In situ method for power re-equalization of wavelength pulses inside of OCDMA codes

A simple in-situ method to equalize power among individual wavelengths pulses representing two-dimensional wavelength-hopping time-spreading OCDMA code originally generated by a fibre Bragg grating-based OCDMA encoder is presented. Experimental data obtained in a field-based multiuser OCDMA testbed shows that applying this method results in system performance enhancements which was demonstrated by observing improved bit error rate (BER) during the field trials

Nitrogen isotope effects on boron vacancy quantum sensors in hexagonal boron nitride

Recently, there has been growing interest in researching the use of hexagonal boron nitride (hBN) for quantum technologies. Here we investigate nitrogen isotope effects on boron vacancy (V$_\text{B}$) defects, one of the candidates for quantum sensors, in $^{15}$N isotopically enriched hBN synthesized using metathesis reaction. The Raman shifts are scaled with the reduced mass, consistent with previous work on boron isotope enrichment. We obtain nitrogen isotopic composition dependent optically detected magnetic resonance spectra of V$_\text{B}$ defects and determine the hyperfine interaction parameter of $^{15}$N spin to be -64 MHz. Our investigation provides a design policy for hBNs for quantum technologies

Optical-power-dependent splitting of magnetic resonance in nitrogen-vacancy centers in diamond

Nitrogen-vacancy (NV) centers in diamonds are a powerful tool for accurate magnetic field measurements. The key is precisely estimating the field-dependent splitting width of the optically detected magnetic resonance (ODMR) spectra of the NV centers. In this study, we investigate the optical power dependence of the ODMR spectra using NV ensemble in nanodiamonds (NDs) and a single-crystal bulk diamond. We find that the splitting width exponentially decays and is saturated as the optical power increases. Comparison between NDs and a bulk sample shows that while the decay amplitude is sample-dependent, the optical power at which the decay saturates is almost sample-independent. We propose that this unexpected phenomenon is an intrinsic property of the NV center due to non-axisymmetry deformation or impurities. Our finding indicates that diamonds with less deformation are advantageous for accurate magnetic field measurements.Comment: 9 pages, 7 figure

Chitosan Derivatives / Calcium Carbonate Composite Capsules Prepared by the Layer - by - Layer Deposition Method II Stabilization of the Shell by Crosslinking

The layer-by-layer deposition method is utilized to prepare rodlike core / shell capsules. Chitosan (polycation)and chitosansulfate (polyanion)were alternatively deposited on the surface of calcium carbonate whisker(rodlikeparticle). The thickness of the obtained shells ranged from 26 to 42 nm. After the deposition, the shell was treated with diisocyanate to form crosslink between the chitosan or chitosansulfate chains in order to stabilize the deposited shell. The obtained shell crosslinked rodlike capsules were successfully converted to hollow particles by immersing them into hydrochloric acid due to the enhanced shell stability, whereas from noncrosslinked shells, no hollow capsules were yielded : the shell was removed by dissolution in hydrochloric acid. It is revealed that the crosslinking reactivity is higher for 1,6-diisocyanatehexane than for tolylene 2,4-diisocyanate, suggesting that the reactivity depends on the size and flxibility of the crosslinking molecule

Quantum key distribution with an efficient countermeasure against correlated intensity fluctuations in optical pulses

Quantum key distribution (QKD) allows two distant parties to share secret keys with the proven security even in the presence of an eavesdropper with unbounded computational power. Recently, GHz-clock decoy QKD systems have been realized by employing ultrafast optical communication devices. However, security loopholes of high-speed systems have not been fully explored yet. Here we point out a security loophole at the transmitter of the GHz-clock QKD, which is a common problem in high-speed QKD systems using practical band-width limited devices. We experimentally observe the inter-pulse intensity correlation and modulation-pattern dependent intensity deviation in a practical high-speed QKD system. Such correlation violates the assumption of most security theories. We also provide its countermeasure which does not require significant changes of hardware and can generate keys secure over 100 km fiber transmission. Our countermeasure is simple, effective and applicable to wide range of high-speed QKD systems, and thus paves the way to realize ultrafast and security-certified commercial QKD systems

Morphology and release kinetics of protein-loaded porous poly(L-lactic acid) spheres prepared by freeze-drying technique

Freeze-drying a biodegradable polymer, poly(L-lactic acid) (PLLA) from 1,4-dioxane solutions provided very porous spherical particles of ca. 3 mm in radius with specific surface area of 8 − 13 m2 g−1. The surface of the particle was found to be less porous compared with its interior. To apply the freeze-dried PLLA (FDPLLA) to drug delivery system, its morphology and drug releasing kinetics were investigated, bovine serum albumin (BSA) being used as a model drug compound. Immersion of FDPLLA into a BSA aqueous solution gave BSA-loaded FDPLLA, where mass fraction of the adsorbed BSA reached up to 79%. Time-dependent release profile of BSA in water suggested a two-step mechanism: (1) very rapid release of BSA deposited on and near the particle surface, which results in an initial burst, and (2) leaching of BSA from the interior of the particle by the diffusion process. It was suggested that the latter process is largely governed by the surface porosity. The porosity of both the interior and surface was found to decrease remarkably as the concentration of the original PLLA / 1,4-dioxane solution increases, C0. Thus, C0 is a key parameter that controls the loading and releasing of BSA

7-Chloro-1,2-dihydro­furo[2,3-c]isoquinolin-5-amine

In the title compound, C11H9ClN2O, the fused-ring system is essentially planar, with a maximum deviation of 0.0323 (16) Å. In the crystal, mol­ecules are connected by N—H⋯O hydrogen bonds forming a zigzag chain along the c axis. Mol­ecules are further stacked along the a axis through weak π–π inter­actions, the shortest distance between ring centroids being 3.6476 (8) Å

Demonstration of geometric diabatic control of quantum states

Geometric effects can play a pivotal role in streamlining quantum manipulation. We demonstrate a geometric diabatic control, that is, perfect tunneling between spin states in a diamond by a quadratic sweep of a driving field. The field sweep speed for the perfect tunneling is determined by the geometric amplitude factor and can be tuned arbitrarily. Our results are obtained by testing a quadratic version of Berry's twisted Landau-Zener model. This geometric tuning is robust over a wide parameter range. Our work provides a basis for quantum control in various systems, including condensed matter physics, quantum computation, and nuclear magnetic resonance

Wide-field quantitative magnetic imaging of superconducting vortices using perfectly aligned quantum sensors

Various techniques have been applied to visualize superconducting vortices, providing clues to their electromagnetic response. Here, we present a wide-field, quantitative imaging of the stray field of the vortices in a superconducting thin film using perfectly aligned diamond quantum sensors. Our analysis, which mitigates the influence of the sensor inhomogeneities, visualizes the magnetic flux of single vortices in YBa$_2$Cu$_3$O$_{7-\delta}$ with an accuracy of $\pm10~\%$. The obtained vortex shape is consistent with the theoretical model, and penetration depth and its temperature dependence agree with previous studies, proving our technique's accuracy and broad applicability. This wide-field imaging, which in principle works even under extreme conditions, allows the characterization of various superconductors