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

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

Kai K. Voges, Philipp Gersema, Torsten Hartmann, Torben A. Schulze, Alessandro Zenesini, and Silke Ospelkaus

Phys. Rev. A 101, 042704 – Published 20 April 2020

Abstract

We create weakly bound bosonic $^{23} {Na}^{39} K$ molecules in a mixture of ultracold ${}^{23}{Na}$ and ${}^{39}K$ . The creation is done in the vicinity of a so far undetected Feshbach resonance at about 196 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 ${}^{23}{Na}$ and ${}^{39}K$ . We find an overall optimal efficiency of $6 %$ referring to the ${}^{39}K$ atom number. The measured lifetime of the molecules in the bath of trapped atoms is about 0.3 ms.

Received 6 November 2019
Revised 28 February 2020
Accepted 9 March 2020

DOI:https://doi.org/10.1103/PhysRevA.101.042704

Physics Subject Headings (PhySH)

Bose gases Cold and ultracold molecules Dipolar gases

Atoms Molecules

Feshbach resonance

Atomic, Molecular & Optical

Authors & Affiliations

Kai K. Voges , Philipp Gersema , Torsten Hartmann ^*, Torben A. Schulze, Alessandro Zenesini , and Silke Ospelkaus^†

Institut für Quantenoptik, Leibniz Universität Hannover, 30167 Hannover, Germany

^*torben.alexander@icloud.com
^†silke.ospelkaus@iqo.uni-hannover.de

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Vol. 101, Iss. 4 — April 2020

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Figure 1
Feshbach resonance characterization. (a) Atom-loss spectroscopy in the ${| f = 1, m_{f} = - 1 〉}_{Na} + {| f = 2, m_{f} = - 2 〉}_{K}$ channel. The remaining atom fraction of ${}^{23}{Na}$ and ${}^{39}K$ for different magnetic field strengths with a holding time of 40 ms. The remaining atom number is normalized to the initial atom number for each species, respectively. Open gray triangles and the dashed gray line refer the to remaining ${}^{23}{Na}$ atom fraction and solid black circles and the solid black line refer to the ${}^{39}K$ atom number fraction. The vertical lines and corresponding shaded area indicate the resonance position and the standard deviation obtained from the two Gaussian fits. (b) Binding energy of the weakly bound state as obtained from rf spectroscopy. The continuous blue line is a fit to the destructive measurements (blue circles) according to universal binding energy [Eq. (1)]. The triangle is the binding energy extracted from the constructive signal from Fig. 2. The vertical lines are the resonance position with the standard deviation; dashed lines for the atom-loss measurement in (a), and solid lines for the binding-energy measurement. The inset shows a sample rf scan for a binding energy of $h \times 103$ kHz with a double-Gaussian fit (dashed blue line). The arrows indicate the binding energy. Error bars in both figures are smaller than the plot markers and are not shown.
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Figure 2
Constructive molecular signal. ${}^{39}K$ atom number as a function of the applied rf radiation. The blue circles are the detected atom number directly after the rf pulse. Fitting a phenomenological double-Lorentzian function (solid blue line) the atomic transition occurs at 209.608(3) MHz, corresponding to a magnetic field of 200.58(3) G. The extracted binding energy is $h \times 171 (4)$ kHz, shown as the black arrow. The value is displayed also in Fig. 1 as a blue triangle. Open gray triangles are the measured background atoms after an additional waiting time of 3 ms (see text) and the solid gray line with the underlying shaded gray area is a Lorentzian fit with the standard error as a darker shaded area. The atom number is normalized to the total number of ${}^{39}K$ atoms. Error bars are the standard deviation and come from different experimental runs.
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Figure 3
Characterization of the association process. (a) The molecule number is plotted as a function of the rf pulse duration. The molecules are imaged directly after switching off the rf. The best creation efficiency is reached at a pulse duration around $350 μ s$ . The solid blue line is the fit modeled with the set of differential equations [Eqs. (3)]. The dashed lines with the enclosed shaded area refer to the fit uncertainties. (b) Normalized molecule number as function of the atom number ratio at a creation time of $500 μ s$ . The bars represent the predictions from the fit results in (a) taking the individual starting conditions for each point as well as the fit uncertainties into account. The normalization is done according to the maximal created molecule number. Error bars in both figures are the standard deviation and come from different experimental runs.
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Figure 4
Lifetime measurement of the molecules in the cODT. The molecule number is normalized to the value of zero waiting time. For this measurement ${}^{23}{Na}$ and ${}^{39}K$ atoms are not removed. A fit to the data (solid line) results in a lifetime of $τ = 299 (17) μ s$ . Error bars are the standard deviation and come from different experimental runs.
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Physical Review A

covering atomic, molecular, and optical physics and quantum information

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

Kai K. Voges, Philipp Gersema, Torsten Hartmann, Torben A. Schulze, Alessandro Zenesini, and Silke Ospelkaus

Phys. Rev. A 101, 042704 – Published 20 April 2020

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Physical Review A

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Formation of ultracold weakly bound dimers of bosonic 23Na39K

Kai K. Voges, Philipp Gersema, Torsten Hartmann, Torben A. Schulze, Alessandro Zenesini, and Silke Ospelkaus

Phys. Rev. A 101, 042704 – Published 20 April 2020

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