1,139 research outputs found
Embryology teaching – improving the learning experience
No full textNikhil V Math, Michael Y MahgereftehFaculty of Medicine, Imperial College London, South Kensington Campus, London, UKWe read with great interest the article by Kazzazi and Bartlett1 regarding embryology teaching methods. While we commend their efforts regarding the condensing of teaching for medical students, we have highlighted the aspects which may be worth considering. The delivery of lectures including case studies is welcomed. Research has shown that not only student satisfaction but also knowledge gained is superior using an integrated teaching approach.2 While a wholly integrated approach also involves exposure to patients and problem-based learning,3 starting by integrating information in the classroom is a cornerstone to success.View the original paper by Kazzazi and Bartlett. 
A hands-on activity to introduce the structure of NV-center quantum bits in diamond
No full textFor the start of a secondary school level lesson series on quantum computing, we designed a hands-on modeling activity where students construct a model diamond lattice with a nitrogen vacancy (NV) defect. NV centers find application as qubits and sensitive magnetometers. This activity aims to help students visualize the structure of such NV centers within the diamond lattice, making the subject matter more tangible. The activity has proven to be challenging but feasible. It features both collaborative and competitive elements thereby surely creating an energizing buzz in the classroom.Science & Engineering EducationScience Education and Communicatio
A 20-bit ±40-mV Range Read-Out IC With 50-nV Offset and 0.04% Gain Error for Bridge Transducers
No full textThis paper presents a 20-b read-out IC with ±40-mV full-scale range that is intended for use with bridge transducers. It consists of a current-feedback instrumentation amplifier (CFIA) followed by a switched-capacitor incremental ΔΣ ADC. The CFIA's offset and 1/ f noise are mitigated by chopping, while its gain accuracy and gain drift are improved by applying dynamic element matching to its input and feedback transconductors. Their mismatch is reduced by a digitally assisted correction loop, which further reduces the CFIA's gain drift. Finally, bulk-biasing and impedance-balancing techniques are used to reduce the common-mode dependency of these transconductors, which would otherwise limit the achievable gain accuracy. The combination of these techniques enables the read-out IC to achieve 140-dB CMRR, a worst-case gain error of 0.04% over a 0-2.5 V common-mode range, a maximum gain drift of 0.7 ppm/°C and an INL of 5 ppm. After applying nested-chopping, the read-out IC achieves 50-nV offset, 6-nV/°C offset drift, a thermal noise floor of 16.2 nV/√Hz and a 0.1-mHz 1/ f noise corner. Implemented in a 0.7-μm CMOS technology, the prototype read-out IC consumes 270 μA from a 5-V supply.Accepted Author ManuscriptElectronic Instrumentatio
Permutation-based presentations for Brin's higher-dimensional Thompson groups
No full textThe higher-dimensional Thompson groups , for , were introduced
by Brin in 2005. We provide new presentations for each of these infinite simple
groups. The first is an infinite presentation, analogous to the Coxeter
presentation for the finite symmetric group, with generating set equal to the
set of transpositions in and reflecting the self-similar structure of
-dimensional Cantor space. We then exploit this infinite presentation to
produce further finite presentations that are considerably smaller than those
previously known.Comment: 23 pages, 2 figures, accepted for publication in J Austral Math So
Detecting and controlling spin pairs near NV centres in diamond
No full textThe development of quantum computers is a monumental challenge for modern physics. One proposed pathway toward a fully scalable and fault-tolerant quantum computer involves the development of a quantum network. Such a network would have applications ranging from distributed quantum computation to fundamentally secure quantum communication. The building blocks of such a network, the nodes, require optical links with which to generate entanglement with other nodes, as well as memory and data qubits to improve the entanglement between nodes and perform computations. In this thesis, we study the dynamics of spin pairs surrounding nitrogen-vacancy(NV) centres in diamond - a promising proposed node for a quantum network. We build on previous work that has successfully detected and controlled pairs of strongly coupled 13C nuclear spins using the NV centre as a probe, and investigate how these spin pairs can be individually addressed using radio frequency pulses.Next, we consider pairs of P1 centres and demonstrate the detection and control of the electron spins of this pair. We show that dynamical decoupling sequences can be used to initialise and readout the electron pair of the P1 centres with high fidelity (∼94 − 96%), and measure natural dephasing times of ∼ 50 ms with the NV centre in the m s = 0 state. The control we demonstrate over pairs of electron spins in P1 centres is an important proof-of-concept that electronic spin defects in diamond can be coherently controlled, and used as memory or data qubits in a future quantum network node.Applied Physic
