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arXiv:1505.01835 · New Journal of Physics

Two-photon pathway to ultracold ground state molecules of23Na40K

Jee Woo Park, Sebastian Will, Martin W. Zwierlein

Published Jul 31, 2015• 43 citations
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Abstract

We report on high-resolution spectroscopy of ultracold fermionic 23 Na 40 K Feshbach molecules, and identify a two-photon pathway to the rovibrational singlet ground state via a resonantly mixed B 1 Π ∼ c 3 Σ + intermediate state.Photoassociation in a 23 Na-40 K atomic mixture and one-photon spectroscopy on 23 Na 40 K Feshbach molecules reveal about 20 vibrational levels of the electronically excited c 3 Σ + state.Two of these levels are found to be strongly perturbed by nearby B 1 Π levels via spinorbit coupling, resulting in additional lines of dominant singlet character in the perturbed complex. The dominantly singlet level is used to locate the absolute rovibrational singlet ground state v J X 0, 0via Autler-Townes spectroscopy.We demonstrate coherent two-photon coupling via dark state spectroscopy between the predominantly triplet Feshbach molecular state and the singlet ground state.Its binding energy is measured to be 5212.0447(1)cm -1 , a thousand-fold improvement in accuracy compared to previous determinations.In their absolute singlet ground state, 23 Na 40 K molecules are chemically stable under binary collisions and possess a large electric dipole moment of 2.72 Debye.Our work thus paves the way towards the creation of strongly dipolar Fermi gases of NaK molecules.

