On-chip electron spin resonance for quantum device applications

Electron Spin Resonance (ESR) is an essential technique for characterising materials with unpaired electrons. Improving the sensitivity of ESR measurements is a major research goal to bring the benefits of such characterisation to ever smaller or more dilute samples. This has been given added prominence by the rise in solid state quantum information processing technology with the concurrent investigation and manipulation of materials and surfaces in solid state devices at ever diminishing length scales. We establish a testbed system for the development of high-sensitivity ESR techniques for small samples at millikelvin temperatures. Our system is centred on a high Q niobium nitride planar superconducting resonator designed to have a concentrated mode volume to couple to a small amount of paramagnetic material, with resilience to magnetic fields of up to 400 mT. In our first set of measurements on our resonator `chip' we demonstrate high-cooperativity coupling between an organic radical microcrystal containing 10^{12} spins in a pico-litre volume, and our resonator mode, at 65 mK. Conventional ESR spectrometers by contrast ordinarily measure sample volumes a million times larger. We detect a saturation recovery relaxation rate via the dispersive frequency shift of the resonator. Techniques such as these could be suitable for reading out the quantum state of the spin ensemble in quantum information memory protocols. The second set of measurements presented here demonstrate the capability of the pulsed ESR spectrometer developed in this thesis. We use the custom-built framework to characterise a sample of rare earth-doped crystalline solid, potentially of interest as a quantum information storage medium, over 10 to 400 mK. This experiment also reaches the high-cooperativity regime, mediated by the high Q superconducting resonator. ESR measurements with even further enhanced coupling might eventually allow for pulsed ESR interrogation of very few spins and provide insights into the surface chemistry of, for example, material defects in superconducting quantum processors. As such, the framework is of interest for developing on-chip ESR techniques of the kind that could, in the future, enhance our understanding of the materials of solid state quantum devices.Open Acces

Tuning the onset voltage of resonant tunneling through InAs quantum dots by growth parameters

We investigated the size dependence of the ground state energy in self-assembled InAs quantum dots embedded in resonant tunneling diodes. Individual current steps observed in the current-voltage characteristics are attributed to resonant single-electron tunneling via the ground state of individual InAs quantum dots. The onset voltage of the first step observed is shown to decrease systematically from 200 mV to 0 with increasing InAs coverage. We relate this to a coverage-dependent size of InAs dots grown on AlAs. The results are confirmed by atomic force micrographs and photoluminescence experiments on reference samples.Comment: 3 pages, 3 figure

Adding a subjective dimension to an ICF-based disability measure for people with multiple sclerosis: development and use of a measure for perception of disabilities

OBJECTIVE: The subjective dimension of disability, the perception of disability, is a dimension missing from the International Classification of Functioning, Disability and Health (ICF), and from health-related quality of life (HRQOL) instruments. However, it is a highly relevant dimension for clinical practice as perceived disability may identify care needs. We therefore developed a measure for this subjective dimension of disability in multiple sclerosis (MS) and examined the contribution of this dimension to QOL. METHOD: A measure named the Multiple Sclerosis Impact Profile-Disability Perception (MSIP-DP) was developed to reflect a person's perception of disabilities reported using the original MSIP-disability (MSIP-D) items. MS patients (n=530) completed both MSIP sections, the medical outcome study short form questionnaire (SF-36), the World Health Organisation Quality Of Life-BREF (WHOQOL-BREF) and questions concerning disease severity. The contribution of disability perception (DP) to QOL in MS was estimated using hierarchical multiple regression analyses after controlling for MS severity. RESULTS: Confirmative factor analysis confirmed the hypothesised disability perception domains that correspond with the related disability domains in the MSIP. DP scales yielded sufficient reliability. DP explained a unique and substantial part of the variance in QOL, particularly the perception of impairments in mental functions. DISCUSSION: Results indicated that the subjective dimension of functioning and health operationalised in the MSIP-DP is a relevant concept in explaining QOL in MS. In clinical practice psychological interventions addressing a patient's perception of disability, particularly of impairments in mental functioning, may contribute to QOL

Back to the Future: How Do We Get There From Here? Making Restoration Work

Extreme temperatures and long periods of drought observed with increasing frequency in the southeastern United States (U.S.) have demonstrated the need to develop more robust forage systems. Native warmseason grasses (NWSGs) are well adapted to fill this role, but their expanded use comes with several challenges, most notably, reliable establishment. The high cost of site preparation, high cost of seed, and slow initial growth of NWSG seedlings must be addressed to achieve increased adoption of NWSG in the eastern U.S. If these challenges are overcome, incorporating NWSG into grazing systems would benefit producers by filling the summer forage gap, mitigating drought risk, and extending the grazing season, while also enhancing native biodiversity

