arXiv subjects

Eberhard Tiemann

Publications and source records attributed to Eberhard Tiemann.

At least 37 records · Page 2Linked to original sources

arXiv2018

Feshbach spectroscopy and dual-species Bose-Einstein condensation of $^{23}\mathrm{Na}-$$^{39}\mathrm{K}$ mixtures

We present measurements of interspecies Feshbach resonances and subsequent creation of dual-species Bose-Einstein condensates of $^{23}\mathrm{Na}$ and $^{39}\mathrm{K}$. We prepare both optically trapped ensembles in the spin state $\left|f = 1,m_{f}=-1\right\rangle$ and perform atom loss spectroscopy in a magnetic field range from 0 to $700 \, \mathrm{G}$. The observed features include several s-wave poles and a zero crossing of the interspecies scattering length as well as inelastic two-body contributions in the $\mathcal{M} = m_{\mathrm{Na}}+m_{\mathrm{K}} = -2$ submanifold. We identify and discuss the suitability of different magnetic field regions for the purposes of sympathetic cooling of \K and achieving dual-species degeneracy. Two condensates are created simultaneously by evaporation at a magnetic field of about $150 \, \mathrm{G}$, which provides sizable intra- and interspecies scattering rates needed for fast thermalization. The impact of the differential gravitational sag on the miscibility criterion for the mixture is discussed. Our results serve as a promising starting point for the magnetoassociation into quantum degenerate $^{23}\mathrm{Na}^{39}\mathrm{K}$ Feshbach molecules.

cond-mat.quant-gas↗

arXiv2017

Laser and Fourier transform spectroscopy of $^7$Li$^{88}$Sr

LiSr was produced in a heat-pipe oven and its thermal emission spectrum around 9300 cm$^{-1}$ was recorded by a high resolution Fourier transform spectrometer. In addition, selected lines of the spectrum of deeply bound vibrational levels of the $1^2Σ^+$ and $2^2Σ^+$ states were studied using laser excitation to facilitate the assignment of the lines. The ground state could be described for $v^{\prime\prime} =$ 0 - 2, $N^{\prime\prime}$ up to 105 and the $2^2Σ^+$ state for $v^{\prime} = 0$ up to $N^\prime = 68$. For both states, Dunham coefficients, spin-rotation parameters and potential energy curves were evaluated. A coupling of the $2^2Σ^+$ state to the $1^2Π$ state was observed, allowing a local description with Dunham coefficients of the $1^2Π$ state and an approximate evaluation of the coupling strength.

physics.atom-ph↗

arXiv2017

Laser and Fourier transform spectroscopy of KCa

KCa was produced in a heatpipe oven and its thermal emission spectrum around 8900 cm$^{-1}$ was recorded by a high resolution Fourier transform spectrometer. In addition, many selected transitions of this spectrum between deeply bound vibrational levels of the $\mathrm{X}(1)^2Σ^+$ and $(2)^2Σ^+$ states were studied using laser excitation to facilitate the assignment of the lines. The ground state is described for $v^{\prime\prime} =$ 0 - 5 and the $(2)^2Σ^+$ state for $v^{\prime} =0$ - 8 with rotational levels up to 175. For both states, Dunham coefficients, spin-rotation parameters and potential energy curves are derived.

physics.atom-ph↗

arXiv2017

Modeling the adiabatic creation of ultracold, polar $\mathrm{^{23}Na^{40}K}$ molecules

In this work we model and realize stimulated Raman adiabatic passage (STIRAP) in the diatomic $\mathrm{^{23}Na^{40}K}$ molecule from weakly bound Feshbach molecules to the rovibronic ground state via the $\left|v_d=5,J=Ω=1\right\rangle$ excited state in the $d^3Π$ electronic potential. We demonstrate how to set up a quantitative model for polar molecule production by taking into account the rich internal structure of the molecules and the coupling laser phase noise. We find excellent agreement between the model predictions and the experiment, demonstrating the applicability of the model in the search of an ideal STIRAP transfer path. In total we produce 5000 fermionic groundstate molecules. The typical phase-space density of the sample is 0.03 and induced dipole moments of up to 0.54 Debye could be observed.

cond-mat.quant-gas↗

arXiv2017

Feshbach Loss Spectroscopy in an Ultracold $^{23}$Na and $^{40}$K Mixture

We perform Feshbach spectroscopy in an ultracold mixture of $^{23}$Na and $^{40}$K with different spin-state combinations. We have observed 24 new interspecies Feshbach resonances at magnetic field up to 350 G. A full coupled-channel calculation is performed to assign these resonances. Among them, 12 resonances are identified as d-wave Feshbach resonances. These d-wave Feshbach resonances are about 5 G systematically smaller than the predications based on previous model potential. Taking into account these new experimental results, we improve the Born-Oppenheimer potentials between Na and K, and achieve good agreement between the theory and experiment for all the observed Feshbach resonances.

