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arXiv:physics/0003085 · Europhysics Letters (EPL)

Search for correlation effects in linear chains of trapped Ca + ions

C. J. S. Donald, D. M Lucas, P. A Barton, M. J McDonnell, J.-P. Stacey, D. Stevens, Derek N. Stacey, Andrew M. Steane

Published Aug 15, 2000• 16 citations

Abstract

We report a precise search for correlation effects in linear chains of 2 and 3 trapped Ca + ions. Unexplained correlations in photon emission times within a linear chain of trapped ions have been reported, which, if genuine, cast doubt on the potential of an ion trap to realize quantum information processing. We observe quantum jumps from the metastable 3 d 2 D 5/2 level for several hours, searching for correlations between the decay times of the different ions. We find no evidence for correlations: the number of quantum jumps with separations of less than 10 ms is consistent with statistics to within errors of 0.05%; the lifetime of the metastable level derived from the data is consistent with that derived from independent single-ion data at the level of the experimental errors (1%); and no rank correlations between the decay times were found with sensitivity to rank correlation coefficients at the level of | R | = 0.024.

DOI: 10.1209/epl/i2000-00506-9

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In a fundamental test of quantum mechanics, we have observed

228 000

quantum jumps of a single trapped and laser cooled

^{88}\mathrm{Sr}^{+}

ion. This represents a statistical increase of two orders of magnitude over previous similar analyses of quantum jumps. Compared to other searches for nonrandomness in quantum-mechanical processes, using quantum jumps simplifies the interpretation of data by eliminated multiparticle effects and providing near-unit detection efficiency of transitions. We measure the fractional reduction in the entropy of information to be $<6.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ when the value of any interval between quantum jumps is known. We also find that the number of runs of successively increasing or decreasing interval times agrees with the theoretically expected values. Furthermore, we analyze

238 000

quantum jumps from two simultaneously confined ions and find that the number of apparently coincidental transitions is as expected. Finally, we observe 8400 spontaneous decays of two simultaneously trapped ions and find that the number of apparently coincidental decays from the metastable state agrees with the expected value. We find no evidence for short- or long-term correlations in the intervals of the quantum jumps or in the decay of the quantum states, in agreement with quantum theory.