Bistable Spin Currents from Quantum Dots Embedded in a Microcavity

We examine the spin current generated by quantum dots embedded in an optical microcavity. The dots are connected to leads, which allow electrons to tunnel into and out of the dot. The spin current is generated by spin flip transitions induced by a quantized electromagnetic field inside the cavity with one of the Zeeman states lying below the Fermi level of the leads and the other above. In the limit of strong Coulomb blockade, this model is analogous to the Jaynes-Cummings model in quantum optics. We find that the cavity field amplitude and the spin current exhibit bistability as a function of the laser amplitude, which is driving the cavity mode. Even in the limit of a single dot, the spin current and the Q distribution of the cavity field have a bimodal structure.Comment: New version includes revised figures and discussion of result

HELIN Federated Search Task Force Final Report

Final report of the HELIN Federated Search Task Force, a group appointed by the HELIN Reference Committee at the request of the HELIN Directors to investigate and report on available federated search engines, which allow users simultaneously to search multiple databases. The task force was not asked to recommend a specific one for licensing by HELIN member libraries and did not do so

Transport of a quantum degenerate heteronuclear Bose-Fermi mixture in a harmonic trap

We report on the transport of mixed quantum degenerate gases of bosonic 87Rb and fermionic 40K in a harmonic potential provided by a modified QUIC trap. The samples are transported over a distance of 6 mm to the geometric center of the anti-Helmholtz coils of the QUIC trap. This transport mechanism was implemented by a small modification of the QUIC trap and is free of losses and heating. It allows all experiments using QUIC traps to use the highly homogeneous magnetic fields that can be created in the center of a QUIC trap and improves the optical access to the atoms, e.g., for experiments with optical lattices. This mechanism may be cascaded to cover even larger distances for applications with quantum degenerate samples.Comment: 7 pages, 8 figure

Phase Coherence in a Driven Double-Well System

We analyze the dynamics of the molecular field incoherently pumped by the photoassociation of fermionic atoms and coupled by quantum tunnelling in a double-well potential. The relative phase distribution of the molecular modes in each well and their phase coherence are shown to build up owing to quantum mechanical fluctuations starting from the vacuum state. We identify three qualitatively different steady-state phase distributions, depending on the ratio of the molecule-molecule interaction strength to interwell tunnelling, and examine the crossover from a phase-coherent regime to a phase-incoherent regime as this ratio increases.Comment: 5 pages, 2 figure

Bifurcations and bistability in cavity assisted photoassociation of Bose-Einstein condensed molecules

We study the photo-association of Bose-Einstein condensed atoms into molecules using an optical cavity field. The driven cavity field introduces a new dynamical degree of freedom into the photoassociation process, whose role in determining the stationary behavior has not previously been considered. The semiclassical stationary solutions for the atom and molecules as well as the intracavity field are found and their stability and scaling properties are determined in terms of experimentally controllable parameters including driving amplitude of the cavity and the nonlinear interactions between atoms and molecules. For weak cavity driving, we find a bifurcation in the atom and molecule number occurs that signals a transition from a stable steady state to nonlinear Rabi oscillations. For a strongly driven cavity, there exists bistability in the atom and molecule number

Suppression of Magnetic State Decoherence Using Ultrafast Optical Pulses

It is shown that the magnetic state decoherence produced by collisions in a thermal vapor can be suppressed by the application of a train of ultrafast optical pulses.Comment: 5 pages, 3 figure

Entrepreneurial Literary Theory: A Debate on Research and the Future of Academia

Across the world at present, researchers and teachers are being exhorted to become entrepreneurial. Universities are being restructured accordingly. The debate presented in this book considers what that involves and portends for academia. Literary studies are often regarded as the most resistant to – unfit for – entrepreneurial purposes. Literary research is therefore taken as a baseline for this debate. The uneasy place of literary research within profit-driven academia is revealing of the prevailing conditions for scholarship in all areas. Questions that are raised and discussed here include: What does doing research for the public good mean? What is the relationship between profits and benefits from research? What are applied and basic research? Are concepts of academic freedom and disinterestedness meaningful? What is the relationship between corporate and academic research? Are skills and knowledge different? Can pursuits like close reading and text interpretation be made profitable? What is literary value and how can it be measured? Can the literary system be modelled to profitable ends? Can university teaching be automatized? What are the differences between a standard publication agreement and a scholarly publication agreement? How can digital and open-access academic publication be made profitable? Does the academic monograph have a future? What sorts of knowledge and skills inform entrepreneurial leadership

Universal Dynamical Control of Local Decoherence for Multipartite and Multilevel Systems

A unified theory is given of dynamically modified decay and decoherence of field-driven multilevel multipartite entangled states that are weakly coupled to zero-temperature baths or undergo random phase fluctuations. The theory allows for arbitrary local differences in their coupling to the environment. Due to such differences, the optimal driving-field modulation to ensure maximal fidelity is found to substantially differ from conventional ``Bang-Bang'' or $\pi$-phase flips of the single-qubit evolution.Comment: 22 pages, 6 figure

A Molecular Matter-Wave Amplifier

We describe a matter-wave amplifier for vibrational ground state molecules, which uses a Feshbach resonance to first form quasi-bound molecules starting from an atomic Bose-Einstein condensate. The quasi-bound molecules are then driven into their stable vibrational ground state via a two-photon Raman transition inside an optical cavity. The transition from the quasi-bound state to the electronically excited state is driven by a classical field. Amplification of ground state molecules is then achieved by using a strongly damped cavity mode for the transition from the electronically excited molecules to the molecular ground state

Input and output in damped quantum systems III: Formulation of damped systems driven by Fermion fields

A comprehensive input-output theory is developed for Fermionic input fields. Quantum stochastic differential equations are developed in both the Ito and Stratonovich forms. The major technical issue is the development of a formalism which takes account of anticommutation relations between the Fermionic driving field and those system operators which can change the number of Fermions within the system