Precision Spectroscopy of Polarized Molecules in an Ion Trap

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Science  06 Dec 2013:
Vol. 342, Issue 6163, pp. 1220-1222
DOI: 10.1126/science.1243683

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Toward a New Physics

The search for physics beyond the Standard Model is carried out at accelerator facilities such as the Large Hadron Collider but also on a smaller scale in atomic and molecular physics experiments. One of the signatures of this “new physics” would be a nonvanishing electric dipole moment of the electron, but experiments designed to look for it need to distinguish between the signal and many potential artifacts. Loh et al. (p. 1220) introduce a method based on the spectroscopy of polarized molecular ions that avoids some of the sources of systematic error.


Polar molecules are desirable systems for quantum simulations and cold chemistry. Molecular ions are easily trapped, but a bias electric field applied to polarize them tends to accelerate them out of the trap. We present a general solution to this issue by rotating the bias field slowly enough for the molecular polarization axis to follow but rapidly enough for the ions to stay trapped. We demonstrate Ramsey spectroscopy between Stark-Zeeman sublevels in 180Hf19F+ with a coherence time of 100 milliseconds. Frequency shifts arising from well-controlled topological (Berry) phases are used to determine magnetic g factors. The rotating-bias-field technique may enable using trapped polar molecules for precision measurement and quantum information science, including the search for an electron electric dipole moment.

  • * Corresponding author. E-mail: loh{at} (H.L.); ye{at} (J.Y.); cornell{at} (E.A.C.)

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