Identification and investigation of new low-dimensional quantum spin systems

This thesis focuses on one area of modern condensed matter physics, namely low-dimensional magnetism, and more specifically one-dimensional linear chains. The work herein can be split into three parts. The first part provides a tool for the greater community. I herein propose a Pad´e approximation for the temperature dependent magnetic susceptibility of a S = 3/2 spin chain, that is more accurate than those already known. The approximation allows one to fit experimentally measured magnetic susceptibilities and ascertain values such as the near-neighbour spin exchange interaction and the g-factor. The second and third parts of this thesis are both concerned with experimentally and theoretically characterizing two isostructural linear S = 1/2 chain compounds on opposite ends of the 3d transition metal series. The compounds, CuCrO4 (3d9) and TiPO4 (3d1), are shown to have completely different ground states despite both being largely isostructural and S = 1/2 quantum spin systems. In this work and the resulting publications it is shown that CuCrO4 is a one-dimensional S = 1/2 spin chain with anti-ferromagnetic nearest- and next nearest-neighbour spin exchange interactions. The ratio of these spin exchange interactions is shown experimentally and theoretically to be approximately 2, putting CuCrO4 in the vicinity of the Majumdar-Ghosh point, for which the magnetic ground-state can ii be solved analytically. Small ferromagnetic inter-chain coupling leads to long-range ferromagnetic ordering between anti-ferromagnetic chains at 8.2(2) K. At this temperature a spontaneous electrical polarization is observed. This classifies CuCrO4 as a type-II multiferroic. Contrary to CuCrO4, TiPO4 has a non-magnetic ground state. At 111 and 74 K TiPO4 undergoes a two stage phase transition, which is interpreted as a spin-Peierls transition. There is evidence that below 74 K TiPO4 has a new crystal structure, in which there are alternating dimerised chains and two different PO4 tetrahedral units. Currently the new structure has not been identified and no super-structure reflections have been confirmed in either low-temperature neutron or x-ray diffraction. In summary this thesis presents some experimental and theoretical contributions to the field of low-dimensional magnetism

A Bayesian analysis of classical shadows

The method of classical shadows heralds unprecedented opportunities for quantum estimation with limited measurements [H.-Y. Huang, R. Kueng, and J. Preskill, Nat. Phys. 16, 1050 (2020)]. Yet its relationship to established quantum tomographic approaches, particularly those based on likelihood models, remains unclear. In this article, we investigate classical shadows through the lens of Bayesian mean estimation (BME). In direct tests on numerical data, BME is found to attain significantly lower error on average, but classical shadows prove remarkably more accurate in specific situations -- such as high-fidelity ground truth states -- which are improbable in a fully uniform Hilbert space. We then introduce an observable-oriented pseudo-likelihood that successfully emulates the dimension-independence and state-specific optimality of classical shadows, but within a Bayesian framework that ensures only physical states. Our research reveals how classical shadows effect important departures from conventional thinking in quantum state estimation, as well as the utility of Bayesian methods for uncovering and formalizing statistical assumptions.Comment: 8 pages, 5 figure

Continuity of Lithic Practice from the Eighteenth to the Nineteenth Centuries at the Nipmuc Homestead of Sarah Boston, Grafton, Massachusetts

Stone tools have been found at all Nipmuc-related house sites in central Massachusetts dating from the 17th through 20th centuries. This article explores in detail the lithic assemblage recovered from the kitchen midden of the late 18th and early 19th century Sarah Burnee/Sarah Boston farmstead in Grafton, Massachusetts. Quartz and quartzite lithics were found in similar concentrations as historic ceramics within the midden suggesting that these tools were in active use within the household. Ground-stone tools of ancient origin indicate curation and reuse of older materials, and knapped glass and re-worked gunflints suggest knowledge of flintknapping. This article argues that despite colonial rules forbidding traditional Native practices, this and other Nipmuc families continued to practice the production and use of lithics for at least 300 years after the arrival of Europeans

Unconventional field induced phases in a quantum magnet formed by free radical tetramers

We report experimental and theoretical studies on the magnetic and thermodynamic properties of NIT-2Py, a free radical-based organic magnet. From magnetization and specific heat measurements we establish the temperature versus magnetic field phase diagram which includes two Bose-Einstein condensates (BEC) and an infrequent half magnetization plateau. Calculations based on density functional theory demonstrates that magnetically this system can be mapped to a quasi-two-dimensional structure of weakly coupled tetramers. Density matrix renormalization group calculations show the unusual characteristics of the BECs where the spins forming the low-field condensate are different than those participating in the high-field one.Comment: 12 pages, 12 figure

The FIRST-Optical-VLA Survey for Lensed Radio Lobes

We present results from a survey for gravitationally lensed radio lobes. Lensed lobes are a potentially richer source of information about galaxy mass distributions than lensed point sources, which have been the exclusive focus of other recent surveys. Our approach is to identify radio lobes in the FIRST catalog and then search optical catalogs for coincident foreground galaxies, which are candidate lensing galaxies. We then obtain higher-resolution images of these targets at both optical and radio wavelengths, and obtain optical spectra for the most promising candidates. We present maps of several radio lobes that are nearly coincident with galaxies. We have not found any new and unambiguous cases of gravitational lensing. One radio lobe in particular, FOV J0743+1553, has two hot spots that could be multiple images produced by a z=0.19 spiral galaxy, but the lensing interpretation is problematic.Comment: 38 pages, 18 figures, aastex, accepted to A

