Why material slow light does not improve cavity-enhanced atom detection

We discuss the prospects for enhancing absorption and scattering of light from a weakly coupled atom in a high-finesse optical cavity by adding a medium with large, positive group index of refraction. The slow-light effect is known to narrow the cavity transmission spectrum and increase the photon lifetime, but the quality factor of the cavity may not be increased in a metrologically useful sense. Specifically, detection of the weakly coupled atom through either cavity ringdown measurements or the Purcell effect fails to improve with the addition of material slow light. A single-atom model of the dispersive medium helps elucidate why this is the case.Comment: 11 pages, 4 figures; QuTiP python file included. This version: changed title and added several references; results are unchanged. Accepted for open access publication in a special issue of Journal of Modern Optics in memory of Prof Danny Segal. Publisher's version available at http://dx.doi.org/10.1080/09500340.2017.138451

Culture Wars on Campus: Academic Freedom, the First Amendment, and Partisan Outrage in Polarized Times

After a California community college professor called the election of President Donald Trump an “act of terrorism” in her classroom the week after the vote, a student-recorded viral video sparked a national conservative media firestorm. Critics said the professor should be fired for outrageous liberal bias, while supporters defended her comments as being protected by academic freedom and the First Amendment. The student, meanwhile, was suspended for his unauthorized recording while defenders decried his punishment as evidence of anti-conservative discrimination and harassment. By examining tensions between faculty and student speech rights, the use of technologies to take ideological disagreements viral through partisan media, and the role of colleges and universities in culture wars, this paper finds deep divisions in views of rights and responsibilities of faculty, students, and institutions in campus free-expression controversies

Scattering Expansion for Localization in One Dimension: from Disordered Wires to Quantum Walks

We present a perturbative approach to a broad class of disordered systems in one spatial dimension. Considering a long chain of identically disordered scatterers, we expand in the reflection strength of any individual scatterer. This expansion accesses the full range of phase disorder from weak to strong. We apply this expansion to several examples, including the Anderson model, a general class of periodic-on-average-random potentials, and a two-component discrete-time quantum walk, showing analytically in the latter case that the localization length can depend non-monotonically on the strength of phase disorder (whereas expanding in weak disorder yields monotonic decrease). Returning to the general case, we extend the perturbative derivation of single-parameter scaling to another order and obtain to all orders a particular non-separable form for the joint probability distribution of the log-transmission and reflection phase. Furthermore, we show that for weak local reflection strength, a version of the scaling theory of localization holds: the joint distribution is determined by just three parameters.Comment: 23+15 pages, 10 figures. Longer version of arXiv:2210.0799

Digital Processing of Remotely Sensed Imagery

Digital images can be acquired from various devices. Image scanners on personal computers can generate digital images of hard copy material. New digital cameras operate without film, recording a digital image of the scene in local solid state memory. Remote sensing instruments routinely return digital imagery to receiving stations for processing and display. Digital processing of remotely sensed imagery is a technology that is now over thirty years old. Earth orbitting and deep space exploration spacecraft have been returning digital imagery for many years. Earth-based systems, including biomedical imaging devices and other commercially available types of equipment, have also been producing digital imagery for many years. Each of these devices produce a digital version of an image as a two dimensional array of numbers. The values in the matrix represent the brightness of the scene at each individual sampled position in the image

Universal localization-delocalization transition in chirally-symmetric Floquet drives

Periodically driven systems often exhibit behavior distinct from static systems. In single-particle, static systems, any amount of disorder generically localizes all eigenstates in one dimension. In contrast, we show that in topologically non-trivial, single-particle Floquet loop drives with chiral symmetry in one dimension, a localization-delocalization transition occurs as the time $t$ is varied within the driving period ($0 \le t \le T_\text{drive}$). We find that the time-dependent localization length $L_\text{loc}(t)$ diverges with a universal exponent as $t$ approaches the midpoint of the drive: $L_\text{loc}(t) \sim (t - T_\text{drive}/2)^{-\nu}$ with $\nu=2$. We provide analytical and numerical evidence for the universality of this exponent within the AIII symmetry class.Comment: 17 + 5 pages, 7 figure

Huntington’s Disease protein huntingtin associates with its own mRNA

Background: The Huntington's disease (HD) protein huntingtin (Htt) plays a role in multiple cellular pathways. Deregulation of one or more of these pathways by the mutant Htt protein has been suggested to contribute to the disease pathogenesis. Our recent discovery-based proteomics studies have uncovered RNA binding proteins and translation factors associated with the endogenous Htt protein purified from mouse brains, suggesting a potential new role for Htt in RNA transport and translation. Objective: To investigate how Htt might affect RNA metabolism we set out to purify and analyze RNA associated with Htt. Methods: RNA was extracted from immunopurified Htt-containing protein complexes and analyzed by microarrays and RNA-Seq. Results: Surprisingly, the most enriched mRNA that co-purified with Htt was Htt mRNA itself. The association of Htt protein and Htt mRNA was detected independent of intact ribosomes suggesting that it is not an RNA undergoing translation. Furthermore, we identified the recently reported mis-spliced Htt mRNA encoding a truncated protein comprised of exon 1 and a portion of the downstream intron in the immunoprecipitates containing mutant Htt protein. We show that Htt protein co-localizes with Htt mRNA and that wild-type Htt reduces expression of a reporter construct harboring the Htt 3' UTR. Conclusions: HD protein is found in a complex with its own mRNA and RNA binding proteins and translation factors. Htt may be involved in modulating its expression through post-transcriptional pathways. It is possible that Htt shares mechanistic properties similar to RNA binding proteins such as TDP-43 and FUS implicated in other neurodegenerative diseases

Cortex-wide, cellular-resolution two-photon microscopy

Functional imaging of the mouse brain in its extreme complexity involves substantial trade-offs. An optical intrinsic spectroscopy system can image the entire cortex but at the expense of spatial and temporal resolution [1]. A two-photon microscope (TPM) can image single neurons with high temporal resolution, but the field of view (FOV) is generally restricted. Advanced techniques like random-access scanning allow for imaging single neurons that are millimeters apart but only by ignoring the neurons and tissue in between [2]. By carefully considering the properties of the optical components as well as the imaging requirements, we present a TPM capable of imaging nearly the entire mouse cortex with 15 Hz frame rates and single neuron resolution. Please click Additional Files below to see the full abstract