100 research outputs found
What Worked, What Did Not: University Instruction during a Pandemic
In this report, we discuss the experience of both lecturing and teaching laboratory classes during a pandemic at the University of Mississippi (UM). UM is a relatively rural university with approximately 20 000 students. The instructional approaches that we attempted would be significantly more difficult to implement at universities with larger class sizes, geographically more restricted with regard to climate, or more urban with confined space, yet we observed many failures, even at a rural, spacious campus. Here, we note the various models of instruction that—in our case—could be separated into three approaches: in-person (i.e., traditional face-to-face instruction), online only, and a hybrid model with some component of the two (1). We discuss our experiences of what went right and what went wrong with each approach. Given that similar approaches have been undertaken around the globe, we use this report to relate what we observed as both effective and noneffective for our style of university, with special emphasis on physical biochemical laboratory training of students
Optical patterning of trapped charge in nitrogen-doped diamond
The nitrogen-vacancy (NV) centre in diamond is emerging as a promising
platform for solid-state quantum information processing and nanoscale
metrology. Of interest in these applications is the manipulation of the NV
charge, which can be attained by optical excitation. Here we use two-color
optical microscopy to investigate the dynamics of NV photo-ionization, charge
diffusion, and trapping in type-1b diamond. We combine fixed-point laser
excitation and scanning fluorescence imaging to locally alter the concentration
of negatively charged NVs, and to subsequently probe the corresponding
redistribution of charge. We uncover the formation of spatial patterns of
trapped charge, which we qualitatively reproduce via a model of the interplay
between photo-excited carriers and atomic defects. Further, by using the NV as
a probe, we map the relative fraction of positively charged nitrogen upon
localized optical excitation. These observations may prove important to
transporting quantum information between NVs or to developing
three-dimensional, charge-based memories
Observation of the dynamic Jahn-Teller effect in the excited states of nitrogen-vacancy centers in diamond
The optical transition linewidth and emission polarization of single
nitrogen-vacancy (NV) centers are measured from 5 K to room temperature.
Inter-excited state population relaxation is shown to broaden the zero-phonon
line and both the relaxation and linewidth are found to follow a T^5 dependence
for T up to 100 K. This dependence indicates that the dynamic Jahn-Teller
effect is the dominant dephasing mechanism for the NV optical transitions at
low temperatures
Spin-flip and spin-conserving optical transitions of the nitrogen-vacancy centre in diamond
We map out the first excited state sublevel structure of single nitrogen-vacancy (NV) colour centres in diamond. The excited state is an orbital doublet where one branch supports an efficient cycling transition, while the other can simultaneously support fully allowed optical Raman spin-flip transitions. This is crucial for the success of many recently proposed quantum information applications of the NV defects. We further find that an external electric field can be used to completely control the optical properties of a single centre. Finally, a group theoretical model is developed that explains the observations and provides good physical understanding of the excited state structure
Spin coherent quantum transport of electrons between defects in diamond
The nitrogen-vacancy color center in diamond has rapidly emerged as an
important solid-state system for quantum information processing. While
individual spin registers have been used to implement small-scale diamond
quantum computing, the realization of a large-scale device requires development
of an on-chip quantum bus for transporting information between distant qubits.
Here we propose a method for coherent quantum transport of an electron and its
spin state between distant NV centers. Transport is achieved by the
implementation of spatial stimulated adiabatic Raman passage through the
optical control of the NV center charge states and the confined conduction
states of a diamond nanostructure. Our models show that for two NV centers in a
diamond nanowire, high fidelity transport can be achieved over distances of
order hundreds of nanometres in timescales of order hundreds of nanoseconds.
Spatial adiabatic passage is therefore a promising option for realizing an
on-chip spin quantum bus
Oral prion neuroinvasion occurs independently of PrPC expression in the gut epithelium
The early replication of certain prion strains within Peyer’s patches in the
small intestine is essential for the efficient spread of disease to the brain after oral exposure.
Our data show that orally acquired prions utilize specialized gut epithelial cells
known as M cells to enter Peyer’s patches. M cells express the cellular isoform of the
prion protein, PrPC, and this may be exploited by some pathogens as an uptake receptor
to enter Peyer’s patches. This suggested that PrPC might also mediate the uptake
and transfer of prions across the gut epithelium into Peyer’s patches in order to establish
infection. Furthermore, the expression level of PrPC in the gut epithelium could influence
the uptake of prions from the lumen of the small intestine. To test this hypothesis,
transgenic mice were created in which deficiency in PrPC was specifically restricted
to epithelial cells throughout the lining of the small intestine. Our data clearly show that
efficient prion neuroinvasion after oral exposure occurred independently of PrPC expression
in small intestinal epithelial cells. The specific absence of PrPC in the gut epithelium
did not influence the early replication of prions in Peyer’s patches or disease susceptibility.
Acute mucosal inflammation can enhance PrPC expression in the intestine, implying
the potential to enhance oral prion disease pathogenesis and susceptibility. However,
our data suggest that the magnitude of PrPC expression in the epithelium lining the
small intestine is unlikely to be an important factor which influences the risk of oral
prion disease susceptibility.