Diamond NV centers for quantum computing and quantum networks
No full textThe exotic features of quantum mechanics have the potential to revolutionize information technologies. Using superposition and entanglement, a quantum processor could efficiently tackle problems inaccessible to current-day computers. Nonlocal correlations may be exploited for intrinsically secure communication across the globe. Finding and controlling a physical system suitable for fulfi lling these promises is one of the greatest challenges of our time. The nitrogen-vacancy (NV) center in diamond has recently emerged as one of the leading candidates for such quantum information technologies thanks to its combination of atom-like properties and solid-state host environment. We review the remarkable progress made in the past years in controlling electrons, atomic nuclei, and light at the single-quantum level in diamond. We also discuss prospects and challenges for the use of NV centers in future quantum technologies.Quantum NanoscienceApplied Science
Characterization and Optimization of NV-ensemble in Bulk Diamond for Sensing Application
No full textThe nitrogen-vacancy (NV) center in diamond is a promising quantum platform for magnetometry applications exhibiting optical readout of minute energy shifts in its spin sub-levels even at room temperature. In particular, NV-ensembles in bulk diamonds are favored for a considerably improved signal-to-noise ratio and sensitivity. Key material requirements for general NV-ensemble-based applications are a high NV⁻ concentration, a long spin coherence time, and a stable charge state. Additionally, for specific applications that require large detection volumes, for example, the multi-pass readout or cavity coupling, a low optical loss in the material is also an essential need, calling for a low diamond absorption and a low birefringence. These requirements, however, are interdependent and can be difficult to optimize during diamond growth and subsequent NV creation. Therefore, better understanding the correlation between these material properties and finding their balances are crucial for improved sensitivity from the material side.
Chemical vapor deposition (CVD) diamonds typically exhibit NV concentrations below 10 parts per million (ppm), but often show a high homogeneity in the NV distribution. Moreover, the nitrogen incorporation during the CVD synthesis can be precisely controlled. With these advantages, the CVD diamond attracts more and more interest in NV research. In contrast, high-pressure high-temperature (HPHT) synthesis with higher NV concentrations (up to dozens of ppm) is also of great interest. However, its inhomogeneity in the nitrogen distribution and less controllability of the nitrogen concentration raise challenges when applying it to the sensing systems. In this thesis, the author investigates optical, NV and spin properties of diamonds, specifically for CVD diamonds with a wide variety of nitrogen densities but also in comparison with HPHT diamonds. This thesis studies the optimal process in the creation of NV centers and the link to optical properties. The author develops novel optical methods in this thesis to determine the defect concentrations, which are more widely accessible and easier to implement than the conventional methods. Additionally, the author establishes various characterization protocols to systematically study NV and diamond properties. Based on these methods, CVD diamond series with varied nitrogen flow over 4 orders of magnitude are investigated, to understand the incorporation of single substitutional nitrogen atoms (P1 centers) and NV creation during the growth. For a fixed nitrogen concentration, varied electron-irradiation fluences are investigated and optimized for two different accelerated electron energies. Defect transformations during the irradiation and annealing treatments are studied via optical characterizations. The author points out that with increasing fluences a turning point exists, above which mainly the undesirable NV charge state (NV⁰) is being created, indicating an optimum that balances the high conversion efficiency and charge stability. A general approach is suggested by the author to determine the optimal irradiation conditions, for which an enhanced NV concentration and an optimum of NV charge states can both be satisfied. Optimizing the treatment, this thesis