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Single-photon detection timing jitter in a visible light photon counter
Burm Baek,Kyle S. McKay,Martin J. Stevens,Jungsang Kim,Henry H. Hogue,Sae Woo Nam
Physics , 2009, DOI: 10.1109/JQE.2010.2042141
Abstract: Visible light photon counters (VLPCs) offer many attractive features as photon detectors, such as high quantum efficiency and photon number resolution. We report measurements of the single-photon timing jitter in a VLPC, a critical performance factor in a time-correlated single-photon counting measurement, in a fiber-coupled closed-cycle cryocooler. The measured timing jitter is 240 ps full-width-at-half-maximum at a wavelength of 550 nm, with a dark count rate of 25 000 counts per second. The timing jitter increases modestly at longer wavelengths to 300 ps at 1000 nm, and increases substantially at lower bias voltages as the quantum efficiency is reduced.
Hybrid superconducting-magnetic memory device using competing order parameters
Burm Baek,William H. Rippard,Samuel P. Benz,Stephen E. Russek,Paul D. Dresselhaus
Physics , 2013, DOI: 10.1038/ncomms4888
Abstract: Superconducting devices, which rely on modulating a complex superconducting order parameter in a Josephson junction, have been developed for low power logic operations, high-frequency oscillators, and exquisite magnetic field sensors. Magnetic devices, which rely on the modulation of a local vector order parameter- the local magnetic moment, have been used as memory elements, high-frequency spin-transfer oscillators, and magnetic field sensors. In a hybrid superconducting-magnetic device, these two order parameters compete, with one type of order suppressing the other. Recent interest in ultra-low-power, high-density cryogenic memories has spurred new interest in merging superconducting and magnetic behavior so as to exploit these two competing order parameters to produce novel switching elements. Here, we describe a reconfigurable two-layer magnetic spin valve integrated within a Josephson junction. Our measurements separate the suppression in the superconducting coupling due to the exchange field in the magnetic layers, which causes depairing of the supercurrent, from the suppression due to the magnetic field generated by the magnetic layers. The exchange field suppression of the superconducting order parameter is a tunable and switchable behavior that is also scalable to nanometer device dimensions. These devices are the first to demonstrate nonvolatile, size-independent switching of the Josephson coupling, in both magnitude and phase, and they may allow for the first nanoscale superconducting memory devices.
Analysis of a distributed fiber-optic temperature sensor using single-photon detectors
Shellee D. Dyer,Michael G. Tanner,Burm Baek,Robert H. Hadfield,Sae Woo Nam
Physics , 2011, DOI: 10.1364/OE.20.003456
Abstract: We demonstrate a high-accuracy distributed fiber-optic temperature sensor using superconducting nanowire single-photon detectors and single-photon counting techniques. Our demonstration uses inexpensive single-mode fiber at standard telecommunications wavelengths as the sensing fiber, which enables extremely low-loss experiments and compatibility with existing fiber networks. We show that the uncertainty of the temperature measurement decreases with longer integration periods, but is ultimately limited by the calibration uncertainty. Temperature uncertainty on the order of 3 K is possible with spatial resolution of the order of 1 cm and integration period as small as 60 seconds. Also, we show that the measurement is subject to systematic uncertainties, such as polarization fading, which can be reduced with a polarization diversity receiver.
Spin-transfer torque switching in nanopillar superconducting-magnetic hybrid Josephson junctions
Burm Baek,William H. Rippard,Matthew R. Pufall,Samuel P. Benz,Stephen E. Russek,Horst Rogalla,Paul D. Dresselhaus
Physics , 2014,
Abstract: The combination of superconducting and magnetic materials to create novel superconducting devices has been motivated by the discovery of Josephson critical current (Ics) oscillations as a function of magnetic layer thickness and the demonstration of devices with switchable critical currents. However, none of the hybrid devices have shown any spintronic effects, such as spin-transfer torque, which are currently used in room-temperature magnetic devices, including spin-transfer torque random-access memory and spin-torque nano-oscillators. We have developed nanopillar Josephson junctions with a minimum feature size of 50 nm and magnetic barriers exhibiting magnetic pseudo-spin-valve behavior at 4 K. These devices allow current-induced magnetization switching that results in 20-fold changes in Ics. The current-induced magnetic switching is consistent with spin-transfer torque models for room-temperature magnetic devices. Our work demonstrates that devices that combine superconducting and spintronic functions show promise for the development of a nanoscale, nonvolatile, cryogenic memory technology.
Observation of Transparency of Erbium-doped Silicon nitride in photonic crystal nanobeam cavities
Yiyang Gong,Maria Makarova,Selcuk Yerci,Rui Li,Martin J. Stevens,Burm Baek,Sae Woo Nam,Luca Dal Negro,Jelena Vuckovic
Physics , 2010, DOI: 10.1364/OE.18.013863
Abstract: One-dimensional nanobeam photonic crystal cavities are fabricated in an Er-doped amorphous silicon nitride layer. Photoluminescence from the cavities around 1.54 um is studied at cryogenic and room temperatures at different optical pump powers. The resonators demonstrate Purcell enhanced absorption and emission rates, also confirmed by time-resolved measurements. Resonances exhibit linewidth narrowing with pump power, signifying absorption bleaching and the onset of stimulated emission in the material at both 5.5 K and room temperature. We estimate from the cavity linewidths that Er has been pumped to transparency at the cavity resonance wavelength.