IMPORTANCE The accumulation of orally acquired prions within Peyer’s patches in the
small intestine is essential for the efficient spread of disease to the brain. Little is known
of how the prions initially establish infection within Peyer’s patches. Some gastrointestinal
pathogens utilize molecules, such as the cellular prion protein PrPC, expressed on
gut epithelial cells to enter Peyer’s patches. Acute mucosal inflammation can enhance
PrPC expression in the intestine, implying the potential to enhance oral prion disease
susceptibility. We used transgenic mice to determine whether the uptake of prions into
Peyer’s patches was dependent upon PrPC expression in the gut epithelium. We show
that orally acquired prions can establish infection in Peyer’s patches independently of
PrPC expression in gut epithelial cells. Our data suggest that the magnitude of PrPC expression
in the epithelium lining the small intestine is unlikely to be an important factor
which influences oral prion disease susceptibility
Magnetic field induced delocalization in hybrid electron-nuclear spin ensembles
We use field-cycling-assisted dynamic nuclear polarization and continuous radio-frequency (RF) driving over a broad spectral range to demonstrate magnetic-field-dependent activation of nuclear spin transport from strongly hyperfine-coupled C13 sites in diamond. We interpret our observations with the help of a theoretical framework where nuclear spin interactions are mediated by electron spins. In particular, we build on the results from a four-spin toy model to show how otherwise localized nuclear spins must thermalize as they are brought in contact with a larger ancilla spin network. Further, by probing the system response to a variable driving field amplitude, we witness stark changes in the RF-absorption spectrum, which we interpret as partly due to contributions from heterogeneous multispin sets, whose zero-quantum transitions become RF active thanks to the hybrid electron-nuclear nature of the system. These findings could prove relevant in applications to dynamic nuclear polarization, spin-based quantum information processing, and nanoscale sensing.Fil: Pagliero, Daniela. City University Of New York. The Graduate Center; Estados UnidosFil: Zangara, Pablo René. Universidad Nacional de Córdoba. Facultad de Matemática, AstronomÃa y FÃsica; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Córdoba. Instituto de FÃsica Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de FÃsica Enrique Gaviola; ArgentinaFil: Henshaw, Jacob. City University of New York. The City College of New York; Estados UnidosFil: Ajoy, Ashok. University of California at Berkeley; Estados UnidosFil: Acosta, Rodolfo Héctor. Universidad Nacional de Córdoba. Facultad de Matemática, AstronomÃa y FÃsica; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Córdoba. Instituto de FÃsica Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de FÃsica Enrique Gaviola; ArgentinaFil: Manson, Neil. Australian National University; AustraliaFil: Reimer, Jeffrey A.. University of California at Berkeley; Estados Unidos. Lawrence Berkeley National Laboratory; Estados UnidosFil: Pines, Alexander. University of California at Berkeley; Estados Unidos. Lawrence Berkeley National Laboratory; Estados UnidosFil: Meriles, Carlos A.. City University Of New York. The Graduate Center; Estados Unido
Magnetic-field-induced delocalization in hybrid electron-nuclear spin ensembles
We use field-cycling-assisted dynamic nuclear polarization and continuous
radio-frequency (RF) driving over a broad spectral range to demonstrate
magnetic-field-dependent activation of nuclear spin transport from
strongly-hyperfine-coupled 13C sites in diamond. We interpret our observations
with the help of a theoretical framework where nuclear spin interactions are
mediated by electron spins. In particular, we build on the results from a
4-spin toy model to show how otherwise localized nuclear spins must thermalize
as they are brought in contact with a larger ancilla spin network. Further, by
probing the system response to a variable driving field amplitude, we witness
stark changes in the RF-absorption spectrum, which we interpret as partly due
to contributions from heterogeneous multi-spin sets, whose 'zero-quantum'
transitions become RF active thanks to the hybrid electron-nuclear nature of
the system. These findings could prove relevant in applications to dynamic
nuclear polarization, spin-based quantum information processing, and nanoscale
sensing
Continuous-wave room-temperature diamond maser
The maser, older sibling of the laser, has been confined to relative
obscurity due to its reliance on cryogenic refrigeration and high-vacuum
systems. Despite this it has found application in deep-space communications and
radio astronomy due to its unparalleled performance as a low-noise amplifier
and oscillator. The recent demonstration of a room-temperature solid- state
maser exploiting photo-excited triplet states in organic pentacene molecules
paves the way for a new class of maser that could find applications in
medicine, security and sensing, taking advantage of its sensitivity and low
noise. However, to date, only pulsed operation has been observed in this
system. Furthermore, organic maser molecules have poor thermal and mechanical
properties, and their triplet sub-level decay rates make continuous emission
challenging: alternative materials are therefore required. Therefore, inorganic
materials containing spin-defects such as diamond and silicon carbide have been
proposed. Here we report a continuous-wave (CW) room-temperature maser
oscillator using optically pumped charged nitrogen-vacancy (NV) defect centres
in diamond. This demonstration unlocks the potential of room-temperature
solid-state masers for use in a new generation of microwave devices.Comment: 7 pages, 4 figure
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