Clarendon College

Abstract Next generation tritium decay experiments to determine the absolute neutrino mass require high-precision measurements of β -decay electron energies close to the kinematic end point. To achieve this, the development of high phase-space density sources of atomic tritium is required, along with the implementation of methods to control the motion of these atoms to allow extended observation times. A promising approach to efficiently and accurately measure the kinetic energies of individual β -decay electrons generated in these dilute atomic gases, is to determine the frequency of the cyclotron radiation they emit in a precisely characterised magnetic field. This cyclotron radiation emission spectroscopy technique can benefit from recent developments in quantum technologies. Absolute static-field magnetometry and electrometry, which is essential for the precise determination of the electron kinetic energies from the frequency of their emitted cyclotron radiation, can be performed using atoms in superpositions of circular Rydberg states. Quantum-limited microwave amplifiers will allow precise cyclotron frequency measurements to be made with maximal signal-to-noise ratios and minimal observation times. Exploiting the opportunities offered by quantum technologies in these key areas, represents the core activity of the Quantum Technologies for Neutrino Mass project. Its goal is to develop a new experimental apparatus that can enable a determination of the absolute neutrino mass with a sensitivity on the order of 10 meV / c 2 .

Physical systems are usually assumed to evolve relative to an external time parameter, which is problematic because in quantum theory that parameter is not a physical observable. Page and Wootters (1984) solved this by proposing that the Universe is in a stationary state, eliminating the need for the external time parameter. Instead, their model contains an isolated subsystem, a clock, with which other subsystems are entangled, making the latter appear to evolve relative to different states of the clock. While this resolves the problem of the time parameter, the assumption that the clock is isolated prevents it from being measured, as this requires an interaction with another system. We prove that the clock can be measured while preserving the core features of the Page-Wootters construction. We also discuss clock synchronization.

Topological insulators (TIs) have drawn considerable attention for next generation high sensitivity, high efficiency devices thanks to their unique metallic surface conductivity via their topologically-protected surface states (TSSs). In this study, we utilized near-field nanoimaging and nanoscale spectroscopy in the Terahertz (THz) frequency range to explore the optical response of the surface layer from Bi2Te3 TI flakes. In all cases, we observe a higher near-field optical response from the TI flakes compared to a Si substrate. This contrast increases for more surface sensitive probing, which indicates the presence of a conductive surface state. In addition, we have performed temperature dependent THz nanoscopy and demonstrate a significantly enhanced near-field contrast for the TI flake at a sample temperature of 8.9 K compared to the Si substrate. This temperature-dependent behavior provides vital insight into the underlying mechanisms behind the observed conductive surface state in TI materials.

Studies of random unitary circuits have shown that the calculation of Rényi entropies of entanglement can be mapped to classical statistical mechanics problems in spacetime. In this paper, we develop an analogous spacetime picture of entanglement generation for random free or weakly interacting fermion systems without conservation laws. We first study a free-fermion model, namely a one-dimensional chain of Majorana modes with nearest-neighbor hoppings, random in both space and time. We analyze the Nth Rényi entropy of entanglement using a replica formalism, and we show that the effective model is equivalent to an SO(2N) Heisenberg spin chain evolving in imaginary time. By applying a saddle-point approximation to the coherent states path integral for the N=2 case, we arrive at a semiclassical picture for the dynamics of the entanglement purity, in terms of two classical fields in spacetime. The classical solutions involve a smooth domain wall that interpolates between two values, with the width of this smooth domain wall spreading diffusively in time. We then study how adding weak interactions to the free-fermion model modifies this spacetime picture. Interactions reduce the symmetry of the effective continuum description. As a result the width of the entanglement domain wall remains finite, rather than growing diffusively in time. This yields a crossover from diffusive to ballistic spreading of information.

In this work, we demonstrate that time-resolved photoluminescence data of metal halide perovskites can be effectively evaluated by combining Bayesian inference with a Markov-chain Monte-Carlo algorithm and a physical model. This approach enables us to infer a high number of parameters that govern the performance of metal halide perovskite-based devices, alongside the probability distributions of those parameters, as well as correlations among all parameters. Via studying a set of halfstacks, comprising electron- and hole-transport materials contacting perovskite thin films, we determine surface recombination velocities at these interfaces with high precision. From the probability distributions of all inferred parameters, we can simulate intensity-dependent photoluminescence quantum efficiency and compare it to experimental data. Finally, we estimate mobility values for vertical charge-carrier transport, which is perpendicular to the plane of the substrate, for all samples using our approach. Since this mobility estimation is derived from charge-carrier diffusion over the length scale of the film thickness and in the vertical direction, it is highly relevant for transport in photovoltaic and light-emitting devices. Our approach of coupling spectroscopic measurements with advanced computational analysis will help speed up scientific research in the field of optoelectronic materials and devices and exemplifies how carefully constructed computational algorithms can derive valuable plurality of information from simple datasets. We expect that our approach can be expanded to a variety of other analysis techniques and that our method will be applicable to other semiconductors.

We study the statistics of matrix elements of local operators in the basis of energy eigenstates in a paradigmatic, integrable, many-particle quantum theory, the Lieb-Liniger model of bosons with repulsive delta-function interactions. Using methods of quantum integrability, we determine the scaling of matrix elements with system size. As a consequence of the extensive number of conservation laws, the structure of matrix elements is fundamentally different from, and much more intricate than, the predictions of the eigenstate thermalization hypothesis for generic models. We uncover an interesting connection between this structure for local operators in interacting integrable models and the one for local operators that are not local with respect to the elementary excitations in free theories. We find that typical off-diagonal matrix elements ⟨μ|O|λ⟩ in the same macrostate scale as exp(−cOLln(L)−LMμ,λO), where the probability distribution function for Mμ,λO is well described by Fréchet distributions and cO depends only on macrostate information. In contrast, typical off-diagonal matrix elements between two different macrostates scale as exp(−dOL2), where dO depends only on macrostate information. Diagonal matrix elements depend only on macrostate information up to finite-size corrections. Published by the American Physical Society 2024

This diachronic corpus-based analysis investigates the use of epistemic stance devices inreports from the United Nations’ Intergovernmental Panel on Climate Change (IPCC)from the date of its first report on the physical science of climate change in 1990 to itssixth contribution in 2021. Applying the framework of stance (Biber & Finegan, 1989),the study focuses upon changes in the use of the epistemic stance markers of modal verbsand adverbs across the approximately 30-year period. To empirically measure thestrength of trends in the use of these stance devices, Kendall’s Tau correlation coefficientwas calculated for each item using their normalized frequencies from the six reports.Analysis displayed that the use of modal verbs has consistently decreased across thisperiod of time in which the scientific consensus regarding the anthropogenic origins ofclimate change expanded and solidified. Additionally, of the greater than twenty stanceadverbs displaying consistent use trajectories across the period, the majority of theseitems were emphatic adverbs declining in use.

This paper offers a case study of two London firms active in the production and distribution of women’s ready-to-wear clothing before 1900, H. J. Nicoll and Alfred Stedall. The sources used are registered advertising images from the Records of the Copyright Office, Stationers’ Company at The National Archives; Companies House records (also at The National Archives); and newspaper advertisements sourced from the British Newspaper Archive. These three archives have allowed me to evaluate the uses made of advertising images, and to relate this to the companies’ development, reflecting on the gaps and omissions between the three sources. This research has uncovered a nationwide chain of women’s ready-to-wear retailers, an unexpected development that may require some rethinking of current historiography. It also throws light on the locations and practices of London-based clothing workshops, which have proven resistant to study.