Cesium Rydberg States Research Articles

Lifetime Measurement of Cesium Atoms Using a Cold Rydberg Gas

The lifetimes of nS1/2 and nD5/2 (n = 60–83) cesium Rydberg states are measured accurately in a magneto-optical trap using the field ionization technique and analyzed with the existing theoretical model. The room temperature blackbody radiation (BBR) and interaction between Rydberg atoms can enhance the decay rate and reduce the spontaneous lifetime of the given Rydberg atom. The measured lifetime shows a good agreement with the calculation accounting a room temperature BBR at low enough Rydberg atomic density. The dependence of measured lifetime on atomic density shows that the collision and interaction between Rydberg atoms have a large effect on the lifetime at higher Rydberg atomic density. The scaling laws of n2.55±0.02 for nD5/2 state and n2.30±0.01 for nS1/2 state within n = 60–83 range are obtained and agreement with the model calculation with a relative deviation less than 3%.

Cesium Rydberg-state ionization study by three-dimensional ion-electron correlation: Toward a monochromatic electron source

We study the excitation and ionization of cesium Rydberg states in an electric field ($\ensuremath{\approx}\phantom{\rule{0.16em}{0ex}}2200\phantom{\rule{4pt}{0ex}}\mathrm{V}/\mathrm{cm}$) near the classical field-ionization threshold ($\ensuremath{\approx}\ensuremath{-}280\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ binding energy) by three-dimensional (3D) ion-electron coincidence spectroscopy. Cesium atoms are produced by an effusive oven and excited with lasers to Stark-shifted Rydberg states or directly ionized. Using a double time-of-flight setup we record 3D ($X, Y$, time of flight) coincidence imaging of electrons and ions. Above-threshold photoionization creates broad images with poor electron-ion spatial correlation. Fast ionizing states produce very good correlations and the images reveal the electric-field map of the ionization region. Slow ionizing states show that the relatively high atomic velocity is detrimental to the correlations. Experimental data are accurately reproduced by detailed Monte Carlo excitation and ionization simulations based on Stark maps obtained with local-frame transformation (LFT) theory. Agreement between our spectroscopic experiment and LFT theory is very good, with better that hundreds of megahertz accuracy. But, on rare particular states, several gigahertz discrepancy is found. This study can be used to select appropriate states for the creation of ion and electron beams with high brightness, good correlation, and low energy dispersion.

Radiative lifetime measurement of ultracold cesium Rydberg states by a simplified optical pumping method.

We demonstrate one simplified all-optical method to measure the radiative lifetime of ultracold cesium (Cs) Rydberg atoms. This method is based on photodetection of one ground state atomic absorption in a ladder-type electromagnetic induced transparency (EIT), which contains one ground state, one intermediate state, and one Rydberg state. In the presence and absence of optical pumping between the Rydberg state and the intermediate state, the absorption difference with varying delay time can reconstruct the population evolution of target Rydberg atoms. By using this method, the radiative lifetimes of 50S1/2 and 50D5/2 of Cs atoms are measured to be 53(9)µs and 42(9)µs, respectively, which are consistent with theoretical calculations. The agreements show the reliability of our presented method, which can provide a route for researching light-matter interaction behavior without the need to quantify absorption characteristic.

Measurement of quantum defect of cesium nP<sub>3/2</sub> (n = 70—94) Rydberg states by using ultraviolet single-photon Rydberg excitation

