Ultrafast optical spin echo for electron spins in semiconductors

Spin-based quantum computing and magnetic resonance techniques rely on the ability to measure the coherence time, T2, of a spin system. We report on the experimental implementation of all-optical spin echo to determine the T2 time of a semiconductor electron-spin system. We use three ultrafast optical pulses to rotate spins an arbitrary angle and measure an echo signal as the time between pulses is lengthened. Unlike previous spin-echo techniques using microwaves, ultrafast optical pulses allow clean T2 measurements of systems with dephasing times T2* fast in comparison to the timescale for microwave control. This demonstration provides a step toward ultrafast optical dynamic decoupling of spin-based qubits.Comment: 4 pages, 3 figure

Millisecond spin-flip times of donor-bound electrons in GaAs

We observe millisecond spin-flip relaxation times of donor-bound electrons in high-purity n-GaAs . This is three orders of magnitude larger than previously reported lifetimes in n-GaAs . Spin-flip times are measured as a function of magnetic field and exhibit a strong power-law dependence for fields greater than 4 T . This result is in qualitative agreement with previously reported theory and measurements of electrons in quantum dots.Comment: 4 pages, 4 figure

Community Experiences of Serious Organised Crime in Scotland

This summary sets out key findings from a research project that aimed to explore the community experiences of serious organised crime ( SOC) in Scotland. The study sought to answer the following questions: 1) What are the relationships that exist between SOC and communities in Scotland? 2) What are the experiences and perceptions of residents, stakeholders and organisations of the scope and nature of SOC within their local area? and 3) How does SOC impact on community wellbeing, and to what extent can the harms associated with SOC be mitigated? The work involved in-depth qualitative research, to understand both direct and indirect forms of harm. Key points pertaining to the research and its results are as follows: - The study involved the selection of three community case study sites based on a typology of ' SOC-affected' communities. These sites were based in varying urban and semi-urban settings. - The impact of SOC at a more 'diffuse' national level was explored via research in a range of smaller case study sites and via interviews with national stakeholders. This included a consideration of SOC impacts in rural and remote areas, and on populations that were not concentrated in any defined geographic community. - The case study areas were selected on the basis of pre-existing academic and policy literature, an initial set of interviews with key experts, and on the basis of aggregated and anonymised intelligence summaries provided by Police Scotland. - 188 individuals participated in the study, which mostly involved semi-structured qualitative interviews, but also a small number of focus groups, unstructured interviews and observational research. Interviews were conducted with residents, local businesses, service providers, community groups, and national organisations, as well as with a small number of individuals with lived experience of SOC. - Interviews comprised of questions about: the relationship between SOC and communities; the experiences and perceptions of residents and local service providers as to the nature and extent of SOC; and the impact of SOC on community wellbeing. - Preliminary findings were presented back to a sub-sample of 33 community residents and representatives, across three of the case study areas, through a feedback method called 'co-inquiry'. This involved the organisation of events designed to assess the integrity of the findings, and elicit reflections on the implications of the findings for potential actions

Ultrafast control of donor-bound electron spins with single detuned optical pulses

The ability to control spins in semiconductors is important in a variety of fields including spintronics and quantum information processing. Due to the potentially fast dephasing times of spins in the solid state [1-3], spin control operating on the picosecond or faster timescale may be necessary. Such speeds, which are not possible to attain with standard electron spin resonance (ESR) techniques based on microwave sources, can be attained with broadband optical pulses. One promising ultrafast technique utilizes single broadband pulses detuned from resonance in a three-level Lambda system [4]. This attractive technique is robust against optical pulse imperfections and does not require a fixed optical reference phase. Here we demonstrate the principle of coherent manipulation of spins theoretically and experimentally. Using this technique, donor-bound electron spin rotations with single-pulse areas exceeding pi/4 and two-pulses areas exceeding pi/2 are demonstrated. We believe the maximum pulse areas attained do not reflect a fundamental limit of the technique and larger pulse areas could be achieved in other material systems. This technique has applications from basic solid-state ESR spectroscopy to arbitrary single-qubit rotations [4, 5] and bang-bang control[6] for quantum computation.Comment: 15 pages, 4 figures, submitted 12/2008. Since the submission of this work we have become aware of related work: J. Berezovsky, M. H. Mikkelsen, N. G. Stoltz, L. A. Coldren, and D. D. Awschalom, Science 320: 349-352 (2008

Liver ‘organ on a chip’

© 2017 The liver plays critical roles in both homeostasis and pathology. It is the major site of drug metabolism in the body and, as such, a common target for drug-induced toxicity and is susceptible to a wide range of diseases. In contrast to other solid organs, the liver possesses the unique ability to regenerate. The physiological importance and plasticity of this organ make it a crucial system of study to better understand human physiology, disease, and response to exogenous compounds. These aspects have impelled many to develop liver tissue systems for study in isolation outside the body. Herein, we discuss these biologically engineered organoids and microphysiological systems. Keywords: Microphysiologic systems; Organoids; 3D culture systemsNational Institutes of Health (U.S.) (Grant UH3TR000496)National Institutes of Health (U.S.) (Grant UH3TR000503

First results from 2+1 dynamical quark flavors on an anisotropic lattice: light-hadron spectroscopy and setting the strange-quark mass

We present the first light-hadron spectroscopy on a set of $N_f=2+1$ dynamical, anisotropic lattices. A convenient set of coordinates that parameterize the two-dimensional plane of light and strange-quark masses is introduced. These coordinates are used to extrapolate data obtained at the simulated values of the quark masses to the physical light and strange-quark point. A measurement of the Sommer scale on these ensembles is made, and the performance of the hybrid Monte Carlo algorithm used for generating the ensembles is estimated.Comment: 24 pages. Hadron Spectrum Collaboratio

Long-Ranged Correlations in Sheared Fluids

The presence of long-ranged correlations in a fluid undergoing uniform shear flow is investigated. An exact relation between the density autocorrelation function and the density-mometum correlation function implies that the former must decay more rapidly than $1/r$, in contrast to predictions of simple mode coupling theory. Analytic and numerical evaluation of a non-perturbative mode-coupling model confirms a crossover from $1/r$ behavior at ''small'' $r$ to a stronger asymptotic power-law decay. The characteristic length scale is $\ell \approx \sqrt{\lambda_{0}/a}$ where $$ is the sound damping constant and $a$ is the shear rate.Comment: 15 pages, 2 figures. Submitted to PR