21 research outputs found
Wide bandwidth instantaneous radio frequency spectrum analyzer based on nitrogen vacancy centers in diamond
We propose an original analog method to perform instantaneous and quantitative spectral analysis
of microwave signals. An ensemble of nitrogen-vacancy (NV) centers held in a diamond plate is
pumped by a 532 nm laser. Its photoluminescence is imaged through an optical microscope and
monitored by a digital camera. An incoming microwave signal is converted into a microwave field
in the area of the NV centers by a loop shaped antenna. The resonances induced by the magnetic
component of that field are detected through a decrease of the NV centers photoluminescence. A
magnetic field gradient induces a Zeeman shift of the resonances and transforms the frequency information
into spatial information, which allows for the simultaneous analysis of the microwave
signal in the entire frequency bandwidth of the device. The time dependent spectral analysis of an
amplitude modulated microwave signal is demonstrated over a bandwidth of 600 MHz, associated
to a frequency resolution of 7MHz , and a refresh rate of 4 ms. With such integration time, a field
of a few hundreds of lW can be detected. Since the optical properties of NV centers can be
maintained even in high magnetic field, we estimate that an optimized device could allow
frequency analysis in a range of 30 GHz, only limited by the amplitude of the magnetic field
gradient. In addition, an increase of the NV centers quantity could lead both to an increase of the
microwave sensitivity and to a decrease of the minimum refresh rate down to a few ls
Nanoscale nuclear magnetic resonance with a 1.9-nm-deep nitrogen-vacancy sensor
We present nanoscale nuclear magnetic resonance (NMR) measurements performed with
nitrogen-vacancy (NV) centers located down to about 2 nm from the diamond surface. NV centers
were created by shallow ion implantation followed by a slow, nanometer-by-nanometer removal of
diamond material using oxidative etching in air. The close proximity of NV centers to the surface
yielded large 1H NMR signals of up to 3.4 lT-rms, corresponding to ~330 statistically polarized or
~10 fully polarized proton spins in a (1.8 nm)3 detection volume
Searching for the optimal number of response alternatives for the distress scale of the four-dimensional symptom questionnaire
BACKGROUND: The Four-Dimensional Symptom Questionnaire (4DSQ) is a self-report questionnaire designed to measure distress, depression, anxiety, and somatization. Prior to computing scale scores from the item scores, the three highest response alternatives ('Regularly', 'Often', and 'Very often or constantly present') are usually collapsed into one category to reduce the influence of extreme responding on item- and scale scores. In this study, we evaluate the usefulness of this transformation for the distress scale based on a variety of criteria. METHODS: Specifically, by using the Graded Response Model, we investigated the effect of this transformation on model fit, local measurement precision, and various indicators of the scale's validity to get an indication on whether the current practice of recoding should be advocated or not. In particular, the effect on the convergent- (operationalized by the General Health Questionnaire and the Maastricht Questionnaire), divergent- (operationalized by the Neuroticism scale of the NEO-FFI), and predictive validity (operationalized as obtrusion with daily chores and activities, the Biographical Problem list and the Utrecht Burnout Scale) of the distress scale was investigated. RESULTS: Results indicate that recoding leads to (i) better model fit as indicated by lower mean probabilities of exact test statistics assessing item fit, (ii) small (<.02) losses in the sizes of various validity coefficients, and (iii) a decrease (DIFF (SE's) = .10-.25) in measurement precision for medium and high levels of distress. CONCLUSIONS: For clinical applications and applications in longitudinal research, the current practice of recoding should be avoided because recoding decreases measurement precision for medium and high levels of distress. It would be interesting to see whether this advice also holds for the three other domains of the 4DSQ
Nanoimplantation and Purcell enhancement of single nitrogen-vacancy centers in photonic crystal cavities in diamond
We present the controlled creation of single nitrogen-vacancy (NV) centers via ion implantation at
the center of a photonic crystal cavity which is fabricated in an ultrapure, single crystal diamond
membrane. High-resolution placement of NV centers is achieved using collimation of a
5 keV-nitrogen ion beam through a pierced tip of an atomic force microscope. We demonstrate
coupling of the implanted NV centers’ broad band fluorescence to a cavity mode and observe
Purcell enhancement of the spontaneous emission. The results are in good agreement with a master
equation model for the cavity coupling
Identifying levels of general distress in first line mental health services:can GP- and eHealth clients' scores be meaningfully compared?
