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arXiv:0903.2942 · New Journal of Physics

Influence of a Feshbach resonance on the photoassociation of LiCs

Johannes Deiglmayr, Philippe Pellegrini, A. Grochola, M. Repp, Robin Côté, Olivier Dulieu, Roland Wester, Matthias Weidemüller

Published May 14, 2009• 40 citations
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Abstract

We analyze the formation of ultracold 7 Li 133 Cs molecules in the rovibrational ground state through photoassociation into the B 1 Π state, which has recently been reported (Deiglmayr et al 2008 Phys. Rev. Lett. 101 133004). Absolute rate constants for photoassociation at large detunings from the atomic asymptote are determined and are found to be surprisingly large. The photoassociation process is modeled using a full coupled-channel calculation for the continuum state, taking all relevant hyperfine states into account. The enhancement of the photoassociation rate is found to be caused by an 'echo' of the triplet component in the singlet component of the scattering wave function at the inner turning point of the lowest triplet a 3 Σ + potential. This perturbation can be ascribed to the existence of a broad Feshbach resonance at low scattering energies. Our results elucidate the important role of couplings in the scattering wave function for the formation of deeply bound ground state molecules via photoassociation.

DOI
10.1088/1367-2630/11/5/055034

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Influence of a Feshbach resonance on the photoassociation of LiCs

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We discovered a sign error in the transformation of the scattering wave function between the atomic basis (equation (6)) and the molecular basis (equation (7)) that we used in our paper [ 1 ] for the case m F = 5 for the following atomic state: | f 1 = 2, m f 1 = 2, f 2 = 3, m f 2 = 3 ⟩ = + √7/16 | S = 0, m S = 0, I = 5, m I = 5 ⟩ + √7/16 | S = 1, m S = 0, I = 5, m I = 5 ⟩ − √3/80 | S = 1, m S = 1, I = 4, m I = 4 ⟩ − √7/80 | S = 1, m S = 1, I = 5, m I = 4 ⟩ Consequently, the results given in the right column of figure 5 in this paper are wrong, while those in the left column are correct. The corrected figure is now displayed as figure 5 below. In particular, the triplet part of the wave function no longer influences the singlet part (see the upper panel of the right column). This also affects figures 6 and 7 of [ 1 ]. The black trace of the upper part of figure 6 is incorrect, and also the results of figure 7. The main consequence concerns the interpretation of the experimental results reported in figure 8 of [ 1 ]. The magnitude and modulation of the photoassociation (PA) rate observed in the experiment can be interpreted only if the triplet component of the scattering wave function is involved, as was discussed in the paper. However, the model employed in [ 1 ] cannot reproduce these results. The role of the triplet component of the scattering wave function can be invoked in the PA towards the B 1 Π levels by considering the small spin–orbit coupling of the B 1 Π state with the neighboring triplet states (see figure 4 of [ 1 ]), while the modulations of the PA rate may be influenced by a slight variation of the scattering length of the lowest a 3 Σ + state. These issues will be considered in a future paper. Figure 5. Components of the energy-normalized radial wave function for a Li–Cs pair colliding at 500 μK, in the atomic basis (left column) and in the molecular basis (right column). The displayed case corresponds to m f 1 + m f 2 = 5. Under the given experimental conditions, the uppermost atomic state f 1 = 2, m f 1 = 2, f 2 = 3, m f 2 = 3 is the only open entrance channel; the three other states shown are closed channels. Note that there is no line-to-line relation between the states listed in each column. We would like to thank Professor E Tiemann for bringing this sign error to our attention. References [1] Deiglmayr J, Pellegrini P, Grochola A, Repp M, Côté R, Dulieu O, Wester R and Weidemüller M 2009 Influence of a Feshbach resonance on the photoassociation of LiCs New J. Phys. 11 055034

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Photoassociation spectroscopy of the B Π1 state of LiCs

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We present an accurate potential energy curve of the B (1)Pi state in the LiCs molecule for which vibrational levels between v(') = 0 and v(') = 35 (bound by 11.4 GHz) were measured by photoassociation spectroscopy in an ultracold ensemble of (7)Li and (133)Cs atoms. By the combination of conventional spectroscopic data of the B-X system and the new photoassociation measurements a very precise value of the dissociation energy of the ground state X (1)Sigma(+) of LiCs was determined to be D(0) = 5783.495(5) cm(-1).

