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Most experiments that claim to show the quantum Zeno paradox fall short, study says

Posted June 5, 2013

By their very nature, unstable particles will eventually decay, some faster than others. But according to the quantum Zeno paradox (QZP), an unstable particle that is observed continuously has been said to never decay. Though counterintuitive, this effect has been claimed to show up experimentally in numerous ways. Now in a new study, physicist Peter Toschek at the University of Hamburg in Hamburg, Germany, has argued that most of these experiments do not provide sufficient evidence of the QZP. By identifying the sufficient conditions necessary for proving the QZP, he confirms the validity of the paradox while probing deeper into its origins.

Toschek’s paper, “The quantum Zeno paradox: A matter of information,” is published in a recent issue of EPL.

“The QZP holds for all unstable quantum systems whose transition (or ‘decay’) is electromagnetically induced,” Toschek told
As he explained, most experiments that have claimed to prove the QZP (or its manifestation, the quantum Zeno effect) rely on measurements of “expectation values,” which are group averages that don’t provide information on individual objects, in particular on their survival times. Instead, he explains that the outcomes of quantum measurements should represent “eigenvalues,” which do provide information on individual quantum objects. He explains that the survival time of a particle can be derived from uninterrupted sequences of the detected eigenvalue of the initial, undecayed state of the quantum system (particle plus radiation field), provided an individual quantum object is addressed.

For example, in some experiments that use light-irradiated atoms to demonstrate the QZP, a continuous measurement has been approximated by a series of short light pulses irradiating a group of 5,000 unstable atoms. Then the mean decay rate of the atoms has been measured. The results of these experiments show that the mean decay rate decreases when the pulse repetition rate increases, and this finding has been interpreted as evidence of the QZP.

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