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| Author |
Yates, S. J. C.; Baryshev, A. M.; Baselmans, J. J. A.; Klein, B.; Güsten, R. |
| Title |
Fast Fourier transform spectrometer readout for large arrays of microwave kinetic inductance detectors |
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Journal Article |
| Year |
2009 |
Publication |
Applied Physics Letters |
Abbreviated Journal |
Appl. Phys. Lett. |
| Volume |
95 |
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4 |
Pages |
3 |
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| Abstract |
Microwave kinetic inductance detectors have great potential for large, very sensitive detector arrays for use in, for example, submillimeter imaging. Being intrinsically readout in the frequency domain, they are particularly suited for frequency domain multiplexing allowing ~1000 s of devices to be readout with one pair of coaxial cables. However, this moves the complexity of the detector from the cryogenics to the warm electronics. We present here the concept and experimental demonstration of the use of fast Fourier transform spectrometer readout, showing no deterioration of the noise performance compared to the low noise analog mixing while allowing high multiplexing ratios. |
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RPLAB @ gujma @ |
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697 |
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Gol'tsman, B. M.; Kutasov, V. A.; Luk'yanova, L. N. |
| Title |
Mechanism of formation of texture and its influence on the strength of thermoelectric p-Bi0.5Sb1.5Te3 |
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Journal Article |
| Year |
2009 |
Publication |
Physics of the Solid State |
Abbreviated Journal |
Phys. Sol. St. |
| Volume |
51 |
Issue |
4 |
Pages |
747-749 |
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| Abstract |
It is established that, in preparing p-Bi0.5Sb1.5Te3 by vertical zone melting, in addition to the directional texture (characteristic of materials exhibiting a highly anisotropic growth rate) in which the cleavage planes of crystal grains are parallel to the direction of propagation of the crystallization front, other texture types can arise, in which the orientation of grain cleavage planes is ordered in a cross-sectional plane of the ingot. Two types of such textures, “radial†and “circular,†were observed. In a radial texture, the lines of intersection of grain cleavage planes with a cross-sectional plane of the ingot are oriented along radii of this cross section and, in a circular texture, these lines of intersection are oriented approximately perpendicular to a radius crossing the grain. The formation of a radial texture is associated with rotation of the ampoule with the crystallizing substance about its vertical axis causing centrifugal flows of the melt. The formation of a circular texture is associated with the orientation effect of the ampoule walls and with circular motion of the melt during torsional oscillations of the ampoule about the vertical axis. Ingots with a radial texture exhibit much lower resistance to splitting along their axis than ingots with a circular texture do. An explanation is provided for this fact. |
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RPLAB @ gujma @ |
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726 |
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Parrott, Edward P. J.; Zeitler, J. Axel; Fris<cc><152>c<cc><152>ic<cc><81>, Tomislav; Pepper, Michael; Jones, William; Day, Graeme M.; Gladden, Lynn F. |
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Testing the sensitivity of terahertz spectroscopy to changes in molecular and supramolecular structure: a study of structurally similar cocrystals |
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Journal Article |
| Year |
2009 |
Publication |
Crystal Growth & Design |
Abbreviated Journal |
Crystal Growth & Design |
| Volume |
9 |
Issue |
3 |
Pages |
1452-1460 |
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supramolecular recognition, infrared, terahertz, IR, THz, TDS |
| Abstract |
Terahertz time-domain-spectroscopy (THz-TDS) has emerged as a versatile spectroscopic technique, and an alternative to powder X-ray diffraction in the characterization of molecular crystals. We tested the ability of terahertz spectroscopy to distinguish between chiral and racemic hydrogen-bonded cocrystals that are similar in molecular and supramolecular structure. Terahertz spectroscopy readily distinguished between the isostructural cocrystals of theophylline with chiral and racemic forms of malic acid which are almost identical in molecular structure and supramolecular architecture. Similarly, the cocrystals of theophylline with chiral and racemic forms of tartaric acid, which are similar at the molecular level but dissimilar in crystal packing, were distinguished unequivocally. The investigation of the same cocrystals using X-ray powder diffraction and Raman spectroscopy suggested that THz-TDS is comparable in sensitivity to diffraction methods and more sensitive than Raman spectroscopy to changes in cocrystal architecture. The differences in spectra acquired by THz-TDS could be further enhanced by cooling the samples to 109 K. |
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1528-7483 |
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567 |
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Rabanus, D.; Graf, U. U.; Philipp, M.; Ricken, O.; Stutzki, J.; Vowinkel, B.; Wiedner, M. C.; Walther, C.; Fischer, M.; Faist, J. |
| Title |
Phase locking of a 1.5 terahertz quantum cascade laser and use as a local oscillator in a heterodyne HEB receiver |
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Journal Article |
| Year |
2009 |
Publication |
Optics Express |
Abbreviated Journal |
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| Volume |
17 |
Issue |
3 |
Pages |
1159-1168 |
| Keywords |
QCL heterodyne, 300 uW at 1.5 THz, HEB mixer |
