Time Evolution Of Spin Research Articles

Higher-spin gravity in AdS3 and folds on Fermi surface

In this paper, we introduce new sets of boundary conditions for higher spin gravity in $AdS_3$ where the boundary dynamics of spin two and other higher spin fields are governed by the interacting collective field theory Hamiltonian of Avan and Jevicki. We show that the time evolution of spin two and higher spin fields can be captured by the classical dynamics of folded fermi surfaces in the similar spirit of Lin, Lunin and Maldacena. We also construct infinite sequences of conserved charges showing the integrable structure of higher spin gravity (for spin 3) under the boundary conditions we considered. Further, we observe that there are two possible sequences of conserved charges depending on whether the underlying boundary fermions are non-relativistic or relativistic.

Dynamics of the angular momentum in narrow quantum rings with Rashba and Dresselhaus spin-orbit interactions

The quantum dynamics of the electron's spin and orbital angular momenta in semiconductor quantum rings is analyzed. Both Rashba and Dresselhaus spin-orbit interactions (SOIs) in their quasi-two-dimensional forms are taken into account. The narrow quantum rings are treated with models including one and two radial modes. We find that when either Rashba or Dresselhaus SOI acts alone, the different angular momentum states are coupled in blocks of two (for a single radial mode) or four (for two radial modes). We also show that the full Hilbert space splits into two disjoint subspaces, which are not coupled by either of the two SOIs, thereby decoupling accordingly the state evolution. When both SOI mechanisms are present, in principle infinitely many states are coupled, but we find by numerical computation of the quantum dynamics that for typical evolution times in practice only a few neighboring states are involved in the dynamics. Thus the exchange of angular momenta proceeds only via very few states. Furthermore, we find a trend that when initially high orbital momenta are prepared, the time evolution of spin and orbital momenta is almost unaffected by the availability of a second radial mode, in sharp contrast to the case of preparing the system in low orbital angular momentum states. The implications of our findings for the coherent control of angular momentum in quantum rings are pointed out.

Continuous phase spaces and the time evolution of spins: star products and spin-weighted spherical harmonics

We study continuous phase spaces of single spins and develop a complete description of their time evolution. The time evolution is completely specified by so-called star products. We explicitly determine these star products for general spin numbers using a simplified approach which applies spin-weighted spherical harmonics. This approach naturally relates phase spaces of increasing spin number to their quantum-optical limit and allows for efficient approximations of the time evolution for large spin numbers. We also approximate phase-space representations of certain quantum states that are challenging to calculate for large spin numbers. All of these applications are explored in concrete examples and we outline extensions to coupled spin systems.

Spin active split-ring resonator for THz high harmonic generation

We explore theoretically the utilization of laser-driven split, semiconductor-based quantum rings as a source for high harmonic generation in the THz regime. Particular attention is paid to spin-related effects mediated by Rashba-type spin orbital coupling. The frequencies of the fundamental harmonics exhibit different time characteristics related to the charge and spin dynamics offering so a tool to access the spin time evolution by monitoring the time dependent harmonic emission.

Evolution of Spin and Charge in a System with InteractingImpurity and Conducting Electrons

We investigate the dynamics of spin and charge in an interactingsystem consisting of impurity and conducting electrons. The timeevolution of spin and charge in the impurity is given by solvingthe time-dependent Schrödinger equations for the many-bodystates of the interacting system. By switching on the interactionbetween impurity and conducting electrons, the spin and charge ofthe impurity begin oscillations with frequencies that reflect theelementary excitations of the interacting system. The dynamicsreflects the basic picture of the Kondo effect.

A spin-product-operator analysis of the dephasing requirement in STEAM-localized NMR spectroscopy

The STEAM sequence (I) is frequently used in volume-localized NMR spectroscopy. Its application requires that the spin coherence created by the first 90” pulse be completely dephased before the application of the second pulse (2, 3). Although the fulfillment of this dephasing requirement is essential for the correct interpretation of the STEAM-localized spectra, its importance has not always been fully recognized in the analysis of the sequence. A recent calculation (4)) which ignored the dephasing requirement, yielded undesired modulations of the stimulated-echo (STE) signal by the chemical shift. The purpose of this paper is to analyze the time evolution of a spin system subjected to the STEAM sequence and to demonstrate the importance of the dephasing requirement when using the STEAM sequence for volume-localized NMR spectroscopy. The time evolution of a single spin (I = 4) system is calculated using the spin product operator formalism (5), with the effects of spin relaxation and diffusion ignored. The STEAM sequence used for the analysis is depicted in Fig. 1 with indication of the points on the time axis where the spin density operator is calculated. For simplicity, the gradients in the three time intervals are the averaged gradients. The calculation is performed under the following conditions: (a) the TE gradients are balanced, i.e., GTr( 1) = GTE( 2); (b) the TM gradient is applied to destroy the transverse magnetization after the second RF pulse. Calculation of the density operator at the successive time points yields