Cruising through molecular bound-state manifolds with radiofrequency

Abstract

The production of ultracold molecules with their rich internal structure is currently attracting considerable interest 1-4 . For future experiments, it will be important to efficiently transfer these molecules from their initial internal quantum state at production to other quantum states of interest. Transfer tools such as optical Raman schemes 5,6 , radiofrequency transitions (see, for example, ref. 7) or magnetic field ramping 8,9 exist, but are either technically involved or limited in their applicability. Here, we demonstrate a simple, highly efficient hybrid transfer method that overcomes a number of the previous limitations. The scheme is based on magnetically tuned mixing of two neighbouring molecular levels, which enables otherwise forbidden radiofrequency transitions between them. By repeating this process at various magnetic fields, molecules can be successively transported through a large manifold of quantum states. Applying nine transfers, we convert very weakly bound Feshbach molecules to a much more deeply bound level with a binding energy corresponding to 3.6 GHz. As an important spin-off of our experiments, we demonstrate a high-precision spectroscopy method for investigating level crossings.Radiofrequency has important applications for ultracold molecules, such as spectroscopy 7,10-14 and molecule production [15][16][17] . Using radiofrequency to transfer ground-state molecules between states of different vibrational quantum numbers, as demonstrated here, is not obvious. For simple molecular potentials, transition matrix elements for magnetic dipole transitions between different vibrational levels are expected to vanish on the basis of an overlap argument of the spatial wavefunctions. However, for real molecules such as Rb 2 , the situation is more complex, for example, owing to exchange interaction, hyperfine structure and the Zeeman effect. The combined effect of these interactions induces mixing of states with different vibrational quantum numbers, leading to new eigenstates between which radiofrequency transitions can be driven (see the Methods section). This mixing effect is maximal at avoided crossings. (As a consequence, it is important for radiofrequency spectroscopy at Feshbach resonances 12 .)We carry out our experiments with a

Hyperfine, rotational, and Zeeman structure of the lowest vibrational levels of theRb872(1)Takekoshi1, Strauss2, Lang3 et al. 2011Phys. Rev. ASelf Cite207252View full textAdd to dashboardCite

“…The preparation of the Feshbach molecules is described in detail in [25,26]. In brief, following laser cooling and evaporative cooling, we trap an ultracold atomic cloud of 3 × 10 5 87 Rb atoms close to quantum degeneracy in a threedimensional (3D) optical lattice.…”

“…It exhibits several avoided crossings with other molecular levels. When ramping down the magnetic field, these avoided crossings are crossed using a adiabatic rf transfer method [26]. In order to count the molecules remaining after the spectroscopy pulse, we retrace our path back to the Feshbach resonance at 1007.4 G where the molecules are dissociated via a reverse Feshbach magnetic field sweep [25] and imaged as atoms using standard absorption imaging techniques [29].…”

Large-amplitude driving of a superconducting artificial atom

“…The quantum interference is robust provided the evolution time of the state through the interferometer is short compared with the atom's coherence times. In addition to superconducting artificial atoms 5,6,14,21,24,25 , this concept is generally applicable to other solid-state artificial atoms 80,81 and generalized spin systems 82 (e.g., molecular magnets 83,84,85 , natural atoms 86,87 , and molecules 88,89,90 ) that exhibit avoided level crossings, and it is extensible to multiple energy levels as we demonstrate in Section 5.…”

Ultracold molecules and ultracold chemistry

“…Though highly excited, Feshbach molecules are produced in specific rovibronic states which can be manipulated (to a limited extent) using radiofrequency magnetic fields [145]; used to investigate universal few-body physics in so-called "Halo states" [146], or three-body Efimov states [147]; and used for the production of molecular BECs [139,148]. Indications of scattering resonances in a Cs 2 molecular gas [149], as well as the observation of collisions with Cs atoms (see Section V), suggest that it may also be possible to form alkali-metal trimers or even tetramers through magnetic-field tuning.…”