Recent analyses with ribosomal RNA-based technologies have revealed the diversity of
bacterial populations within dental biofilms, and have highlighted their important
contributions to oral health ...and disease. Dental biofilms are exceedingly complex and
multispecies ecosystems, where oral bacteria interact cooperatively or competitively
with other members. Bacterial interactions that influence dental biofilm communities
include various different mechanisms. During the early stage of biofilm formation, it
is known that planktonic bacterial cells directly attach to surfaces of the oral
cavity or indirectly bind to other bacterial cells that have already colonized.
Adherence through co-aggregation may be critical for the temporary retention of
bacteria on dental surfaces, and may facilitate eventual bacterial colonization. It
is likely that metabolic communication, genetic exchange, production of inhibitory
factors (e.g., bacteriocins, hydrogen peroxide, etc.), and
quorum-sensing are pivotal regulatory factors that determine the bacterial
composition and/or metabolism. Since each bacterium can easily access a neighboring
bacterial cell and its metabolites, genetic exchanges and metabolic communication may
occur frequently in dental biofilms. Quorum-sensing is defined as gene regulation in
response to cell density, which influences various functions, e.g.,
virulence and bacteriocin production. In this review, we discuss these important
interactions among oral bacteria within the dental biofilm communities.
Over the past few years, single-photon generation has been realized in numerous systems: single molecules, quantum dots, diamond colour centres and others. The generation and detection of single ...photons play a central role in the experimental foundation of quantum mechanics and measurement theory. An efficient and high-quality single-photon source is needed to implement quantum key distribution, quantum repeaters and photonic quantum information processing. Here we report the identification and formation of ultrabright, room-temperature, photostable single-photon sources in a device-friendly material, silicon carbide (SiC). The source is composed of an intrinsic defect, known as the carbon antisite-vacancy pair, created by carefully optimized electron irradiation and annealing of ultrapure SiC. An extreme brightness (2×10(6) counts s(-1)) resulting from polarization rules and a high quantum efficiency is obtained in the bulk without resorting to the use of a cavity or plasmonic structure. This may benefit future integrated quantum photonic devices.
Abstract
The nitrogen-vacancy (NV) center in diamond is a promising quantum system for magnetometry applications exhibiting optical readout of minute energy shifts in its spin sub-levels. Key ...material requirements for NV ensembles are a high NV
−
concentration, a long spin coherence time and a stable charge state. However, these are interdependent and can be difficult to optimize during diamond growth and subsequent NV creation. In this work, we systematically investigate the NV center formation and properties in bulk chemical vapor deposition (CVD) diamond. The nitrogen flow during growth is varied by over four orders of magnitude, resulting in a broad range of single substitutional nitrogen concentrations of 0.2–20 parts per million. For a fixed nitrogen concentration, we optimize electron-irradiation fluences with two different accelerated electron energies, and we study defect formation via optical characterizations. We discuss a general approach to determine the optimal irradiation conditions, for which an enhanced NV concentration and an optimum of NV charge states can both be satisfied. We achieve spin–spin coherence times
T
2
ranging from 45.5 to 549
μ
s for CVD diamonds containing 168 to 1 parts per billion NV
−
centers, respectively. This study shows a pathway to engineer properties of NV-doped CVD diamonds for improved sensitivity.
Error correction is important in classical and quantum computation. Decoherence caused by the inevitable interaction of quantum bits with their environment leads to dephasing or even relaxation. ...Correction of the concomitant errors is therefore a fundamental requirement for scalable quantum computation. Although algorithms for error correction have been known for some time, experimental realizations are scarce. Here we show quantum error correction in a heterogeneous, solid-state spin system. We demonstrate that joint initialization, projective readout and fast local and non-local gate operations can all be achieved in diamond spin systems, even under ambient conditions. High-fidelity initialization of a whole spin register (99 per cent) and single-shot readout of multiple individual nuclear spins are achieved by using the ancillary electron spin of a nitrogen-vacancy defect. Implementation of a novel non-local gate generic to our electron-nuclear quantum register allows the preparation of entangled states of three nuclear spins, with fidelities exceeding 85 per cent. With these techniques, we demonstrate three-qubit phase-flip error correction. Using optimal control, all of the above operations achieve fidelities approaching those needed for fault-tolerant quantum operation, thus paving the way to large-scale quantum computation. Besides their use with diamond spin systems, our techniques can be used to improve scaling of quantum networks relying on phosphorus in silicon, quantum dots, silicon carbide or rare-earth ions in solids.
