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Paper: Non-destructive state detection for quantum logic spectroscopy of molecular ions

Authors: Fabian Wolf, Yong Wan, Jan C. Heip, Florian Gebert, Chunyan Shi & Piet O. Schmidt

Reference: Nature 530, 457 (2016)

Abstract：

Precision laser spectroscopy1 of cold and trapped molecular ions is a powerful tool in fundamental physics—used, for example, in determining fundamental constants2, testing for their possible variation in the laboratory3,4, and searching for a possible electricdipole moment of the electron5. However, the absence of cycling transitions in molecules poses a challenge for direct laser cooling of the ions6, and for controlling7–11 and detecting their quantum states. Previously used state-detection techniques based on photodissociation12 or chemical reactions13 are destructive and therefore inefficient, restricting the achievable resolution in laser spectroscopy. Here, we experimentally demonstrate nondestructive detection of the quantum state of a single trapped molecular ion through its strong Coulomb coupling to a well controlled, co-trapped atomic ion. An algorithm based on a statedependent
optical dipole force14 changes the internal state of the atom according to the internal state of the molecule. We show that individual quantum states in the molecular ion can be distinguished by the strength of their coupling to the optical dipole force. We also observe quantum jumps (induced by black-body radiation) between rotational states of a single molecular ion. Using the detuning dependence of the state-detection signal, we implement a variant of quantum logic spectroscopy15,16 of a molecular resonance. Our state-detection technique is relevant to a wide range of molecular ions, and could be applied to state-controlled quantum chemistry17 and to spectroscopic investigations of molecules that serve as probes for interstellar clouds18,19.

 

Paper: Spectroscopy Using Quantum Logic

Authors: P. O. Schmidt, T. Rosenband, C. Langer, W. M. Itano, J. C. Bergquist, D. J. Wineland

Reference: Science 309, 749 (2005)

Abstract：

We present a general technique for precision spectroscopy of atoms that lack suitable transitions for efficient laser cooling, internal state preparation, and detection. In our implementation with trapped atomic ions, an auxiliary ‘‘logic’’ ion provides sympathetic laser cooling, state initialization, and detection for a simultaneously trapped ‘‘spectroscopy’’ ion. Detection is achieved by applying a mapping operation to each ion, which results in a coherent transfer of the spectroscopy ion’s internal state onto the logic ion, where it is then measured with high efficiency. Experimental realization, by using 9Beþ as the logic ion and 27Alþ as the spectroscopy ion, indicates the feasibility of applying this technique to make accurate optical clocks based on single ions.