A quantum treatment of magnetization dynamics of a nanomagnet between a thousand and a million spins may be needed as the magnet interacts with quantum control. The advantage of the all-quantum approach over the classical treatment of magnetization is the accounting for the correlation between the magnet and the control agent and the first-principles source of noise. This supplement to the conference talk will concentrate on an overview of the theory with a presentation of the basic ideas which could have wide applications and illustrations with some results. Details of applications to specific models are or will be published elsewhere. A clear concept of the structure of the ground and excited macrospin states as magnetization rotation states and magnons in the Bloch/Dyson sense gives rise to a consistent theory of the magnetization dynamics of a ferromagnet modeled by the Heisenberg Hamiltonian. An example of quantum control is the spin torque transfer, treated here as a sequence of scatterings of each current electron with the localized electrons of the ferromagnet, yields in each encounter a probability distribution of the magnetization recoil state correlated with each outgoing state of the electron. This picture provides a natural Monte Carlo process for simulation of the dynamics in which the probability is determined by quantum mechanics. The computed results of mean motion, noise and damping of the magnetization will be discussed.
This paper presents a novel design concept for spintronic nanoelectronics that emphasizes a seamless integration
of spin-based memory and logic circuits. The building blocks are magneto-logic gates based on a hybrid
graphene/ferromagnet material system. We use network search engines as a technology demonstration vehicle
and present a spin-based circuit design with smaller area, faster speed, and lower energy consumption than the
state-of-the-art CMOS counterparts. This design can also be applied in applications such as data compression,
coding and image recognition. In the proposed scheme, over 100 spin-based logic operations are carried
out before any need for a spin-charge conversion. Consequently, supporting CMOS electronics requires little
power consumption. The spintronic-CMOS integrated system can be implemented on a single 3-D chip. These
nonvolatile logic circuits hold potential for a paradigm shift in computing applications.
The ability to manipulate the spin states of charges confined in quantum dots (QDs) is essential for the realization
of a quantum computer based on such spins. Here, we present experimentally realized electron spin qubit gates
in a single self-assembled InAs QD using a combination of picosecond optical pulses, spin precession about
an external DC magnetic field and optically generated geometric phases. Arbitrary unitary operations on the
electron spin qubit may be constructed using a combination of optical pulses and either spin precession or the
optically generated geometric phases.
We show that the initial dynamics of resonantly excited excitons in quantum wells is controlled by several processes, such as radiative recombination, spin-relaxation of excitons, electrons and holes, and scattering between different momentum states of excitons. We present results of experiments designed to simultaneously probe these processes. By a unified analysis of the results we extract quantitative information about radiative, spin-relaxation and momentum- relaxation rates, obtaining a good physical understanding of the initial dynamics of non- equilibrium excitons.
We present the results of a comprehensive investigation of spin-relaxation processes of electrons, holes and excitons in quantum wells using subpicosecond spectroscopy of luminescence polarization. Spin relaxation rates of electrons and holes are measured directly in modulation-doped quantum wells and give a good understanding of spin-relaxation processes of electrons and holes. We show that spin-relaxation dynamics of excitons, on the other hand, is quite complicated and is strongly influenced by their formation dynamics, many-body effects and localization dynamics. Although we have made good progress towards understanding exciton spin relaxation processes, some other outstanding issues will require further attention. We compare our results to those in bulk GaAs, and those in quantum wells obtained by other techniques.