Quantum Zeno effect

The meaning of the term has since expanded, leading to a more technical definition, in which time evolution can be suppressed not only by measurement: the quantum Zeno effect is the suppression of unitary time evolution in quantum systems provided by a variety of sources: measurement, interactions with the environment, stochastic fields, among other factors.

[3] As an outgrowth of study of the quantum Zeno effect, it has become clear that applying a series of sufficiently strong and fast pulses with appropriate symmetry can also decouple a system from its decohering environment.

[4] The first rigorous and general derivation of the quantum Zeno effect was presented in 1974 by Antonio Degasperis, Luciano Fonda, and Giancarlo Ghirardi,[5] although it had previously been described by Alan Turing.

In the quantum Zeno effect an unstable state seems frozen – to not 'move' – due to a constant series of observations.

However, there is controversy over the interpretation of the effect, sometimes referred to as the "measurement problem" in traversing the interface between microscopic and macroscopic objects.

But the request that the measurement last only a very short time implies that the energy spread of the state in which reduction occurs becomes increasingly large.

An explicit evaluation of these two competing requests shows that it is inappropriate, without taking into account this basic fact, to deal with the actual occurrence and emergence of Zeno's effect.

[10][11][12][13] Unstable quantum systems are predicted to exhibit a short-time deviation from the exponential decay law.

[14][15] This universal phenomenon has led to the prediction that frequent measurements during this nonexponential period could inhibit decay of the system, one form of the quantum Zeno effect.

Subsequently, it was predicted that measurements applied more slowly could also enhance decay rates, a phenomenon known as the quantum anti-Zeno effect.

[22] By its nature, the effect appears only in systems with distinguishable quantum states, and hence is inapplicable to classical phenomena and macroscopic bodies.

The idea is implicit in the early work of John von Neumann on the mathematical foundations of quantum mechanics, and in particular the rule sometimes called the reduction postulate.

One realization refers to the observation of an object (Zeno's arrow, or any quantum particle) as it leaves some region of space.

In order to cover all of these phenomena (including the original effect of suppression of quantum decay), the Zeno effect can be defined as a class of phenomena in which some transition is suppressed by an interaction – one that allows the interpretation of the resulting state in the terms 'transition did not yet happen' and 'transition has already occurred', or 'The proposition that the evolution of a quantum system is halted' if the state of the system is continuously measured by a macroscopic device to check whether the system is still in its initial state.

In 1989, David J. Wineland and his group at NIST[33] observed the quantum Zeno effect for a two-level atomic system that was interrogated during its evolution.

Ultracold sodium atoms were trapped in an accelerating optical lattice, and the loss due to tunneling was measured.

[35] The quantum Zeno effect is used in commercial atomic magnetometers and proposed to be part of birds' magnetic compass sensory mechanism (magnetoreception).

[36] It is still an open question how closely one can approach the limit of an infinite number of interrogations due to the Heisenberg uncertainty involved in shorter measurement times.

It has been shown, however, that measurements performed at a finite frequency can yield arbitrarily strong Zeno effects.

[37] In 2006, Streed et al. at MIT observed the dependence of the Zeno effect on measurement pulse characteristics.