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arXiv:1412.1720 · Physical Review A

Zeeman-splitting-assisted quantum-logic spectroscopy of trapped ions

Huanqian Loh, Shiqian Ding, Roland Hablützel, Gleb Maslennikov, Dzmitry Matsukevich

Published Dec 29, 2014• 4 citations
arXivHTMLPDF

Abstract

We present a quantum logic scheme to detect atomic and molecular ions in different states of angular momentum based on their magnetic $g$ factors. The state-dependent magnetic $g$ factors mean that electronic, rotational, or hyperfine states may be distinguished by their Zeeman splittings in a given magnetic field. Driving motional sidebands of a chosen Zeeman splitting enables reading out the corresponding state of angular momentum with an auxiliary logic ion. As a proof-of-principle demonstration, we show that we can detect the ground electronic state of a $^{174}\mathrm{Yb}^{+}$ ion using $^{171}\mathrm{Yb}^{+}$ as the logic ion. Further, we can distinguish between the $^{174}\mathrm{Yb}^{+}$ ion being in its ground electronic state versus the metastable ${}^{2}{D}_{3/2}$ state. We discuss the suitability of this scheme for the detection of rotational states in molecular ions.

DOI
10.1103/physreva.90.061402

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We present a quantum logic scheme to detect atomic and molecular ions in different states of angular momentum based on their magnetic ggg factors. The state-dependent magnetic ggg factors mean that electronic, rotational, or hyperfine states may be distinguished by their Zeeman splittings in a given magnetic field. Driving motional sidebands of a chosen Zeeman splitting enables reading out the corresponding state of angular momentum with an auxiliary logic ion. As a proof-of-principle demonstration, we show that we can detect the ground electronic state of a 174Yb+^{174}\mathrm{Yb}^{+}174Yb+ ion using 171Yb+^{171}\mathrm{Yb}^{+}171Yb+ as the logic ion. Further, we can distinguish between the 174Yb+^{174}\mathrm{Yb}^{+}174Yb+ ion being in its ground electronic state versus the metastable 2D3/2{}^{2}{D}_{3/2}2D3/2​ state. We discuss the suitability of this scheme for the detection of rotational states in molecular ions.
High-precision spectroscopy of atomic and molecular ions is an established platform for investigating fundamental aspects of physics. An important step in this direction was the development of quantum logic techniques that enable the spectroscopy of ions whose electronic structure does not allow direct laser cooling. Particularly challenging in this context is the investigation of atomic and molecular systems with many long-lived metastable states. The preparation of a pure quantum state for spectroscopy purposes often requires the prior detection of these long-lived states. For molecular ions, schemes for the detection of their rotational degree of freedom have already been developed in the past. However, quantum logic control of transition metals, in which the many metastable states result from several valence electrons, remained elusive. In this cumulative thesis, the first experimental implementation of a quantum logic assisted scheme for internal state detection of atomic systems as complex as a titanium ion is presented. Furthermore, a scheme based on simultaneous co-magnetometry for measuring the Landé g factor was developed and demonstrated for different fine structure states in 48Ti+. The presented method allows the suppression of systematic uncertainties arising from varying magnetic fields at the position of the ion and can be transferred to a variety of other species. Crucial for quantum logic based applications is the reliable preparation of a two-ion crystal consisting of one spectroscopy ion and one logic ion. A third aspect of this work is the deterministic preparation of such a two-ion crystal. The method based on fluorescence imaging is associated with a significantly reduced calibration effort compared to other schemes and can be easily transferred to other combinations of spectroscopy and logic ions. The quantum logic control capabilities demonstrated in this work are applicable to a wide range of other atoms with complex electronic structures as well as to molecular ions. The investigation of transition metals can provide important reference data for the calibration of absorption spectra from astrophysical objects. Molecular ions have applications in the search for a possible variation of fundamental constants or the measurement of energy shifts caused by an electron electric dipole moment, both representing promising approaches to test the standard model of particle physics.
We demonstrate a general method for state detection of trapped ions that can be applied to a large class of atomic and molecular species. We couple a spectroscopy ion (27Al+) to a control ion (25Mg+) in the same trap and perform state detection through off-resonant laser excitation of the spectroscopy ion that induces coherent motion. The motional amplitude, dependent on the spectroscopy ion state, is measured either by time-resolved photon counting or by resolved sideband excitations on the control ion. The first method provides a simplified way to distinguish clock states in 27Al+, which avoids ground-state cooling and sideband transitions. The second method reduces spontaneous emission and optical pumping on the spectroscopy ion, which we demonstrate by nondestructively distinguishing Zeeman sublevels in the (1)S0 ground state of 27Al+.
We propose a fast and nondestructive spectroscopic method for single molecular ions that implements quantum logic schemes between an atomic ion and the molecular ion of interest. Our proposal relies on a hybrid coherent manipulation of the two-ion system, using optical or magnetic forces depending on the types of molecular levels to be addressed (e.g., Zeeman, rotational, vibrational or electronic degrees of freedom). The method is especially suited for the nondestructive precision spectroscopy of single molecular ions and sets a starting point for new hybrid quantum computation schemes that combine molecular and atomic ions, covering the measurement and entangling steps.
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Abstract Quantum-logic spectroscopy has become an increasingly important tool for the state detection and readout of trapped atomic and molecular ions which do not possess easily accessible closed-cycling optical transitions. In this approach, the internal state of the target ion is mapped onto a co-trapped auxiliary ion. This mapping is typically mediated by normal modes of motion of the two-ion Coulomb crystal in the trap. The present study investigates the role of spectator modes not directly involved in a measurement protocol relying on a state-dependent optical-dipole force. We identify a Debye-Waller-type effect that modifies the response of the two-ion string to the force. We show that cooling the spectator modes of the string allows for the detection of the rovibrational ground state of an N2+{{{{\rm{N}}}}}_{2}^{+}N2+​ N 2 + molecular ion with a computed statistical fidelity exceeding 99.99%, improving on previous experiments by more than an order of magnitude while also halving the experimental time. This enhanced sensitivity enables the simultaneous identification of multiple rotational states with markedly weaker signals.
Recently developed techniques for quantum computation using trapped ions allow precise coherent control of the internal and external states of single atoms. Here we report how these techniques can be employed to perform precision spectroscopy of atomic and molecular ions that lack accessible transitions for laser cooling and detection. Furthermore, we discuss how quantum logic can be used to laser‐cool molecules to near their rotational and vibrational ground state by avoiding detrimental spontaneous emission of photons from the molecule.