BACKGROUND: The Four-Dimensional Symptom Questionnaire (4DSQ) (Huisarts Wetenschap 39: 538-47, 1996) is a self-report questionnaire developed in the Netherlands to distinguish non-specific general distress from depression, anxiety, and somatization. This questionnaire is often used in different populations and settings and there is a paper-and-pencil and computerized version. METHODS: We used item response theory to investigate whether the 4DSQ measures the same construct (structural equivalence) in the same way (scalar equivalence) in two samples comprised of primary mental health care attendees: (i) clients who visited their General Practitioner responded to the 4DSQ paper-and-pencil version, and (ii) eHealth clients responded to the 4DSQ computerized version. Specifically, we investigated whether the distress items functioned differently in eHealth clients compared to General Practitioners' clients and whether these differences lead to substantial differences at scale level. RESULTS: Results showed that in general structural equivalence holds for the distress scale. This means that the distress scale measures the same construct in both General Practitioners' clients and eHealth clients. Furthermore, although eHealth clients have higher observed distress scores than General Practitioners' clients, application of a multiple group generalized partial credit response model suggests that scalar equivalence holds. CONCLUSIONS: The same cutoff scores can be used for classifying respondents as having low, moderate and high levels of distress in both settings
Statistical investigations on nitrogen-vacancy center creation
Quantum information technologies require networks of interacting defect bits. Color centers,
especially the nitrogen vacancy (NV-) center in diamond, represent one promising avenue, toward
the realisation of such devices. The most successful technique for creating NV- in diamond is ion
implantation followed by annealing. Previous experiments have shown that shallow nitrogen
implantation (<10 keV) results in NV- centers with a yield of 0.01%–0.1%. We investigate the
influence of channeling effects during shallow implantation and statistical diffusion of vacancies
using molecular dynamics and Monte Carlo simulation techniques. Energy barriers for the
diffusion process were calculated using density functional theory. Our simulations show that 25%
of the implanted nitrogens form a NV center, which is in good agreement with our experimental
findings
Stark shift and field ionization of arsenic donors in 28Si-silicon-on-insulator structures
We develop an efficient back gate for silicon-on-insulator (SOI) devices operating at cryogenic
temperatures and measure the quadratic hyperfine Stark shift parameter of arsenic donors in
isotopically purified 28Si-SOI layers using such structures. The back gate is implemented using
MeV ion implantation through the SOI layer forming a metallic electrode in the handle wafer,
enabling large and uniform electric fields up to 2V/lm to be applied across the SOI layer. Utilizing
this structure, we measure the Stark shift parameters of arsenic donors embedded in the 28Si-SOI
layer and find a contact hyperfine Stark parameter of na=-1.9+/-0.7x10-3 lm2/V2. We also
demonstrate electric-field driven dopant ionization in the SOI device layer, measured by electron
spin resonance
Nanoscale nuclear magnetic resonance with a 1.9-nm-deep nitrogen-vacancy sensor
We present nanoscale nuclear magnetic resonance (NMR) measurements performed with
nitrogen-vacancy (NV) centers located down to about 2 nm from the diamond surface. NV centers
were created by shallow ion implantation followed by a slow, nanometer-by-nanometer removal of
diamond material using oxidative etching in air. The close proximity of NV centers to the surface
yielded large 1H NMR signals of up to 3.4 lT-rms, corresponding to ~330 statistically polarized or
~10 fully polarized proton spins in a (1.8 nm)3 detection volume
Nanoscale nuclear magnetic resonance with a 1.9-nm-deep nitrogen-vacancy sensor
We present nanoscale nuclear magnetic resonance (NMR) measurements performed with
nitrogen-vacancy (NV) centers located down to about 2 nm from the diamond surface. NV centers
were created by shallow ion implantation followed by a slow, nanometer-by-nanometer removal of
diamond material using oxidative etching in air. The close proximity of NV centers to the surface
yielded large 1H NMR signals of up to 3.4 lT-rms, corresponding to ~330 statistically polarized or
~10 fully polarized proton spins in a (1.8 nm)3 detection volume
Wide bandwidth instantaneous radio frequency spectrum analyzer based on nitrogen vacancy centers in diamond
We propose an original analog method to perform instantaneous and quantitative spectral analysis
of microwave signals. An ensemble of nitrogen-vacancy (NV) centers held in a diamond plate is
pumped by a 532 nm laser. Its photoluminescence is imaged through an optical microscope and
monitored by a digital camera. An incoming microwave signal is converted into a microwave field
in the area of the NV centers by a loop shaped antenna. The resonances induced by the magnetic
component of that field are detected through a decrease of the NV centers photoluminescence. A
magnetic field gradient induces a Zeeman shift of the resonances and transforms the frequency information
into spatial information, which allows for the simultaneous analysis of the microwave
signal in the entire frequency bandwidth of the device. The time dependent spectral analysis of an
amplitude modulated microwave signal is demonstrated over a bandwidth of 600 MHz, associated
to a frequency resolution of 7MHz , and a refresh rate of 4 ms. With such integration time, a field
of a few hundreds of lW can be detected. Since the optical properties of NV centers can be
maintained even in high magnetic field, we estimate that an optimized device could allow
frequency analysis in a range of 30 GHz, only limited by the amplitude of the magnetic field
gradient. In addition, an increase of the NV centers quantity could lead both to an increase of the
microwave sensitivity and to a decrease of the minimum refresh rate down to a few ls