Spin relaxation time, spin dephasing time and ensemble spin dephasing time in nn-type GaAs quantum wells

We investigate the spin relaxation and spin dephasing of $n$-type GaAs quantum wells. We obtain the spin relaxation time $T_1$, the spin dephasing time $T_2$ and the ensemble spin dephasing time $T_2^{\ast}$ by solving the full microscopic kinetic spin Bloch equations, and we show that, analogous to the common sense in an isotropic system for conduction electrons, $T_1$, $T_2$ and $T_2^{\ast}$ are identical due to the short correlation time. The inhomogeneous broadening induced by the D'yakonov-Perel term is suppressed by the scattering, especially the Coulomb scattering, in this system.Comment: 4 pages, 2 figures, to be published in Phys. Lett.

Superfluid-Mott-Insulator Transition in a One-Dimensional Optical Lattice with Double-Well Potentials

We study the superfluid-Mott-insulator transition of ultracold bosonic atoms in a one-dimensional optical lattice with a double-well confining trap using the density-matrix renormalization group. At low density, the system behaves similarly as two separated ones inside harmonic traps. At high density, however, interesting features appear as the consequence of the quantum tunneling between the two wells and the competition between the "superfluid" and Mott regions. They are characterized by a rich step-plateau structure in the visibility and the satellite peaks in the momentum distribution function as a function of the on-site repulsion. These novel properties shed light on the understanding of the phase coherence between two coupled condensates and the off-diagonal correlations between the two wells.Comment: 5 pages, 7 figure

Intense terahertz laser fields on a quantum dot with Rashba spin-orbit coupling

We investigate the effects of the intense terahertz laser field and the spin-orbit coupling on single electron spin in a quantum dot. The laser field and the spin-orbit coupling can strongly affect the electron density of states and can excite a magnetic moment. The direction of the magnetic moment depends on the symmetries of the system, and its amplitude can be tuned by the strength and frequency of the laser field as well as the spin-orbit coupling.Comment: 5 pages, 4 figures, to be published in J. Appl. Phy

Aqueous in-flow synthesis of T1 enhancing iron oxide nanoparticles for breast cancer theranostics

Superparamagnetic iron oxide nanoparticles (SPIONs) have gained signif- icant interest over the past decades because of their wide range of appli- cations. In biomedicine, SPIONs had been used extensively in the past as MRI contrast agents but they are currently being investigated for hyperther- mia therapies, magnetic manipulation and as part of diagnostic devices. The main aim of this study is to develop a method to synthesise positive MRI enhancing iron oxide nanoparticles (T1) and use these as the diagnos- tic component to produce a theranostic (therapeutic and diagnostic) agent. An aqueous flow-based synthesis method was assembled and tested producing 25nm iron oxide nanoparticles with T1 enhancement, CMDxUS- PIONs. The devised synthetic method enabled the fabrication of the desired nanoparticles without the use of organic solvents and at higher outputs than previously reported with flow-based methods, with 12 clinical doses being produced per hour using a lab-scale system. Surface functionalisation of CMDxUSPIONs with aptamers for active targeting was accomplished using a recently discovered anti-annexin 2A aptamer (ACE4). Particle uptake results show that ACE4-CMDxUSPIONs presented at least a two-fold increase in cell uptake when compared to un- modified CMDxUSPIONs. Further modifications of CMDxUSPIONs included drug-loading with cisplatin. Cisplatin loaded CMDxUSPIONs (CPt-CMDxUSPIONs) were achieved following pre-optimisation using a Design of Experiments ap- proach. The drug-loaded CPt-CMDxUSPIONs containing 0.64mg of CPt/mg of iron were able to retain both the activity of free cisplatin (in vitro) and the imaging capabilities of CMDxUSPIONs. In vivo experiments using a 4T1 mammary carcinoma cell line in Balb/C mice showed that CPt-CMDxUSPIONs were trackable in a 1T preclinical MRI and therapeutically, CPt-CMDxUSPIONs reduced tumour size and minimised cisplatin’s nephro- toxicity. Moreover, preclinical MRI scans show that it is possible to use CMDxUSPIONs as reporters for nanoparticle uptake detected by a T1-T2 signal switch in MRI. Iron oxide based theranostic systems reported in this thesis could play an important role in future cancer treatments by enabling a personalised therapy approach and modifying current chemotherapeutic drug biodistribu- tion as a carrier. The facile synthesis together with the addition of therapeu- tic agents to iron oxide nanoparticles demonstrates that the production of an experimental theranostic is possible

Accurate determination of tensor network state of quantum lattice models in two dimensions

We have proposed a novel numerical method to calculate accurately the physical quantities of the ground state with the tensor-network wave function in two dimensions. We determine the tensor network wavefunction by a projection approach which applies iteratively the Trotter-Suzuki decomposition of the projection operator and the singular value decomposition of matrix. The norm of the wavefunction and the expectation value of a physical observable are evaluated by a coarse grain renormalization group approach. Our method allows a tensor-network wavefunction with a high bond degree of freedom (such as D=8) to be handled accurately and efficiently in the thermodynamic limit. For the Heisenberg model on a honeycomb lattice, our results for the ground state energy and the staggered magnetization agree well with those obtained by the quantum Monte Carlo and other approaches.Comment: 4 pages 5 figures 2 table

Topological quantum phase transition in an S=2 spin chain

We construct a model Hamiltonian for S = 2 spin chain, where a variable parameter $\alpha$ is introduced. The edge spin is S = 1 for $\alpha = 0$, and S = 3/2 for $\alpha = 1$. Due to the topological distinction of the edge states, these two phases must be separated by one or several topological quantum phase transitions. We investigate the nature of the quantum phase transition by DMRG calculation, and propose a phase diagram for this model.Comment: 5 pages, 4 figure