Constructing quantum devices comprises various challenging tasks, especially when concerning their nanoscale geometry. For quantum color centers, the traditional approach is to fabricate the device ...structure after the nondeterministic placement of the centers. Reversing this approach, we present the controlled generation of quantum centers in silicon carbide (SiC) by focused proton beam in a noncomplex manner without need for pre- or postirradiation treatment. The generation depth and resolution can be predicted by matching the proton energy to the material’s stopping power, and the amount of quantum centers at one specific sample volume is tunable from ensembles of millions to discernible single photon emitters. We identify the generated centers as silicon vacancies through their characteristic magnetic resonance signatures and demonstrate that they possess a long spin–echo coherence time of 42 ± 20 μs at room temperature. Our approach hence enables the fabrication of quantum hybrid nanodevices based on SiC platform, where spin centers are integrated into p-i-n diodes, photonic cavities, and mechanical resonators.
Human T-cell leukemia virus type-1 (HTLV-1) infection causes adult T-cell leukemia (ATL). Modulation of the transcriptional control of cellular genes by HTLV-1 is thought to be associated with the ...development of ATL. The viral protein HTLV-1 basic leucine-zipper factor (HBZ) has been shown to dysregulate the activity of cellular transcription factors. Here, we demonstrate that HBZ is exported from the nucleus to the cytoplasm, where it activates the mammalian target of rapamycin (mTOR) signaling pathway through an association with growth arrest and DNA damage gene 34 (GADD34). The N-terminal region of HBZ interacts with the C-terminal region of GADD34. HBZ contains a functional nuclear export signal (NES) sequence within its N-terminal region and it is exported from the nucleus via the CRM1-dependent pathway. Nuclear export of HBZ is essential for its interaction with GADD34 and increased phosphorylation of S6 kinase, which is an established downstream target of the mTOR pathway. Starvation-induced autophagy is significantly suppressed by the overexpression of HBZ. These findings indicate that HBZ is actively exported to the cytoplasm, where it dysregulates the function of cellular factors.
Quantum adiabatic passages can be greatly accelerated by a suitable control field, called a counter-diabatic field, which varies during the scan through resonance. Here, we implement this technique ...on the electron spin of a single nitrogen-vacancy center in diamond. We demonstrate two versions of this scheme. The first follows closely the procedure originally proposed by Demirplak and Rice J. Phys. Chem. A 107, 9937 (2003). In the second scheme, we use a control field whose amplitude is constant but whose phase varies with time. This version, which we call the rapid-scan approach, allows an even faster passage through resonance and therefore makes it applicable also for systems with shorter decoherence times.
The nitrogen-vacancy (NV) centre is a fluorescent defect in diamond that is of critical importance for applications from ensemble sensing to biolabelling. Hence, understanding and optimising the ...creation of NV centres in diamond is vital for technological progress in these areas. We demonstrate that simultaneous electron irradiation and annealing of a high-pressure high-temperature diamond sample increases the NV centre creation efficiency from substitutional nitrogen defects by up to 117% with respect to a sample where the processes are carried out consecutively, but using the same process parameters. This increase in fluorescence is supported by visible and infrared absorption spectroscopy experiments. Our results pave the way for a more efficient creation of NV centres in diamond as well as higher overall NV densities in the future.
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We demonstrate that silicon carbide (SiC) with a natural isotope abundance can preserve a coherent spin superposition in silicon vacancies over an unexpectedly long time exceeding 20 ms. The ...spin-locked subspace with a drastically reduced decoherence rate is attained through the suppression of heteronuclear spin crosstalking by applying a moderate magnetic field in combination with dynamic decoupling from the nuclear spin baths. Furthermore, we identify several phonon-assisted mechanisms of spin-lattice relaxation and find that it can be extremely long at cryogenic temperatures, equal to or even longer than 10 s. Our approach may be extended to other polyatomic compounds and opens a path towards improved qubit memory for wafer-scale quantum technologies.
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