Trapped-Ion State Detection through Coherent Motion

Published

December 9, 2011

Author(s)

Till P. Rosenband, David Hume, Chin-Wen Chou, David R. Leibrandt, Michael J. Thorpe, David J. Wineland

Abstract

Coherent control of trapped atomic ions has led to several recent advances in quantum information processing¹ and precision spectroscopy². A basic requirement for these and other quantum-metrology experiments is the ability to detect the state of an individual ion. Current detection techniques^3–6 are applicable only to relatively simple atomic systems, which precludes precision measurement and control of most atomic and molecular species. Here, we explore a detection strategy based on state-dependent excitation of coherent motion that can be applied to a larger class of ion systems. We couple a “spectroscopy” ion to a “control” ion in the same trap via mutual Coulomb repulsion. For state detection, off-resonant laser excitation induces harmonic motion of the two ions with an amplitude that depends on the state of the spectroscopy ion. We implement two methods of measuring this motion with the control ion. In the first, the ion velocity modulates fluorescence from the control ion, which is observed via time-resolved photon counting^{7, 8}. We demonstrate this technique by detecting the “clock” states in ²⁷Al⁺ (¹S₀ or ³P₀) using ²⁵Mg⁺ as a control ion. In the second method, coherent motion near the ground state switches the atomic state of the control ion via resolved sideband transitions^{4, 9}. This approach provides higher sensitivity to motion at small amplitudes and is demonstrated by performing projective measurements of several Zeeman sublevels in the ²⁷Al⁺¹S₀ ground state. As opposed to previous methods^{5, 6}, state detection can be performed without spontaneous emission, thereby avoiding optical pumping on the spectroscopy ion. Applications ranging from simplified detection in portable optical clocks to precision molecular spectroscopy¹⁰ could benefit from these techniques.

Citation

Physical Review Letters

Volume

107

Pub Type

Journals

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Keywords

Aluminum ion, precision spectroscopy, quantum measurement

Citation

Rosenband, T. , Hume, D. , Chou, C. , Leibrandt, D. , Thorpe, M. and Wineland, D. (2011), Trapped-Ion State Detection through Coherent Motion, Physical Review Letters, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=908888 (Accessed October 13, 2025)