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Acceleration of quantum decay processes by frequent observations


In theory, the decay of any unstable quantum state can be inhibited by sufficiently frequent measurements—the quantum Zeno effect1,2,3,4,5,6,7,8,9,10. Although this prediction has been tested only for transitions between two coupled, essentially stable states5,6,7,8, the quantum Zeno effect is thought to be a general feature of quantum mechanics, applicable to radioactive3 or radiative decay processes6,9. This generality arises from the assumption that, in principle, successive observations can be made at time intervals too short for the system to change appreciably1,2,3,4. Here we show not only that the quantum Zeno effect is fundamentally unattainable in radiative or radioactive decay (because the required measurement rates would cause the system to disintegrate), but also that these processes may be accelerated by frequent measurements. We find that the modification of the decay process is determined by the energy spread incurred by the measurements (as a result of the time–energy uncertainty relation), and the distribution of states to which the decaying state is coupled. Whereas the inhibitory quantum Zeno effect may be feasible in a limited class of systems, the opposite effect—accelerated decay—appears to be much more ubiquitous.

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Figure 1: The QZE characteristics and a frequent-measurement scheme.
Figure 2: The AZE characteristics and a frequent-measurement scheme for two-level systems.


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G.K. is the G. Dunne Professor of Chemical Physics, A.K. is supported by the Israel Ministry of Absorption. This work was supported by the ISF, Minerva and EU (TMR).

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Correspondence to G. Kurizki.

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Kofman, A., Kurizki, G. Acceleration of quantum decay processes by frequent observations. Nature 405, 546–550 (2000).

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