arXiv subjects

Johannes Deiglmayr

Publications and source records attributed to Johannes Deiglmayr.

At least 19 recordsLinked to original sources

arXiv2026

Spin-orbit-dependent lifetimes of long-range Rydberg molecules

Long-range Rydberg molecules (LRMs) form when a highly excited Rydberg electron scatters from ground-state atoms inside its orbit, creating oscillatory, long-range potentials. We present a combined theoretical and experimental study of caesium dimers correlated to 402P3/2 Rydberg states, with an emphasis on decay via autoionisation (associative ionisation). Our model includes a relativistic treatment of electron-atom scattering with spin-orbit coupling, the perturber's hyperfine structure, and coupling of vibrational levels to a continuum of short-range decay channels. Calculated potential-energy curves predict two families of wells: outer wells near the classical outer turning point supporting long-lived states, and inner wells at shorter range whose lifetimes are limited by tunneling and subsequent vibronic decay. Using photoassociation in an ultracold Cs gas and an analysis of pulsed-field-ionisation signals which are highly selective for the detection of molecules, we assign resonances by binding energy and measure lifetimes. The measured lifetimes of inner-well states increase systematically with increasing detuning and agree with calculated lifetimes; detection of Cs2+ product ions supports autoionisation as a dominant channel. We show that the lifetimes are strongly reduced by spin-orbit interactions in the transient Cs-collision complex, which lift the near-degeneracy in Omega observed for states in the outer well and control the inner-well binding. The identified states also provide promising pathways to create ultracold molecules in ion-pair states.

physics.atom-ph↗

arXiv2024

Realization of topological Thouless pumping in a synthetic Rydberg dimension

The simulation of synthetic dimensions by manipulating internal states of atoms and molecules has opened the door to investigate regimes outside those of more traditional quantum many-body platforms. Highly excited Rydberg states of atoms are a particularly promising platform to engineer Hamiltonians in such synthetic dimensions due to their large number of addressable states and the readily available technologies for manipulating their couplings and for detecting them. In this letter, we demonstrate the realization of topological quantum pumping in synthetic dimensions by engineering a one-dimensional Rice-Mele chain from the Rydberg states of cesium atoms, and manipulating their couplings in a time-dependent fashion through radio-frequency fields. We implement Thouless protocols for topological pumping and investigate the efficiency for pumping an effective quantum particle as a function of the period of pumping and other parameters while allowing for rates of change that are not necessarily adiabatic. We demonstrate that optimal pumping efficiencies of up to 90% can be achieved when the pump is operated in the topological Thouless regime, even when the pumping is accompanied by the wave-packet spread that arises from the energy dispersion of the particle along the synthetic dimension.

quant-ph↗

arXiv2022

Observation of quantum capture in an ion-molecule reaction

In 1954, Vogt and Wannier (Phys. Rev. 95, 1190) predicted that the capture rate of a polarizable neutral atom or molecule by an ion should increase by a factor of two compared to the classical Langevin rate as the collision energy approaches zero. This prediction has not been verified experimentally. The H$_2^+$ + H$_2$ reaction is ideally suited to observe this effect, because the small reduced mass makes quantum effects related to s-wave scattering observable at higher collision energies than in other systems. Moreover, the reaction rate for this barrierless, strongly exothermic reaction follows the classical Langevin capture model down to cold-collision conditions (about $k_\mathrm{B} \cdot~1\,\mathrm{K}$) and is not affected by short-range interactions. Below this temperature, a strong enhancement of the reaction rate resulting from charge--quadrupole interaction between H$_2^+$ and ground-state ortho H$_2$ ($J=1$) was observed. Here we present an experimental study of the reaction of H$_2^+$ and para H$_2$ ($J=0$), which has no dipole and no quadrupole moments, at collision energies below $k_\mathrm{B}\cdot 1\,\mathrm{K}$. We observe an enhancement at the lowest collision energies which is attributed to the quantum enhancement predicted by Vogt and Wannier. Measurements of the reaction of HD$^+$ with HD support this conclusion.

physics.atom-ph↗

arXiv2022

The role of Coulomb anti-blockade in the photoassociation of long-range Rydberg molecules

