Modelling and feedback control design for quantum state preparation

The goal of this article is to provide a largely self-contained introduction to the modelling of controlled quantum systems under continuous observation, and to the design of feedback controls that prepare particular quantum states. We describe a bottom-up approach, where a field-theoretic model is subjected to statistical inference and is ultimately controlled. As an example, the formalism is applied to a highly idealized interaction of an atomic ensemble with an optical field. Our aim is to provide a unified outline for the modelling, from first principles, of realistic experiments in quantum control

Feedback control of quantum state reduction

Feedback control of quantum mechanical systems must take into account the probabilistic nature of quantum measurement. We formulate quantum feedback control as a problem of stochastic nonlinear control by considering separately a quantum filtering problem and a state feedback control problem for the filter. We explore the use of stochastic Lyapunov techniques for the design of feedback controllers for quantum spin systems and demonstrate the possibility of stabilizing one outcome of a quantum measurement with unit probability

Time Dependent Relative Risk Aversion

Risk management and the thorough understanding of the relations between financial markets and the standard theory of macroeconomics have always been among the topics most addressed by researchers, both financial mathematicians and economists. This work aims at explaining investors’ behavior from a macroeconomic aspect (modeled by the investors’ pricing kernel and their relative risk aversion) using stocks and options data. Daily estimates of investors’ pricing kernel and relative risk aversion are obtained and used to construct and analyze a three-year long time-series. The first four moments of these time-series as well as their values at the money are the starting point of a principal component analysis. The relation between changes in a major index level and implied volatility at the money and between the principal components of the changes in relative risk aversion is found to be linear. The relation of the same explanatory variables to the principal components of the changes in pricing kernels is found to be log-linear, although this relation is not significant for all of the examined maturities.risk aversion, pricing kernels, time dependent preferences

What has African cultural studies done for you lately? Autobiographical and global Considerations of a floating signifier

Abstract: This essay poses and attempts to answer the central question, “what does African cultural studies do?” It takes an autobiographical approach to address the genealogy, status quo and the potential future of the floating signifier that is African Cultural Studies. It unpacks and multiplies African cultural studies and contextualizes it as a form of African studies and as both interventionist in and contributory to transnational cultural studies. African cultural studies marginality in the global discourse is rearticulated as both a positioning of disempowerment on the one hand and one of generative and insurgent politics on the other. Stressing the need for continental and diasporic Africans to self-identify issues to be addressed (in place Eurocentric, imposed preoccupations), the essay identifies as examples the always already complex nature of identity and belonging (and the irony of emergent zenophobia); continental and diasporic relations that trouble the taken for grantedness of what constitutes Africa(ns), and queer Africa in the face of institutionalized homophobia. Whether local nativist or globally engaged approaches are taken, the essay concludes, African cultural studies ought to be self-reflexively, dedicated not only to doing cultural studies but to what the doing of African cultural studies does for Africa(ns) and for transnational cultural studies

Quantum Fluctuations of Coulomb Potential as a Source of Flicker Noise. The Influence of External Electric Field

Fluctuations of the electromagnetic field produced by quantized matter in external electric field are investigated. A general expression for the power spectrum of fluctuations is derived within the long-range expansion. It is found that in the whole measured frequency band, the power spectrum of fluctuations exhibits an inverse frequency dependence. A general argument is given showing that for all practically relevant values of the electric field, the power spectrum of induced fluctuations is proportional to the field strength squared. As an illustration, the power spectrum is calculated explicitly using the kinetic model with the relaxation-type collision term. Finally, it is shown that the magnitude of fluctuations produced by a sample generally has a Gaussian distribution around its mean value, and its dependence on the sample geometry is determined. In particular, it is demonstrated that for geometrically similar samples, the power spectrum is inversely proportional to the sample volume. Application of the obtained results to the problem of flicker noise is discussed.Comment: 14 pages, 3 figure

Deterministic Dicke state preparation with continuous measurement and control

We characterize the long-time projective behavior of the stochastic master equation describing a continuous, collective spin measurement of an atomic ensemble both analytically and numerically. By adding state based feedback, we show that it is possible to prepare highly entangled Dicke states deterministically.Comment: Additional information is available at http://minty.caltech.edu/Ensemble

Introduction : contemporary orientations in African cultural studies

Abstract: This paper offers a glimpse of work generated by the 2014 John Douglas Taylor conference on ‘Contemporary Orientations in African Cultural Studies’. The conference generated a number of inquiries into the time and place of contemporary African cultural work, many of which theorized beyond the frameworks that postcolonial and globalization studies frequently offer. Under the shifting paradigms of cultural studies, the work of this conference, as well as the current project, moves away from reading the African everyday as exclusively a construction out of a series of colonial histories and relationalities, or global cultural flows. In line with Jean and John Comaroffs’ Theory From the South, this issue is instead dedicated to relocating the global centres from which cultural studies emanates and positing African work’s challenge to normative zones of cultural critique. ‘Contemporary orientations’ attempts to relocate the time and space of critique in African studies, but it resists the gesture to posit a stable trajectory through which time moves. Rather, the terms of the contemporary and the orientation depend on how they are read in relation to a multitude of other temporalities, orientations, and objects

The effect of ε-aminocaproic acid on blood product requirement, outcome and thromboelastography parameters in severely thrombocytopenic dogs

Background: No treatment other than platelet administration is known to protect against spontaneous hemorrhage in thrombocytopenic dogs. Objectives: Primary: determine if treatment with ε-aminocaproic acid (EACA) decreases the requirement for blood transfusions and improves outcome in dogs with severe thrombocytopenia. Secondary: find evidence of hyperfibrinolysis and determine the effect EACA administration on rapid (rTEG) and tissue plasminogen activator-spiked (tPA-rTEG) thromboelastography parameters. Animals: Twenty-seven dogs with severe thrombocytopenia were treated with EACA, and data from an additional 33 were obtained from the hospital database as historical control (HC) cohort. Methods: Single arm clinical trial with HCs. The EACA group dogs received EACA (100 mg/kg IV followed by a constant-rate infusion [CRI] of 400 mg/kg/24 hours). Thromboelastography before and during EACA infusion, hospitalization days, number of transfusions, and mortality were compared. Results: No difference was found in number of transfusions per dog (median, interquartile range; 1, 0-2.5 vs 0.9, 0-2; P =.5) and hospitalization days (4, 4-6 vs 4.5, 3.75-6; P =.83) between HC and EACA groups, respectively, and no difference in survival was identified by log-rank analysis (P =.15). Maximum amplitude on both rTEG and tPA-rTEG increased after EACA administration (rTEG baseline: 23.6, 9.6-38.9; post-EACA: 27.3, 19.8-43.2; P &lt;.001; tPA-rTEG baseline: 23, 10.9-37.2; post-EACA: 24.7, 16.7-44.8; P &lt;.002). Conclusions and Clinical Importance: Although EACA increased clot strength, there was no effect on outcome. Treatment with EACA at this dosage cannot be recommended as a routine treatment but may be considered for dogs with severe ongoing hemorrhage.</p