Highly-excited Rydberg States Research Articles

Strong-field ionization and AC-Stark shifted Rydberg states in OCS

We present theoretical results for intensity-dependent above-threshold ionization (ATI) spectra from oriented OCS molecules probed by intense femtosecond laser pulses with wavelengths of 800 and 400 nm. The calculations were performed using the time-dependent Schrödinger equation within the single-active-electron approximation and including multielectron polarization effects. The results capture some of the experimental findings (Yu et al 2017 J. Phys. B: At. Mol. Opt. Phys. 50 235602), in particular when considering the sensitivity of the ATI spectra on the molecular orientation. We identify characteristic features in the ATI spectra which correspond to resonant multiphoton ionization via highly-excited Rydberg states are captured by the theory.

Realizing Distance-Selective Interactions in a Rydberg-Dressed Atom Array.

Measurement-based quantum computing relies on the rapid creation of large-scale entanglement in a register of stable qubits. Atomic arrays are well suited to store quantum information, and entanglement can be created using highly-excited Rydberg states. Typically, isolating pairs during gate operation is difficult because Rydberg interactions feature long tails at large distances. Here, we engineer distance-selective interactions that are strongly peaked in distance through off-resonant laser coupling of molecular potentials between Rydberg atom pairs. Employing quantum gas microscopy, we verify the dressed interactions by observing correlated phase evolution using many-body Ramsey interferometry. We identify atom loss and coupling to continuum modes as a limitation of our present scheme and outline paths to mitigate these effects, paving the way towards the creation of large-scale entanglement.

High-fidelity entanglement and detection of alkaline-earth Rydberg atoms

Trapped neutral atoms have become a prominent platform for quantum science, where entanglement fidelity records have been set using highly-excited Rydberg states. However, controlled two-qubit entanglement generation has so far been limited to alkali species, leaving the exploitation of more complex electronic structures as an open frontier that could lead to improved fidelities and fundamentally different applications such as quantum-enhanced optical clocks. Here we demonstrate a novel approach utilizing the two-valence electron structure of individual alkaline-earth Rydberg atoms. We find fidelities for Rydberg state detection, single-atom Rabi operations, and two-atom entanglement surpassing previously published values. Our results pave the way for novel applications, including programmable quantum metrology and hybrid atom-ion systems, and set the stage for alkaline-earth based quantum computing architectures.

Narrow-band pulsed electron source based on near-threshold photoionization of Cs in a magneto-optical trap

The newly developed method of time-of-flight (ToF) momentum microscopy was used to analyse the cold electron emission from a Cs 3D magneto-optical trap (MOT). Three-step resonant photoionization was implemented via two intermediate states (6P3/2 pumped with 852 nm laser and 7S1/2 with 1470 nm) and a tuneable femtosecond Ti:sapphire laser for the final ionization step. The magnetic field of the MOT is switched off during the photoionization step. The natural bandwidth of the fs-laser is reduced to 4 meV using optical spectral filters. Precise tuning of the photon energy makes it possible to observe the transition regime between direct photoemission into the open continuum and field induced ionization of highly-excited Rydberg states. The paths can be identified by their characteristic dependency on the extraction field and on the Ti:sapphire polarization. ToF analysis allowed us to disentangle the ionization paths and the dependence of the spatio-temporal distribution of the cold electrons on the polarization of the ionizing laser.

Density-wave steady-state phase of dissipative ultracold fermions with nearest-neighbor interactions

In this work we investigate the effect of local dissipation on the presence of density-wave ordering in spinful fermions with both local and nearest-neighbor interactions as described by the extended Hubbard model. We find density-wave order to be robust against decoherence effects up to a critical point where the system becomes homogeneous with no spatial ordering. Our results will be relevant for future cold-atom experiments using fermions with non-local interactions arising from the dressing by highly-excited Rydberg states, which have finite lifetimes due to spontaneous emission processes.

