Excited Rydberg States Research Articles

Parity effects in Rydberg-state excitation in intense laser fields

Parity effects in Rydberg-state excitation in intense laser fields

Avalanche Terahertz Photon Detection in a Rydberg Tweezer Array.

We propose a protocol for the amplified detection of low-intensity terahertz radiation using Rydberg tweezer arrays. The protocol offers single photon sensitivity together with a low dark count rate. It is split into two phases: during a sensing phase, it harnesses strong terahertz-range transitions between highly excited Rydberg states to capture individual terahertz photons. During an amplification phase it exploits the Rydberg facilitation mechanism which converts a single terahertz photon into a substantial signal of Rydberg excitations. We discuss a concrete realization based on realistic atomic interaction parameters, develop a comprehensive theoretical model that incorporates the motion of trapped atoms and study the many-body dynamics using tensor network methods.

A new parameterization of the DFT/CIS method with applications to core-level spectroscopy.

Time-dependent density functional theory (TD-DFT) within a restricted excitation space is an efficient means to compute core-level excitation energies using only a small subset of the occupied orbitals. However, core-to-valence excitation energies are significantly underestimated when standard exchange-correlation functionals are used, which is partly traceable to systemic issues with TD-DFT's description of Rydberg and charge-transfer excited states. To mitigate this, we have implemented an empirically modified combination of configuration interaction with single substitutions (CIS) based on Kohn-Sham orbitals, which is known as "DFT/CIS." This semi-empirical approach is well-suited for simulating x-ray near-edge spectra, as it contains sufficient exact exchange to model charge-transfer excitations yet retains DFT's low-cost description of dynamical electron correlation. Empirical corrections to the matrix elements enable semi-quantitative simulation of near-edge x-ray spectra without the need for significant a posteriori shifts; this should be useful in complex molecules and materials with multiple overlapping x-ray edges. Parameter optimization for use with a specific range-separated hybrid functional makes this a black-box method intended for both core and valence spectroscopy. Results herein demonstrate that realistic K-edge absorption and emission spectra can be obtained for second- and third-row elements and 3d transition metals, with promising results for L-edge spectra as well. DFT/CIS calculations require absolute shifts that are considerably smaller than what is typical in TD-DFT.

Rydberg-state excitation and ionization of argon atoms subject to elliptically polarized strong laser fields

Rydberg-state excitation and ionization of argon atoms subject to elliptically polarized strong laser fields

Efficient Time-Dependent Method for Strong-Field Ionization of Atoms with Smoothly Varying Radial Steps

We present an efficient numerical method to solve the time-dependent Schrödinger equation in the single-active electron picture for atoms interacting with intense optical laser fields. Our approach is based on a non-uniform radial grid with smoothly increasing steps for the electron distance from the residual ion. We study the accuracy and efficiency of the method, as well as its applicability to investigate strong-field ionization phenomena, the process of high-order harmonic generation, and the dynamics of highly excited Rydberg states.

Quantum dynamics of a fully blockaded Rydberg atom ensemble

Classical simulation of quantum systems plays an important role in the study of many-body phenomena and in the benchmarking and verification of quantum technologies. Exact simulation is often limited to small systems because the dimension of the Hilbert space increases exponentially with the size of the system. For systems that possess a high degree of symmetry, however, classical simulation can reach much larger sizes. Here we consider an ensemble of strongly interacting atoms with permutation symmetry, enabling the computation of certain collective observables for hundreds of atoms at arbitrarily long evolution times. The system is realized by an ensemble of three-level atoms, where one of the levels corresponds to a highly excited Rydberg state. In the limit of all-to-all Rydberg blockade, the Hamiltonian is invariant under permutation of the atoms. Using techniques from representation theory, we construct a block-diagonal form of the Hamiltonian, where the size of the largest block increases only linearly with the system size. We apply this formalism to derive efficient pulse sequences to prepare arbitrary permutation-invariant quantum states. Moreover, we study the quantum dynamics following a quench, uncovering a parameter regime in which the system thermalizes slowly and exhibits pronounced revivals. Our results create opportunities for the experimental and theoretical study of large interacting and nonintegrable quantum systems. Published by the American Physical Society 2024

