Showing papers on "Open quantum system published in 1971"
TL;DR: In this paper, the formalism developed in previous papers is simplified and generalized to systems with superselection rules, which describes a rather general class of linear mappings of states (density matrices).
745 citations
TL;DR: In this paper, the operator solutions of the Schwinger model are given in several gauges and the correct interpretation for the covariant solution with indefinite metric is discussed, and a class of noncovariant gauges, particularly well suited to the analysis of the gauge-invariant algebra is obtained.
480 citations
TL;DR: The classical motion of a particle on a surface is simulated in quantum mechanics by forcing the particle to move between two parallel surfaces with distance d. In the limit d → 0 one obtains an equation which differs from the equation proposed originally by Schrodinger by an additional potential depending on the curvature of the surface as discussed by the authors.
320 citations
TL;DR: In this paper, a theory to describe the scattering of energetic electrons or photons off an external field is developed, which proves to be a realization of Feymnan's "parton" ideas.
Abstract: Using a formulation of quantum electrodynamics in the infinite-momentum frame, we develop a theory to describe the scattering of energetic electrons or photons off an external field. A physical picture emerges which proves to be a realization of Feymnan's "parton" ideas. In this picture the incoming electron is composed of bare constituents (the quanta of the Schrodinger fields) which, at high laboratory energies, interact slowly with one another. Each bare constitutent is scattered from the external field in a simple way and then the constituents again interact among themselves to form the final state. This formalism is applied to elastic electron and photon scattering, bremsstrahlung and pair production, and deep-inelastic electro-production of lepton pairs, and the results of Cheng and Wu and others are recovered in a simple way. In these applications, perturbation theory is used to construct the wave functions of the constituents in the initial and final states.
250 citations
149 citations
95 citations
TL;DR: In this article, a method for extracting from data the quantum theoretical state representation belonging to any reproducible empirical scheme for preparing a physical system, provided only that at least one observable has its possible values limited to a finite set.
Abstract: This paper develops a method for extracting from data the quantum theoretical state representation belonging to any reproducible empirical scheme for preparing a physical system, provided only that at least one observable has its possible values limited to a finite set. In Part I, we formulate a general systematic procedure, based on the concept of irreducible tensor operators, for the selection of sets of observables sufficiently large to permit the unambiguous determination of an unknown quantum state.
61 citations
01 Jan 1971
45 citations
TL;DR: In this paper, a bound electron with external radiation fields of finite intensity is treated with the standard quantum-electrodynamical (QED) formalism of Feynman and Dyson and the Green's function for the equation so obtained enables us to compute the induced transition probabilities for various systems of interest.
Abstract: The interaction of a bound electron with external radiation fields of finite intensity is treated with the standard quantum-electrodynamical (QED) formalism of Feynman and Dyson. We first construct an equation for a bound electron in finite-intensity radiation fields, such as those encountered in early molecular-beam experiments and in recent masers and lasers. The Green's function for the equation so obtained enables us to compute the induced transition probabilities for various systems of interest. In this paper, we carry out the calculations on the two-level and three-level systems explicitly, where we find that, to order ${e}^{4}$, the QED method based on forward scattering and the semiclassical treatment differ. As we consider only the interaction of electrons with low-energy photons, we may ignore the virtual photon processes, in accordance with the low-energy theorem. As a result, this treatment contains only finite calculations. We demonstrate explicitly that our results are in qualitative agreement with the molecular-beam experiments of Kusch, for which the semiclassical treatment of Salwen fails to predict the results. Consequently, we expect an intensity-dependent effect which can be properly explained only by QED and not by the semiclassical treatment. We also include the effect of nonelectromagnetic relaxation on the induced transition probability of a two-level system, for which we obtain an expression slightly different from that used by Ramsey for the hydrogen maser. Finally, we derive some expressions which will be of interest in experiments related to lasers and masers.
TL;DR: In this article, a nonrelativistic quantum theory of a particle having both electric and magnetic charges moving in an arbitrary external electromagnetic field is presented, which is based on the hydrodynamic formulation of quantum mechanics.