A narrow-linewidth continuous-wave single-frequency tunable 318.6-nm ultraviolet laser system with watt-level output power is developed in our experiment based on well-developed fiber lasers, fiber amplifiers, and efficient laser frequency conversion technique. Cesium 6S<sub>1/2</sub>—<i>n</i>P<sub>3/2</sub> (<i>n</i> = 70—94) single-photon Rydberg excitation in a room-temperature cesium atomic vapor cell is realized by using our ultraviolet laser system. The single-photon Rydberg excitation signal is obtained via the V-type three-level atomic system which contains 6S<sub>1/2</sub> (<i>F</i> = 4) ground state, 6P<sub>3/2</sub> (<i>F</i> = 5) excited state and one of <i>n</i>P<sub>3/2</sub> (<i>n</i> = 70—94) Rydberg states. When cesium atoms populated on the ground state are partially excited to Rydberg state by the ultraviolet laser, absorption of 852.3-nm probe beam which is locked to 6S<sub>1/2</sub> (<i>F</i> = 4)—6P<sub>3/2</sub> (<i>F</i> ′ = 5) hyperfine transition will decrease. In this way, the cesium Rydberg states are detected. The quantum defects for cesium <i>n</i>P<sub>3/2</sub> (<i>n</i> = 70—94) Rydberg states are experimentally measured with a high-precision wavemeter. The variation trend of experimentally measured data deviates from that of calculated values. Due to the fact that the cesium vapor cell is positioned in a magnetic shielding tank, the Zeeman effect can be ignored. Considering that the polarizability of Rydberg atoms is proportional to (<i>n</i>*)<sup>7</sup>, in which <i>n</i>* is the effective principal quantum number, the Rydberg screen effect of cesium atomic vapor cell cannot completely protect cesium atoms from being perturbed by an external DC electric field. Therefore the residual DC electric field existing inside the cesium vapor cell will have a significant influence on quantum defect measurement of Rydberg atoms. Using the theoretical model of Stark effect and the relationship between polarizability of Rydberg atoms and the effective principal quantum number <i>n</i>*, the corrected experimental value of quantum defect for cesium <i>n</i>P<sub>3/2</sub> (<i>n</i> = 70—94) Rydberg states is found to be ~(3.5591 ± 0.0007). The corrected experimental value of quantum defect is consistent with the calculation.

Measurement of the fine structure of cesium Rydberg state

The spectra of Rydberg atoms are of great significance for studying the energy levels of Rydberg atoms and the interaction between neutral atoms, especially, the high-precision spectra of Rydberg atoms can be used to measure the energy level shifts of Rydberg atoms resulting from the dipole-dipole interactions in room-temperature vapor cells. In this paper we report the preparation of cesium Rydberg states based on the cascaded two-photon excitation of 509 nm laser and 852 nm laser in opposite, and the measurements of the fine structure of cesium Rydberg states. In this experiment, the 509 nm laser is generated by the cavity-enhanced second-harmonic generation from 1018 nm laser with a periodically-poled KTP crystal and has a maximum power of about 1 W, and the 852 nm probe laser is provided by an external-cavity diode laser with a maximum output power of 5 mW and a typical linewidth of 1 MHz. By scanning the frequency of 509 nm coupling laser, it is presented that the Doppler-free spectra based on electromagnetically-induced transparency (EIT) of 509 nm coupling laser and 852 nm probe laser. The velocity-selective EIT spectra are used to study the spectral splitting of 6S1/26P3/257S(D) ladder-type system of cesium Rydberg atoms in a room-temperature vapor cell. The powers of 852 nm probe laser and 509 nm coupling laser are 0.3 upW and 200 mW, respectively. Their waist radii are both approximately 50 m. The intervals of hyperfine splitting of the intermediate state 6P3/2(F'=3, 4, 5) and fine splitting of 57D3/2 and 57D5/2 Rydberg states are measured by a frequency calibrating. Concretely, the velocity-selective spectrum with a radio frequency (RF) modulation of 30 MHz is used as a reference to calibrate the Rydberg fine-structure states in the hot vapor cell, where the RF frequency precision is smaller than a hertz on long time scales and the EIT linewidth is smaller than 13 MHz. The experimental value of the fine structure splitting of 57D3/2 and 57D5/2 Rydberg states is (354.72.5) MHz, that is in consistence with the value of 346.8 MHz calculated by Rydberg-Ritz equation and quantum defects of 57D3/2 and 57D5/2 Rydberg states. The experimental values of hyperfine splitting of intermediate state 6P3/2(F'=3, 4, 5) are also coincident with the theoretical calculated values. The dominant discrepancy existing between the experimental and calculated results may arise from the nonlinear correspondence of the PZT while the 509 nm wavelength cavity is scanned, and the measurement accuracy influenced by the spectral linewidth. The velocity-selective spectroscopy technique can also be used to measure the energy level shifts caused by the interactions of Rydberg atoms.

Lifetime measurement of ultracold caesium Rydberg states

We measure the nS and nD (n = 30–40) state lifetimes of caesium Rydberg atoms in a conventional magneto-optical trap using the field ionization technique, which is consistent with the existing theoretical model through suppressing collisions and super-radiance effects. We also investigate variation of the lifetimes with densities of Rydberg atoms by changing the pulse energy of the dye laser. The results indicate that collisions and super-radiance effects have a large influence on the accuracy of lifetime measurement at high densities of Rydberg atoms.

