Excited Rydberg States Research Articles

Absence of Fibonacci anyons in Rydberg chains

Recent experiments have focused attention on the properties of chains of atoms in which the atoms are either in their ground states or in highly excited Rydberg states which block similar excitations in their immediate neighbors. As the low energy Hilbert space of such chains is isomorphic to that of a chain of Fibonacci anyons, they have been proposed as a platform for topological quantum computation and for simulating anyon dynamics. We show that generic local operators in the Rydberg chain correspond to non-local anyonic operators that do not preserve a topological symmetry of the physical anyons. Consequently, we argue that Rydberg chains do not yield Fibonacci anyons and quantum computation with Rydberg atoms is not topologically protected.

Photodissociation branching ratios of 12C16O from 108000 cm−1 to 113200 cm-1 measured by two-color VUV-VUV laser pump-probe time-slice velocity-map ion imaging method: Observation of channels for producing O(1D)

The photoabsorption and photodissociation of carbon monoxide (CO) in the vacuum ultraviolet (VUV) region is one of the most important photochemical processes in the interstellar medium, thus it has attracted numerous experimental and theoretical studies. Here, we employed the two-color VUV-VUV laser pump-probe time-slice velocity-map ion imaging method to measure the relative branching ratios [C(3P0)+O(1D)]/ {[C(3P0)+O(3P)]+ [C(3P0)+O(1D)]} and [C(3P2)+O(1D)]/ {[C(3P2)+O(3P)]+[C(3P2)+O(1D)]} in the VUV photoexcitation energy range of 108000−113200 cm−1. Here, one tunable VUV laser beam is used to excite CO to specific rovibronic states, and a second independently tunable VUV laser beam is used to state-selectively ionize C(3P0) and C(3P2) for detection. State-selective photoionization through the 1VUV+1UV/visible resonance-enhanced multiphoton ionization scheme has greatly enhanced the detection sensitivity, which makes many new weak absorption bands observable in the current study. The branching ratio measurement shows that the spin-forbidden channels C(3P0)+O(1D) and C(3P2)+O(1D) only open at several discrete narrow energy windows. This might be caused by certain accidental resonance-enhanced spin-orbit interactions between the directly excited Rydberg states and valence states of triplet type which finally dissociate into the spin-forbidden channels.

Quench dynamics of Rydberg-dressed bosons on two-dimensional square lattices

We study the dynamics of bosonic atoms on a two-dimensional square lattice, where atomic interactions are long-ranged with either a box or soft-core shape. The latter can be realized through laser dressing ground-state atoms to electronically excited Rydberg states. When the range of interactions is equal or larger than the lattice constant, the system is governed by an extended Bose-Hubbard model. We propose a quench process by varying the atomic hopping linearly across phase boundaries of the Mott insulator-supersolid and supersolid-superfluid phases. Starting from a Mott insulating state, the dynamical evolution of the superfluid order parameter exhibits a universal behaviour at the early stage, largely independent of interactions. The dynamical evolution is significantly altered by strong, long-range interactions at later times. Particularly, we demonstrate that density wave excitation is important when the quench rate is small. Moreover, we show that the quench dynamics can be analyzed through time-of-flight images, i.e., measuring the momentum distribution and noise correlations.

Accuracy of Spin-Component Scaled ADC(2) Excitation Energies and Potential Energy Surfaces.

In a recent paper of this journal ( Tajti ; ; Szalay . J. Chem. Theory Comput. 2019 , 15 , 5523 ), we have shown that failures of the CC2 method to describe Rydberg excited states as well as potential energy surfaces of certain valence excited states can be cured by spin-component scaled (SCS) versions SCS-CC2 and SOS-CC2 to a large extent. In this paper, the related and popular second-order algebraic diagrammatic construction (ADC(2)) method and its SCS variants are inspected with the previously established methodology. The results reflect the similarity of the CC2 and ADC(2) models, showing identical problems in the case of the canonical form and the same improvement when spin-component scaling is applied.

