Entanglement entropy of Wilson loops: Holography and matrix models

A half-BPS circular Wilson loop in $\mathcal{N}=4$ $SU(N)$ supersymmetric Yang-Mills theory in an arbitrary representation is described by a Gaussian matrix model with a particular insertion. The additional entanglement entropy of a spherical region in the presence of such a loop was recently computed by Lewkowycz and Maldacena using exact matrix model results. In this note we utilize the supergravity solutions that are dual to such Wilson loops in a representation with order $N^2$ boxes to calculate this entropy holographically. Employing the matrix model results of Gomis, Matsuura, Okuda and Trancanelli we express this holographic entanglement entropy in a form that can be compared with the calculation of Lewkowycz and Maldacena. We find complete agreement between the matrix model and holographic calculations.Comment: 17 pages, 1 figur

Holographic entanglement entropy of surface defects

We calculate the holographic entanglement entropy in type IIB supergravity solutions that are dual to half-BPS disorder-type surface defects in ${\cal N}=4$ Super Yang-Mills theory. The entanglement entropy is calculated for a ball-shaped region bisected by a surface defect. Using the bubbling supergravity solutions we also compute the expectation value of the defect operator. Combining our result with the previously-calculated one-point function of the stress tensor in the presence of the defect, we adapt the calculation of Lewkowycz and Maldacena to obtain a second expression for the entanglement entropy. Our two expressions agree up to an additional term, whose possible origin and significance is discussedComment: 41 pages. pdflatex, 3 figures. v2: typos corrected, reference corrected, some comments on CFT interpretation added. v3: references added, some clarification

First detection of a low-mass stellar halo around the young open cluster Eta Chamaeleontis

We have identified several lithium-rich low-mass (0.08<M<0.3 Msun) stars within 5.5 deg of the young open cluster Eta Chamaeleontis, nearly four times the radius of previous search efforts. Of these stars we propose 4 new probable cluster members, and 3 possible members requiring further investigation. These findings are consistent with a dynamical origin for the current configuration of the cluster, without the need to invoke an abnormal Initial Mass Function deficient in low-mass objects. Candidates were selected on the basis of DENIS and 2MASS photometry, NOMAD astrometry and extensive follow-up spectroscopy.Comment: 5 Pages. 5 Figures and 1 Table. Accepted for publication in MNRAS Letters. Higher resolution figures available at http://www.mso.anu.edu.au/~murphysj/

Effects of self-modeling on batting performance

The effect of a self-modeling video plus batting practice program on teaching baseball players to hit from the nondominant side was investigated with 9 male subjects. [This is an excerpt from the abstract. For the complete abstract, please see the document.

A Silicon Surface Code Architecture Resilient Against Leakage Errors

Spin qubits in silicon quantum dots are one of the most promising building blocks for large scale quantum computers thanks to their high qubit density and compatibility with the existing semiconductor technologies. High fidelity single-qubit gates exceeding the threshold of error correction codes like the surface code have been demonstrated, while two-qubit gates have reached 98\% fidelity and are improving rapidly. However, there are other types of error --- such as charge leakage and propagation --- that may occur in quantum dot arrays and which cannot be corrected by quantum error correction codes, making them potentially damaging even when their probability is small. We propose a surface code architecture for silicon quantum dot spin qubits that is robust against leakage errors by incorporating multi-electron mediator dots. Charge leakage in the qubit dots is transferred to the mediator dots via charge relaxation processes and then removed using charge reservoirs attached to the mediators. A stabiliser-check cycle, optimised for our hardware, then removes the correlations between the residual physical errors. Through simulations we obtain the surface code threshold for the charge leakage errors and show that in our architecture the damage due to charge leakage errors is reduced to a similar level to that of the usual depolarising gate noise. Spin leakage errors in our architecture are constrained to only ancilla qubits and can be removed during quantum error correction via reinitialisations of ancillae, which ensure the robustness of our architecture against spin leakage as well. Our use of an elongated mediator dots creates spaces throughout the quantum dot array for charge reservoirs, measuring devices and control gates, providing the scalability in the design

Protein-based molecular contrast optical coherence tomography with phytochrome as the contrast agent

We report the use of phytochrome A (phyA), a plant protein that can reversibly switch between two states with different absorption maxima (at 660 and 730 nm), as a contrast agent for molecular contrast optical coherence tomography (MCOCT). Our MCOCT scheme builds up a difference image revealing the distribution of phyA within a target sample from pairs of consecutive OCT A-scans acquired at a probe wavelength of 750 nm, both with and without additional illumination of the target sample with 660-nm light. We demonstrate molecular imaging with this new MCOCT modality in a target sample containing a mixture of 0.2% Intralipid and 83 µM of phyA

Preliminary X-ray diffraction analysis of YqjH from Escherichia coli: a putative cytoplasmic ferri-siderophore reductase

YqjH is a cytoplasmic FAD-containing protein from Escherichia coli; based on homology to ViuB of Vibrio cholerae, it potentially acts as a ferri-siderophore reductase. This work describes its overexpression, purification, crystallization and structure solution at 3.0 A resolution. YqjH shares high sequence similarity with a number of known siderophore-interacting proteins and its structure was solved by molecular replacement using the siderophore-interacting protein from Shewanella putrefaciens as the search model. The YqjH structure resembles those of other members of the NAD(P)H:flavin oxidoreductase superfamily

Better by design: Business preferences for environmental regulatory reform

We present the preferences for environmental regulatory reform expressed by 30 UK businesses and industry bodies from 5 sectors. While five strongly preferred voluntary regulation, seven expressed doubts about its effectiveness, and 18 expressed no general preference between instrument types. Voluntary approaches were valued for flexibility and lower burdens, but direct regulation offered stability and a level playing field. Respondents sought regulatory frameworks that: are coherent; balance clarity, prescription and flexibility; are enabled by positive regulatory relationships; administratively efficient; targeted according to risk magnitude and character; evidence-based and that deliver long-term market stability for regulatees. Anticipated differences in performance between types of instrument can be undermined by poor implementation. Results underline the need for policy makers and regulators to tailor an effective mix of instruments for a given sector, and to overcome analytical, institutional and political barriers to greater coherence, to better coordinate existing instruments and tackle new environmental challenges as they emerge