of high Rydberg optical nonlinearities, which paves the way towards quantum optical applications and fundamental studies of strongly correlated photonic (polaritonic) states in a solid state system.

Electromagnetically Induced Transparency Spectra of 6Li Rydberg Atoms

Rydberg atoms possess highly excited valence electrons that are far away from atomic cations. Compared with ground states, Rydberg states are excited states with a high principal quantum number n that exhibit large electric dipole moments and have a variety of applications in quantum information processing. In this communication, we report the measurement of the 6Li Rydberg excitation spectrum by ladder-type electromagnetically induced transparency (EIT) in a vapor cell. The 2p→ns/nd EIT spectra were recorded by sweeping the frequency of an ultraviolet Rydberg pumping laser while keeping the probing laser resonant to the 2s→2p transition. All lasers were locked on an ultrastable optical Fabry-Pérot cavity and measured by an optical frequency comb. Our results provide valuable information to precisely determine quantum defects and enable novel experiments with Rydberg-dressed ultracold Fermi gases.

Resonance ionization spectroscopy of high-lying 4sns and 4snd Rydberg levels of odd calcium isotopes

Calcium Rydberg levels are of significant interest for efficient and isotope-selective resonance ionization of trace radionuclides such as calcium-41 (41Ca). In this study, we report novel, to our knowledge, measurement data on the energy level shifts of 43Ca for 4sns 1S0 and 4s(n−1)d1D2 (n=40, 45, 50, 55, 60) Rydberg levels due to hyperfine-induced singlet–triplet mixing specific to isotopes with an odd mass number. Both 3S1 and 3D J triplet signals corresponding to forbidden transitions were enhanced for 43Ca at the high principal quantum numbers n=55 and 60, indicating a mixing of singlet components to some extent.

State-selective charge exchange cross sections in collisions of highly-charged sulfur ions with helium and molecular hydrogen

The state-selective cross section data are useful for understanding and modeling the x-ray emission in celestial observations. In the present work, using the cold target recoil ion momentum spectroscopy, for the first time we investigated the state-selective single electron capture processes for S q+–He and H2 (q = 11–15) collision systems at an impact energy of q × 20 keV and obtained the relative state-selective cross sections. The results indicate that only a few principal quantum states of the projectile energy level are populated in a single electron capture process. In particular, the increase of the projectile charge state leads to the population of the states with higher principal quantum numbers. It is also shown that the experimental averaged n-shell populations are reproduced well by the over-barrier model. The database is openly available in Science Data Bank at 10.57760/sciencedb.j00113.00091.

Atomic Rydberg-state excitation in strong spatially inhomogeneous fields

We investigated the Rydberg-state excitation process of a hydrogen atom subjected to spatially homogeneous and inhomogeneous laser fields by means of ab initio calculations. It is found that, comparing with atoms exposed to spatially homogeneous laser fields, the excitation probability decreases and the electron tends to occupy the states with lower principal quantum numbers and angular quantum numbers for atoms in spatially inhomogeneous laser pulses. Furthermore, calculations of a quantum model without taking into account ionization of the electron after it is coherently captured by the Rydberg state are inconsistent with the above-stated findings by ab initio calculations. Analysis indicates that the aforementioned intriguing features can be attributed to the enhanced ionization of the Rydberg states by inhomogeneous laser fields since the distributions of Rydberg states of high principal quantum numbers and angular quantum numbers locate far away from the core where the inhomogeneous electric fields become significant.

On the Pasternack–Sternheimer theorem for bound states in hydrogenic atoms and ions derived by operator calculus

The Pasternack–Sternheimer theorem for bound states (Pasternack and Sternheimer 1962 J. Math. Phys. 3 1280) is obtained directly by the methods of operator calculus set out earlier (Hey 2006 J. Phys. B: At. Mol. Phys. 39 2641–64), on the basis of the factorisation technique of Infeld and Hull (Infeld and Hull 1951 Rev. Mod. Phys. 23 21–68). The present derivation, which complements the group theoretical treatments of Armstrong (Armstrong 1970 J. Phys. Colloq. 31 C4-17–23) and Cunningham (Cunningham 1972 J. Math. Phys. 13 33–9), not only elucidates the original result in terms of fundamental quantum mechanical theory, but also reveals some apparently new inter-connections between different radial matrix elements (for given n, diagonal and off-diagonal in ℓ, ℓ′) of hydrogenic atoms and ions. The key equation used to derive the theorem here is shown to follow identically in the non-relativistic limit from the treatment of the generalised Kepler problem by Crubellier and Feneuille (Crubellier and Feneuille 1971 J. Physique 32 405–11). This work is a continuation of studies employing operator methods to provide results of potential usefulness for spectroscopic studies of laboratory and astrophysical plasmas, in particular to transitions between states of high principal quantum number, as in the high-n radio recombination lines (Hey 2013 J. Phys. B: At. Mol. Opt. Phys. 46 175702; Peach 2014 Adv. Space Res. 54 1180-83).

