Quantum anti-Zeno effect

M. Lewenstein, K. Rzazewski, Quantum anti-Zeno effect, Phys. Rev. A 61 (2000) 022105. 

Decoherence in condensed phase typically slows down chemical reactions as has been exemplified by the non-radiative relaxation of solvated electrons [3,18,67]. In the case of an electron in water the difference in the rates of quantum decoherence induced in the electron subsystem by water and deuterated water explains the absence of a solvent isotope effect on the relaxation rate [18,67]. In rare instances, decoherence can enhance chemical reactivity. The SMF approach has been used to provide evidence for acceleration of a chemical reaction in a condensed phase due to the quantum anti-Zeno effect [55]. The mechanism indicates that the anti-Zeno effect involves both delocalization of the quantum dynamics and a feedback loop by coupling to the solvent. Believed to be the first example of the quantum anti-Zeno effect in chemistry, the observed phenomenon suggests the possibility of quantum control of chemical reactivity by choice of solvent. 

Figure 4.4 Frequency-domain representation of the dynamically controlled decoherence rate in various limits (Section 4.4). (a) Golden-Rule limit, (b) Anti-Zeno effect (AZE) limit (c) Quantum Zeno effect (QZE) limit. Here, F,( ) and G(w) are the modulation and bath spectra, respectively and F are the interval of change and width of G( ), respectively and is the interruption rate.

The prevailing view until recently has been that successive frequent measurements (interruptions of the evolution) known as the quantum Zeno effect must slow down the decay of any unstable system. A few years ago, Kofman et al. [Kofman 2000 Kofman 2001 (a)] showed that, in fact, the opposite is commonly true for decay into open-space continua the anti-Zeno effect (AZE), i.e., decay acceleration by frequent measurements1, is far more ubiquitous than the QZE [Milonni 2000 Seife 2000]. How can this conclusion be understood and what was missing in standard treatments that claimed the QZE universality The last paper of this part, by G. Kurizki et al. shows that ... 

The phenomenon known as the quantum Zeno effect takes place in a system which is subject to frequent measurements projecting it onto its (necessarily known) initial state if the time interval between two projections is small enough the evolution of the system is nearly "frozen". This effect, and its inverse (the anti-Zeno effect), have been widely investigated theoretically [Khalhn 1957-58 Winter 1961 Misra 1977 Fonda 1978 Kofman 1996 Kof-man 2000 Lewenstein 2000 Kofman 2001 (a) Schmidt 2003 / 2004] as well as experimentally [Cook 1988 Itano 1990 Wilkinson 1997 Fischer 2001], Generalizations have been proposed which employ incomplete measurements [Facchi 2002] in this setting, the Hilbert space is split into "Zeno subspaces" (degenerate multidimensional eigenspaces of the measured observable), and the state vector of the system is compelled by frequent measurements of the physical observable to remain in its initial Zeno subspace. The dynamics of the system in the Zeno subspaces has also been studied in different specific situations [Facchi 2001 (b)]. 

ZENO AND ANTI-ZENO EFFECTS IN DRIVEN JOSEPHSON JUNCTIONS CONTROL OF MACROSCOPIC QUANTUM TUNNELING... 

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