Quantum dynamics of atomic Rydberg excitation in strong laser fields.

Neutral atoms have been observed to survive intense laser pulses in high Rydberg states with surprisingly large probability. Only with this Rydberg-state excitation (RSE) included is the picture of intense-laser-atom interaction complete. Various mechanisms have been proposed to explain the underlying physics. However, neither one can explain all the features observed in experiments and in time-dependent Schrödinger equation (TDSE) simulations. Here we propose a fully quantum-mechanical model based on the strong-field approximation (SFA). It well reproduces the intensity dependence of RSE obtained by the TDSE, which exhibits a series of modulated peaks. They are due to recapture of the liberated electron and the fact that the pertinent probability strongly depends on the position and the parity of the Rydberg state. We also present measurements of RSE in xenon at 800 nm, which display the peak structure consistent with the calculations.

Sub-Doppler Spectroscopy of Excited Atoms in a Multilayer Gas Cell

The potential for spectroscopy in a multilayer cell with rarefied gas medium is theoretically investigated where said cell can be used as a compact analog of a large number of plane-parallel beams of atoms (or molecules) in an optically excited quantum level. In particular, this situation occurs for metastable and highly excited long-lived Rydberg states of atoms and molecules. Velocity selection of atoms (molecules) excited to said quantum level by broadband optical pumping was found to be efficient because of their characteristic transit and collisional relaxation in said cell. Sub-Doppler resonances at the optical transition frequencies from a given level were narrow as a result of the selection when the monochromatic probe light beam was absorbed.

An interacting topological phase

Quantum Simulation Most topologically nontrivial systems discovered to date consist of noninteracting particles. Their properties can therefore be explained within a single-particle picture. De Leseleuc et al. engineered a topological phase of bosonic atoms in which interactions play a crucial role. The atoms, which were in highly excited Rydberg states, were held in an array of optical tweezers. Depending on the spatial arrangement of the tweezers, the dipole-dipole interactions between the atoms gave rise to two configurations with different topological properties. Science , this issue p. [775][1] [1]: /lookup/doi/10.1126/science.aav9105

Observation of a symmetry-protected topological phase of interacting bosons with Rydberg atoms

The concept of topological phases is a powerful framework for characterizing ground states of quantum many-body systems that goes beyond the paradigm of symmetry breaking. Topological phases can appear in condensed-matter systems naturally, whereas the implementation and study of such quantum many-body ground states in artificial matter require careful engineering. Here, we report the experimental realization of a symmetry-protected topological phase of interacting bosons in a one-dimensional lattice and demonstrate a robust ground state degeneracy attributed to protected zero-energy edge states. The experimental setup is based on atoms trapped in an array of optical tweezers and excited into Rydberg levels, which gives rise to hard-core bosons with an effective hopping generated by dipolar exchange interaction.

Controlling Rydberg excitation process with shaped intense ultrashort laser pulses**Project supported by the National Natural Science Foundation of China (Grant No. 11874246).

We perform a theoretical investigation on the control over the atomic excitation of Rydberg states with shaped intense ultrashort laser pulses. By numerically solving the time-dependent Schrödinger equation (TDSE), we systematically study the dependence of the population of the Rydberg states on the π phase step position in the frequency spectra of the laser pulse for different intensities, central wavelengths and pulse durations. Our results show that the Rydberg excitation process can be effectively modulated using shaped intense laser pulses with the laser intensity as high as 1×1014 W/cm2. Our work also have benefit to the future investigation to find out the dominant mechanism behind the excitation of Rydberg states in strong laser fields.

Solid-state pulsed microwave emitter based on Rydberg excitons.

We theoretically demonstrate how the cuprous oxide Cu2O could be used as a gain medium in a solid-state maser. By taking advantage of radiative microwave transitions between highly excited Rydberg states, one can achieve population inversion and masing in a wide range of wavelengths. In the pulsed emission regime, the considered excitonic system is characterized by intricate and rich dynamics, which are investigated numerically, taking into account several key features of the medium, such as strong Stark shift of energy levels and the presence of the Rydberg blockade effect.

