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Quantum Spin Dynamics (QSD)  [PDF]
T. Thiemann
Physics , 1996, DOI: 10.1088/0264-9381/15/4/011
Abstract: An anomaly-free operator corresponding to the Wheeler-DeWitt constraint of Lorentzian, four-dimensional, canonical, non-perturbative vacuum gravity is constructed in the continuum. This operator is entirely free of factor ordering singularities and can be defined in symmetric and non-symmetric form. We work in the real connection representation and obtain a well-defined quantum theory. We compute the complete solution to the Quantum Einstein Equations for the non-symmetric version of the operator and a physical inner product thereon. The action of the Wheeler-DeWitt constraint on spin-network states is by annihilating, creating and rerouting the quanta of angular momentum associated with the edges of the underlying graph while the ADM-energy is essentially diagonalized by the spin-network states. We argue that the spin-network representation is the ``non-linear Fock representation" of quantum gravity, thus justifying the term ``Quantum Spin Dynamics (QSD)".
Quantum Spin Dynamics (QSD) : VII. Symplectic Structures and Continuum Lattice Formulations of Gauge Field Theories  [PDF]
T. Thiemann
Physics , 2000, DOI: 10.1088/0264-9381/18/17/301
Abstract: Interesting non-linear functions on the phase spaces of classical field theories can never be quantized immediately because the basic fields of the theory become operator valued distributions. Therefore, one is usually forced to find a classical substitute for such a function depending on a regulator which is expressed in terms of smeared quantities and which can be quantized in a well-defined way. Namely, the smeared functions define a new symplectic manifold of their own which is easy to quantize. Finally one must remove the regulator and establish that the final operator, if it exists, has the correct classical limit. In this paper we investigate these steps for diffeomorphism invariant quantum field theories of connections. We introduce a generalized projective family of symplectic manifolds, coordinatized by the smeared fields, which is labelled by a pair consisting of a graph and another graph dual to it. We show that there exists a generalized projective sequence of symplectic manifolds whose limit agrees with the symplectic manifold that one started from. This family of symplectic manifolds is easy to quantize and we illustrate the programme outlined above by applying it to the Gauss constraint. The framework developed here is the classical cornerstone on which the semi-classical analysis developed in a new series of papers called ``Gauge Theory Coherent States'' is based.
Quantum Scent Dynamics (QSD): A new composite model of physical particles  [PDF]
Gy?rgy Darvas,Tamás F. Farkas
Physics , 2008,
Abstract: The paper introduces an alternative rishon model for a composite structure of quarks and leptons. The model builds matter from six basic blocks (and their antiparticles). For this reason it introduces new properties of rishons, called "scents", that can take two values, called masculine and feminine scents, which can appear in three colours both. The Quantum Scent Dynamics (QSD) model calculates new electric charges for the rishons. Then it discusses the construction of the known families of particles from scents, as well as the constraints and advantages of the proposed hypothetic model.
Relaxation and coherent oscillations in the spin dynamics of II-VI diluted magnetic quantum wells  [PDF]
Florian Ungar,Moritz Cygorek,Pablo I. Tamborenea,V. Martin Axt
Physics , 2015, DOI: 10.1088/1742-6596/647/1/012010
Abstract: We study theoretically the ultrafast spin dynamics of II-VI diluted magnetic quantum wells in the presence of spin-orbit interaction. We extend a recent study where it was shown that the spin-orbit interaction and the exchange sd coupling in bulk and quantum wells can compete resulting in qualitatively new dynamics when they act simultaneously. We concentrate on Hg$_{1-x-y}$Mn$_x$Cd$_y$Te quantum wells, which have a highly tunable Rashba spin-orbit coupling. Our calculations use a recently developed formalism which incorporates electronic correlations originating from the exchange $sd$-coupling. We find that the dependence of electronic spin oscillations on the excess energy changes qualitatively depending on whether or not the spin-orbit interaction dominates or is of comparable strength with the sd interaction.
