Simultaneous measurement of several noncommuting observables is modeled by using semigroups of completely positive maps on an algebra with a non-trivial center. The resulting piecewise-deterministic dynamics leads to chaos and to nonlinear iterated function systems (quantum fractals) on complex projective spaces.
Departing from classical concepts of ergodic theory, formulated in terms of probability densities, measures describing the mixing behavior and the loss of information in quantum open systems are proposed. As application we discuss the chaotic outcomes of continuous measurement processes in the EEQT framework. Simultaneous measurement of four noncommuting spin components is shown to lead to a chaotic jumps on the quantum spin sphere and to generate specific fractal images of a nonlinear iterated function system. (C) 2001 Published by Elsevier Science B.V.
An iterated function system (IFS) is defined by specifying a set of functions in a classical phase space, which act randomly on an initial point. In an analogous way, we define a quantum IFS (QIFS), where functions act randomly with prescribed probabilities in the Hilbert space. In a more general setting, a QIFS consists of completely positive maps acting in the space of density operators. This formalism is designed to describe certain problems of nonunitary quantum dynamics. We present exemplary classical IFSs, the invariant measure of which exhibits fractal structure, and study properties of the corresponding QIFSs and their invariant states.
We analyze the consequences of iterative measurement-induced nonlinearity on the dynamical behavior of qubits. We present a one-qubit scheme where the equation governing the time evolution is a complex-valued nonlinear map with one complex parameter. In contrast to the usual notion of quantum chaos, exponential sensitivity to the initial state occurs here. We calculate analytically the Lyapunov exponent based on the overlap of quantum states, and find that it is positive. We present a few illustrative examples of the emerging dynamics.
We review Event Enhanced Quantum Theory (EEQT), discuss applications of EEQT to tunnelling time, and compare its quantitative predictions with other approaches, in particular with phase time and the Büttiker-Larmor approach. We discuss quantum chaos and quantum fractals resulting from simultaneous continuous monitoring of several non-commuting observables. In particular we show self-similar, nonlinear, iterated function system type, patterns arising from quantum jumps and from the associated Markov operator.
The present work develops a classification of finite-dimensional irreducible invariant subspaces for quantum Markov semigroups (GKSL semigroups) whose generators are algebraically generated from two non-commuting orthogonal projections. The central mechanism is commutant collapse: a Hermitian rank-1 operator—the “bridge”—couples a two-dimensional Halmos fiber to a trivial direction, forces the commutant of the generated C^*-algebra to become trivial, and thereby saturates the algebra to a full matrix algebra by the double commutant theorem. We identify i-axis symmetry—the requirement that the noise operators generate a *-closed algebra—as the structural condition that guarantees bridges appear in Hermitian form. A single bridge connecting one Halmos fiber to one trivial direction forces the algebra M_3(\mathbb{C}); the resulting semigroup is primitive on that subspace. For k\ge 2 trivial directions coupled to the same fiber, we introduce the concept of center-breaking bridges. Whether the algebra saturates to M_{2+k}(\mathbb{C}) or stabilises at an intermediate barrier subalgebra depends on whether each successive bridge breaks the centre of the intermediate algebra. The dimension of the minimal non-trivial irreducible block is 2+k when all k bridges act in a centre-breaking manner. The Lie envelope of the three-dimensional sector is \mathfrak{su}(3) for generic parameters, with degeneracies at symmetric projection angles. We discuss dynamical closure rigidity—the property that a finitely generated operator system becomes irreducible under C^*-closure—and distinguish kinematic capacity from dynamical accessibility.