AN ADVANCED LASER PHOTOIONIZATION SEPARATION SCHEME FOR RADIOACTIVE ISOTOPES AND PRODUCTS OF ATOMIC ENERGETICS: URANIUM AND THE TRANSURANIUM ELEMENTSV.

We present an advanced, optimal laser-photoionization scheme of separating heavy radioactive isotopes and nuclear isomers, in particular, the uranium isotopes and the transuranium elements. The advanced scheme is based on the selective laser excitation of the isotope atom into the highly-excited Rydberg states and further electric field ionization mechanism. Some preliminary data for the autoionization resonance characteristics for U and transuranium isotopes are obtained. An appreciable dependence of the reorientation decay velocity of the autoionization resonances at an electric field is analyzed. Two autoionization resonances decay channels are predicted as well as the effect of the giant autoionization resonance width broadening in the relatively weak electric field for uranium and transuranium elements. Using the optimal laser action model and density matrices formalism it has been carried out modelling the optimal scheme of the U isotopes separation. It is presented The optimal scheme g- laser on quickly decayed nuclear isomers with using laser photoionization sorting excited nuclei with autoionization and electric field ionization mechanisms.

Velocity-selective spectroscopy measurements of Rydberg fine structure states in a hot vapor cell**Project supported by the National Natural Science Foundation of China (Grant Nos. 61475091 and 61227902), the National Key Research and Development Program of China (Grant No. 2017YFA0304502), and the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi, China (Grant No. 2017101).

A velocity-selective spectroscopy technique for studying the spectra of Rydberg gases is presented. This method provides high-resolution spectrum measurements. We present experimental results for a ladder system 6S1/2 → 6P3/2 →nS(D) electromagnetically-induced transparency involving highly-excited Rydberg states. Based on a radio-frequency modulation technique, we measure the hyperfine structure splitting of intermediate states and the fine structure splitting of Rydberg states in a room temperature 133Cs vapor cell. The experimental data and theoretical predictions show excellent agreement.

ARC: An open-source library for calculating properties of alkali Rydberg atoms

We present an object-oriented Python library for the computation of properties of highly-excited Rydberg states of alkali atoms. These include single-body effects such as dipole matrix elements, excited-state lifetimes (radiative and black-body limited) and Stark maps of atoms in external electric fields, as well as two-atom interaction potentials accounting for dipole and quadrupole coupling effects valid at both long and short range for arbitrary placement of the atomic dipoles. The package is cross-referenced to precise measurements of atomic energy levels and features extensive documentation to facilitate rapid upgrade or expansion by users. This library has direct application in the field of quantum information and quantum optics which exploit the strong Rydberg dipolar interactions for two-qubit gates, robust atom-light interfaces and simulating quantum many-body physics, as well as the field of metrology using Rydberg atoms as precise microwave electrometers. Program summaryProgram Title: ARC: Alkali Rydberg CalculatorProgram Files doi:http://dx.doi.org/10.17632/hm5n8w628c.1Licensing provisions: BSD-3-ClauseProgramming language: Python 2.7 or 3.5, with C extensionExternal Routines: NumPy [1], SciPy [1], Matplotlib [2]Nature of problem: Calculating atomic properties of alkali atoms including lifetimes, energies, Stark shifts and dipole–dipole interaction strengths using matrix elements evaluated from radial wavefunctions.Solution method: Numerical integration of radial Schrödinger equation to obtain atomic wavefunctions, which are then used to evaluate dipole matrix elements. Properties are calculated using second order perturbation theory or exact diagonalisation of the interaction Hamiltonian, yielding results valid even at large external fields or small interatomic separation.Restrictions: External electric field fixed to be parallel to quantisation axis.Supplementary material: Detailed documentation (.html), and Jupyter notebook with examples and benchmarking runs (.html and .ipynb).[1] T.E. Oliphant, Comput. Sci. Eng. 9, 10 (2007). http://www.scipy.org/.[2] J.D. Hunter, Comput. Sci. Eng. 9, 90 (2007). http://matplotlib.org/.

