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Physical Review A

Observing quantum gases in real time: Single-atom detection on a chip

Andreas Günther, H. Bender, Alexander Stibor, József Fortágh, Claus Zimmermann

Published Jul 29, 2009• 15 citations
Publisher

Abstract

Single magnetically trapped $^{87}\text{R}\text{b}$ atoms on an atom chip are detected with $67\ifmmode\pm\else\textpm\fi{}12\text{ }%$ efficiency by three photon ionization and subsequent ion detection in a channel electron multiplier. State selective detection of single atoms and high-resolution optical spectroscopy on trapped atom clouds are demonstrated. The temperature and particle density of a trapped atomic gas is monitored in situ and in real time with negligible atom loss due to ionization below 5%.

DOI
10.1103/physreva.80.011604

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We experimentally demonstrate optical spectroscopy of magnetically trapped atoms on an atom chip. High resolution optical spectra of individual trapped clouds are recorded within a few hundred milliseconds. Detection sensitivities close to the single atom level are obtained by photoionization of the excited atoms and subsequent ion detection with a channel electron multiplier. Temperature and decay rates of the trapped atomic cloud can be monitored in real time for several seconds with only little detection losses. The spectrometer can be used for investigations of ultracold atomic mixtures and for the development of interferometric quantum sensors on atom chips.
We report on photoionization of ultracold magnetically trapped Rb atoms on an atom chip. The atoms are trapped at $5\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$ in a strongly anisotropic trap. Through a hole in the chip with a diameter of $150\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$, two laser beams are focused onto a fraction of the atomic cloud. A first laser beam with a wavelength of 778nm778\phantom{\rule{0.3em}{0ex}}\mathrm{nm}778nm excites the atoms via a two-photon transition to the 5D5D5D level. With a fiber laser at 1080nm1080\phantom{\rule{0.3em}{0ex}}\mathrm{nm}1080nm the excited atoms are photoionized. Ionization leads to depletion of the atomic density distribution observed by absorption imaging. The resonant ionization spectrum is reported. The setup used in this experiment is suitable not only to investigate mixtures of Bose-Einstein condensates and ions but also for single-atom detection on an atom chip.
We propose a new technique for the detection of single atoms in ultracold quantum gases. The technique is based on scanning electron microscopy and employs the electron impact ionization of trapped atoms with a focused electron probe. Subsequent detection of the resulting ions allows for the reconstruction of the atom's position. This technique is expected to achieve a much better spatial resolution compared to any optical detection method. In combination with the sensitivity to single atoms, it makes new in situ measurements of atomic correlations possible. The detection principle is also well suited for the addressing of individual sites in optical lattices.
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We experimentally demonstrate a detection scheme suitable for state analysis of single optically trapped atoms in less than 1 μs with an overall detection efficiency η exceeding 98%. The method is based on hyperfine-state-selective photoionization and subsequent registration of the correlated photoion-electron pairs by coincidence counting via two opposing channel electron multipliers. The scheme enables the calibration of absolute detection efficiencies and might be a key ingredient for future quantum information applications or precision spectroscopy of ultracold atoms.