arXiv subjects

Torsten Hartmann

Publications and source records attributed to Torsten Hartmann.

7 recordsLinked to original sources

arXiv2021

Hyperfine dependent atom-molecule loss analyzed by the analytic solution of few-body loss equations

We prepare mixtures of ultracold $^{39}$K atoms in various hyperfine spin states and $^{23}$Na$^{39}$K molecules in an optical dipole trap at a fixed magnetic field and study inelastic two-body atom-molecule collisions. We observe atom-molecule losses that are hyperfine dependent with a two-body loss rate far below the universal limit. We analyze the two-body loss dynamics based on the derivation of general and easy applicable analytic solutions for the differential equations describing the loss of an arbitrary number $\gamma$ of particles in a single collisional event.

physics.atom-ph↗

arXiv2020

An Ultracold Gas of Bosonic $^{23}\textrm{Na}^{39}\textrm{K}$ Ground-State Molecules

We report the creation of ultracold bosonic dipolar $^{23}\textrm{Na}^{39}\textrm{K}$ molecules in their absolute rovibrational ground state. Starting from weakly bound molecules immersed in an ultracold atomic mixture, we coherently transfer the dimers to the rovibrational ground state using an adiabatic Raman passage. We analyze the two-body decay in a pure molecular sample and in molecule-atom mixtures and find an unexpectedly low two-body decay coefficient for collisions between molecules and $^{39}\textrm{K}$ atoms in a selected hyperfine state. The preparation of bosonic $^{23}\textrm{Na}^{39}\textrm{K}$ molecules opens the way for future comparisons between fermionic and bosonic ultracold ground-state molecules of the same chemical species.

cond-mat.quant-gas↗

arXiv2019

Beyond Born-Oppenheimer approximation in ultracold atomic collisions

We report on deviations beyond the Born-Oppenheimer approximation in the potassium inter-atomic potentials. Identifying three up-to-now unknown $d$-wave Feshbach resonances, we significantly improve the understanding of the $^{39}$K inter-atomic potentials. Combining these observations with the most recent data on known inter- and intra-isotope Feshbach resonances, we show that Born-Oppenheimer corrections can be determined from atomic collisional properties alone and that significant differences between the homo- and heteronuclear case appear.

physics.atom-ph↗

arXiv2019

Formation of ultracold weakly bound dimers of bosonic $^{23}\textrm{Na}^{39}\textrm{K}$

We create weakly bound bosonic $^{23}\textrm{Na}^{39}\textrm{K}$ molecules in a mixture of ultracold $^{23}\textrm{Na}$ and $^{39}\textrm{K}$. The creation is done in the vicinity of a so far undetected Feshbach resonance at about $196\,\text{G}$ which we identify in this work by atom-loss spectroscopy. We investigate the involved molecular state by performing destructive radio frequency binding energy measurements. For the constructive molecule creation we use radio frequency pulses with which we assemble up to $6000$ molecules. We analyze the molecule creation efficiency as a function of the radio frequency pulse duration and the atom number ratio between $^{23}\textrm{Na}$ and $^{39}\textrm{K}$. We find an overall optimal efficiency of $6\,\%$ referring to the $^{39}\textrm{K}$ atom number. The measured lifetime of the molecules in the bath of trapped atoms is about $0.3\,\textrm{ms}$.

cond-mat.quant-gas↗

arXiv2019

A pathway to ultracold bosonic $^{23}\textrm{Na}^{39}\textrm{K}$ ground state molecules

We spectroscopically investigate a pathway for the conversion of $^{23}\textrm{Na}^{39}\textrm{K}$ Feshbach molecules into rovibronic ground state molecules via STImulated Raman Adiabatic Passage (STIRAP). Using photoassociation spectroscopy from the diatomic scattering threshold in the $a^3\Sigma^+$ potential, we locate the resonantly mixed electronically excited intermediate states $|B^1\Pi, v=8\rangle$ and $|c^3\Sigma^+, v=30\rangle$ which, due to their singlet-triplet admixture, serve as an ideal bridge between predominantly $a^3\Sigma^+$ Feshbach molecules and pure $X^1\Sigma^+$ ground state molecules. We investigate their hyperfine structure and present a simple model to determine the singlet-triplet coupling of these states. Using Autler-Townes spectroscopy, we locate the rovibronic ground state of the $^{23}\textrm{Na}^{39}\textrm{K}$ molecule ($|X^1\Sigma^+, v=0, N=0\rangle$) and the second rotationally excited state $N=2$ to unambiguously identify the ground state. We also extract the effective transition dipole moment from the excited to the ground state. Our investigations result in a fully characterized scheme for the creation of ultracold bosonic $^{23}\textrm{Na}^{39}\textrm{K}$ ground state molecules.

cond-mat.quant-gas↗

arXiv2018

Feshbach resonances in $^{23}\mathrm{Na}+$$^{39}\mathrm{K}$ mixtures and refined molecular potentials for the NaK molecule

We present a detailed study of interspecies Feshbach resonances of the bosonic $^{23}\mathrm{Na}+$$^{39}\mathrm{K}$ mixture for magnetic fields up to $750 \, \mathrm{G}$ in various collision channels. A total of fourteen Feshbach resonances are reported, as well as four zero crossings of the scattering length and three inelastic two-body loss features. We use the observed magnetic field locations of the resonant features together with the known data on $^{23}\mathrm{Na}+$$^{40}\mathrm{K}$ to refine the singlet and triplet ground state potentials of NaK and achieve a consistent description of Feshbach resonances for both, the Bose-Bose mixture of $^{23}\mathrm{Na}+$$^{39}\mathrm{K}$ as well as the Bose-Fermi mixture of $^{23}\mathrm{Na}+$$^{40}\mathrm{K}$.

physics.atom-ph↗

arXiv2017

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↗