Observation of Rydberg Transitions in Resonance Fluorescence of Ultracold Lithium-7 Atoms

We describe our experimental technique for preparation and study of ultracold gas of Rydberg atoms. A magneto-optical trap for 7Li atoms is assembled. Using an ultraviolet laser, we perform a cw two-step excitation of atoms in the ground state to highly-excited states. For identification of highly-excited Rydberg states (n = 41 and 110), we record the resonance fluorescence of ultra-cold atoms in the trap.

Lithium Hydrides and Lithium Dimers: Sub‐Doppler Spectroscopy and Dynamics

AbstractDeep insights into molecular structures and dynamics were obtained for lithium dimers and lithium hydrides by sub‐Doppler spectroscopy combining molecular beams and cw tunable laser beams. For 7Li7Li species, accurate spectroscopic studies of the B 1Πu‐X 1Σg+ system were carried out, with the measurement of hundreds of wave numbers and with the determination of dissociation rates due to tunneling through the potential barrier of the B 1πu state. They led to the full description of the B state potential, including its barrier. For 6Li7Li species, weak but non‐negligible dissociation rates in the B 1Πu state were observed, measured and interpreted assuming that an electronic coupling between the B 1Πu and 1 1Πg states takes place through an ungerade‐gerade symmetry breaking. For LiH species, the A 1Σ+‐X 1 Σ+ system was revisited for both isotopomers. For this molecule, dynamical effects are predicted in highly‐excited Rydberg states, that could be studied by use of similar sub‐Doppler techniques.

Energies of Sr states with excited valence shell

Singly- and doubly-excited Sr states emerging upon excitation of the valence shell have been investigated. Only states with low values of the principal quantum numbern of the valence electrons have been considered: 5s4d, 5s5p, 5p2, 4d2 and 4d5p. These states have been treated by a perturbation theory based on the Dirac equations with model potential, the valence electrons interaction being considered as a perturbation. The zero-order approximation accounts for the main contributing interactions including the strong core potential screening. The applied calculation method was previously developed for highly-excited Rydberg states but its application also for states with lown was proved to be suitable.

Origin of the blue bands in the luminescence spectrum of core excited O2

Molecular oxygen was excited by 1.5–3.0 keV electrons. Luminescence spectra from the decay products of K-shell excitation were obtained at high resolution (bandwidth of 0.3 Å). With this resolution it was possible to identify and assign the observed lines to transitions from highly-excited Rydberg states of O+ and O fragments. These states appear to result from inner valence two-hole states and three-hole, one-electron states produced by Auger decay of the core hole in molecular oxygen.

Final-state distributions in charge transfer from sodium Rydberg atoms near the matching velocity

Reports measurements of the distribution of final n states that are populated in charge transfer collisions of Na+ ions with Na in highly-excited Rydberg states. Relative cross sections for final principal quantum numbers n'=18-42 are shown for laser-excited Na initial states 24d, 25s, 28d, 29s, 33d and 34s at kinetic energies 550-2000 eV. These results span the velocity-matching region in which projectile and orbital speeds are comparable. At the matching velocity the final-state distribution exhibits a maximum close to the n' that corresponds to the smallest change of internal energy relative to the initial state. The distribution shifts toward lower n' and becomes broader as collision velocity is increased. Initial s and d states yield similar distributions above but not at the matching velocity. The results are consistent with excitation of only mod m1 mod <or=1 sublevels referred to the incident beam direction, but several l' orbital angular momentum values appear to be present. Results for Ne+ and Ar+ incident on Na(24d) are similar to Na+ at equal velocity. The range of orbital speeds in a final-state distribution is approximately proportional to the projectile speed irrespective of initial state. The electronic orbital speed that corresponds to the centre of the distribution is a linear function of the projectile speed and initial orbital speed. The distributions disagree with predictions of the Brinkman-Kramers approximation.