high-Rydberg Atoms Research Articles

A sensitive detection of high Rydberg atom with large dipole moment**Project supported by the National Natural Science Foundation of China (Grant Nos. 91421305, 91121005, and 11674359) and the National Key Basic Research Program of China (Grant No. 2013CB922003).

We report a sensitive detection of high Rydberg atom with large dipole moment utilizing its deflection near a pair of parallel cylindrical copper rods which are oppositely charged. When the low-field seeking state Rydberg atoms fly across the gradient electric field formed by the pair of rods, they will be pushed away from the rods while the high-field seeking state ones will be attracted towards the rods. These atoms will form different patterns on an ion imaging system placed downwards at the end of the rods. The spatial distribution of the deflected atoms on the imaging system is also simulated, in good agreement with the experimental results, from which we can deduce the quantum state information of the excited atoms. This state resolvable Rydberg atom detection can be used for the dynamics research of the dipole–dipole interaction between atoms with large dipole moments.

Measurement of the Spatial Distribution of Ultracold Cesium Rydberg Atoms by Time-of-Flight Spectroscopy

We prepare nS (n = 49) cesium Rydberg atoms by two-photon excitation in a standard magnetooptical trap to obtain the spatial distribution of the Rydberg atoms by measuring the time-of-flight (TOF) spectra in the case of a low Rydberg density. We analyze the time evolution of the ultracold nS Rydberg atoms distribution by changing the delay time of the pulsed ionization field, defined as the duration from the moment of switching off the excitation lasers to the time of switching on the ionization field. TOF spectra of Rydberg atoms are observed as a function of the delay time and initial Rydberg atomic density. The corresponding full widths at half maximum (FWHMs) are obtained by fitting the spectra with a Gaussian profile. The FWHM decreases with increasing delay time at a relatively high Rydberg atom density (>5 × 107/cm3) because of the decreasing Coulomb interaction between released charges during their flight to the detector. The temperature of the cold atoms is deduced from the dependence of the TOF ...

Effective Elimination of Space Charge Effects in Ion-Beam Experiments

An experimental method is proposed for the effective elimination of space-charge effects in ion-beam experiments based on collisions of high-Rydberg atoms with neutral species. One can effectively avoid the space-charge effects encountered in ion-beam experiments by the provision of an extra electron in a circular high-Rydberg state on the ion. This procedure is expected to achieve accurate probing of the interaction between the ion and the neutral species without space-charge effects at low energies.

Electrometry near a dielectric surface using Rydberg electromagnetically induced transparency

Electrometry near a dielectric surface is performed using Rydberg electromagnetically induced transparency (EIT). The large polarizability of high n-state Rydberg atoms gives this method extreme sensitivity. We show that adsorbates on the dielectric surface produce a significant electric field that responds to an applied field with a time constant of order one second. For transient applied fields (with a time scale of < 1 s) we observe good agreement with calculations based on numerical solutions of Laplace's equation using an effective dielectric constant to simulate the bulk dielectric.

Highly excited Rydberg electron as a spectator to an ion-molecule reaction

We have theoretically studied the conditions of the behavior of a high Rydberg electron as a spectator to an ion-molecule reaction in high Rydberg neutral collisions. Adoption of a circular high Rydberg atom in the initial channel of the high Rydberg neutral collisions ensures the behavior of the high Rydberg electron as the spectator to interaction between an ion core of the high Rydberg atom and an incoming neutral species; i.e., the ion-molecule reaction. This theoretical consideration leads to equivalence between the high Rydberg neutral collision and the ion-molecule reaction with high accuracy. This equivalence gives us a possibility of probing the ion-molecule reaction at low energies without space-charge effects encountered in ion-beam experiments.

Possible mechanism for enhancing the trapping and cooling of antihydrogen

We propose a usage of microwave radiation in a magnetic trap for improving the cooling and trapping of cold antihydrogen atoms which are initially produced in high magnetic moment states. Inducing transitions toward lower magnetic moments near the turning points of the atom in the trap, followed by spontaneous emission, should enhance the number of trappable atoms. We present results of simulations based on a typical experimental condition of the antihydrogen experiments at CERN. This technique should also be applicable to other trapped high magnetic moment Rydberg atoms.

Single-photon detection of microwave blackbody radiations in a low-temperature resonant-cavity with high Rydberg atoms

Blackbody radiations in a microwave resonant cavity have been measured in a single-photon counting mode at low temperature from 67 mK to 1 K with Rydberg atoms. Specifically the 111 p 3 / 2 states excited from the initially prepared 111 s 1 / 2 states of 85Rb by absorbing 2527 MHz blackbody photons have been selectively detected with a newly developed selective-field-ionization scheme. Fraction of the number of 111 p 3 / 2 states to the total incident Rydberg atoms was observed to decrease abruptly with decreasing temperature. A simple theoretical prediction in over-damped regime reproduces well the experimental results. This observation confirms in a realistic situation that the Rydberg atoms provide a very sensitive low-noise single-quantum detector for microwave radiations.