Coupling between Rydberg States and Landau Levels of Electrons Trapped on Liquid Helium.

We investigate the coupling between Rydberg states of electrons trapped on a liquid helium surface and Landau levels induced by a perpendicular magnetic field. We show that this realizes a prototype quantum system equivalent to an atom in a cavity, where their coupling strength can be tuned by a parallel magnetic field. We determine experimentally the renormalization of the atomic transition energies induced by the coupling to the cavity, which can be seen as an analog of the Lamb shift. When the coupling is sufficiently strong, the transition between the ground and first excited Rydberg states splits into two resonances corresponding to dressed states with vacuum and one photon in the cavity. Our results are in quantitative agreement with the energy shifts predicted by the effective atom in a cavity model where all parameters are known with high accuracy.

H-, He-like recombination spectra – III. n-changing collisions in highly excited Rydberg states and their impact on the radio, IR, and optical recombination lines

ABSTRACT At intermediate to high densities, electron (de-)excitation collisions are the dominant process for populating or depopulating high Rydberg states. In particular, the accurate knowledge of the energy changing (n-changing) collisional rates is determinant for predicting the radio recombination spectra of gaseous nebula. The different data sets present in the literature come either from impact parameter calculations or semi-empirical fits and the rate coefficients agree within a factor of 2. We show in this paper that these uncertainties cause errors lower than 5 per cent in the emission of radio recombination lines of most ionized plasmas of typical nebulae. However, in special circumstances where the transitions between Rydberg levels are amplified by maser effects, the errors can increase up to 20 per cent. We present simulations of the optical depth and Hnα line emission of active galactic nuclei broad-line regions and the Orion Nebula Blister to showcase our findings.

Electron-nuclear correlated multiphoton-route to Rydberg fragments of molecules

Atoms and molecules exposed to strong laser fields can be excited to the Rydberg states with very high principal quantum numbers and large orbitals. It allows acceleration of neutral particles, generate near-threshold harmonics, and reveal multiphoton Rabi oscillations and rich photoelectron spectra. However, the physical mechanism of Rydberg state excitation in strong laser fields is yet a puzzle. Here, we identify the electron-nuclear correlated multiphoton excitation as the general mechanism by coincidently measuring all charged and neutral fragments ejected from a H2 molecule. Ruled by the ac-Stark effect, the internuclear separation for resonant multiphoton excitation varies with the laser intensity. It alters the photon energy partition between the ejected electrons and nuclei and thus leads to distinct kinetic energy spectra of the nuclear fragments. The electron-nuclear correlation offers an alternative visual angle to capture rich ultrafast processes of complex molecules.

Dissociative frustrated multiple ionization of hydrogen chloride in intense femtosecond laser fields

The dissociative frustrated multiple ionization of hydrogen chloride (HCl) molecules in intense femtosecond laser fields is investigated by employing the coincidence measurement technique in cold target recoil ion momentum spectroscopy. Various dissociative frustrated multiple ionization channels caused by populating one or two electrons to highly excited Rydberg states can be clearly distinguished for HCl in linearly polarized intense laser fields. The excited charged fragmentations, depending on their occupied principle quantum numbers, can be either directly identified forming a ``knee'' structure in the kinetic energy release spectrum, or singly ionized by the weak electric field in the spectrometer, or by blackbody radiation after the conclusion of the laser pulse. The inherent feature of the potential energy curves of HCl plays an important role in the strong-field dissociative frustrated multiple ionization process.

Dynamic Instability of Rydberg Atomic Complexes

Atoms and molecules in highly excited (Rydberg) states have a number of unique characteristics due to the strong dependence of their properties on the values of principal quantum numbers. The paper discusses the results of an investigation of collisional Rydberg complexes specific features, resulting in the development of dynamic chaos and the accompanying diffusion autoionization processes. It is shown (experiment and theory) that, in subthermal low energies, the global chaotic regime that evolved in quasimolecular systems leads to significant changes in the Rydberg gases radiation/ionization kinetics. The effect of Förster resonance on the width of the fluorescence spectra and stochastic ionization processes in Rydberg systems is also discussed.