We present a new mechanism contributing to the detection of photoassociated long-range Rydberg molecules via pulsed-field ionization: ionic products, created by the decay of a long-range Rydberg molecule, modify the excitation spectrum of surrounding ground-state atoms and facilitate the excitation of further atoms into Rydberg states by the photoassociation light. Such an ion-mediated excitation mechanism has been previously called "Coulomb anti-blockade". Pulsed-field ionisation typically doesn't discriminate between the ionization of a long-range Rydberg molecule and an isolated Rydberg atom, and thus the number of atomic ions detected by this mechanism is not proportional to the number of long-range Rydberg molecules present in the probe volume. By combining high-resolution UV and RF spectroscopy of a dense, ultracold gas of cesium atoms, theoretical modeling of the molecular level structures of long-range Rydberg molecules bound below nP_3/2 Rydberg states of cesium, and a rate model of the photoassociation and decay processes, we unambiguously identify the signatures of this detection mechanism in the photoassociation of long-range Rydberg molecules bound below atomic asymptotes with negative Stark shifts.

physics.atom-ph↗

arXiv2021

Photodissociation of long-range Rydberg molecules

We present photodissociation of ultracold long-range Rydberg molecules as a tool to characterize their electronic properties. We photoassociate K2 37P molecules with highly entangled electronic and nuclear spins of the two bound atoms and quantify the entanglement by projection of the molecular state onto non-interacting atoms using radiofrequency photodissociation. By comparison of experimental photodissociation rates with theoretical predictions we further characterize the electronic and nuclear wavefunction of the photoassociated molecules. Based on the complete characterization of the formed long-range Rydberg molecules, we demonstrate a full hyperfine-spin flip of a free ground-state atom through the interaction with a Rydberg atom.

physics.atom-ph↗

arXiv2021

Heteronuclear long-range Rydberg molecules

We present the formation of homonuclear Cs2, K2, and heteronuclear CsK long-range Rydberg molecules in a dual-species magneto-optical trap for 39K and 133Cs by one-photon UV photoassociation. The different ground-state-density dependence of homo- and heteronuclear photoassociation rates and the detection of stable molecular ions resulting from auto-ionization provide an unambiguous assignment. We perform bound-bound millimeter-wave spectroscopy of long-range Rydberg molecules to access molecular states not accessible by one-photon photoassociation. Calculations based on the most recent theoretical model and atomic parameters do not reproduce the full set of data from homo- and heteronuclear long-range Rydberg molecules consistently. This shows that photoassociation and millimeter-wave spectroscopy of heteronuclear long-range Rydberg molecules provide a benchmark for the development of theoretical models.

physics.atom-ph↗

arXiv2020

Formation of ultracold ion pairs through long-range Rydberg molecules

We propose a new approach to excite ion-pair states of ultracold dimers. The central idea is a two-step process where first long-range Rydberg molecules are formed by photoassociation, which are then driven by stimulated emission towards the ion-pair state, a process bearing features of a photo-induced harpooning reaction. We assess the feasibility of this approach through a detailed experimental and theoretical study on a specific system, p-wave-scattering dominated long-range Rydberg molecules in caesium, and discuss potential applications for the study of strongly correlated plasmas consisting of oppositely charged particles of equal or similar mass.

physics.atom-ph↗

arXiv2019

Single-shot Non-destructive Detection of Rydberg Atom Ensembles by Transmission Measurement of a Microwave Cavity

Rydberg atoms are at the core of an increasing number of experiments, which frequently rely on destructive detection methods, such as field ionization. Here, we present an experimental realization of single-shot non-destructive detection of ensembles of helium Rydberg atoms. We use the dispersive frequency shift of a superconducting microwave cavity interacting with the ensemble. By probing the transmission of the cavity and measuring the change in its phase, we determine the number of Rydberg atoms or the populations of Rydberg quantum states when the ensemble is prepared in a superposition. At the optimal probe power, determined by the critical photon number, we reach single-shot detection of the atom number with 13% precision for ensembles of about 500 Rydberg atoms with a measurement backaction characterized by approximately 2%-population transfer.

