We modify the theory of the Quantum Zeno Effect to make it consistent with
the postulates of quantum mechanics. This modification allows one, throughout a
sequence of observations of an excited system, to address the nature of the
observable and thereby to distinguish survival from non-decay, which is
necessary whenever excited states are degenerate. As a consequence, one can
determine which types of measurements can possibly inhibit the exponential
decay of the system. We find that continuous monitoring taken as the limit of a
sequence of ideal measurements will only inhibit decay in special cases, such
as in well-controlled experiments. Uncontrolled monitoring of an unstable
system, however, can cause exponentially decreasing non-decay probability at
all times. Furthermore, calculating the decay rate for a general sequence of
observations leads to a straightforward derivation of Fermi's Golden Rule, that
avoids many of the conceptual difficulties normally encountered. When multiple
decay channels are available, the derivation reveals how the total decay rate
naturally partitions into a sum of the decay rates for the various channels, in
agreement with observations. Continuous and unavoidable monitoring of an
excited system by an uncontrolled environment may therefore be a mechanism by
which to explain the exponential decay law.Comment: 18 pages, no figures. Added references to theory and experiments,
distinguished survival from non-decay, and added derivation for multiple
decay channel