Abstract: The nonrelativistic quantum theory of a particle having both electric and magnetic charges moving in an arbitrary external electromagnetic field is presented The theory is based on the hydrodynamic formulation of quantum mechanics Dirac's quantization condition for the electric and magnetic charges is rederived as a consistency condition for the motion of the probability fluid Neither the wave function nor the electromagnetic potential, which were the source of ambiguities in all other formulations, appears in our approach Nevertheless, this theory has all the essential features of the standard quantum mechanics, including the superposition principle
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01 Jan 1971
TL;DR: In this paper, the mathematical methods used in quantum mechanics are developed, with emphasis on linear algebra and complex variables, and Dirac notation for vectors in Hilbert space is introduced, and the representation of coordinates and momenta is analyzed and applied to the Heisenberg uncertainty principle.
Abstract: The mathematical methods used in quantum mechanics are developed, with emphasis on linear algebra and complex variables. Dirac notation for vectors in Hilbert space is introduced. The representation of coordinates and momenta in quantum mechanics is analyzed and applied to the Heisenberg uncertainty principle.
TL;DR: In this article, the Von Neumann algebra model for quantum systems has been applied to the analysis of partially ordered vector spaces, and some properties of these properties are derived and applications to quantum theory are discussed.
Abstract: Recent work of Davies and Lewis has shown how partially ordered vector spaces provide a setting in which the operational approach to statistical physical systems may be studied. In this paper, certain physically relevant classes of operations are identified in the abstract framework, some of their properties are derived and applications to the Von Neumann algebra model for quantum theory are discussed.
TL;DR: In this article, it is demonstrated how the one-time formulation of quantum field theory leads to the quasipotential equation for three-particle system, which is the same as the equation in this paper.
Abstract: It is demonstrated how the one-time formulation of quantum field theory leads to the quasipotential equation for three-particle system.
TL;DR: In this article, the relationship between the time dependence of quantum operators and the corresponding dynamical variables in the underlying classical theory is discussed. But the authors focus on the quantum system in the Heisenberg picture.
30 Aug 1971
TL;DR: In this article, a quantum channel model corresponding to a given classical space-time varying linear random channel is established under suitable conditions, and a proper density-operator representation applicable to any receiver configuration can be constructed directly from the channel output field.
Abstract: Communication theory problems incorporating quantum effects for optical-frequency applications are discussed. Under suitable conditions, a unique quantum channel model corresponding to a given classical space-time varying linear random channel is established. A procedure is described by which a proper density-operator representation applicable to any receiver configuration can be constructed directly from the channel output field. Some examples illustrating the application of our methods to the development of optical quantum channel representations are given. Optimizations of communication system performance under different criteria are considered. In particular, certain necessary and sufficient conditions on the optimal detector in M-ary quantum signal detection are derived. Some examples are presented. Parameter estimation and channel capacity are discussed briefly.
TL;DR: In this article, the authors extend an earlier canonical formulation of quantum electrodynamics in the infinite-momentum frame by replacing the photons with massive vector mesons, and the structure of the theory remains nearly the same except that a new term appears in the Hamiltonian describing the emission of helicity-zero vector meson with an amplitude proportional to the meson mass.
Abstract: We extend an earlier canonical formulation of quantum electrodynamics in the infinite-momentum frame by replacing the photons with massive vector mesons. The structure of the theory remains nearly the same except that a new term appears in the infinite-momentum Hamiltonian describing the emission of helicity-zero vector mesons with an amplitude proportional to the meson mass.
TL;DR: In this paper, the golden rule of time dependent perturbation theory is derived using the formalism of quantum field theory in statistical physics, and the proof is more satisfying than that of some conventional presentations and is a simple illustration of the use of the quantum field theoretical formalism (e.g., Green's functions, linked cluster expansions, and Dyson's equation) in the context of solid state theory.
Abstract: The golden rule of time dependent perturbation theory is derived using the formalism of quantum field theory in statistical physics. The proof is more satisfying than that of some conventional presentations and is a simple illustration of the use of the quantum field theoretical formalism (e.g., Green's functions, linked cluster expansions, and Dyson's equation) in the context of solid state theory.
TL;DR: In this article, the decay time for the kernel of a generalized master equation and the evolution of macroscopic quantities of the measuring device were investigated. And they were found to justify the possibility of a macro-scopic description of the measurement apparatus, and a relevant hypothesis was found to be the separation of two characteristic times.
Abstract: A contribution is given to the attempts towards a solution of the measurement problem in quantum mechanics, in the spirit of some previous papers. In order to justify the possibility of a macroscopic description of the measuring apparatus, a relevant hypothesis is found to be the separation of two characteristic times: the decay time for the kernel of a generalized master equation and the characteristic time for the evolution of macroscopic quantities of the measuring device.