Antimicrobial Activity of Eucosterol Oligosaccharides Isolated from Bulb of Squill (Scilla scilloides)  [PDF]
Hyang Burm Lee, Sang Myung Lee
Pharmacology & Pharmacy (PP) , 2013, DOI: 10.4236/pp.2013.41016
Abstract: Antimicrobial activity of methanol extract from bulb of Scilla scilloides as well as the purified eucosterol oligosaccharides (EOs) against bacteria, fungi and alga was evaluated in vitro using paper disc bioassay. EOs including scillascilloside E-1, E-2, E-3 and G-1 were isolated from the bulbs by methanol extraction, gel filtration on Sephadex LH-20 and preparative HPLC. The metabolites were identified by MS (HR-FAB-MS) and 1H- and 13C-NMR spectral data analyses. Methanol (MeOH) extract and purified compounds, EOs showed a selective inhibitory activity against eukaryotic cells including fungal species such as Aspergillus flavus, Candida albicans, Pyricularia oryzae and an alga such as Chlorella regulsris at the concentration of 200 μg/paper disc, but little active against bacteria. Out of four EO compounds, Scilla-scilloside E-3 revealed the highest activity. These results show that the MeOH extract and EOs from the medicinal plant, S. scilloides, may be applied as a natural fungicide or a food preservative for control of molds.
Design Strategy of Global e-School in Learning Ecology for Global-Citizenship
Kee-Burm Park
Asian Journal of Information Technology , 2012, DOI: 10.3923/ajit.2012.1.6
Abstract: Today, countries are exchanging by own needs. For the first time, globalization has been in progress for market orientation. However, the globalization of market orientation causes many problems because of the lack of knowledge for cultural specificity in different areas. This study focuses on making a Global e-School (GeS) for global citizen education. I tried to make GeS by adopting ecology. When building a GeS, comparing and applying with ecology is needed, emergent learning by entering into a relation with specific culture based members, coevolution of a study community which creates opulent learning environments that consist of strong intelligence and understanding and acceptance of mutual culture in lens of multicultural education. GeS has a mission to develop qualities of global citizens in the global society based digital network environment.
Malaysian Journal of Pharmaceutical Sciences , 2005,
Abstract: This study evaluates the compatibility and stability of Taxol with ondansetron, ranitidine, vancomycin and cephalosporins in 5% dextrose injection and 0.9% sodium chloride injection during simulated Y-site administration. Two stock solutions of Taxol 0.3 and 1.2 mg/mL and each stock solutions of ondansetron 0.03, 0.1 and 0.3 mg/mL, ranitidine 0.5 and 2 mg/mL, vancomycin 1, 5 and 10 mg/mL and cephalosporins 20 mg/mL were prepared in glass bottles. Two mL of Taxol stock solution was mixed with 2 mL of each stock solution. Samples were removed at room temperature at time zero, one, two, four and 12 hours for immediate assay. Taxol concentrations were analyzed by High Performance Liquid Chromatography. All solutions were prepared in triplicate, and each drug was assayed in duplicate. At the time of sampling assay and before any dilution, each sample was visually inspected for clarity, color and precipitation. The pH was also determined. Taxol in concentrations of 0.3 and 1.2 mg/mL was stable when mixed with either ondansetron (0.03, 0.1 or 0.3 mg/mL, as the hydrochloride salt), ranitidine (0.5 or 2.0 mg/mL, as the hydrochloride salt), vancomycin (1, 5 or 10 mg/mL, as the hydrochloride salt) or cephalosporins 20 mg/mL and stored in glass containers for 12 hours. No precipitates, color changes, or haziness was seen. The changes in pH were minor.
Ultra fast quantum key distribution over a 97 km installed telecom fiber with wavelength-division multiplexing clock synchronization
Akihiro Tanaka,Mikio Fujiwara,Sae Woo Nam,Yoshihiro Nambu,Seigo Takahashi,Wakako Maeda,Ken-ichiro Yoshino,Shigehito Miki,Burm Baek,Zhen Wang,Akio Tajima,Masahide Sasaki,Akihisa Tomita
Physics , 2008, DOI: 10.1364/OE.16.011354
Abstract: We demonstrated ultra fast BB84 quantum key distribution (QKD) transmission at 625 MHz clock rate through a 97 km field-installed fiber using practical clock synchronization based on wavelength-division multiplexing (WDM). We succeeded in over-one-hour stable key generation at a high sifted key rate of 2.4 kbps and a low quantum bit error rate (QBER) of 2.9%. The asymptotic secure key rate was estimated to be 0.78-0.82 kbps from the transmission data with the decoy method of average photon numbers 0, 0.15, and 0.4 photons/pulse.
Higher-order photon correlations in pulsed photonic crystal nanolasers
David Elvira,Xavier Hachair,V. Verma,Remy Braive,Gregoire Beaudoin,Isabelle Robert-Philip,Isabelle Sagnes,Burm Baek,Sae Woo Nam,Eric A. Dauler,Izo Abram,Martin J. Stevens,Alexios Beveratos
Physics , 2011, DOI: 10.1103/PhysRevA.84.061802
Abstract: We report on the higher-order photon correlations of a high-$\beta$ nanolaser under pulsed excitation at room temperature. Using a multiplexed four-element superconducting single photon detector we measured g$^{(n)}(\vec{0})$ with $n$=2,3,4. All orders of correlation display partially chaotic statistics, even at four times the threshold excitation power. We show that this departure from coherence and Poisson statistics is due to the quantum fluctuations associated with the small number of dipoles and photons involved in the lasing process.
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