Transition frequency measurement of highly excited Rydberg states of 87Rb for a wide range of principal quantum numbers

We report our measurements of the absolute transition frequencies of 5P3/2, F = 3 to nS and nD Rydberg states of 87Rb with high principal quantum numbers in a wide range of values (n = 45-124). The measurements were performed using Rydberg Electromagnetically Induced Transparency (EIT) in ladder-type three-level systems. We measure the transition frequencies with an accuracy of ≤ 2 MHz. We determine the values of the Rydberg-Ritz parameter for 87Rb from our experimental measurements of the transition frequencies. Our measurements of the absolute transition frequencies of the highly excited Rydberg states would be useful for diverse applications in quantum information processing, quantum simulation and quantum sensing with Rydberg atoms.

K-shell Emission from O vi Near 19 Å

Laboratory measurements of O vi K-shell emission lines are presented that are situated near the O viii Lyα line at 19 Å. The data provide additional rest-frame references for velocity determinations based on absorption features in the spectra of warm absorbers in active galactic nuclei and other astrophysical objects. They also provide benchmarks for testing atomic structure calculations of energy levels with electrons in a high principal quantum number (n = 3, 4). Excellent agreement is found with our calculations using the many-body perturbation theory method, and we provide a complete listing of the O vi energy levels calculated with this approach.

Scrutinizing the Debye plasma model: Rydberg excitons unravel the properties of low-density plasmas in semiconductors

For low-density plasmas, the classical limit described by the Debye-H\"uckel theory is still considered as an appropriate description even though a clear experimental proof of this paradigm is lacking due to the problems in determining the plasma-induced shift of single-particle energies in atomic systems. We show that Rydberg excitons in states with a high principal quantum number are highly sensitive probes for their surrounding making it possible to unravel accurately the basic properties of low-density nondegenerate electron-hole plasmas. To this end, we accurately measure the parameters of Rydberg excitons such as energies and linewidths in absorption spectra of bulk cuprous oxide crystals in which a tailored electron-hole plasma has been generated optically. Since from the absorption spectra exciton energies, as well as the shift of the single-particle energies given by the band edge, can be directly derived, the measurements allow us to determine the plasma density and temperature independently, which has been a notoriously hard problem in semiconductor physics. Our analysis shows unambiguously that the impact of the plasma cannot be described by the classical Debye model, but requires a quantum many-body theory, not only for the semiconductor plasma investigated here, but in general. Furthermore, it reveals an exciton scattering mechanism with coupled plasmon-phonon modes becoming important even at very low plasma densities.

The use of photoionization cross section for evaluating contribution of continuum to the blackbody radiation induced shift and broadening of Rydberg-state energy levels of group IIb ions

General properties of n-dependence at the threshold and regularities of above-threshold ionization cross sections for states with high principal quantum numbers n and arbitrary angular momenta l are determined and used for evaluating the blackbody-radiation(BBR)-induced ionization broadening of nS, nP, nD and nF Rydberg-state energy levels of the group IIb ions Zn+, Cd+, Hg+ at temperatures from T=100 K to T=3000 K. The contributions to the energy level shifts from transitions into continuum are also determined with the use of the ionization cross sections. The single-electron quantum defect method (QDM) was used, which appears rather precise and suitable for calculating the amplitudes of radiation transitions from Rydberg states, and specifically for summation of matrix-element-dependent terms over infinite number of discrete states. The dependencies on temperature and binding energy are determined and approximate analytic equations are proposed for simplified evaluations of the BBR-induced ionization broadening and shifts. Numerical parameters of approximate equations are tabulated for S, P, D and F Rydberg states of the group IIb ions.

Response characteristics of radio frequency pulse of Rydberg atoms

Rydberg atom is an atom with a high principal quantum number. Its quantum coherence effect enables the measuring of radio frequency electric fields in space. In this work, the radio frequency pulse response characteristics of the radio frequency receiving system based on the Rydberg atom under different pulse widths and intensities are studied. In the experiment, lasers with wavelengths of 852 nm and 510 nm are used to excite cesium atoms. Moreover, a radio frequency source emits pulse signals with different parameters to irradiate Rydberg atoms. The probe signal transmitted from the atomic vapor cell is directed at the photodetector. Moreover, the oscilloscope records the electrical signal obtained by photoelectric conversion. In addition, the simulation ranging is performed by setting different pulse delay times through the fiber delay instrument. It preliminarily proves that the radio frequency receiving system based on Rydberg atoms has a function of pulse ranging.

Perpendicular magnetic anisotropy induced by 6p atomic layers: Crucial role of interface structural order

Two-dimensional atomic layers composed of metallic atoms with a high principal quantum number in valence shells are promising materials for applications in state-of-the-art magnetic devices due to the presence of a strong spin-orbit coupling. In this work we experimentally explored the effects of triggering perpendicular magnetic anisotropy (PMA) of ferromagnetic (FM) films by applying a series of $6p$-Pb, Bi and $4d$-Pd (reference) atomic layers with high-level atomic orbital and low-level lattice strain. Our research indicates that, compared with Pd atoms, Pb and Bi atoms can produce higher-strength PMA on adjacent FM films through orbital hybridization at the interface. Moreover, we demonstrate that the PMA induced by Pb and Bi atoms is highly sensitive to the ordering degree of the wetting layer which is determined by the interplay of surface free, cohesive, and strain energies within the grown materials; the Pb(Bi) atoms added on the wetting layer can enhance the PMA of the adjacent FM film only when the wetting layer maintains an ordered structure. This work clarifies the critical interface effects of $6p$-HMs on the FM layer, thus providing important clues to increase control over the spin-orbit interaction engendered by HMs through the interface.