Field-ionization processes in high Rydberg states of Rb under a rotating electric field

Field ionization of high Rydberg manifold states $(n=112\text{--}137)$ of rubidium-85 under a rotating electric field has been investigated experimentally and theoretically. Applying a rapidly reversed electric field with a small static perpendicular field to rotate the total electric field around zero, we have observed substantial increase of the fraction of the tunneling field-ionization process and a profound broadening of its ionization peak over a wide range of field strengths with increasing transverse electric field. The observed tunneling field-ionization fraction is almost independent of the slew rate of the applied electric field, and also on the principal quantum number $n$ over the range investigated. To compare with these experimental results, theoretical calculations have been performed with a successive two-step regime. As the first step we calculated the redistributions of magnetic quantum number ${m}_{\ensuremath{\ell}}$ and parabolic quantum number ${n}_{1}\ensuremath{-}{n}_{2}$ of the states under the rotating electric field. Then the following time evolution of the manifold states with $\ensuremath{\mid}{m}_{\ensuremath{\ell}}\ensuremath{\mid}\ensuremath{\leqslant}3$ was traced on the Stark map in a coherent as well as an incoherent model. The calculated results are generally in good agreement with the experimental ones. The increase of the tunneling field-ionization fraction under a rotating electric field plays an essential role in achieving the high efficiency in the recently proposed selective-field-ionization scheme for high Rydberg atoms.

Dissociation dynamics of acetylene Rydberg states as a function of excited state lifetime

The state selective photodissociation of acetylene, C2H2/C2D2, was studied in the wavelength range 121.2–132.2 nm by high resolution Rydberg atom time-of-flight measurements on the atomic fragment, H/D. In the wavelength region studied members of all four Rydberg series and the highly excited Ẽ valence state were state selectively excited using tunable vacuum-ultraviolet laser radiation. The lifetime of the excited states which were studied varied from 58 fs to more than 2 ps. Formation of the ethynyl radical in its X̃ electronic ground state and its first electronically excited à state is observed with practically no indication of B̃ state fragments. Two decay channels with different dissociation dynamics were also observed. In both channels the observed decay dynamics depended strongly on the excited state of the parent molecule. Further there are major differences between these two dissociation pathways with respect to the measured internal energy and angular distributions. In one channel the dissociation is dominated by dynamical effects and the C2H fragments are formed with a high degree of vibrational excitation. In contrast to this in the second channel a smooth internal energy distribution is observed indicating that the fragment quantum state distribution is spread over a considerable range of the available phase space. Moreover, this second channel can be fit with a phase space model constrained only by conservation of energy and angular momentum. This is further evidence for the randomization of internal energy during the dissociation process.

Rydberg atom-ion collisions: classical overbarrier model for charge exchange

A novel classical overbarrier model for the charge exchange is formulated for low and medium collision velocities. The charge-exchange probability is expressed in analytical form. The results are compared with the classical Monte Carlo trajectory calculations for various partners (ground-state atom+multicharged ion, high Rydberg atom+ion with unit charge). The model reproduces well the experimental data for the collisions Na++Na(29s).

Rubidium Rydberg atoms in strong static fields

A report on experiments performed in Munich on Rydberg atoms in strong static fields is presented. These include high-resolution laser spectroscopy and wavepacket generation and detection. The results are mainly interpreted by semiclassical techniques. Using the Fourier analysis of high-resolution scaled spectra in strong crossed electric and magnetic fields, quasi-Landau resonances in a particular parameter range are investigated. The problem of singularities in the semiclassical models describing the quasi-Landau spectra is discussed, and a qualitative solution to this problem is given. Rydberg wavepackets in strong magnetic fields were investigated. For this purpose Rydberg atoms are excited by pairs of time-separated short UV laser pulses. In these experiments the superior performance of a recently proposed technique is demonstrated. The obtained results for strong magnetic fields are interpreted semiclassically. Wavepacket propagation along a particular quasi-Landau orbit is clearly identified. In the last part of the paper, properties of high angular momentum Rydberg atoms in strong crossed electric and magnetic fields are discussed. The classically regular motion in that regime corresponds to situations well known from the motion of charged particles in Penning traps. A simple method for the preparation and isolation of this type of Rydberg atom is presented.

A Rydberg-atom ionization source for negative ion mass spectrometry

An ion source for negative ion mass spectrometry has been developed. The ionization method is based on the collisional electron transfer from a high-Rydberg atom (A **) to a target molecule which possesses a positive electron affinity. In this ionization process, negative ions are directly produced via resonance capture of the “quasi-free” Rydberg electrons: A ** + M → A + + M −. In contrast to negative chemical ionization, the Rydberg-atom ionization proceeds at a low pressure of ≈ 10 −3 Pa. The method was applied to several molecular systems, such as 1-decanethiol, 3-nitrobenzyl alcohol and o-nitrophenyl octyl ether.

