Sudarshan: Seven Science Quests
Quantum Zeno Effect
Instability and Decay
In a closed quantum system an "unstable particle" which seems to decay, is a metastable state which evolves in a probability conserving manner; some of the probability goes with the fraction that has "decayed." A systematic analysis of the decay amplitude in terms of the spectral density of the decaying state determines the evolution.

Classical law of radioactivity has a strict exponential decay, but in quantum theory this is only approximately so; for very short times the decay probability increases as the square of the time interval; so a metastable quantum system which is frequently observed (and reset) would remain essentially unchanged. This is the Quantum Zeno effect discovered by Misra and Sudarshan (J. Math. Phys.).

Chiu and Sudarshan studied the rigorous theory of decay and exhibited the short time Zeno regime, and the long term Khalfin regime in addition to the exponential regime. With Gorini and Chiu, Sudarshan developed a formalism of analytic continuation of the vector space of quantum mechanics; he developed it fully into Quantum Mechanics in Dual Spaces.

Valanju, Chiu, and Sudarshan analyzed the data on multiple meson production in hadronic collisions with complex nuclei in cosmic rays and found the first evidence in published data for the Zeno effect manifested in the successive encounters of incoming cosmic rays with successive nucleons.

A laboratory test using atomic physics was carried out by Itano, Heinzen, and collaborators in NIST, Colorado, who “interrogated” the atom to see if it has decayed by shining light of a different frequency which would be excited only if the atom decayed. A follow up test was carried out by Raizen and collaborators in UT-Austin. All these verified the Quantum Zeno Effect.

The study on the Quantum Zeno Effect in a system with constraints was carried out by Sudarshan, Pascazio, and collaborators. They were able to show that the continuous action of the constraints is to restrict the motion of the domain of phase space allowed.

See more detailed REVIEW and REFERENCES below.
Schedule of symposium talks for Quantum Zeno Effect.
Next topic overview: VI. Theory of Tachyons


The Zeno's Paradox in Quantum Theory; with B. Misra, J. Math Phys. 18(4) 756 (1977).

Time Evolution of Unstable Quantum States and a Resolution of Zeno's Paradox; with C. B. Chiu and B. Misra, Phys. Rev. D 16, 520 (1977).

Decaying States as Complex Energy Eigen Vectors in Generalised Quantum Mechanics; with C. B. Chiu and V. Gorini, Phys. Rev. D18, 2914 (1978).

Spatio-temporal Development of Hadron-Nucleus Collisions; with C. B. Chiu and P. Valanju, Phys. Rev. D 21, 1304 (1980).

The Time Scale for Quantum Zeno Paradox and Proton Decay; with B. Misra and C. B. Chiu, Phys. Lett. B 117, 34 (1982)

Natural Law, Proceedings of 1983 Theoretical Physics Meeting at Amalfi (May 6-7, 1983), Dell'Universita Degli Studi Di Salerno, Italy (1984).

Decay and Evolution of the Neutral Kaon; with C. B. Chiu, Phys. Rev. D42, 3712 (1990).

Unstable Systems in Generalised Quantum Theory, with Charles B Chiu and G. Bhamathi, Advances in Chemical Physics XCIX, John Wiley & Sons, Inc. (1997), pp.121-210.

Quantum Zeno Dynamics; with P. Facchi, V. Gorini, G. Marmo, S. Pascazio, Phys. Lett. A 275, 12 (2000).

Zeno Dynamics with Constraints; with P. Facchi, G. Marmo, S. Pascazio and A. Scardicchio, J. Optics B: Quantum Optics 6, S492 (2004).

REVIEW: Quantum Zeno Effect; Instability and Decay

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Next topic overview: VI. Theory of Tachyons


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Sudarshan Symposium, Nov. 5-7, 2006
Curriculum Vitae
Seven Science Quests
V-A: Universal Theory
of Weak Interaction
Spin Statistics
Quantum Optical Coherence:
Sudarshan Representation
Quantum Zeno Effect
Theory of Tachyons
Quantum Mechanics
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