Realization of a Rydberg-Dressed Ramsey Interferometer and Electrometer.

We present the experimental realization and characterization of a Ramsey interferometer based on optically trapped ultracold potassium atoms, where one state is continuously coupled by an off-resonant laser field to a highly excited Rydberg state. We show that the observed interference signals can be used to precisely measure the Rydberg atom-light coupling strength as well as the population and coherence decay rates of the Rydberg-dressed states with subkilohertz accuracy and for Rydberg state fractions as small as one part in 10^{6}. We also demonstrate an application for measuring small, static electric fields with high sensitivity. This provides the means to combine the outstanding coherence properties of Ramsey interferometers based on atomic ground states with a controllable coupling to strongly interacting states, thus expanding the number of systems suitable for metrological applications and many-body physics studies.

Quasiparticle spectra of supersolid lattice gases at near-resonant Rydberg dressing

One of the major challenges in realizing a strongly interacting lattice gas using Rydberg states is the occurrence of avalanche loss processes. As these are directly proportional to the total Rydberg fraction, the commonly suggested solution is using far off-resonantly excited Rydberg states. We instead propose the realization of a correlated bosonic lattice gas at near-resonant excitation, where the total Rydberg fraction in the bulk is low due to the strong, interaction-driven effective detuning. Using real-space dynamical mean-field theory we show that its reduced effect at the boundary of a system can easily be compensated by considering a tailored beam-waist of the driving Rabi-laser. In this geometry we discuss the spectral properties at the crossover between the supersolid and the superfluid state and present the momentum resolved spectral properties of the supersolid bulk. The latter results are obtained within an extended quasiparticle method which also yields a correction of the mean-field phase transition.

The lowest-lying electronic states of isoflurane and sevoflurane in the 5.0–10.8 eV energy range investigated by experimental and theoretical methods

Photoabsorption spectra of isoflurane and sevoflurane have been measured with synchrotron radiation over the photon range 5.0–10.8 eV. Low-lying excited singlet valence and Rydberg states are investigated and the assignments supported by quantum chemical calculations, the latter also helping to identify the triplet states. This provides the first comprehensive investigation of all excited electronic states up to the first ionisation energy. The Rydberg series converging to the ionisation energy limits are identified according to the magnitude of the quantum defects. The measured absolute cross-sections have been used to calculate the photolysis lifetimes of isoflurane and sevoflurane in the Earth’s atmosphere.

Excitation of strongly interacting moving Rydberg atoms by photon recoil momentum

Based on the fact that an ensemble of moving Rydberg atoms in two counterpropagating laser beams in the limit of complete dipole blocking is isomorphic to a Jaynes–Cummings model, a scheme for robust and efficient excitation of atomic Rydberg states is proposed. It is shown that the Doppler frequency shifts play an important role in atomic population transfer processes. The suggested method can be employed to detect the symmetric entangled states and paves the way to preparing entangled states with a single excited atom in a Rydberg state. It is shown that this process is robust with respect to parameter fluctuations, such as the laser pulse area, the relative spatial offset (the delay) of the laser beams and the number of atoms.

Coherent Excitation of Rydberg States in the Gas of Cold 40Ca Atoms

The spectra of highly excited 40Ca atoms prepared using a magneto-optical trap and an ultraviolet laser are experimentally studied. The dependence of the atomic density in the magneto-optical trap on the detuning frequency of cooling radiation and on the magnetic field gradient is determined. By using the technique based on the reduction of resonance fluorescence, the energy of the 761S0 Rydberg state for 40Ca atoms is determined. A new scheme for stabilization of the laser frequency to create highly excited Rydberg atoms is demonstrated. This scheme employs the saturated absorption spectrum in a cell with rubidium atomic gas.