Photocleavage of Aliphatic C–C Bonds in the Interstellar Medium

Ultraviolet (UV) processing in the interstellar medium (ISM) induces the dehydrogenation of hydrocarbons. Aliphatics, including alkanes, are present in different interstellar environments, being prevalently formed in evolved stars; thus, the dehydrogenation by UV photoprocessing of alkanes plays an important role in the chemistry of the ISM, leading to the formation of unsaturated hydrocarbons and eventually to aromatics, the latter ubiquitously detected in the ISM. Here, through combined experimental results and ab initio calculations, we show that UV absorption (mainly at the Lyα emission line of hydrogen at 121.6 nm) promotes an alkane to an excited Rydberg state from where it evolves toward fragmentation, inducing the formation of olefinic C=C bonds, which are necessary precursors of aromatic hydrocarbons. We show that the photochemistry of aliphatics in the ISM does not primarily produce direct hydrogen elimination but preferential C–C photocleavage. Our results provide an efficient synthetic route for the formation of unsaturated aliphatics, including propene and dienes, and suggest that aromatics could be formed in dark clouds by a bottom-up mechanism involving molecular fragments produced by UV photoprocessing of aliphatics.

Excitonic Rydberg States in a Trilayer to Monolayer H2-Aided CVD-Grown Large-Area MoS2 Film with Excellent UV to Visible Broad Band Photodetection Applications.

The diverse nature of optoelectronic properties of few-layer or monolayer MoS2 is generally dominated by A and B excitons. Occasionally, strong Coulombic interactions within the 2D monolayer led to the creation of hydrogen-like Rydberg states of excitons in MoS2 similar to other 2D monolayers. In this paper, a simple process is used to convert trilayer MoS2 films to a monolayer by introducing H2 gas during chemical vapor deposition. Remarkably, alongside the usual A, B excitons, and A- trion, the appearance of the Rydberg states is evidenced by photoluminescence spectra even at room temperature; also, there is an increase in their areal percentage with an increase in H2 content. The s-type excited Rydberg states up to the fourth order (n = 5) and third order (n = 4) of A and B excitons, respectively, have been probed from the photoluminescence spectra at 93 K. Unprecedentedly, the first-order derivative of room-temperature photocurrent spectrum reveals the Rydberg states concurrently and elaboratively. Furthermore, the large-area MoS2 films exhibit photoresponse in a broad UV to visible region with excellent photosensitivity (∼102) toward both UV and visible lights. Not only does this provide a profound understanding of the excitonic Rydberg states but also highlights the considerable potential of large-area monolayer MoS2 overcoming the difficulty of tiny flake-related 2D device endeavors.

Excitation dynamics in molecule resolved by internuclear distance driven by the strong laser field.

Rydberg-state excitation of stretched model molecules subjected to near-infrared intense laser fields has been investigated based on a fully quantum model (QM) proposed recently and the numerical solutions of time-dependent Schrödinger equation (TDSE). Given the good agreement between QM and TDSE, it is found that, as the molecules are stretched, the electron tends to be trapped into low-lying Rydberg-states after its ionization from the core, which can be attributed to the shift of the ionization moments corresponding to maximum excitation populations. Moreover, the n-distribution is broadened for molecules with increasing internuclear distance, which results from the change of momentum distribution of emitted electrons. Analysis indicates that both of the above phenomena are closely related to the interference effect of electronic wave packets emitted from different nuclei. Our study provides a more comprehensive understanding of the molecular excitation in intense laser fields, as well as a means of possible applications to related experimental observations.

