Quantum Zeno Effect

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.