1,370 research outputs found
Polarization mode dispersion in radio-frequency interferometric embedded fiber-optic sensors
The effect of fiber birefringence on the propagation delay in an embedded fiber-optic strain sensor is studied. The polarization characteristics of the sensor are described in terms of polarization mode dispersion through the principal states of polarization and their differential group delay. Using these descriptors, an analytical expression for the response of the sensor for an arbitrary input state of polarization is given and experimentally verified. It is found that the differential group delay, as well as the input and output principal states of polarization, vary when the embedded fiber is strained, leading to fluctuations in the sensor output. The use of high birefringence fibers and different embedding geometries is examined as a means for reducing the polarization dependency of the sensor
Identification of Si-vacancy related room temperature qubits in 4H silicon carbide
Identification of microscopic configuration of point defects acting as
quantum bits is a key step in the advance of quantum information processing and
sensing. Among the numerous candidates, silicon vacancy related centers in
silicon carbide (SiC) have shown remarkable properties owing to their
particular spin-3/2 ground and excited states. Although, these centers were
observed decades ago, still two competing models, the isolated negatively
charged silicon vacancy and the complex of negatively charged silicon vacancy
and neutral carbon vacancy [Phys. Rev. Lett.\ \textbf{115}, 247602 (2015)] are
argued as an origin. By means of high precision first principles calculations
and high resolution electron spin resonance measurements, we here unambiguously
identify the Si-vacancy related qubits in hexagonal SiC as isolated negatively
charged silicon vacancies. Moreover, we identify the Si-vacancy qubit
configurations that provide room temperature optical readout.Comment: 3 figure
Dark states of single NV centers in diamond unraveled by single shot NMR
The nitrogen-vacancy (NV) center in diamond is supposed to be a building
block for quantum computing and nanometer scale metrology at ambient
conditions. Therefore, precise knowledge of its quantum states is crucial.
Here, we experimentally show that under usual operating conditions the NV
exists in an equilibrium of two charge states (70% in the expected negative
(NV-) and 30% in the neutral one (NV0)). Projective quantum non-demolition
measurement of the nitrogen nuclear spin enables the detection even of the
additional, optically inactive state. The nuclear spin can be coherently driven
also in NV0 (T1 ~ 90 ms and T2 ~ 6 micro-s).Comment: 4 pages, 3 figure
Characterization of the nitrogen split interstitial defect in wurtzite aluminum nitride using density functional theory
We carried out Heyd-Scuseria-Ernzerhof hybrid density functional theory plane
wave supercell calculations in wurtzite aluminum nitride in order to
characterize the geometry, formation energies, transition levels and hyperfine
tensors of the nitrogen split interstitial defect. The calculated hyperfine
tensors may provide useful fingerprint of this defect for electron paramagnetic
resonance measurement.Comment: 5 pages, 3 figure
Entrepreneurial orientation and firm performance in the context of upper echelon theory.
Entrepreneurial Orientation (EO) is a firm-level phenomenon, which
involves the firm’s prospects to take risks, be proactive, and be innovative.
Most of the research assumes a positive EO-performance relationship
adopting the EO-as-advantage perspective without providing enough
theoretical foundations of the way EO enhances performance. This paper
provides insights into the EO and firm performance relationship looking into
the EO-as-experimentation perspective. Through EO-as-experimentation
perspective, we argue for the importance of looking into the differential
effects of each of the EO dimensions on firm performance in active and
inactive firms. We hypothesized that the effect of each of the proactiveness
and innovativeness dimension of EO on firm performance is positive among
active firms and negative among inactive firms. Whereas risk taking
dimension of EO is negative among active and inactive firms. Based on the
results of firm fixed effect regression some empirical support for the
hypotheses is presented and discussed
Single-photon emitting diode in silicon carbide
Electrically driven single-photon emitting devices have immediate
applications in quantum cryptography, quantum computation and single-photon
metrology. Mature device fabrication protocols and the recent observations of
single defect systems with quantum functionalities make silicon carbide (SiC)
an ideal material to build such devices. Here, we demonstrate the fabrication
of bright single photon emitting diodes. The electrically driven emitters
display fully polarized output, superior photon statistics (with a count rate
of 300 kHz), and stability in both continuous and pulsed modes, all at room
temperature. The atomic origin of the single photon source is proposed. These
results provide a foundation for the large scale integration of single photon
sources into a broad range of applications, such as quantum cryptography or
linear optics quantum computing.Comment: Main: 10 pages, 6 figures. Supplementary Information: 6 pages, 6
figure
Effects of low energy electron irradiation on formation of nitrogen-vacancy centers in single-crystal diamond
Exposure to beams of low energy electrons (2 to 30 keV) in a scanning
electron microscope locally induces formation of NV-centers without thermal
annealing in diamonds that have been implanted with nitrogen ions. We find that
non-thermal, electron beam induced NV-formation is about four times less
efficient than thermal annealing. But NV-center formation in a consecutive
thermal annealing step (800C) following exposure to low energy electrons
increases by a factor of up to 1.8 compared to thermal annealing alone. These
observations point to reconstruction of nitrogen-vacancy complexes induced by
electronic excitations from low energy electrons as an NV-center formation
mechanism and identify local electronic excitations as a means for spatially
controlled room-temperature NV-center formation
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