= Beryllium-ion quantum Zeno experiment of 1990
In 1990, <Wayne M. Itano>, <Daniel J. Heinzen>, <J. J. Bollinger> and <David J. Wineland> reported inhibited transitions in about 5,000 $^{9}\mathrm{Be}^{+}$ <ions> held in a cylindrical <Penning trap>. Trapped <magnesium> <ions>, illuminated at 280 nm, kept the <beryllium> <ions> cold. A 320.7 MHz <radio frequency> field coupled two ground-state <hyperfine structure> sublevels during a 256 ms pulse adjusted for complete transfer. Up to 64 intervening 313 nm pulses addressed an optical transition from level 1: scattering distinguished it from level 2. Afterward, calibrated <fluorescence> counts over 100 ms measured the final <quantum state population>. This ensemble readout did not select <ions> that remained in the initial <quantum state> at every check; departure followed by return also contributes. The apparatus made inhibition by repeated <quantum measurements> experimentally accessible.<Quantum Zeno effect by Wayne M. Itano, Daniel J. Heinzen, John J. Bollinger and David J. Wineland>[§III, p. 2297 and Fig. 2: apparatus, levels, pulses and fluorescence calibration; §V, p. 2299: ensemble measurement. Final-population versus full-record distinction follows from this readout protocol.]{ref}
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