Twin-Capture Rydberg State Excitation Enhanced with Few-Cycle Laser Pulses

Quantum excitation is usually regarded as a transient process occurring instantaneously, leaving the underlying physics shrouded in mystery. Recent research shows that Rydberg-state excitation with ultrashort laser pulses can be investigated and manipulated with state-of-the-art few-cycle pulses. We theoretically find that the efficiency of Rydberg state excitation can be enhanced with a short laser pulse and modulated by varying the laser intensities. We also uncover new facets of the excitation dynamics, including the launching of an electron wave packet through strong-field ionization, the re-entry of the electron into the atomic potential and the crucial step where the electron makes a U-turn, resulting in twin captures into Rydberg orbitals. By tuning the laser intensity, we show that the excitation of the Rydberg state can be coherently controlled on a sub-optical-cycle timescale. Our work paves the way toward ultrafast control and coherent manipulation of Rydberg states, thus benefiting Rydberg-state-based quantum technology.

Emergence of Synchronization in a Driven-Dissipative Hot Rydberg Vapor.

We observe synchronization in a thermal (35-60 °C) atomic (Rb) ensemble driven to a highly excited Rydberg state (principle quantum number n ranging from 43 to 79). Synchronization in this system is unexpected due to the atomic motion; however, we show theoretically that sufficiently strong interactions via a global Rydberg density mean field cause frequency and phase entrainment. The emergent oscillations in the vapor's bulk quantities are detected in the transmission of the probe laser for a two-photon excitation scheme.

Rydberg excitation through detuned microwave transition in rubidium

We study the excitation of Rydberg states in warm rubidium vapor. Using an inverted wavelength excitation scheme, we observe the effect of microwave coupling between Rydberg states through electromagnetically induced transparency. We observe AC stark shifts of the Rydberg states from the microwave coupling, and demonstrate detuned excitation to a secondary Rydberg state. These results show flexibility in the excitation process and state selection necessary for a variety of wave-mixing processes using Rydberg states.

Wavelength Dependence of Atomic Excitation for Ar Subject to Intense Midinfrared Laser Pulses

We report experimental and theoretical investigations of wavelength dependence of Rydberg state excitation (RSE) process of Ar subject to intense laser fields. By simultaneously measuring ionization and RSE yields of Ar atoms subject to strong laser fields at a series of wavelengths, we obtain the wavelength scaling law of the ratio of Ar* over Ar+ with respect to the laser intensity, and this result can be well reproduced by a nonadiabatic model, but not by the classical-trajectory Monte Carlo model. Our results indicate that the nonadiabatic corrections of the photoelectron tunneling exit and tunneling probability play a significant role at shorter wavelengths. Analysis shows that the wavelength dependence phenomenon is due to the interplay of the nonadiabatic effect, wave-packet diffusion and Coulomb focusing effect of the liberated electron.

Rydberg State Single-Mode Polariton Lasing with Ultralow Threshold via Symmetry Engineering.

Symmetry plays an essential role in the fundamental properties of a physical system. In this work, we report on the realization of tunable single-mode polariton lasing from highly excited Rydberg states via symmetry engineering. By breaking the symmetry of the polaritonic wave function through potential wells and controlling the spatial overlap between the gain region and the eigen mode, we are able to generate single-mode polariton lasing, reversibly and dynamically, from quantized polariton states. Increasing the asymmetry of the potential well, single-mode lasing can be achieved even for the highly excited Rydberg state with a principle quantum number of N = 14. Moreover, as a result of the excellent reservoir-eigen mode overlap and efficient spatial confinement, the threshold of lasing can be reduced up to 6 orders of magnitude, compared with those conventional pumping schemes. Our results present a new strategy toward the realization of thresholdless polariton lasing with dynamical tunability.