achieves spin-spin coherence times T₂ ranging from 45.5 to 549 μs for CVD diamonds containing 168 to 1~parts per billion (ppb) NV⁻ centers, respectively. This enables better combinations of high NV concentrations and long coherence times in bulk diamonds compared to previous works. Diamond is an excellent host for advanced optical/photonic applications, however, doping can compromise the optical properties significantly. Therefore, the author further investigates relationships and ways of combining high NV concentrations with improved optical properties, specifically absorption and birefringence. Based on this, high temperature (HT) treatments are introduced as a promising candidate to reduce optical loss, while not conflicting with the requirement for high NV⁻ concentrations. This thesis shows a pathway to engineering properties of NV-doped CVD diamonds for improved sensitivity
An Energy-Efficient 3.7-nV/√ Hz Bridge Readout IC With a Stable Bridge Offset Compensation Scheme
No full textThis paper describes an energy-efficient bridge readout IC (ROIC), which consists of a capacitively coupled instrumentation amplifier (CCIA) that drives a continuous-time delta–sigma modulator (CTM). By exploiting the CCIA’s abilityto block dc common-mode voltages, the bridge’s bias voltage may exceed the ROIC’s supply voltage, allowing these voltages to be independently optimized. Since bridge output is typically much smaller than bridge offset, a digital to analog converter (DAC) is used to compensate this offset before amplification andthus increase the CCIA’s useful dynamic range. Bridge loading is reduced by using a dual-path positive feedback scheme to boost the CCIA’s input impedance. Furthermore, the CCIA’s output is gated to avoid digitizing its output spikes, which would otherwise limit the ROIC’s linearity and stability. The ROIC achieves an input-referred noise density of 3.7 nV/Hz, a noise efficiency factor (NEF) of 5, and a power efficiency factor (PEF) of 44, which both represent the state of the art. A pressure sensing system, built with the ROIC and a differential pressure sensor (AC4010), achieves 10.1-mPa (1) resolution in a 0.5-ms conversion time. The ROIC dissipates about 30% of the system’s power dissipation and contributes about 6% of its noise power. To reduce the sensor’s offset drift, a temperature compensation scheme based on an external reference resistor is used. After a two-point calibration, this scheme reduces bridge offset drift by 80× over a 50 °C range.Accepted Author ManuscriptElectronic InstrumentationMicroelectronic
Telecom-Band Quantum Interference of Frequency-Converted Photons from Remote Detuned NV Centers
No full textEntanglement distribution over quantum networks has the promise of realizing fundamentally new technologies. Entanglement between separated quantum processing nodes has been achieved on several experimental platforms in the past decade. To move toward metropolitan-scale quantum network test beds, the creation and transmission of indistinguishable single photons over existing telecom infrastructure is key. Here, we report the interference of photons emitted by remote spectrally detuned NV-center-based network nodes, using quantum frequency conversion to the telecom L band. We find a visibility of 0.79±0.03 and an indistinguishability between converted NV photons around 0.9 over the full range of the emission duration, confirming the removal of the spectral information present. Our approach implements fully separated and independent control over the nodes, time multiplexing of control and quantum signals, and active feedback to stabilize the output frequency. Our results demonstrate a working principle that can be readily employed on other platforms and shows a clear path toward generating metropolitan-scale solid-state entanglement over deployed telecom fibers.QID/Hanson LabQN/vanderSarlabQID/Taminiau LabQID/Software GroupBUS/TNO STAFFQN/Hanson La
Interaction between alkali metals and diamond: Etching and charge states of NV centers
No full textSingle crystal diamond particles were heated with liquid phase alkali metals (Li, Na, K) in an argon atmosphere. It was found that Li reacts with the diamond above 600 degrees C, Na makes the surface rougher on a nm scale at 800 degrees C, and K did not change the surface morphology. The etching speed by the reaction with Li is the fastest on the (001) surface. Photoluminescence of the NV- (negatively charged nitrogen vacancy) center decreased only after the annealing with K. DFT calculations explained the strong chemical interaction between Li and the diamond (001) surfaces, and upward band bending at the interfaces with Na and K. The behavior of the NV-center photoluminescence is consistent with the extent of band bending. (C) 2021 Elsevier Ltd. All rights reserved
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