Scattering of Rydberg excitons by phonon-plasmon modes

We propose a new scattering mechanism of Rydberg excitons, i.e., those with high principal quantum numbers, namely scattering by coupled LO phonon-plasmon modes, which becomes possible due to small differences in energies of the states due to different quantum defects. Already in very low-density electron–hole plasmas these provide a substantial contribution to the excitonic linewidth. This effect should allow determining plasma densities by a simple line shape analysis. Whenever one expects that low-density electron–hole plasma is present the plasmon induced broadening is of high significance and must be taken into account in the interpretation.

Coherent transfer matrix analysis of the transmission spectra of Rydberg excitons in cuprous oxide

In this study we analyze the transmission spectrum of a thin plate of Cuprous Oxide in the range of the absorption of the yellow exciton states with the coherent transfer matrix method. We demonstrate that, in contrast to the usual analysis using Beer's law, which turns out to be a rather good approximation only in the spectral region of high principal quantum numbers, a consistent quantitative description over the whole spectral range under consideration is possible. This leads to new and more accurate parameters not only for the Rydberg exciton states, but also for the strengths of indirect transitions. Furthermore, the results have consequences on the determination of the density of electron-hole pairs after optical excitation.

Perturbation approach to ab initio effective mass calculations

A degenerate perturbation k⋅p approach for effective mass calculations is implemented in the all-electron density functional theory (DFT) package WIEN2k. The accuracy is tested on major group IVA, IIIA–VA, and IIB–VIA semiconductor materials. Then, the effective mass in graphene and CuI with defects is presented as illustrative applications. For states with significant Cu-d character additional local orbitals with higher principal quantum numbers (more radial nodes) have to be added to the basis set in order to converge the results of the perturbation theory. Caveats related to a difference between velocity and momentum matrix elements are discussed in the context of application of the method to non-local potentials, such as Hartree–Fock/DFT hybrid functionals and DFT+U.

Spectroscopy of Highly Excited States of the Hydrogen Atom.

In this contribution, we describe the status of the development of a precision-spectroscopic experiment aimed at measuring transitions to states of high principal quantum number n of the hydrogen atom (H). These states form series (called Rydberg series) which converge for n → ∞ to the ionization threshold of H. The ionization energy of H can thus be determined directly by measuring the frequencies of transitions to high-n states and extrapolating the Rydberg series to n → ∞.

Dissipative dynamics of atomic and molecular Rydberg gases: Avalanche to ultracold plasma states of strong coupling

Not long after metastable xenon was photoionized in a magneto-optical trap, groups in Europe and North America found that similar states of ionized gas evolved spontaneously from state-selected, high principal quantum number Rydberg gases. Studies of atomic xenon and molecular nitric oxide entrained in a supersonically cooled molecular beam subsequently showed much the same final state evolved from a sequence of prompt Penning ionization and electron-impact avalanche to plasma, well-described by coupled rate-equation simulations. But, measured over longer times, the molecular ultracold plasma was found to exhibit an anomalous combination of very long lifetime and very low apparent electron temperature. This review first summarizes early developments in the general study of ultracold plasmas formed by atomic and molecular Rydberg gases, and then turns to describe the particular properties of the nitric oxide molecular ultracold plasma that appear to call for an explanation beyond the realm of conventional plasma physics.

Измерение напряженности электрического поля СВЧ излучения на частоте радиационного перехода между ридберговскими состояниями атомов -=SUP=-85-=/SUP=-Rb

Authors: E.F. Stelmashenko(1), O.A. Klezovich(1), V.N. Baryshev(1), V.A. Tischenko(1), I.Yu. Blinov(1), V.G.Palchikov (1,2(, V. D. Ovsiannikov (1,3) Affiliation: (1)National Research Institute for Physical-Technical and Radiotechnical Measurements, Mendeleevo, Moscow Region , Russia (2)National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow, Russia (3)Voronezh State University, University sq.1, 394018, Voronezh, Russia Abstract: Spectral characteristics are determined for the resonance electromagnetically induced transparency (EIT) effect on atomic rubidium vapours, induced by an intense radiation of the wavelength in the region from 479 to 486 nm in presence of a microwave (MW) radiation of a frequency from 1 to 300 GHz, which splits the energy of transition from the 5P3/2 state to a Rydberg state nD5/2 . The magnitude of the EIT peak splitting is proportional to the MW-radiation electric field. Simple approximation equations are derived for evaluating numerically the amplitude of transition between Rydberg nD5/2 and (n+1)P3/2 states with high principal quantum numbers n. An experimental setup is constructed for measuring the MW electric field on the basis of the EIT resonance-splitting measurements in absorption spectra of a probe radiation.