The observation of decay

David C. MacPherson, R. C. Swanson, John L. Carlsten

Although \ensuremath{\pi} phase shifts in an input Stokes beam are known to initiate soliton formation in a Raman amplifier, the observed shot-to-shot amplitude fluctuations have gone unexplained. It has been suggested that recently observed frequency shifts caused by quantum fluctuations may be related to the observed soliton decay. We show that frqequency shifts of the magnitude observed from these quantum fluctuations lead to soliton decay, and thus, are indeed the probable cause of observed soliton decay.

E. Torrontegui, Juan Gonzalo Muga, Joan Martorell +1 more

We study the elusive transition from exponential to postexponential (algebraic) decay of the probability density of a quantum particle emitted by an exponentially decaying source in one dimension. The main finding is that the probability density at the transition time, and thus its observability, increases with the distance of the detector from the source up to a critical distance beyond which exponential decay is no longer observed. Solvable models provide explicit expressions for the dependence of the transition on resonance and observational parameters, facilitating the choice of optimal conditions.

Peter William Bryant

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.