quant-ph↗

arXiv2019

Precision measurement of the ionization energy and quantum defects of 39K I

We present absolute-frequency measurements in ultracold 39K samples of the transitions from the ground state to np Rydberg states. A global nonlinear regression of the np1/2 and np3/2 term values yields an improved wave number of 35009.8139710(22)(sys)(3)(stat) cm-1 for the first ionization threshold of 39K and the quantum defects of the np1/2 and np3/2 series. In addition, we report the frequencies of selected one-photon transitions n's <- np3/2, n'd <- np3/2, n'f <- nd and n'g <- nf and two-photon transitions nf <- np determined by millimeter-wave spectroscopy. By combining the results from the laser and millimeter-wave spectroscopic experiments, we obtain improved values for the quantum defects of the s1/2, d3/2, d5/2, f and g states. For the d series, the inverted fine structure was confirmed for n >= 32. The fine-structure splitting of the f series is less than 100 kHz at n=31, significantly smaller than the hydrogenic splitting, and the fine structure of the g series is regular for n >= 30, with a fine-structure splitting compatible with the hydrogenic prediction. From the measured quantum defects of the f and g series we derive an estimate for the static dipole and quadrupole polarizabilities of the K+ ion core. Additionally, the hyperfine splitting of the 4s1/2 ground state of 39K was determined to be 461.719700(5) MHz using radio-frequency spectroscopy and Ramsey-type interferometry.

physics.atom-ph↗

arXiv2017

New method to study ion-molecule reactions at low temperatures and application to the H$_2^+$ + H$_2$ $\rightarrow$ H$_3^+$ + H reaction

Studies of ion-molecule reactions at low temperatures are difficult because stray electric fields in the reaction volume affect the kinetic energy of charged reaction partners. We describe a new experimental approach to study ion-molecule reactions at low temperatures and present, as example, a measurement of the ${\rm H}_2^+ + {\rm H}_2\rightarrow {\rm H}_3^+ + {\rm H}$ reaction with the ${\rm H}_2^+$ ion prepared in a single rovibrational state at collision energies in the range $E_{\rm col}/k_{\rm B} = 5$-60 K. To reach such low collision energies, we use a merged-beam approach and observe the reaction within the orbit of a Rydberg electron, which shields the ions from stray fields. The first beam is a supersonic beam of pure ground-state H$_2$ molecules and the second is a supersonic beam of H$_2$ molecules excited to Rydberg-Stark states of principal quantum number $n$ selected in the range 20-40. Initially, the two beams propagate along axes separated by an angle of 10$^\circ$. To merge the two beams, the Rydberg molecules in the latter beam are deflected using a surface-electrode Rydberg-Stark deflector. The collision energies of the merged beams are determined by measuring the velocity distributions of the two beams and they are adjusted by changing the temperature of the pulsed valve used to generate the ground-state ${\rm H}_2$ beam and by adapting the electric-potential functions to the electrodes of the deflector. The collision energy is varied down to below $E_{\rm col}/k_{\rm B}= 10$ K, i.e., below $E_{\rm col}\approx 1$ meV, with an energy resolution of 100 $μ$eV. We demonstrate that the Rydberg electron acts as a spectator and does not affect the cross sections, which are found to closely follow a classical-Langevin-capture model in the collision-energy range investigated. Because all neutral atoms and molecules can be excited to Rydberg states, this method of studying

physics.chem-ph↗

arXiv2017

Infrared spectroscopy of molecular ions in selected rotational and spin-orbit states

First results are presented obtained with an experimental setup developed to record IR spectra of rotationally state-selected ions. The method we use is a state-selective version of a method developed by S. Schlemmer, D. Gerlich and coworkers (Int. J. Mass. Spec. 185, 589 (1999); J. Chem. Phys. 117, 2068 (2002)) to record IR spectra of ions. Ions are produced in specific rotational levels using mass-analyzed-threshold-ionization spectroscopy. The state-selected ions generated by pulsed-field ionization of Rydberg states of high principal quantum number ($n\approx200$) are extracted toward an octupole ion guide containing a neutral target gas. Prior to entering the octupole, the ions are excited by an IR laser. The target gas is chosen so that only excited ions react to form product ions. These product ions are detected mass selectively as a function of the IR laser wavenumber. To illustrate this method, we present IR spectra of C$_2$H$_2^+$ in selected rotational levels of the $^2Π_{\textrm{u,}3/2}$ and $^2Π_{\textrm{u,}1/2}$ spin-orbit components of the vibronic ground state.