Study of two-photon transition probability of Cs Rydberg states by field ionization

The two-photon transition probability of cesium atom from ground state to n 2S, n 2D Rydberg states are measured by means of the field ionization. Corresponding calculations give results in good agreement with the experimental measurements, and the approximate scaling law of n −4for the two-photon transition probability of cesium Rydberg states has been deduced from the study.

Self-quenching mechanism in caesium Rydberg states

The authors report a study on the depopulation mechanism of low Rydberg states. Caesium atoms have been excited to the 9d and 10d levels by absorption of two resonant photons; collisional transfer from these states to the nearby levels has been studied. The related cross sections show strong dependence on both energy defect and angular momentum l.

Millimeter-wave spectroscopy in cesium Rydberg states. Quantum defects, fine- and hyperfine-structure measurements

High-resolution double-resonance spectroscopy experiments in the millimeter-wave domain have yielded precise values of quantum defects in the $S$, $P$, $D$, and $F$ Rydberg levels of cesium (principal quantum number $n$ ranging from 23 to 45). In addition, fine and hyperfine structures have been measured in these levels. These experiments provide a precise mapping of the cesium Rydberg levels, allowing us to predict with an accuracy of about a MHz any transition frequency between two states with $n\ensuremath{\ge}20$ and $l\ensuremath{\le}3$.

MILLIMETER-WAVE SPECTROSCOPY OF CESIUM RYDBERG STATES AND POSSIBLE APPLICATIONS TO FREQUENCY METROLOGY

An extensive high-resolution study of the millimeter-wave spectrum of Cesium Rydberg states is presented, yielding new precise values of the nS, nP, nD and nF states quantum defects (23 ⩽ n ⩽ 45), and of their fine and hyperfine structures. The quantum defects values allow us to predict the frequency of any n,l → n',l' (n ⩾ 20, l ⩽ 3) transition, with a MHz accuracy. This precise mapping of the Cesium Rydberg states can provide a new secondary frequency standard in the 50 GHz - 10 THz range. Possible interesting metrological applications are discussed.

Multiphoton ionisation probabilities of multiple continua in alkali atoms

By using a perturbative treatment based on the central field approximation, the authors have calculated multiphoton ionisation probabilities in several cases of experimental interest (two-, three- and four-photon ionisation of the caesium and potassium ground states at the doubled Nd glass laser frequency and one-, two- and three-photon ionisation of some s, p, d and caesium Rydberg states). Some of these probabilities have been calculated beyond the minimum non-vanishing order. They have also performed some calculations for hydrogen. The comparison of their results with previous ones obtained by analytical methods provides a good test of the numerical techniques involved in the calculations.

Laser measurement of intensity ratio anomalies in principal series doublets of caesium Rydberg states: does the D1line vanish?

The authors have measured the anomalous ratio of the oscillator strengths in the principal series doublet lines of caesium for quantum numbers n=18 to 30. The light of a frequency-doubled tunable pulsed laser was absorbed by an atomic beam of caesium and the resonances were detected by the very sensitive field ionisation method. The results show a regular increase of the ratio rho of the D2 over D1 line strengths as a function of n. rho values in excess of 103 are obtained for n around 30. However, the analysis of the data rules out the possibility of a pole for rho (i.e. a disappearance of the D1 line) in the discrete spectrum. This experiment is in very good agreement with recent theoretical calculations.

Collisional disalignment of caesium Rydberg states

Cross sections for the disalignment of excited caesium atoms, by collision with atoms in ground states, have been determined by studying the damping of quantum beats in fluorescence. Atoms in a sealed cell were excited selectively to 122D3/2 and 132S3/2 by a pulsed tunable laser and discharge lamp. Alignment was induced by linear polarisation of the exciting light and monitored correspondingly. The quantum beats originate in the coherent excitation of hyperfine states whose structures have been determined in previous work. Collisional damping is investigated studying the quantum-beat signal over a range of atomic densities. The fluorescence contains a component representing the decay of population as well as of alignment, and extraction of the alignment cross sections relies on previous measurements of the depopulation cross sections. The results for disalignment cross sections are: sigma (2)(122D3/2)=4.1+or-0.8*10-16 m2, sigma (2)(132D3/2)=5.3+or-0.9*10-16 m2, about three times larger than the depopulation cross sections. Radiative lifetimes obtained from the analysis agree with previous determinations.