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Journal of Physics B Atomic Molecular and Optical Physics

Formation of ultracold singlet ground state 39K87Rb molecules via Feshbach-optimized photoassociation

Zong-Han Yu, Bo-Wen Si, Zhi-Xin Sun, Bing-Kuan Lyu, Shu‐Lin Cong

Published Oct 21, 2022• 1 citation
Publisher

Abstract

Abstract We investigate theoretically the formation of ultracold 39K87Rb molecules on the lowest vibrational level of singlet ground electronic X 1Σ+ state via the Feshbach-optimized photoassociation. The probability density of colliding atomic pair at the short-range interatomic separation is significantly enhanced near Feshbach resonances. Due to the limitation of transition selection rule, the direct transition between singlet and triplet electronic states is forbidden. The electronic spin–orbit couplings between excited electronic states are used to transfer the population from the triplet electronic state to the singlet electronic state. By using the magnetic field and four laser pulses, the colliding 39K and 87Rb atoms near a magnetically induced Feshbach resonance are converted into the 39K87Rb molecule. The final population on the lowest vibrational level of the X 1Σ+ state reaches 0.02126.

DOI
10.1088/1361-6455/ac9cad

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Abstract We investigate theoretically the formation of ultracold 39K87Rb molecules on the lowest vibrational level of singlet ground electronic X 1Σ+ state via the Feshbach-optimized photoassociation. The probability density of colliding atomic pair at the short-range interatomic separation is significantly enhanced near Feshbach resonances. Due to the limitation of transition selection rule, the direct transition between singlet and triplet electronic states is forbidden. The electronic spin–orbit couplings between excited electronic states are used to transfer the population from the triplet electronic state to the singlet electronic state. By using the magnetic field and four laser pulses, the colliding 39K and 87Rb atoms near a magnetically induced Feshbach resonance are converted into the 39K87Rb molecule. The final population on the lowest vibrational level of the X 1Σ+ state reaches 0.02126.
A Feshbach-optimized photoassociation for preparing ultracold 40K87Rb^{40}\mathrm{K}^{87}\mathrm{Rb}40K87Rb molecules with short pulses is investigated theoretically. The total probability density of the coupled hyperfine states is greatly enhanced at short interatomic separations in the vicinity of magnetically tuned Feshbach resonances. Due to the coupling of the free hyperfine state with different bound hyperfine states, the maximal probability density distributes at different interatomic regions and determines the choice of the intermediate state. By using the spin-orbit coupling of the excited states, the population is successfully transferred to the singlet ground state $X{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}$ from the initial state mostly having triplet state character. By comparing the final population in the vicinity of Feshbach resonances at B0=546.80{B}_{0}=546.80B0​=546.80 and 659.34 G, our results show that a Feshbach resonance corresponding to a more deeply bound vibrational level can enhance the photoassociation efficiency of ultracold atoms to some degree.
Abstract We investigate theoretically the formation of ultracold ground-state CsYb molecules on the lowest vibrational level via the Feshbach-optimized photoassociation process. Three s-wave Feshbach resonances of CsYb are found. The probability density of the scattering state in the short-range internuclear distance is significantly enhanced near the resonance positions. The population transfer efficiency reaches its maximum when the pulse duration equals half a period of the Rabi oscillation. By using the optimized laser parameters including the peak intensity and detuning, the final population of the lowest vibrational level of the ground electronic state reaches order of 10 −1 in the four-laser scheme.
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.
Cs molecules is studied theoretically. Under the joint action of the magnetic field and short laser pulse, the colliding atoms in a superposition state composed of eight hyperfine components are converted into a molecule in the vibrational level of the excited state via two transition processes, the transition between singlet states and the transition between triplet states. The association efficiency can be significantly enhanced by taking advantage of Feshbach resonance. At different resonance positions, different hyperfine components of the superposition state dominate over the FOPA process, and the quantum interference displays different behaviors. Compared with the FOPA process only including a single hyperfine component, the quantum interference in the FOPA process containing all hyperfine components has a visible effect on the association efficiency.
Photoassociation of two ultracold rubidium atoms and the subsequent formation of stable molecules in the singlet ground and lowest triplet states is investigated theoretically. The method employs laser pulses inducing transitions via excited states correlated to the 5S+5P1∕25S+5{P}_{1∕2}5S+5P1∕2​ asymptote. Weakly bound molecules in the singlet ground or lowest triplet state can be created by a single pulse while the formation of more deeply bound molecules requires a two-color pump-dump scenario. More deeply bound molecules in the singlet ground or lowest triplet state can be produced only if efficient mechanisms for both pump and dump steps exist. While long-range 1∕R31∕{R}^{3}1∕R3 potentials allow for efficient photoassociation, stabilization is facilitated by the resonant spin-orbit coupling of the 0u+{0}_{u}^{+}0u+​ states. Molecules in the singlet ground state bound by a few wave numbers can thus be formed. This provides a promising first step toward ground-state molecules which are ultracold in both translational and vibrational degrees of freedom.
We form ultracold ground-state Rb 2 molecules by photoassociating pairs of atoms in a magneto-optical trap into the 0 u + state, which decays radiatively into high vibrational levels of the X 1 Σ g + state. Sensitive and vibrationally state-selective detection is achieved by means of resonantly-enhanced two-photon ionization with a pulsed laser. Frequency scans of the detection laser reveal a long vibrational progression to a previously unobserved electronic excited state, which we identify as the 2 1 Σ u + state. Most of its vibrational spectrum is in excellent agreement with predictions based on ab initio potentials, although the lowest vibrational levels exhibit strong perturbative mixing with the triplet 2 3 Π u state. The detection method reported here, with minor variations, should be effective for the entire potential well of the X state. In this work no transitions are observed from vibrational levels above v = 118, but this turns out to be a limitation not of the detection method but rather of the photoassociative formation scheme, due to re-excitation of the highest- v levels by the same photoassociation laser that produces them.