Orbital and spin relaxation in single and coupled quantum dots

Phonon-induced orbital and spin relaxation rates of single electron states in lateral single and double quantum dots are obtained numerically for realistic materials parameters. The rates are calculated as a function of magnetic field and interdot coupling, at various field and quantum dot orientations. It is found that orbital relaxation is due to deformation potential phonons at low magnetic fields, while piezoelectric phonons dominate the relaxation at high fields. Spin relaxation, which is dominated by piezoelectric phonons, in single quantum dots is highly anisotropic due to the interplay of the Bychkov-Rashba and Dresselhaus spin-orbit couplings. Orbital relaxation in double dots varies strongly with the interdot coupling due to the cyclotron effects on the tunneling energy. Spin relaxation in double dots has an additional anisotropy due to anisotropic spin hot spots which otherwise cause giant enhancement of the rate at useful magnetic fields and interdot couplings. Conditions for the absence of the spin hot spots in in-plane magnetic fields (easy passages) and perpendicular magnetic fields (weak passages) are formulated analytically for different growth directions of the underlying heterostructure. It is shown that easy passages disappear (spin hot spots reappear) if the double dot system loses symmetry by an xy-like perturbation.Comment: 13 pages, 9 figure

Using quantum state protection via dissipation in a quantum-dot molecule to solve the Deutsch problem

The wide set of control parameters and reduced size scale make semiconductor quantum dots attractive candidates to implement solid-state quantum computation. Considering an asymmetric double quantum dot coupled by tunneling, we combine the action of a laser field and the spontaneous emission of the excitonic state to protect an arbitrary superposition state of the indirect exciton and ground state. As a by-product we show how to use the protected state to solve the Deutsch problem.Comment: 8 pages, 1 figure, 2 table

Virtual Processes and Superradiance in Spin-Boson Models

We consider spin-boson models composed by a single bosonic mode and an ensemble of $N$ identical two-level atoms. The situation where the coupling between the bosonic mode and the atoms generates real and virtual processes is studied, where the whole system is in thermal equilibrium with a reservoir at temperature $\beta^{-1}$. Phase transitions from ordinary fluorescence to superradiant phase in three different models is investigated. First a model where the coupling between the bosonic mode and the $j-th$ atom is via the pseudo-spin operator $\sigma^{,z}_{(j)}$ is studied. Second, we investigate the generalized Dicke model, introducing different coupling constants between the single mode bosonic field and the environment, $g_{1}$ and $g_{2}$ for rotating and counter-rotating terms, respectively. Finally it is considered a modified version of the generalized Dicke model with intensity-dependent coupling in the rotating terms. In the first model the zero mode contributes to render the canonical entropy a negative quantity for low temperatures. The last two models presents phase transitions, even when only Hamiltonian terms which generates virtual processes are considered

The Minimal Overlap Rule: Restrictions on Mergers for Creditors' Consensus

As it is known, there is no rule satisfying Additivity in the complete domain of bankruptcy problems. This paper proposes a notion of partial Additivity in this context, to be called µ-additivity. We find that µ-additivity, together with two quite compelling axioms, anonymity and continuity, identify the Minimal Overlap rule, introduced by Neill (1982)

Enabling secure subsurface storage in future energy systems: An introduction

Geological structures in the subsurface have been used for the storage of energy and waste products for over a century. Depleted oil and gas fields, saline aquifers or engineered caverns in salt or crystalline rocks are used worldwide to store energy fluids intended to provide demand buffers and sustained energy supply. The transition of our energy system into a clean, renewable-based system will most likely require an expansion of these subsurface storage activities, to host a wide variety of energy products (e.g. natural gas, hydrogen, heat or waste energy products, like CO2) to balance the inherent intermittence of the renewable energy supply. Ensuring the safety and effectiveness of these subsurface storage operations is therefore crucial to achieve the sought-after renewable energy transition while ensuring energy security

Anti-Angiogenic Treatment (Sunitinib) for Disseminated Malignant Haemangiopericytoma: A Case Study and Review of the Literature

Introduction: A meningeal haemangiopericytoma (HP) is a mesenchymal tumour that makes up less than 1% of all CNS tumours. HPs arise from pericytes and present high rates of recurrence and distant metastasis. The primary treatment option is surgery. When the disease is disseminated, chemotherapy produces a weak and short-lived response; therefore, new drugs are needed. Case Presentation: We describe the case of a 65-year-old woman with a 13-year history of recurrent HP. After local treatment with radiotherapy, she developed metastases that required systemic treatment, and treatment with sunitinib, an oral inhibitor of the vascular endothelial growth factor receptor and the platelet-derived growth factor receptor, was initiated. As a result, radiological stabilisation of the systemic disease was maintained for over 12 months. Conclusions: Anti-angiogenic agents can be useful for treating disseminated HP, but further studies are needed to confirm their possible role in controlling metastatic disease