cond-mat.quant-gas↗

arXiv2017

State-to-state chemistry at ultra-low temperature

Fully understanding a chemical reaction on the quantum level is a long-standing goal in physics and chemistry. Experimental investigation of such state-to-state chemistry requires both the preparation of the reactants and the detection of the products in a quantum state resolved way, which has been a long term challenge. Using the high level control in the ultracold domain, we prepare a few-body quantum state of reactants and demonstrate state-to-state chemistry with unprecedented resolution. We present measurements and accompanying theoretical analysis for the recombination of three spin-polarized ultracold Rb atoms forming a weakly bound Rb$_2$ dimer. Detailed insights of the reaction process are obtained that suggest propensity rules for the distribution of reaction products. The scheme can readily be adapted to other species and opens a door to detailed investigations of inelastic or reactive processes in domains never before accessible.

cond-mat.quant-gas↗

arXiv2017

Ground-state properties of Ca$_2$ from narrow line two-color photoassociation

By two-color photoassociation of $^{40}$Ca four weakly bound vibrational levels in the Ca$_2$ \Xpot ground state potential were measured, using highly spin-forbidden transitions to intermediate states of the coupled system $^3Π_{u}$ and $^3Σ^+ _{u}$ near the ${^3P_1}$+${^1S_0}$ asymptote. From the observed binding energies, including the least bound state, the long range dispersion coefficients $\mathrm{C}_6, \mathrm{C}_8,\mathrm{C}_{10}$ and a precise value for the s-wave scattering length of 308.5(50)~$a_0$ were derived. From mass scaling we also calculated the corresponding scattering length for other natural isotopes. From the Autler-Townes splitting of the spectra, the molecular Rabi frequency has been determined as function of the laser intensity for one bound-bound transition. The observed value for the Rabi-frequency is in good agreement with calculated transition moments based on the derived potentials, assuming a dipole moment being independent of internuclear separation for the atomic pair model.

physics.atom-ph↗

arXiv2017

Level structure of deeply bound levels of the $c^3Σ_g^+$ state of $^{87}\text{Rb}_2$

We spectroscopically investigate the hyperfine, rotational and Zeeman structure of the vibrational levels $\text{v}'=0$, $7$, $13$ within the electronically excited $c^3Σ_g^+$ state of $^{87}\text{Rb}_2$ for magnetic fields of up to $1000\,\text{G}$. As spectroscopic methods we use short-range photoassociation of ultracold Rb atoms as well as photoexcitation of ultracold molecules which have been previously prepared in several well-defined quantum states of the $a^3Σ_u^+$ potential. As a byproduct, we present optical two-photon transfer of weakly bound Feshbach molecules into $a^3Σ_u^+$, $\text{v}=0$ levels featuring different nuclear spin quantum numbers. A simple model reproduces well the molecular level structures of the $c^3Σ_g^+$ vibrational states and provides a consistent assignment of the measured resonance lines. Furthermore, the model can be used to predict the relative transition strengths of the lines. From fits to the data we extract for each vibrational level the rotational constant, the effective spin-spin interaction constant, as well as the Fermi contact parameter and (for the first time) the anisotropic hyperfine constant. In an alternative approach, we perform coupled-channel calculations where we fit the relevant potential energy curves, spin-orbit interactions and hyperfine functions. The calculations reproduce the measured hyperfine level term frequencies with an average uncertainty of $\pm9\:$MHz, similar as for the simple model. From these fits we obtain a section of the potential energy curve for the $c^3Σ_g^+$ state which can be used for predicting the level structure for the vibrational manifold $\text{v}'=0$ to $13$ of this electronic state.

cond-mat.quant-gas↗

arXiv2016

Mixing of 0$^+$ and 0$^-$ observed in hyperfine and Zeeman structure of ultracold Rb$_2$ molecules

