Renormalization of the tunnel splitting in a rotating nanomagnet

We study spin tunneling in a magnetic nanoparticle with biaxial anisotropy that is free to rotate about its anisotropy axis. Exact instanton of the coupled equations of motion is found that connects degenerate classical energy minima. We show that mechanical freedom of the particle renormalizes magnetic anisotropy and increases the tunnel splitting.Comment: 4 pages, 3 figure

Hamiltonian engineering with constrained optimization for quantum sensing and control

While quantum devices rely on interactions between constituent subsystems and with their environment to operate, native interactions alone often fail to deliver targeted performance. Coherent pulsed control provides the ability to tailor effective interactions, known as Hamiltonian engineering. We propose a Hamiltonian engineering method that maximizes desired interactions while mitigating deleterious ones by conducting a pulse sequence search using constrained optimization. The optimization formulation incorporates pulse sequence length and cardinality penalties consistent with linear or integer programming. We apply the general technique to magnetometry with solid state spin ensembles in which inhomogeneous interactions between sensing spins limit coherence. Defining figures of merit for broadband Ramsey magnetometry, we present novel pulse sequences which outperform known techniques for homonuclear spin decoupling in both spin-1/2 and spin-1 systems. When applied to nitrogen vacancy (NV) centers in diamond, this scheme partially preserves the Zeeman interaction while zeroing dipolar coupling between negatively charged NV - centers. Such a scheme is of interest for NV - magnetometers which have reached the NV - -NV - coupling limit. We discuss experimental implementation in NV ensembles, as well as applicability of the current approach to more general spin bath decoupling and superconducting qubit control.Air Force Contract (FA8702-15-D-0001

Plastic scintillator-based fibre dosimeters for measurement of X-ray pulses in a clinical setting

This work presents the development of plastic scintillator (BCF-10) based optical fibre sensors for medical radiotherapy dosimetry. Two different designs of BCF10 joined to PMMA (Polymethyl methacrylate) fibre were considered, based on simple Plug and Play designs for the rapid and effective assembly of radiation sensors. The first design was a simple butt-coupling arrangement sheathed in tubing, with an outer diameter of <2 mm. The second design explored the coupling joint of a cylindrical protrusion and hollow part of BCF10-PMMA that were achieved using femtosecond laser machining; the purpose of which was to maintain the original 1-mm fibre diameter for the sensor probe. The two fibres were pressed together and sealed with UV curing, hence the reference to a Plug and Play architecture. Both sensors exhibit higher output counts at the higher dose rate (due to the higher number of radiation pulses), although a discernible signal is observed at 50 MU/min for 6 MV, 15 MV energies and both sensors. When comparing both sensors with the different joint coupling designs, the flat surface connection of BCF-10 to PMMA demonstrates slightly higher photon counts compared with the micro-machined sensor (Plug n Play). However, the difference is small and the Plug n Play sensor benefits from the smaller sensor diameter (1 mm diameter), which is suitable for inserting into a small applicator or in-vivo monitoring. In the second section, micro-pulses of X-Ray radiation from Siemens Linear Accelerator (linac) were obtained and compared for two different energies and dose rates. Both of the sensors demonstrate the feasibility to be used for characterisation of X-ray pulses from a clinical linac

Cavity-enhanced microwave readout of a solid-state spin sensor

Overcoming poor readout is an increasingly urgent challenge for devices based on solid-state spin defects, particularly given their rapid adoption in quantum sensing, quantum information, and tests of fundamental physics. However, in spite of experimental progress in specific systems, solid-state spin sensors still lack a universal, high-fidelity readout technique. Here we demonstrate high-fidelity, room-temperature readout of an ensemble of nitrogen-vacancy centers via strong coupling to a dielectric microwave cavity, building on similar techniques commonly applied in cryogenic circuit cavity quantum electrodynamics. This strong collective interaction allows the spin ensemble’s microwave transition to be probed directly, thereby overcoming the optical photon shot noise limitations of conventional fluorescence readout. Applying this technique to magnetometry, we show magnetic sensitivity approaching the Johnson–Nyquist noise limit of the system. Our results pave a clear path to achieve unity readout fidelity of solid-state spin sensors through increased ensemble size, reduced spin-resonance linewidth, or improved cavity quality factor

Deconstruction of Crystalline Networks into Underlying Nets: Relevance for Terminology Guidelines and Crystallographic Databases

This communication briefly reviews why network topology is an important tool (for understanding, comparing, communicating, designing, and solving crystal structures from powder diffraction data) and then discusses the terms of an IUPAC project dealing with various aspects of network topology. One is the ambiguity in node assignment, and this question is addressed in more detail. First, we define the most important approaches: the &quot;all node&quot; deconstruction considering all branch points of the linkers, the &quot;single node&quot; deconstruction considering only components mixed, and the ToposPro &quot;standard representation&quot; also considering linkers as one node but, if present, takes each metal atom as a separate node. These methods are applied to a number of metal organic framework structures (MOFs, although this is just one example of materials this method is applicable on), and it is concluded that the &quot;all node&quot; method potentially yields more information on the structure in question but cannot be recommended as the only way of reporting the network topology. In addition, several terms needing definitions are discussed

Resilient Characteristics as Described in Empirical Studies on Health Care

The concept of resilience needs greater empirical clarity. The literature on resilience in health care, published between 2006 and 2016, was reviewed with the aim of describing resilient characteristics in empirical studies. The chapter documents resilient characteristics at the individual, team, management, and organizational level. The characteristics were related to four overall conceptual categories: anticipation, sensemaking, trade-offs and adaptation. Based on empirical accounts resilience is described as a set of cognitive and behavioral strategies of individuals who enact resilience within an organizational context. The characteristics represented should be seen as examples of how resilience is described in the applied health care research, thus informing possible operationalization of resilience