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Quantum 2.0 Conference and Exhibition

Low-Phase-Noise High-Power Diode Laser Systems for the STIRAP Transfer of Ultracold 6Li40K Molecules

Anbang Yang, Xiaoyu Nie, Victor Avalos Pinilos, Canming He, Sunil Kumar, Sofia Botsi, Kai Dieckmann

Published Jan 1, 2022• 0 citations
Publisher

Abstract

We investigate the phase noise properties of our Raman laser system for its application in the coherent ground state transfer of LiK polar molecules and discuss recent improvements.
DOI
10.1364/quantum.2022.qth3b.4

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Abstract Ultracold polar molecules represent a rapidly advancing platform at the forefront of quantum simulation, quantum computation, quantum chemistry, and precision measurement. We report an experimental investigation for improving the creation efficiency of ultracold 6Li40K ground state molecules using stimulated Raman adiabatic passage (STIRAP). We address laser amplitude/phase noise and polarization impurity to improve STIRAP efficiency. The phase noise of our two Raman lasers is suppressed effectively by extending the cavity length for the external-cavity diode lasers (ECDLs). Further, we find that even a weak polarization impurity significantly reduces the STIRAP efficiency on the single-photon resonance (Δ = 0) for 6Li40K, due to coupling to undesired molecular levels. However, STIRAP efficiencies over 90% can be achieved by increasing Δ/2π to 10 MHz, which is comparable to the excited-state scattering rate. Our work holds significance for achieving efficient STIRAP transfer in ultracold molecules with unresolved excited-state hyperfine splittings and large scattering rates.
Efficient Creation of Ultracold Ground State 6Li40K^{6}\textrm{Li}^{40}\textrm{K}6Li40K Polar Molecules
We report the creation of ultracold ground state 6Li40K^{6}\textrm{Li}^{40}\textrm{K}6Li40K polar molecules with high efficiency. Starting from weakly-bound molecules state, stimulated Raman adiabatic passage (STIRAP) is adopted to coherently transfer the molecules to their singlet ro-vibrational ground state ∣X1Σ+,v=0,J=0>|\textrm{X}^{1}Σ^{+},v=0,J=0>∣X1Σ+,v=0,J=0>. By employing a singlet STIRAP pathway and low-phase-noise narrow-linewidth lasers, we observed a one-way transfer efficiency of 96(4)\,\%. Held in an optical dipole trap, the lifetime of the ground-state molecules is measured to be 5.0(3)\,ms. The large permanent dipole moment of LiK is confirmed by applying a DC electric field on the molecules and performing Stark shift spectroscopy of the ground state. With recent advances in the quantum control of collisions, our work paves the way for exploring quantum many-body physics with strongly-interacting 6Li40K^{6}\textrm{Li}^{40}\textrm{K}6Li40K molecules.
We report the creation of ultracold ground state ^{6}Li^{40}K polar molecules with high efficiency. Starting from weakly bound molecules, stimulated Raman adiabatic passage is adopted to coherently transfer the molecules to their singlet rovibrational ground state |X^{1}Σ^{+},v=0,J=0⟩. By employing a singlet stimulated Raman adiabatic passage pathway and low-phase-noise narrow-linewidth lasers, we observed a one-way transfer efficiency of 96(4)%. Held in an optical dipole trap, the lifetime of the ground state molecules is measured to be 5.0(3) ms. The large permanent dipole moment of LiK is confirmed by applying a dc electric field on the molecules and performing Stark shift spectroscopy of the ground state. With recent advances in the quantum control of collisions, our work paves the way for exploring quantum many-body physics with strongly interacting ^{6}Li^{40}K molecules.
Many experimental platforms for quantum science depend on state control via laser fields. Frequently, however, the control fidelity is limited by optical phase noise. This is exacerbated in stabilized laser systems where high-frequency phase noise is an unavoidable consequence of feedback. Here we implement an optical feedforward technique to suppress laser phase noise in the stimulated Raman adiabatic passage state transfer of ultracold RbCs molecules, across 114 THz, from a weakly bound Feshbach state to the rovibrational ground state. By performing over 100 state transfers on single molecules, we measure a significantly enhanced transfer efficiency of 98.7(1)% limited only by available laser intensity.
One possibility for the creation of ultracold, high phase space density quantum gases of molecules in the rovibronic ground state relies on first associating weakly-bound molecules from quantum-degenerate atomic gases on a Feshbach resonance and then transferring the molecules via several steps of coherent two-photon stimulated Raman adiabatic passage (STIRAP) into the rovibronic ground state. Here, in ultracold samples of Cs2 Feshbach molecules produced out of ultracold samples of Cs atoms, we observe several optical transitions to deeply-bound rovibrational levels of the excited 0(u)+ molecular potentials with high resolution. At least one of these transitions, although rather weak, allows efficient STIRAP transfer into the deeply-bound vibrational level (see text for symbols)v = 73 > of the singlet X1 sigma(g)+ ground state potential, as recently demonstrated (J. G. Danzl, E. Haller, M. Gustavsson, M. J. Mark, R. Hart, N. Bouloufa, O. Dulieu, H. Ritsch, and H.-C. Nägerl, Science, 2008, 321, 1062). From this level, the rovibrational ground state (see text for symbols)v = 0, J = 0 > can be reached with one more transfer step. In total, our results show that coherent ground state transfer for Cs2 is possible using a maximum of two successive two-photon STIRAP processes or one single four-photon STIRAP process.
Ultracold fermionic 23{}^{23}23Na40{}^{40}40K polar molecules are produced in their ground rovibrational state. A multilevel stimulated Raman adiabatic passage (STIRAP) state-transfer process is employed with an intermediate state having an unresolved hyperfine structure, which can be a situation commonly encountered in performing the state transfer.