We study the combination of hyperfine and Zeeman structure in the spin-orbit coupled $A^1Σ_u^+-b^3Π_u$ complex of $^{87}\textrm{Rb}_2$. For this purpose, absorption spectroscopy at a magnetic field around $B=1000\:\textrm{G}$ is carried out. We drive optical dipole transitions from the lowest rotational state of an ultracold Feshbach molecule to various vibrational levels with $0^+$ symmetry of the $A-b$ complex. In contrast to previous measurements with rotationally excited alkali-dimers, we do not observe equal spacings of the hyperfine levels. In addition, the spectra vary substantially for different vibrational quantum numbers, and exhibit large splittings of up to $160\:\textrm{MHz}$, unexpected for $0^+$ states. The level structure is explained to be a result of the repulsion between the states $0^+$ and $0^-$ of $b^3Π_u$, coupled via hyperfine and Zeeman interactions. In general, $0^-$ and $0^+$ have a spin-orbit induced energy spacing $Δ$, that is different for the individual vibrational states. From each measured spectrum we are able to extract $Δ$, which otherwise is not easily accessible in conventional spectroscopy schemes. We obtain values of $Δ$ in the range of $\pm 100\:\textrm{GHz}$ which can be described by coupled channel calculations if a spin-orbit coupling is introduced that is different for $0^-$ and $0^+$ of $b^3Π_u$.

cond-mat.quant-gas↗

arXiv2015

Nonlinear Zeeman effect in photoassociation spectra of $^{40}$Ca near the $^3$P$_1$+$^1$S$_0$ asymptote

We present calculations of the Zeeman effect of narrow photoassociation lines of $^{40}$Ca near the $^3$P$_1$ + $^1$S$_0$ asymptote. Using a coupled-channel model we find a nonlinear Zeeman effect that even at low fields of a few mT amounts to several kHz. With this model we analyze previous measurements and give corrected long range dispersion coefficients of the $^3Π_{u}$ and $^3Σ^+ _{u}$ states.

physics.atom-ph↗

arXiv2014

Analyzing Feshbach resonances -- A $^6$Li -$^{133}$Cs case study

We provide a comprehensive comparison of a coupled channels calculation, the asymptotic bound state model (ABM), and the multichannel quantum defect theory (MQDT). Quantitative results for $^6$Li -$^{133}$Cs are presented and compared to previously measured $^6$Li -$^{133}$Cs Feshbach resonances (FRs) [M. Repp et al., Phys. Rev. A 87 010701(R) (2013)]. We demonstrate how the accuracy of the ABM can be stepwise improved by including magnetic dipole-dipole interactions and coupling to a non-dominant virtual state. We present a MQDT calculation, where magnetic dipole-dipole and second order spin-orbit interactions are included. A frame transformation formalism is introduced, which allows the assignment of measured FRs with only three parameters. All three models achieve a total rms error of < 1G on the observed FRs. We critically compare the different models in view of the accuracy for the description of FRs and the required input parameters for the calculations.

cond-mat.quant-gas↗

arXiv2014

The $A^{1}Σ^{+}_{u}$ + (1)$^1Π_u$ system of Mg$_2$

The $A^1Σ^+_u$ - $X^1Σ^+_g$ UV spectrum of Mg$_2$ has been investigated with high resolution employing Fourier-transform spectroscopy and laser excitation. Computer simulation and fit of line positions to the overlapping structures in the spectra yield precise transition frequencies. Starting with the well characterized ground state $X^1Σ^+_g$ from former work we derived excited energy levels and report on the evaluation of the $A^1Σ^+_u$ excited state, which is found to interact with another electronic state, which we identify as the lower part of the (1)$^1Π_u$ state. A coupled channels fit to the level energies of the upper state yields a reliable potential energy curve for the $A^1Σ^+_u$ for the range of vibrational levels 1 $\le$ $v'$ $\le$ 46. A potential energy curve for the (1)$^1Π_u$ state is proposed, but the (1)$^1Π_u$ state is only characterized by its coupling to the A state, and no direct transition to a level of the (1)$^1Π_u$ could be uniquely identified due to the overlapping spectral structures.

physics.atom-ph↗

arXiv2013

High accuracy photoassociation of $^{40}$Ca near the ${^3P_1}+{^1S_0}$ asymptote and its Zeeman effect

We report on the first measurement of narrow photoassociation lines of $^{40}$Ca near the ${^3P_1}+{^1S_0}$ asymptote related to the molecular states $^3Π_u$ and $^3Σ^+_u$. The highly accurate binding energies and Zeeman splittings are well described by a coupled channel theoretical model, confirming theoretical predictions of long-range coefficients. Our analysis shows that only the inclusion of both energies and Zeeman splittings provides an accurate description of the long-range interaction potentials.

