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Chinese Physics B

Stark effect of the hyperfine structure of ICl in its rovibronic ground state: Towards further molecular cooling

Qinghui Wang, Xuping Shao, Xiaohua Yang

Published Jan 1, 2016• 2 citations
Publisher

Abstract

Hyperfine structures of ICl in its vibronic ground state due to the nuclear spin and electric quadruple interactions are determined by diagonalizing the effective Hamiltonian matrix. Furthermore, the Stark sub-levels are precisely determined as well. The results are helpful for electro-static manipulation (trapping or further cooling) of cold ICl molecules. For example, an electric field of 1000 V/cm can trap ICl molecules less than 637 μK in the lowest hyperfine level.

DOI
10.1088/1674-1056/25/1/013301

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Hyperfine structures of ICl in its vibronic ground state due to the nuclear spin and electric quadruple interactions are determined by diagonalizing the effective Hamiltonian matrix. Furthermore, the Stark sub-levels are precisely determined as well. The results are helpful for electro-static manipulation (trapping or further cooling) of cold ICl molecules. For example, an electric field of 1000 V/cm can trap ICl molecules less than 637 μK in the lowest hyperfine level.
The mixed-field effect at the hyperfine level of the rovibronic ground state of the 127I79Br (X1Σ, v = 0, J = 0) molecule is computed on the J–I uncoupled basis of |JMJI 1 M 1 I 2 M 2〉, where J is the molecular total angular momentum excluding nuclear spin, MJ is the projection number of J, I 1 and I 2 are the nuclear spins of the iodine and bromine atoms, and M 1 and M 2 are the projection numbers of I 1 and I 2, respectively. When the two applied electric and magnetic fields are parallel, the perturbations are rare and only one perturbation is observed in a relatively large field regime in our computation range. However, when the two fields are off-parallel, the perturbations increase significantly and some sublevels show the Feshbach-like resonance phenomenon. Therefore, such sublevels transit between weak-field seeking and strong-field seeking repeatedly, which can be utilized to enhance or suppress cold molecular collision and chemical reaction rates. Such behavior of the molecular hyperfine structure in the mixed off-parallel fields may also be utilized to construct an electric-field-assisted anti-Helmholtz magnetic trap for cold molecules and to realize evaporative cooling of cold molecules (sub-mK) into the ultracold regime (μK).
Abstract The Zeeman-hyperfine-rotational spectra of 40K87Rb within its vibronic ground state at a magnetic field of 545.9 G are investigated by adopting the latest molecular constants available, and the results are in good agreement with the experimental observation made by Ospelkaus et al. [Phys. Rev. Lett. 104 030402 (2010)]. However, the calculated spectra generally shift by −3.6 kHz from the experimental ones, which implies the inaccuracy of the effective rotational constant. Therefore, we refit the spectra and obtain a new B eff = 1113952(1) kHz, which reduces the overall root-mean-square deviation from 10.8 kHz to 7.9 kHz. Furthermore, the pure hyperfine spectra within the J = 0 and 1 rotational states are simulated. We find that the scalar nuclear spin–spin interaction dominates the hyperfine splitting of J = 0 despite it being slightly indirectly affected by the nuclear electric quadruple interaction due to the rotational perturbation, while the nuclear electric quadrupole interactions dominate the splitting, and the scalar and tensor nuclear spin–spin interactions also affect the splitting of J = 1. The detailed hyperfine-rotational perturbations are studied. Therefore, the scalar and tensor nuclear spin–spin interaction constants can be precisely determined by simultaneously measuring the pure hyperfine radio-frequency spectra of the J = 0 and 1 states in the vibronic ground state.
We investigate single-particle energy spectra of the hydroxyl free radical (OH) in the lowest electronic and rovibrational level under combined static electric and magnetic fields, as an example of heteronuclear polar diatomic molecules. In addition to the fine-structure interactions, the hyperfine interactions and centrifugal distortion effects are taken into account to yield the zero-field spectrum of the lowest 2 Π 3 / 2 manifold to an accuracy of less than 2 kHz. We also examine level crossings and repulsions in the hyperfine structure induced by applied electric and magnetic fields. Compared to previous work, we found more than 10% reduction of the magnetic fields at level repulsions in the Zeeman spectrum subjected to a perpendicular electric field. In addition, we find new level repulsions, which we call Stark-induced hyperfine level repulsions, that require both an electric field and hyperfine structure. It is important to take into account hyperfine structure when we investigate physics of OH molecules at micro-Kelvin temperatures and below.
The response of an atom to external electric and magnetic fields can reveal fundamental atomic properties. It has long been verified that, in a static magnetic field, those atomic energy levels with hyperfine interactions shift according to the Breit-Rabi formula, which introduces nonlinear dependence on the magnetic field. On the other hand, the corresponding Breit-Rabi dependence on a static electric field has not been observed before due to a combination of experimental challenges. Here, we precisely measure the Stark shift of the [Formula: see text] transition of [Formula: see text]Yb ([Formula: see text] = 1/2) with cold atoms held by an optical dipole trap in a static electric field up to 120 kV/cm. We observe the electric Breit-Rabi effect displaying high-order ([Formula: see text] and [Formula: see text]) DC Stark shifts. These effects arise from the influence of the strong electric field on hyperfine interactions.
We report the preparation of a rovibronic ground-state molecular quantum gas in a single hyperfine state and, in particular, the absolute lowest quantum state. This addresses the last internal degree of freedom remaining after the recent production of a near quantum degenerate gas of molecules in their rovibronic ground state, and provides a crucial step towards full control over molecular quantum gases. We demonstrate a scheme that is general for bialkali polar molecules and allows the preparation of molecules in a single hyperfine state or in an arbitrary coherent superposition of hyperfine states. The scheme relies on electric-dipole, two-photon microwave transitions through rotationally excited states and makes use of electric nuclear quadrupole interactions to transfer molecular population between different hyperfine states.