DOI
10.1088/1367-2630/17/7/075016

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We report on high-resolution spectroscopy of ultracold fermionic 23 Na 40 K Feshbach molecules, and identify a two-photon pathway to the rovibrational singlet ground state via a resonantly mixed B 1 Π ∼ c 3 Σ + intermediate state.Photoassociation in a 23 Na-40 K atomic mixture and one-photon spectroscopy on 23 Na 40 K Feshbach molecules reveal about 20 vibrational levels of the electronically excited c 3 Σ + state.Two of these levels are found to be strongly perturbed by nearby B 1 Π levels via spinorbit coupling, resulting in additional lines of dominant singlet character in the perturbed complex. The dominantly singlet level is used to locate the absolute rovibrational singlet ground state v J X 0, 0via Autler-Townes spectroscopy.We demonstrate coherent two-photon coupling via dark state spectroscopy between the predominantly triplet Feshbach molecular state and the singlet ground state.Its binding energy is measured to be 5212.0447(1)cm -1 , a thousand-fold improvement in accuracy compared to previous determinations.In their absolute singlet ground state, 23 Na 40 K molecules are chemically stable under binary collisions and possess a large electric dipole moment of 2.72 Debye.Our work thus paves the way towards the creation of strongly dipolar Fermi gases of NaK molecules.
We report on high-resolution spectroscopy of ultracold fermionic [superscript 23]Na[superscript 40]K Feshbach molecules, and identify a two-photon pathway to the rovibrational singlet ground state via a resonantly mixed B[superscript 1]Π ~ c[superscript 3]Σ[superscript +]intermediate state. Photoassociation in a [superscript 23]Na–[superscript 40]K atomic mixture and one-photon spectroscopy on [superscript 23]Na[superscript 40]K Feshbach molecules reveal about 20 vibrational levels of the electronically excited c[superscript 3]Σ[superscript +]state. Two of these levels are found to be strongly perturbed by nearby B[superscript 1]Π levels via spin–orbit coupling, resulting in additional lines of dominant singlet character in the perturbed complex B[superscript 1}Π |v = 4〉 ~ c[superscript 3]∑[superscript +] v = 25〉, or of resonantly mixed character in B[superscript 1}Π |v = 12〉 ~ c[superscript 3]∑[superscript +] v = 35〉. The dominantly singlet level is used to locate the absolute rovibrational singlet ground state X[superscript 1]∑[superscript +] |v = 0, J = 0〉 via Autler–Townes spectroscopy. We demonstrate coherent two-photon coupling via dark state spectroscopy between the predominantly triplet Feshbach molecular state and the singlet ground state. Its binding energy is measured to be 5212.0447(1) cm[superscript −1], a thousand-fold improvement in accuracy compared to previous determinations. In their absolute singlet ground state, [superscript 23]Na[superscript 40]K molecules are chemically stable under binary collisions and possess a large electric dipole moment of 2.72 Debye. Our work thus paves the way towards the creation of strongly dipolar Fermi gases of NaK molecules.
Abstract We spectroscopically investigate a pathway for the conversion of 23Na39K Feshbach molecules into rovibronic ground state molecules via stimulated Raman adiabatic passage. Using photoassociation spectroscopy from the diatomic scattering threshold in the a 3Σ+ potential, we locate the resonantly mixed electronically excited intermediate states ∣ B 1 Π , v = 8 〉 and ∣ c 3 Σ + , v = 30 〉 which, due to their singlet–triplet admixture, serve as an ideal bridge between predominantly a 3Σ+ Feshbach molecules and pure X 1Σ+ 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 23Na39K molecule ( ∣ X 1 Σ + , v = 0 , N = 0 〉 ) 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 23Na39K ground state molecules.
We report on the creation of an ultracold dipolar gas of fermionic 23Na40 K molecules in their absolute rovibrational and hyperfine ground state. Starting from weakly bound Feshbach molecules, we demonstrate hyperfine resolved two-photon transfer into the singlet X 1Σ+|v=0,J=0⟩ ground state, coherently bridging a binding energy difference of 0.65 eV via stimulated rapid adiabatic passage. The spin-polarized, nearly quantum degenerate molecular gas displays a lifetime longer than 2.5 s, highlighting NaK's stability against two-body chemical reactions. A homogeneous electric field is applied to induce a dipole moment of up to 0.8 D. With these advances, the exploration of many-body physics with strongly dipolar Fermi gases of 23Na40K molecules is within experimental reach.
We report on the creation of an ultracold dipolar gas of fermionic [superscript 23]Na[superscript 40]Kmolecules in their absolute rovibrational and hyperfine ground state. Starting from weakly bound Feshbach molecules, we demonstrate hyperfine resolved two-photon transfer into the singlet X[superscript 1]Σ[superscript +]|v = 0,J = 0⟩ ground state, coherently bridging a binding energy difference of 0.65 eV via stimulated rapid adiabatic passage. The spin-polarized, nearly quantum degenerate molecular gas displays a lifetime longer than 2.5 s, highlighting NaK’s stability against two-body chemical reactions. A homogeneous electric field is applied to induce a dipole moment of up to 0.8 D. With these advances, the exploration of many-body physics with strongly dipolar Fermi gases of [superscript 23]Na[superscript 40]K molecules is within experimental reach.
We perform one- and two-photon high resolution spectroscopy on ultracold samples of RbCs Feshbach molecules with the aim to identify a suitable route for efficient ground-state transfer in the quantum-gas regime to produce quantum gases of dipolar RbCs ground-state molecules. One-photon loss spectroscopy allows us to probe deeply bound rovibrational levels of the mixed excited (A(1)Σ(+)-b(3)Π)0(+) molecular states. Two-photon dark state spectroscopy connects the initial Feshbach state to the rovibronic ground state. We determine the binding energy of the lowest rovibrational level |v'' = 0, J'' = 0> of the X(1)Σ(+) ground state to be D = 3811.5755(16) cm(-1), a 300-fold improvement in accuracy with respect to previous data. We are now in the position to perform stimulated two-photon Raman transfer to the rovibronic ground state.
We report the successful production of an ultracold sample of absolute ground-state ^{23}Na^{87}Rb molecules. Starting from weakly bound Feshbach molecules formed via magnetoassociation, the lowest rovibrational and hyperfine level of the electronic ground state is populated following a high-efficiency and high-resolution two-photon Raman process. The high-purity absolute ground-state samples have up to 8000 molecules and densities of over 10^{11} cm^{-3}. By measuring the Stark shifts induced by external electric fields, we determined the permanent electric dipole moment of the absolute ground-state ^{23}Na^{87}Rb and demonstrated the capability of inducing an effective dipole moment over 1 D. Bimolecular reaction between ground-state ^{23}Na^{87}Rb molecules is endothermic, but we still observed a rather fast decay of the molecular sample. Our results pave the way toward investigation of ultracold molecular collisions in a fully controlled manner and possibly to quantum gases of ultracold bosonic molecules with strong dipolar interactions.