Neutral-atom entanglement using adiabatic Rydberg dressing

We revisit the implementation of a two-qubit entangling gate, the M\o{}lmer-S\o{}rensen gate, using the adiabatic Rydberg dressing paradigm for neutral atoms as studied in [A. Mitra et al., Phys. Rev. A 101, 030301(R) (2020)]. We study the implementation of rapid adiabatic passage using a two-photon transition, which does not require the use of an ultraviolet laser, and can be implemented using only amplitude modulation of one field with all laser frequencies fixed. We find that entangling gate fidelities, comparable to the one-photon excitation, are achievable with the two-photon excitation. Moreover, we address how the adiabatic dressing protocol can be used to implement entangling gates outside the regime of a perfect Rydberg blockade. We show that, by using adiabatic dressing, we can achieve scaling of the gate fidelity set by the fundamental limits to entanglement generated by the Rydberg interactions while simultaneously retaining a limited population in the doubly excited Rydberg state. This allows for fast high-fidelity gates for atoms separated beyond the blockade radius.

Electron Localization in Rydberg States

We discuss the possibility of localizing an electron in a highly excited Rydberg state. The second-order correlation of emitted photons is the tool for the determination of electron position. This second-order correlation of emitted radiation and, therefore, the correlation of operators describing the acceleration of the electron allows for a partial localization of the electron in its orbit. The correlation function is found by approximating the transition matrix elements by their values in the classical limit. It is shown that the second-order correlation, depending on two times, is a function of the time difference and is a periodic function of this argument with the period equal to the period of the corresponding classical motion. The function has sharp maxima corresponding to large electron acceleration in the vicinity of the "perihelion". This allows the localization of the electron in its consecutive approach to the perihelion point.

Engineering Knill–Laflamme–Milburn Entanglement via Dissipation and Coherent Population Trapping in Rydberg Atoms

We present a scheme for dissipatively preparing bipartite Knill–Laflamme–Milburn (KLM) entangled state in a neutral atom system, where the spontaneous emission of excited Rydberg states, combined with the coherent population trapping, is actively exploited to engineer a steady KLM state from an arbitrary initial state. Instead of commonly used antiblockade dynamics of two Rydberg atoms, we particularly utilize the Rydberg–Rydberg interaction as the pumping source to drive the undesired states so that it is unnecessary to satisfy a certain relation with laser detuning. The numerical simulation of the master equation signifies that both the fidelity and the purity above 98% is available with the current feasible parameters, and the corresponding steady-state fidelity is robust to the variations of the dynamical parameters.

The ellipticity dependence of Rydberg state excitation of noble gas atoms subject to strong laser fields

In this work, we theoretically investigate the ellipticity dependence of the Rydberg state excitation (RSE) and ionization of noble gas atoms subject to strong laser fields at a series of intensities and wavelengthes by a semiclassical model, where the nonadiabtic effect is considered or ignored. Our results demonstrate that, if the nonadiabatic effect has been ignored, the ratio between RSE and ionization yields exhibits an anomalous maximum at a nonzero ellipticity. On the other hand, if the nonadiabatic effect has been considered, this anomalous behavior disappears. The analysis indicates that the absence of this anomalous behavior can be attributed to the nonadiabatic corrections of instantaneous ionization rate and the initial photoelectron momentum distribution at the tunnel exit.

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.

Cramér–Rao, Fisher–Shannon and LMC–Rényi Complexity-like Measures of Multidimensional Hydrogenic Systems with Application to Rydberg States

Statistical measures of complexity hold significant potential for applications in D-dimensional finite fermion systems, spanning from the quantification of the internal disorder of atoms and molecules to the information–theoretical analysis of chemical reactions. This potential will be shown in hydrogenic systems by means of the monotone complexity measures of Cramér–Rao, Fisher–Shannon and LMC(Lopez-Ruiz, Mancini, Calbet)–Rényi types. These quantities are shown to be analytically determined from first principles, i.e., explicitly in terms of the space dimensionality D, the nuclear charge and the hyperquantum numbers, which characterize the system’ states. Then, they are applied to several relevant classes of particular states with emphasis on the quasi-spherical and the highly excited Rydberg states, obtaining compact and physically transparent expressions. This is possible because of the use of powerful techniques of approximation theory and orthogonal polynomials, asymptotics and generalized hypergeometric functions.