Anisotropic diffusion of spherical particles in closely confining microchannels

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.We present here the measurement of the diffusivity of spherical particles closely confined by narrow microchannels. Our experiments yield a two-dimensional map of the position-dependent diffusion coefficients parallel and perpendicular to the channel axis with a resolution down to 129 nm. The diffusivity was measured simultaneously in the channel interior, the bulk reservoirs, as well as the channel entrance region. In the channel interior we found strongly anisotropic diffusion. While the perpendicular diffusion coefficient close to the confining walls decreased down to approximately 25% of the value on the channel axis, the parallel diffusion coefficient remained constant throughout the entire channel width. In addition to the experiment, we performed finite element simulations for the diffusivity in the channel interior and found good agreement with the measurements. Our results reveal the distinctive influence of strong confinement on Brownian motion, which is of significance to microfluidics as well as quantitative models of facilitated membrane transport.S.L.D. acknowledges funding from the German Academic Exchange Service (DAAD) and the German National Academic Foundation. S.P. and U.F.K. were supported by an ERC starting grant. S.P. also acknowledges support from the Leverhulme Trust and the Newton Trust through an Early Career Fellowship

Specific Biosensing Using DNA Aptamers and Nanopores

The multiplexed biosensing of target molecules with high specificity and accuracy is of fundamental importance in both biological research and medical diagnostics. In this paper, the working range of the recent nanopore-DNA carrier based method is extended by introducing a two-step assay using specific DNA aptamers. A signal translation step allows for binding of the target in physiological conditions before the nanopore measurements. Using protein encoded DNA carriers, the simultaneous detection of three targets spanning several orders of magnitude in molecular weight is demonstrated. The single-molecule method may be integrated into nanopore sensing devices for future applied research and point-of-care applications

Lean Restaurants: Improving the Dining Experience

Myriad examples exist to describe how lean concepts are applied in the manufacturing and healthcare industries; however, research regarding how lean is applied in the food service industry is sparse. The purpose of this case study is to discover how lean applications are currently being applied in three different full-service dining establishments located in Knoxville, Tennesse

Nondeterministic self-assembly with asymmetric interactions.

We investigate general properties of nondeterministic self-assembly with asymmetric interactions, using a computational model and DNA tile assembly experiments. By contrasting symmetric and asymmetric interactions we show that the latter can lead to self-limiting cluster growth. Furthermore, by adjusting the relative abundance of self-assembly particles in a two-particle mixture, we are able to tune the final sizes of these clusters. We show that this is a fundamental property of asymmetric interactions, which has potential applications in bioengineering, and provides insights into the study of diseases caused by protein aggregation.Winton Programme for the Physics of Sustainability, Gates Cambridge, Oppenheimer PhD studentship, NanoDTC Cambridge (Grant ID: EP/L015978/1), Engineering and Physical Sciences Research Council (Grant ID: EP/L504920/1), Royal SocietyThis is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevE.94.02240

Nondecaying hydrodynamic interactions along narrow channels

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Particle-particle interactions are of paramount importance in every multibody system as they determine the collective behavior and coupling strength. Many well-known interactions such as electrostatic, van der Waals, or screened Coulomb interactions, decay exponentially or with negative powers of the particle spacing r. Similarly, hydrodynamic interactions between particles undergoing Brownian motion decay as 1/r in bulk, and are assumed to decay in small channels. Such interactions are ubiquitous in biological and technological systems. Here we confine two particles undergoing Brownian motion in narrow, microfluidic channels and study their coupling through hydrodynamic interactions. Our experiments show that the hydrodynamic particle-particle interactions are distance independent in these channels. This finding is of fundamental importance for the interpretation of experiments where dense mixtures of particles or molecules diffuse through finite length, water-filled channels or pore networks.U. F. K. was supported by an ERC starting Grant No. (PassMembrane 261101). S. P. acknowledges funding from a Leverhulme Early Career Fellowship. K. M. was supported by a grant from the EPSRC. E. L. was supported by a Marie Curie CIG grant from the EU

TGFBR3 variation is not a common cause of Marfan-like syndrome and Loeys-Dietz-like syndrome

Marfan syndrome (MFS) is caused by mutations in the fibrillin-1 (FBN1) gene, and mutations in FBN1 are known to be responsible for over 90% of all MFS cases. Locus heterogeneity has also been reported and confirmed, with mutations in the receptor genes TGFBR1 and TGFBR2 identified in association with MFS-related phenotypes. It is now known that dysregulation of TGF-ß signaling is involved in MFS pathogenesis. To test the hypothesis that dysregulation of TGFBR3-associated TGF-ß signaling is implicated in MFS or related phenotype pathogenesis, we selected a cohort of 49 patients, fulfilling or nearly fulfilling the diagnostic criteria for MFS. The patients were known not to carry a mutation in the FBN1 gene (including three 5' upstream alternatively spliced exons), the TGFBR1 and TGFBR2 genes. Mutation screening for the TGFBR3 gene in these patients and in controls led to the identification of a total of ten exonic (one novel), four intronic (one novel) and one 3'UTR variant in the TGFBR3 gene. Our data suggest that variations in TGFBR3 gene appear not to be associated with MFS or related phenotype