physics.chem-ph↗

arXiv2016

Observation of enhanced rate coefficients in the H$_2^+$ + H$_2$ $\rightarrow$ H$_3^+$ + H reaction at low collision energies

The energy dependence of the rate coefficient of the H$_2^+\ + {\rm H}_2 \rightarrow {\rm H}_3^+ + {\rm H}$ reaction has been measured in the range of collision energies between $k_\mathrm{B}\cdot 10$ K and $k_\mathrm{B}\cdot 300$ mK. A clear deviation of the rate coefficient from the value expected on the basis of the classical Langevin-capture behavior has been observed at collision energies below $k_\mathrm{B}\cdot 1$ K, which is attributed to the joint effects of the ion-quadrupole and Coriolis interactions in collisions involving ortho-H$_2$ molecules in the $j = 1$ rotational level, which make up 75% of the population of the neutral H$_2$ molecules in the experiments. The experimental results are compared to very recent predictions by Dashevskaya, Litvin, Nikitin and Troe (J. Chem. Phys., in press), with which they are in agreement.

physics.chem-ph↗

arXiv2016

Observation of Rydberg-atom macrodimers: micrometer-sized diatomic molecules

Long-range metastable molecules consisting of two cesium atoms in high Rydberg states have been observed in an ultracold gas. A sequential three-photon two-color photoassociation scheme was employed to form these molecules in states which correlate to $np(n+1)s$ dissociation asymptotes. Spectral signatures of bound molecular states are clearly resolved at the positions of avoided crossings between long-range van der Waals potential curves. The experimental results are in agreement with simulations based on a detailed model of the long-range multipole-multipole interactions of Rydberg-atom pair states. We show that a full model is required to accurately predict the occurrence of bound Rydberg macrodimers. The macrodimers are distinguished from repulsive molecular states by their behavior with respect to spontaneous ionization and possible decay channels are discussed.

physics.atom-ph↗

arXiv2016

Long-range Rydberg molecules, Rydberg macrodimers and Rydberg aggregates in an ultracold Cs gas

We present an overview of our recent investigations of long-range interactions in an ultracold Cs Rydberg gas. These interactions are studied by high-resolution photoassociation spectroscopy, using excitation close to one-photon transitions into $n$p$_{3/2}$ Rydberg states with pulsed and continuous-wave ultraviolet laser radiation, and lead to the formation of long-range Cs$_2$ molecules. We observe two types of molecular resonances. The first type originates from the correlated excitation of two atoms into Rydberg-atom-pair states interacting at long range via multipole-multipole interactions. The second type results from the interaction of one atom excited to a Rydberg state with one atom in the electronic ground state. Which type of resonances is observed in the experiments depends on the laser intensity and frequency and on the pulse sequences used to prepare the Rydberg states. We obtain insights into both types of molecular resonances by modelling the interaction potentials, using a multipole expansion of the long-range interaction for the first type of resonances and a Fermi-contact pseudo-potential for the second type of resonances. We analyse the relation of these long-range molecular resonances to molecular Rydberg states and ion-pair states, and discuss their decay channels into atomic and molecular ions. In experiments carried out with a two-colour two-photon excitation scheme, we observe a large enhancement of Rydberg-excitation probability, which we interpret as a saturable autocatalytic antiblockade phenomenon.

physics.atom-ph↗

arXiv2016

Precision measurement of the ionization energy of Cs I

We present absolute-frequency measurements for the transitions from the 6s$_{1/2}$ ground state of $^{133}$Cs to $n$p$_{1/2}$ and $n$p$_{3/2}$ Rydberg states. The transition frequencies are determined by one-photon UV spectroscopy in ultracold samples of Cs atoms using a narrowband laser system referenced to a frequency comb. From a global fit of the ionization energy $E_\mathrm{I}$ and the quantum defects of the two series we determine an improved value of $E_\mathrm{I} = h c \cdot 31 406.467 732 5(14)$ cm$^{-1}$ for the ionization energy of Cs with a relative uncertainty of $5\times10^{-11}$. We also report improved values for the quantum defects of the $n$p$_{1/2}$, $n$p$_{3/2}$, $n$s$_{1/2}$, and $n$d$_{5/2}$ series.