Earmarked: The political economy of agricultural research appropriations

Since 1965 a significant portion of the US Department of Agriculture's extramural research budget has been earmarked by Congress for particular research projects. We analyze the process by which a minority of Congress induces the USDA to carry out its budgetary suggestions. We present evidence demonstrating the influence that appropriators possess over the allocation of earmarked grants. Finally, we argue that this program provides an excellent illustration of path-dependence in government policy, and that an understanding of the special grants program may shed light on the decline of science at the USDA and Congress's reluctance to increase agricultural research funding. A t the National Institutes of Health (NIH) and the National Science Foundation (NSF), decisions about which scientific research projects to fund are largely made by other scientists through the competitive peer-review process. Decisions about the allocation of research projects at other agencies, especially those at the Department of Defense, National Aeronautics and Space Administration, and the Department of Agriculture (USDA) are not. For instance, less than 20% of USDA extramural research dollars were allocated through the competitive peer-review process. 1 At these agencies, research projects are often "earmarked" by members of Congress. 2 In the context of agriculture, the House and Senate Agricultural Appropriations Subcommittees let the USDA know which research projects should be funded through a system of "special grants." Since 1965, an increasing amount of federal agricultural research dollars has been spent on earmarked special grants. How did agricultural appropriators acquire this power over the allocation of agricultural research funds

The Archaeology of Hassanamesit Woods: The Sarah Burnee/Sarah Boston Farmstead

Between 2003 and 2013 the Fiske Center for Archaeological Research at the University of Massachusetts Boston conducted an intensive investigation of the Sarah Burnee/Sarah Boston Farmstead on Keith Hill in Grafton, Massachusetts. The project employed a collaborative method that involved working closely with the Town of Grafton, through the Hassanmesit Woods Management Committee, and the Nipmuc Nation, the state recognized government of the Nipmuc people. Yearly excavation and research plans were decided through consultation with both the Nipmuc Tribal Council, their designated representative, Dr. D. Rae Gould, and the Hassanamesit Woods Management Committee. Dr. Gould also played a continuous and active role in reviewing and collaborating on research activities including scholarly presentations at national and international academic meetings and public presentations at the community level. Large scale excavation between 2006 and 2013 focused on the Sarah Burnee/Sarah Boston farmstead that was occupied intensively between 1750 and 1840. Sarah Burnee and Sarah Boston were two of four Nipmuc women to own and possibly reside on the 206 acre parcel that today comprises Hassanamesit Woods. The other two, Sarah Robins and Sarah Muckamaug, were Sarah Burnee’s grandmother and mother respectively. Excavation, archaeogeophysical survey, soil chemistry, and micromorphological and macrobotanical analysis were combined with the analysis of material culture and faunal material to generate a detailed picture of Nipmuc life during the 18th and 19th centuries. Excavation also found evidence of earlier indigenous occupations spanning some 6,000 years. The most intensive period of occupation covered the period 1750 to 1840, but with a significant spike the period 1790 to 1830. This appears to coincide with the coming of age of Sarah Boston who continues to live in the household with her mother Sarah Burnee Philips. Based on a combination of the documentary, architectural and archaeological data, it seems that an addition was made the structure between 1799 and 1802. A rich material assemblage of more than 120,000 artifacts was recovered from the site that provides detailed information on cultural practices including foodways, exchange networks, agricultural activities and other work-related activities such as basket making. A wealth of foodways related artifacts as well as faunal and floral remains provide ample evidence of daily meals and feasting. The latter conclusion is particularly important because of the implications is has for demonstrating that the Hassanamisco Nipmuc were regularly engaged in political activities. We believe the findings of the project provide empirical evidence that counters arguments made by the Bureau of Indian Affairs that the Hassanamisco Nipmuc did not persist as a politically and culturally continuous community

The Host Galaxy and Redshift of the Repeating Fast Radio Burst FRB 121102

The precise localization of the repeating fast radio burst (FRB 121102) has provided the first unambiguous association (chance coincidence probability $p\lesssim3\times10^{-4}$) of an FRB with an optical and persistent radio counterpart. We report on optical imaging and spectroscopy of the counterpart and find that it is an extended ($0.6^{\prime\prime}-0.8^{\prime\prime}$) object displaying prominent Balmer and [OIII] emission lines. Based on the spectrum and emission line ratios, we classify the counterpart as a low-metallicity, star-forming, $m_{r^\prime} = 25.1$ AB mag dwarf galaxy at a redshift of $z=0.19273(8)$, corresponding to a luminosity distance of 972 Mpc. From the angular size, the redshift, and luminosity, we estimate the host galaxy to have a diameter $\lesssim4$ kpc and a stellar mass of $M_*\sim4-7\times 10^{7}\,M_\odot$, assuming a mass-to-light ratio between 2 to 3$\,M_\odot\,L_\odot^{-1}$. Based on the H$\alpha$ flux, we estimate the star formation rate of the host to be $0.4\,M_\odot\,\mathrm{yr^{-1}}$ and a substantial host dispersion measure depth $\lesssim 324\,\mathrm{pc\,cm^{-3}}$. The net dispersion measure contribution of the host galaxy to FRB 121102 is likely to be lower than this value depending on geometrical factors. We show that the persistent radio source at FRB 121102's location reported by Marcote et al (2017) is offset from the galaxy's center of light by $\sim$200 mas and the host galaxy does not show optical signatures for AGN activity. If FRB 121102 is typical of the wider FRB population and if future interferometric localizations preferentially find them in dwarf galaxies with low metallicities and prominent emission lines, they would share such a preference with long gamma ray bursts and superluminous supernovae.Comment: 12 pages, 3 figures, Published in ApJ Letters. V2: Corrected mistake in author lis