9,531 research outputs found
Exponential Decay and Fermi's Golden Rule from an Uncontrolled Quantum Zeno Effect
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
Recommended from our members
Asymmetric Time Evolution And Indistinguishable Events
With a time asymmetric theory, in which quantum mechanical time evolution is given by a semigroup of operators rather than by a group, the states of open systems are represented by density operators exhibiting a branching behavior. To treat the indistinguishably of the members of experimental ensembles, we hypothesize that environmental interference occurs during events that are themselves fundamentally indistinguishable.Center for Complex Quantum System
Dynamics of hard-sphere suspension using Dynamic Light Scattering and X-Ray Photon Correlation Spectroscopy: dynamics and scaling of the Intermediate Scattering Function
Intermediate Scattering Functions (ISF's) are measured for colloidal hard
sphere systems using both Dynamic Light Scattering (DLS) and X-ray Photon
Correlation Spectroscopy (XPCS). We compare the techniques, and discuss the
advantages and disadvantages of each. Both techniques agree in the overlapping
range of scattering vectors. We investigate the scaling behaviour found by
Segre and Pusey [1] but challenged by Lurio et al. [2]. We observe a scaling
behaviour over several decades in time but not in the long time regime.
Moreover, we do not observe long time diffusive regimes at scattering vectors
away from the peak of the structure factor and so question the existence of a
long time diffusion coefficients at these scattering vectors.Comment: 21 pages, 11 figure
An Experimental Investigation of Flow Conditions in the Vicinity of an NACA D(sub S)-type Cowling
Data are presented of the flow conditions in the vicinity of an NACA D sub S -type cowling. Tests were made of a 1/2 scale-nacelle model at inlet-velocity ratios ranging from 0.23 to 1.02 and angles of attack from 6 deg to 10 deg. The velocity and direction of flow in the vertical plane of symmetry of the cowling were determined from orifices and tufts installed on a board aligned with the flow. Diagrams showing velocity ratio contours and lines of constant flow angles are given
Numerical Linked-Cluster Algorithms. I. Spin systems on square, triangular, and kagome lattices
We discuss recently introduced numerical linked-cluster (NLC) algorithms that
allow one to obtain temperature-dependent properties of quantum lattice models,
in the thermodynamic limit, from exact diagonalization of finite clusters. We
present studies of thermodynamic observables for spin models on square,
triangular, and kagome lattices. Results for several choices of clusters and
extrapolations methods, that accelerate the convergence of NLC, are presented.
We also include a comparison of NLC results with those obtained from exact
analytical expressions (where available), high-temperature expansions (HTE),
exact diagonalization (ED) of finite periodic systems, and quantum Monte Carlo
simulations.For many models and properties NLC results are substantially more
accurate than HTE and ED.Comment: 14 pages, 16 figures, as publishe
- …