The Journal of Chemical Physics•Aug 4, 2009•23 citations
We analyze the formation of ultracold 7 Li 133 Cs molecules in the rovibrational ground state through photoassociation into the B 1 Π state, which has recently been reported (Deiglmayr et al 2008 Phys. Rev. Lett. 101 133004). Absolute rate constants for photoassociation at large detunings from the atomic asymptote are determined and are found to be surprisingly large. The photoassociation process is modeled using a full coupled-channel calculation for the continuum state, taking all relevant hyperfine states into account. The enhancement of the photoassociation rate is found to be caused by an 'echo' of the triplet component in the singlet component of the scattering wave function at the inner turning point of the lowest triplet a 3 Σ + potential. This perturbation can be ascribed to the existence of a broad Feshbach resonance at low scattering energies. Our results elucidate the important role of couplings in the scattering wave function for the formation of deeply bound ground state molecules via photoassociation.
We discovered a sign error in the transformation of the scattering wave function between the atomic basis (equation (6)) and the molecular basis (equation (7)) that we used in our paper [ 1 ] for the case m F = 5 for the following atomic state: | f 1 = 2, m f 1 = 2, f 2 = 3, m f 2 = 3 ⟩ = + √7/16 | S = 0, m S = 0, I = 5, m I = 5 ⟩ + √7/16 | S = 1, m S = 0, I = 5, m I = 5 ⟩ − √3/80 | S = 1, m S = 1, I = 4, m I = 4 ⟩ − √7/80 | S = 1, m S = 1, I = 5, m I = 4 ⟩ Consequently, the results given in the right column of figure 5 in this paper are wrong, while those in the left column are correct. The corrected figure is now displayed as figure 5 below. In particular, the triplet part of the wave function no longer influences the singlet part (see the upper panel of the right column). This also affects figures 6 and 7 of [ 1 ]. The black trace of the upper part of figure 6 is incorrect, and also the results of figure 7. The main consequence concerns the interpretation of the experimental results reported in figure 8 of [ 1 ]. The magnitude and modulation of the photoassociation (PA) rate observed in the experiment can be interpreted only if the triplet component of the scattering wave function is involved, as was discussed in the paper. However, the model employed in [ 1 ] cannot reproduce these results. The role of the triplet component of the scattering wave function can be invoked in the PA towards the B 1 Π levels by considering the small spin–orbit coupling of the B 1 Π state with the neighboring triplet states (see figure 4 of [ 1 ]), while the modulations of the PA rate may be influenced by a slight variation of the scattering length of the lowest a 3 Σ + state. These issues will be considered in a future paper. Figure 5. Components of the energy-normalized radial wave function for a Li–Cs pair colliding at 500 μK, in the atomic basis (left column) and in the molecular basis (right column). The displayed case corresponds to m f 1 + m f 2 = 5. Under the given experimental conditions, the uppermost atomic state f 1 = 2, m f 1 = 2, f 2 = 3, m f 2 = 3 is the only open entrance channel; the three other states shown are closed channels. Note that there is no line-to-line relation between the states listed in each column. We would like to thank Professor E Tiemann for bringing this sign error to our attention. References [1] Deiglmayr J, Pellegrini P, Grochola A, Repp M, Côté R, Dulieu O, Wester R and Weidemüller M 2009 Influence of a Feshbach resonance on the photoassociation of LiCs New J. Phys. 11 055034
Two-color photoassociation of ground state 6{}^{6}6Li87{}^{87}87Rb molecules via the $B\phantom{\rule{0.16em}{0ex}}{}^{1}\ensuremath{\Pi}$ electronic state using short pulses near a magnetic Feshbach resonance is studied theoretically. A near-resonant magnetic field is applied to mix the hyperfine singlet and triplet components of the initial wave function and enhance the photoassociation rate, before the population is transferred to the ground state by a second pulse. We show that an increase of up to three orders of magnitude in the absolute number of molecules produced is attainable for deeply bound vibrational levels. This technique can be generalized to other molecules with accessible magnetic Feshbach resonances.
We recently reported the formation of ultracold LiCs molecules in the rovibrational ground state X1sigma+, v" = 0,J" = 0 (J. Deiglmayr et al., Phys. Rev. Lett., 2008, 101, 133004). Here we discuss details of the experimental setup and present a thorough analysis of the photoassociation step including the photoassociation line shape. We predict the distribution of produced ground state molecules using accurate potential energy curves combined with an ab initio dipole transition moment and compare this prediction with experimental ionization spectra. Additionally we improve the value of the dissociation energy for the X1sigma+ state by high resolution spectroscopy of the vibrational ground state.
We report the formation of ultracold (7)Li(85)Rb molecules in the a(3)Σ(+) electronic state by photoassociation (PA) and their detection via resonantly enhanced multiphoton ionization (REMPI). With our dual-species Li and Rb magneto-optical trap apparatus, we detect PA resonances with binding energies up to ∼62 cm(-1) below the (7)Li 2s (2)S1/2 + (85)Rb 5p (2)P1/2 asymptote. In addition, we use REMPI spectroscopy to probe the a(3)Σ(+) state and excited electronic 3(3)Π and 4(3)Σ(+) states and identify a(3)Σ(+) (v″ = 7-13), 3(3)Π (vΠ' = 0-10), and 4(3)Σ(+) (vΣ' = 0-5) vibrational levels. Our line assignments agree well with ab initio calculations. These preliminary spectroscopic studies on previously unobserved electronic states are crucial to discovering transition pathways for transferring ultracold LiRb molecules created via PA to deeply bound rovibrational levels of the electronic ground state.
We report on the observation of 19 interspecies Feshbach resonances in an optically trapped ultracold Bose-Fermi mixture of 133Cs{}^{133}\text{Cs}133Cs and 6Li{}^{6}\text{Li}6Li in the two energetically lowest spin states. We assign the resonances to sss- and ppp-wave molecular channels by a coupled-channels calculation, resulting in an accurate determination of LiCs ground-state potentials. Fits of the resonance position based on the undressed asymptotic bound state model do not provide the same level of accuracy as the coupled-channels calculation. Several broad sss-wave resonances provide prospects to create fermionic LiCs molecules with a large dipole moment via Feshbach association followed by stimulated Raman passage. Two of the sss-wave resonances overlap with a zero crossing of the Cs scattering length, which offers prospects for the investigation of polarons in an ultracold Li-Cs mixture.
We present an accurate potential energy curve of the B (1)Pi state in the LiCs molecule for which vibrational levels between v(') = 0 and v(') = 35 (bound by 11.4 GHz) were measured by photoassociation spectroscopy in an ultracold ensemble of (7)Li and (133)Cs atoms. By the combination of conventional spectroscopic data of the B-X system and the new photoassociation measurements a very precise value of the dissociation energy of the ground state X (1)Sigma(+) of LiCs was determined to be D(0) = 5783.495(5) cm(-1).