Intensity enhancement in the size distributions of acrylate cluster anions

Cluster anions of methyl acrylate (MA) and methyl methacrylate (MMA) clusters were produced by electron transfer from high-Rydberg atoms of krypton and the mass spectra of the cluster anions were measured. The intensity of (MA) − 5 was particularly enhanced in the size distribution of MA) − n with an increase in the stagnation pressure of a sample gas seeded in helium, while no significant intensity enhancement was observed in the case of MMA) − n . These results were interpreted as the occurrence of intracluster anionic polymerization in the formation of (MA) − 5.

Dissociation of aliphatic hydrocarbons excited by electrons: Translational energy distributions of the excited hydrogen atom

The Doppler profiles of the Balmer lines produced in collisions of ethane, propane, pentane and hexane with electrons have been measured precisely and the translational energy distributions of H* ( n = 3, 4) have been obtained. There are four major dissociation processes for all these molecules, just as in the case of methane. Their translational energy distributions and threshold energies correspond well with those of methane. The translational energy distributions of H* ( n = 3, 4) agree qualitatively with those of H + and the high-Rydberg atom. Thus, these molecules and fragments display qualitatively similar dissociation behavior and the core ion model is valid. However, there are some systematic differences related to the size of the molecules. The emission cross sections were determined separately for H* ( n = 3) with different translational energies.

Observation of acrylonitrile molecular anion in the gas phase

The molecular anion of acrylonitrile was produced in the gas phase by collisional electron transfer from a high-Rydberg atom, Rg ** (RgKr or Ar), to an acrylonitrile or acrylonitrile- d 1 molecule. The observed negative-ion mass spectra of m/ z 53 or 54 indicate that both vertical and adiabatic electron affinities of the molecules are positive. The molecular anion of acrylonitrile was also produced by evaporative electron attachment to acrylonitrile clusters.

Formation of negative ions of water clusters by electron transfer from high-Rydberg atoms

Negative ions of H 2O and D 2O clusters were produced by collisional electron transfer from highly excited Rydberg atoms, where no evaporation of monomers after electron transfer is expected. The threshold sizes observed in the mass spectra of (H 2O) − n and (D 2O) − n , n ⩾ 11 and 13 respectively, are interpreted as the critical sizes beyond which the vertical electron affinities of water clusters are positive. A comparison with previous reports shows that the negative-ion states of water clusters with near-threshold sizes are likely to be far from the solvated electron state.

Electron excitation energy transfer from highly excited cesium atoms forming high Rydberg state atoms and molecules

Electron excitation energy transfer from highly excited cesium atoms forming high Rydberg state atoms and molecules

Formation of negative cluster ions from (CO2)m in collision with high-Rydberg atoms

Negative ions of CO2 clusters (CO2)m produced by electron transfer from highly excited Rydberg atoms were investigated by mass spectrometry. The relative intensities of (CO2)−n (n≥3) (size distribution) showed a characteristic structure with magic numbers at 9, 14, and 16. The dependence of the intensities of (CO2)−n (n=7–20) on the stagnation pressure of the cluster beam source was measured. The threshold pressure at which a cluster anion of a given size started to appear increased irregularly with the size. These observations suggest that evaporation of CO2 molecules occurs by dissipation of the excess energy after electron attachment and that the number of evaporating molecules m–n depends on the size of the resulting ion. The evaporating molecules are fewer at n=9, 14, and 16 than those at adjacent sizes. The cluster ions of these sizes are shown to have higher dissociation energies than other ions, and the magic numbers observed in the mass spectrum are ascribed to the difference in the stability of the ions.

MICROWAVE SPECTROSCOPY OF HIGH RYDBERG ATOMS FOR ELEMENTAL AND ISOTOPIC ANALYSIS OF INTERSTELLAR CLOUDS

A novel method is proposed to study the elemental and isotopic abundance of light elements in interstellar clouds by the observation of millimeter wave emission from high Rydberg atoms formed during the recombination process. A laboratory experiment to provide transition frequencies of Rydberg atoms for such study is demonstrated by laser-microwave triple resonance in Yb.

Dissociative electron attachment to cyanogen bromide in the reaction with autoionizing high-Rydberg rare gas atoms

The ratio of the dissociation products, [Br − ]/[CN − ], in electron attachment to BrCN from high-Rydberg atoms, Rg**, in autoionizing states was found to be 0.19 for Kr** and 1.5 for Xe**. The difference in the branching ratio is explained by the Coulomb interaction between the positive rare gas ion and the negative ion produced in the electron-transfer process. This provides evidence that the ion core of a high-Rydberg atom plays a significant role in dissociative electron attachment, which is disregarded in the «free»-electron model applied to reactions of high-Rydberg atoms