physics.atom-ph↗

arXiv2015

Pulsed excitation of Rydberg-atom-pair states in an ultracold Cs gas

Pulsed laser excitation of a dense ultracold Cs vapor has been used to study the pairwise interactions between Cs atoms excited to $n$p$_{3/2}$ Rydberg states of principal quantum numbers in the range $n=22-36$. Molecular resonances were observed that correspond to excitation of Rydberg-atom-pair states correlated not only to the $n$p$_{3/2}+n$p$_{3/2}$ dissociation asymptotes, but also to $n$s$_{1/2}+(n+1)$s$_{1/2}$, $n$s$_{1/2}+n'$f$_{j}$, and $(n-4)$f$_{j}+(n-3)$f$_{j}$ $(j=5/2,7/2)$ dissociation asymptotes. These pair resonances are interpreted as arising from dipole-dipole, and higher-order long-range-interaction terms between the Rydberg atoms on the basis of i) their spectral positions, ii) their response to static and pulsed electric fields, and iii) millimeter-wave spectra between pair states correlated to different pair-dissociation asymptotes. The Rydberg-atom--pair states were found to spontaneously decay by Penning ionization and the dynamics of the ionization process were investigated during the first 10 $μ$s following initial photoexcitation. To interpret the experimental observations, a potential model was derived that is based on the numerical determination of the eigenvalues and eigenfunctions of the long-range interaction Hamiltonian. With this potential model, which does not include adjustable parameters, all experimental observations could be accounted for, and the results demonstrate that long-range-interaction models provide a global and accurate description of interactions in ultracold Rydberg gases and that they correctly account for, and enable the analysis of, phenomena as diverse as the formation of Rydberg macrodimers, Penning ionization in dense Rydberg gases, and Rydberg-excitation blockade effects.

physics.atom-ph↗

arXiv2015

Experimental characterization of singlet scattering channels in long-range Rydberg molecules

We observe the formation of long-range Cs$_2$ Rydberg molecules consisting of a Rydberg and a ground-state atom by photoassociation spectroscopy in an ultracold Cs gas near 6s$_{1/2}$($F$=3,4)$\rightarrow$np$_{3/2}$ resonances (n=26-34). The spectra reveal two types of molecular states recently predicted by D. A. Anderson, S. A. Miller, and G. Raithel [Phys. Rev. A 90, 062518 (2014)]: states bound purely by triplet s-wave scattering with binding energies ranging from 400 MHz at n=26 to 80 MHz at n=34, and states bound by mixed singlet-triplet s-wave scattering with smaller and F-dependent binding energies. The experimental observations are accounted for by an effective Hamiltonian including s-wave scattering pseudopotentials, the hyperfine interaction of the ground-state atom, and the spin-orbit interaction of the Rydberg atom. The analysis enabled the characterization of the role of singlet scattering in the formation of long-range Rydberg molecules and the determination of an effective singlet s-wave scattering length for low-energy electron-Cs collisions.

physics.atom-ph↗

arXiv2014

Observation of dipole-quadrupole interaction in an ultracold gas of Rydberg atoms

We observe the direct excitation of pairs of Cs atoms from the ground state to molecular states correlating asymptotically to $ns\,n'f$ asymptotes. The molecular resonances are interpreted as originating from the dipole-quadrupole interaction between the $ns\,n'f$ pair states and close-by $np\,np$ asymptotes ($22\leq n \leq 32$). This interpretation is supported by Stark spectroscopy of the pair states and a detailed modeling of the interaction potentials. The dipole-quadrupole interaction mixes electronic states of opposite parity and thus requires a coupling between electronic and nuclear motion to conserve the total parity of the system. This non-Born-Oppenheimer coupling is facilitated by the near-degeneracy of even and odd $L$ partial waves in the atom-atom scattering which have opposite parity.

physics.atom-ph↗