Electron-nuclei spin dynamics in II-VI semiconductor quantum dots  [PDF]
C. Le Gall,A. Brunetti,H. Boukari,L. Besombes
Physics , 2012, DOI: 10.1103/PhysRevB.85.195312
Abstract: We report on the dynamics of optically induced nuclear spin polarization in individual CdTe/ZnTe quantum dots loaded with one electron by modulation doping. The fine structure of the hot trion (charged exciton $X^-$ with an electron in the $P$-shell) is identified in photoluminescence excitation spectra. A negative polarisation rate of the photoluminescence, optical pumping of the resident electron and the built-up of dynamic nuclear spin polarisation (DNSP) are observed in time-resolved optical pumping experiments when the quantum dot is excited at higher energy than the hot trion triplet state. The time and magnetic field dependence of the polarisation rate of the $X^-$ emission allows to probe the dynamics of formation of the DNSP in the optical pumping regime. We demonstrate using time-resolved measurements that the creation of a DNSP at B=0T efficiently prevents longitudinal spin relaxation of the electron caused by fluctuations of the nuclear spin bath. The DNSP is built in the microsecond range at high excitation intensity. A relaxation time of the DNSP in about 10 microseconds is observed at $B=0T$ and significantly increases under a magnetic field of a few milli-Tesla. We discuss mechanisms responsible for the fast initialisation and relaxation of the diluted nuclear spins in this system.
Quantum many-body theory of qubit decoherence in a finite-size spin bath. II. Ensemble dynamics  [PDF]
Wen Yang,Ren-Bao Liu
Physics , 2009, DOI: 10.1103/PhysRevB.79.115320
Abstract: Decoherence of a center spin or qubit in a spin bath is essentially determined by the many-body bath evolution. The bath dynamics can start either from a pure state or, more generally, from a statistical ensemble. In the preceding article [W. Yang and R. B. Liu, Phys. Rev. B \textbf{78}, 085315 (2008)], we have developed the cluster-correlation expansion (CCE) theory for the so-called single-sample bath dynamics initiated from a factorizable pure state. Here we present the ensemble CCE theory, which is based on similar ideas of the single-sample CCE: The bath evolution is factorized into the product of all possible cluster correlations, each of which accounts for the authentic (non-factorizable) collective excitation of a group of bath spins, and for the finite-time evolution in the qubit decoherence problem, convergent results can be obtained by truncating the ensemble CCE by keeping cluster correlations up to a certain size. A difference between the ensemble CCE and single-sample CCE is that the mean-field treatment in the latter formalism of the diagonal part of the spin-spin interaction in the bath is not possible in the former case. The ensemble CCE can be applied to non-factorizable initial states. The ensemble CCE is checked against the exact solution of an XY spin bath model. For small spin baths, it is shown that single-sample dynamics is sensitive to the sampling of the initial state from a thermal ensemble and hence very different from the ensemble average.
Quantum spin dynamics  [PDF]
Robert Wieser
Physics , 2014,
Abstract: The classical Landau-Lifshitz equation has been derived from quantum mechanics. Starting point is the assumption of a non-Hermitian Hamilton operator to take the energy dissipation into account. The corresponding quantum mechanical time dependent Schr\"odinger, Liouville and Heisenberg equation have been described and the similarities and differences between classical and quantum mechanical spin dynamics have been discussed. Furthermore, a time dependent Schr\"odinger equation corresponding to the classical Landau-Lifshitz-Gilbert equation and two ways to include temperature into the quantum mechanical spin dynamics have been proposed.
Spin Solitons and Quantum Control of Spin Chain Dynamics  [PDF]
Navin Khaneja,Steffen Glaser
Physics , 2002,
Abstract: Experiments in coherent spectroscopy correspond to control of quantum mechanical ensembles guiding them from initial to final target states by unitary transformations. The control inputs (pulse sequences) that accomplish these unitary transformations should take as little time as possible so as to minimize the effects of relaxation and to optimize the sensitivity of the experiments. Here, we present a radically different and generally applicable approach to efficient control of dynamics in spin chains of arbitrary length. The approach relies on the creation of localized spin waves, ``spin solitons'', and efficient propagation of these soliton states through the spin chain. The methods presented are expected to find immediate applications in control of spin dynamics in coherent spectroscopy and quantum information processing.
Quantum dynamics in single spin measurement  [PDF]
Stefano Mancini,David Vitali,Hector Moya-Cessa
Physics , 2003, DOI: 10.1103/PhysRevB.71.054406
Abstract: We study the quantum dynamics of a model for the single-spin measurement in magnetic-resonance force microscopy. We consider an oscillating driven cantilever coupled with the magnetic moment of the sample. Then, the cantilever is damped through an external bath and its readout is provided by a radiation field. Conditions for reliable measurements will be discussed.
Exciton Spin Dynamics in Semiconductor Quantum Wells  [PDF]
Thierry Amand,Xavier Marie
Physics , 2007, DOI: 10.1007/978-3-540-78820-1_3
Abstract: In this paper we will review Exciton Spin Dynamics in Semiconductor Quantum Wells. The spin properties of excitons in nanostructures are determined by their fine structure. We will mainly focus in this review on GaAs and InGaAs quantum wells which are model systems.
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