physics.atom-ph↗

arXiv2013

Observation of Feshbach resonances between ultracold Na and Rb atoms

We have successfully prepared an optically trapped ultracold mixture of $^{23}$Na and $^{87}$Rb atoms and studied their interspecies Feshbach resonances. Using two different spin combinations, several s-wave and p-wave resonances are identified by observing a high inelastic loss and a temperature rising for both species near resonant magnetic field values. The two s-wave resonances observed below 500 G between atoms in the lowest energy level are possible candidates for Feshbach molecule association. Our results are well characterized by a coupled-channel model and are used refining the ground state interaction potentials between $^{23}$Na and $^{87}$Rb. This work opens up the prospect for preparing ultracold ensembles of ground-state bosonic NaRb molecules which are chemically stable and can provide strong dipolar interactions.

cond-mat.quant-gas↗

arXiv2013

Shedding Light on Three-Body Recombination in an Ultracold Atomic Gas

Three-body recombination is a prime example of the fundamental interaction between three particles. Due to the complexity of this process it has resisted a comprehensive description. Experimental investigations have mainly focussed on the observation of corresponding loss rates without revealing information on the reaction products. Here, we provide the first general experimental study on the population distribution of molecular quantum states after three-body recombination in a non-resonant regime. We have developed a highly sensitive detection scheme which combines photoionization of the molecules with subsequent ion trapping. By analyzing the ionization spectrum, we identify the population of energy levels with binding energies up to $h\times 750\:$GHz. We find a broad population of electronic and nuclear spin states and determine a range of populated vibrational and rotational states. The method presented here can be expanded to provide a full survey of the products of the recombination process. This may be pivotal in developing an in-depth model that can qualitatively and quantitatively predict the reaction products of three-body recombination.

physics.atom-ph↗

arXiv2012

Towards the production of ultracold ground-state RbCs molecules: Feshbach resonances, weakly bound states, and coupled-channel model

We have studied interspecies scattering in an ultracold mixture of $^{87}$Rb and $^{133}$Cs atoms, both in their lowest-energy spin states. The three-body loss signatures of 30 incoming s- and p-wave magnetic Feshbach resonances over the range 0 to 667 G have been catalogued. Magnetic field modulation spectroscopy was used to observe molecular states bound by up to 2.5 MHz$\times h$. Magnetic moment spectroscopy along the magneto-association pathway from 197 to 182 G gives results consistent with the observed and calculated dependence of the binding energy on magnetic field strength. We have created RbCs Feshbach molecules using two of the resonances. We have set up a coupled-channel model of the interaction and have used direct least-squares fitting to refine its parameters to fit the experimental results from the Feshbach molecules, in addition to the Feshbach resonance positions and the spectroscopic results for deeply bound levels. The final model gives a good description of all the experimental results and predicts a large resonance near 790 G, which may be useful for tuning the interspecies scattering properties. Quantum numbers and vibrational wavefunctions from the model can also be used to choose optimal initial states of Feshbach molecules for their transfer to the rovibronic ground state using stimulated Raman adiabatic passage (STIRAP).

physics.atom-ph↗

arXiv2011

The states 1^1Σ^+_u, 1^1Π_u and 2^1Σ^+_u of Sr_2 studied by Fourier-transform spectroscopy

A high resolution study of the electronic states 1^1Σ^+_u and 1^1Π_u which belong to the asymptote 4^1D + 5^1S and of the state 2(A)^1Σ^+_u, which correlates to the asymptote 5^1P + 5^1S, is performed by Fourier-transform spectroscopy of fluorescence progressions induced by single frequency laser excitation. Precise descriptions of the potentials up to 2000 cm^{-1} above the bottom are derived and compared to currently available ab initio calculations. Especially for the state 1^1Σ^+_u large deviations are found. Rather weak and local perturbations are observed for the states 1^1Π_u and 2^1Σ^+_u, while a strong coupling of the state 1^1Σ^+_u to the component Ω=0^+_u of the state 1^3Π_u, which belongs to the asymptote 5^3P + 5^1S, is indicated.

physics.chem-ph↗

arXiv2010

Hyperfine, rotational, and vibrational structure of the triplet ground state of Rb molecules

We have performed high-resolution two-photon dark-state spectroscopy of an ultracold gas of Rb molecules in the triplet ground state at a magnetic field of about 1000 G. The vibrational ladder as well as the hyperfine and low-lying rotational structure is mapped out. Energy shifts in the spectrum are observed due to singlet-triplet mixing at binding energies as deep as a few hundred GHz x h. This information together with data from other sources is used to optimize the potentials of the triplet and singlet states in a coupled-channel model. We find that the hyperfine structure depends weakly on the vibrational level. This provides a possible explanation for inaccuracies in recent Feshbach resonance calculations.

physics.atom-ph↗