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We may infer a transition | n 〉 → | m 〉 between energy eigenstates of an open quantum system by observing the emission of a photon of Bohr frequency ω m n = (E n − E m) / ℏ. In addition to the "collapses" to the state | m 〉 , the measurement must also have brought into existence the pre-measurement state | n 〉. As quantum trajectories are based on past observations, the condition state will jump to | m 〉 , but the state | n 〉 does not feature in any essential way. We resolve this paradox by looking at quantum smoothing and derive the time-symmetric model for quantum jumps. [ABSTRACT FROM AUTHOR]

The apparent dichotomy between quantum jumps on the one hand, and continuous time evolution according to wave equations on the other hand, provided a challenge to Bohr's proposal of quantum jumps in atoms. Furthermore, Schrödinger's time-dependent equation also seemed to require a modification of the explanation for the origin of line spectra due to the apparent possibility of superpositions of energy eigenstates for different energy levels. Indeed, Schrödinger himself proposed a quantum beat mechanism for the generation of discrete line spectra from superpositions of eigenstates with different energies. However, these issues between old quantum theory and Schrödinger's wave mechanics were correctly resolved only after the development and full implementation of photon quantization. The second quantized scattering matrix formalism reconciles quantum jumps with continuous time evolution through the identification of quantum jumps with transitions between different sectors of Fock space. The continuous evolution of quantum states is then recognized as a sum over continually evolving jump amplitudes between different sectors in Fock space. In today's terminology, this suggests that linear combinations of scattering matrix elements are epistemic sums over ontic states. Insights from the resolution of the dichotomy between quantum jumps and continuous time evolution therefore hold important lessons for modern research both on interpretations of quantum mechanics and on the foundations of quantum computing. They demonstrate that discussions of interpretations of quantum theory necessarily need to take into account field quantization. They also demonstrate the limitations of the role of wave equations in quantum theory, and caution us that superpositions of quantum states for the formation of qubits may be more limited than usually expected. [ABSTRACT FROM AUTHOR]

The observation of intermittent fluorescence of a single atomic ion, a phenomenon better known as ‘macroscopic quantum jumps,’ was an important early scientific application of the three-dimensional rf quadrupole (Paul) trap. The prediction of the phenomenon by Cook and Kimble grew out of a proposal by Dehmelt for a sensitive optical double-resonance technique, called ‘electron shelving.’ The existence of the quantum jumps was viewed with skepticism by some in the quantum optics community, perhaps due to the failure of some conventional calculations, for example the solutions to the optical Bloch equations, to predict them. Quantum jumps were observed nearly simultaneously by three different experimental groups, all with single, isolated ions in Paul traps. Some slightly earlier observations of excessive fluctuations in the laser-induced fluorescence of a single Hg + ion by a group at the National Institute of Standards and Technology, viewed in retrospect, were due to quantum jumps. Similarly, sudden changes in the resonance fluorescence of trapped Ba + ions observed by a group at the University of Hamburg were due to quantum jumps, although this was not understood at first. This shows how discoveries can be missed if unanticipated observations are ignored rather than investigated. A fourth experiment, performed not with a single, trapped ion, but with neutral atoms transiently observed in an atomic beam, and published at about the same time as the other experiments, has been almost totally neglected. [ABSTRACT FROM AUTHOR]

We investigate the relevance of dynamic quantum coherence in the energy transfer efficiency of molecular aggregates. We derive the time evolution of the density matrix for an open quantum system excited by light or by a neighboring antenna. Unlike in the classical case, the quantum description does not allow for a formal decomposition of the dynamics into sudden jumps in an observable quantity - an expectation value. Rather, there is a natural finite time-scale associated with the excitation process. We propose a simple experiment to test the influence of this time scale on the yield of photosynthesis. We demonstrate, using typical parameters of the Fenna-Matthews-Olson (FMO) complex and a typical energy transfer rate from the chlorosome baseplate, that dynamic coherences are averaged out in the complex even when the FMO model is completely free of all dissipation and dephasing. [ABSTRACT FROM AUTHOR]

Abstract: We study numerically the evolution of the cavity electromagnetic field mode which is in resonance with an oscillating boundary (dynamical Casimir effect), taking into account the interaction between the field and a two-level atom, that may or not be continuously monitored by a coupled atomic excitation detector. We analyze the behavior of the field statistics and the quadrature squeezing properties in different regimes, demonstrating that at the expense of decreasing the number of produced photons and the degree of squeezing, one can create qualitatively new types of cavity field states. [Copyright &y& Elsevier]

Abstract: It is shown that piecewise deterministic dissipative quantum dynamics in a vector space withindefinite metric can lead to well defined, positive probabilities. The case of quantum jumps on the Poincar''e disk is studied in detail including results of numerical simulations of quantum fractals. [Copyright &y& Elsevier]

It is argued that the conventional formulation of quantum mechanics is inadequate: the usual interpretation of the mathematical formalism in terms of the results of measurements cannot be applied to situations in which discontinuous transitions (“quantum jumps”) are observed as they happen, since nothing that can be called a measurement happens at the moment of observation. Attempts to force such observations into the standard mould lead to absurd results: “a watched pot never boils”. Experiments show both that this result is correct when the experiment does indeed consist of a series of measurements, and that it is not when the experiment consists of a period of observation: quantum jumps do happen. The possibilities for improving the formulation by incorporating transitions in the basic postulates are reviewed, and a satisfactory postulate is obtained by modifying a suggestion of Bell''s. This requires a distinction between the external description of the whole of a physical system and internal descriptions which are themselves physical events in the system. It is shown that this gives correct results for simple unstable systems and for the quantum-jump experiments. [Copyright &y& Elsevier]