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We demonstrate for the first time the closure of an electronic phase lock loop for a continuous–wave quantum cascade laser (QCL) at 1.5 THz. The QCL is operated in a closed cycle cryo cooler. We achieved a frequency stability of better than 100 Hz, limited by the resolution bandwidth of the spectrum analyser. The PLL electronics make use of the intermediate frequency (IF) obtained from a hot electron bolometer (HEB) which is downconverted to a PLL IF of 125 MHz. The coarse selection of the longitudinal mode and the fine tuning is achieved via the bias voltage of the QCL. Within a QCL cavity mode, the free-running QCL shows frequency fluctuations of about 5 MHz, which the PLL circuit is able to control via the Stark–shift of the QCL gain material. Temperature dependent tuning is shown to be nonlinear, and of the order of -16 MHz/K. Additionally we have used the QCL as local oscillator (LO) to pump an HEB and perform, again for the first time at 1.5 THz, a heterodyne experiment, and obtain a receiver noise temperature of 1741 K. |
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628 |
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Ryabchun, Sergey; Tong, Cheuk-Yu Edward; Paine, Scott; Lobanov, Yury; Blundell, Raymond; Goltsman, Gregory |
| Title |
Temperature resolution of an HEB receiver at 810 GHz |
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Journal Article |
| Year |
2009 |
Publication |
IEEE Trans. Appl. Supercond. |
Abbreviated Journal |
IEEE Trans. Appl. Supercond. |
| Volume |
19 |
Issue |
3 |
Pages |
293-296 |
| Keywords |
HEB mixer |
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We present the results of direct measurements of the temperature resolution of an HEB receiver operating at 810 GHz, in both continuum and spectroscopic modes. In the continuum mode, the input of the receiver was switched between black bodies with different physical temperatures. With a system noise temperature of around 1100 K, the receiver was able to resolve loads which differed in temperature by about 1 K over an integration time of 5 seconds. This resolution is significantly worse than the value of 0.07 K given by the radiometer equation. In the spectroscopic mode, a gas cell filled with carbonyl sulphide (OCS) gas was used and the emission line at 813.3537060 GHz was measured using the receiver in conjunction with a digital spectrometer. From the observed spectra, we determined that the measurement uncertainty of the equivalent emission temperature was 2.8 K for an integration time of 0.25 seconds and a spectral resolution of 12 MHz, compared to a 1.4 K temperature resolution given by the radiometer equation. This relative improvement is due to the fact that at short integration times the contribution from 1/f noise and drift are less dominant. In both modes, the temperature resolution was improved by about 40% with the use of a feedback loop which adjusted the level of an injected microwave radiation to maintain a constant operating current of the HEB mixer. This stabilization scheme has proved to be very effective to keep the temperature resolution of the HEB receiver to close to the theoretical value given by the radiometer equation. |
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636 |
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Xiaolong Hu; Holzwarth, C.W.; Masciarelli, D.; Dauler, E.A.; Berggren, K.K. |
| Title |
Efficiently coupling light to superconducting nanowire single-photon detectors |
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Journal Article |
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2009 |
Publication |
IEEE Trans. Appl. Supercond. |
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19 |
Issue |
3 |
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336-340 |
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optical antennas; SNSPD |
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We designed superconducting nanowire single-photon detectors (SNSPDs) integrated with silver optical antennae for free-space coupling and a dielectric waveguide for fiber coupling. According to our finite-element simulation, (1) for the free-space coupling, the absorptance of the NbN nanowire for TM-polarized photons at the wavelength of 1550 nm can be as high as 96% by adding silver optical antennae; (2) for the fiber coupling, the absorptance of the NbN nanowire for TE-like-polarized photons can reach 76% including coupling efficiency at the wavelength of 1550 nm by adding a silicon nitride waveguide and an inverse-taper coupler. |
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RPLAB @ gujma @ |
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647 |
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Kern, Pierre; Le Coärer, Etienne; Benech, Pierre |
| Title |
On-chip spectro-detection for fully integrated coherent beam combiners |
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Journal Article |
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2009 |
Publication |
Optics Express |
Abbreviated Journal |
Opt.Express |
| Volume |
17 |
Issue |
3 |
Pages |
1976-1987 |
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This paper presents how photonics associated with new arising detection technologies is able to provide fully integrated instrument for coherent beam combination applied to astrophysical interferometry. The feasibility and operation of on-chip coherent beam combiners has been already demonstrated using various interferometric combination schemes. More recently we proposed a new detection principle aimed at directly sampling and extracting the spectral information of an input signal together with its flux level measurement. The so-called SWIFTS demonstrated concept that stands for Stationary-Wave Integrated Fourier Transform Spectrometer, provides full spectral and spatial information recorded simultaneously thanks to a motionless detecting device. Due to some newly available detection principles considered for the implementation of the SWIFTS concept, some technologies can even provide photo-counting operation that brought a significant extension of the interferometry domain of investigation in astrophysics. The proposed concept is applicable to most of the interferometric instrumental modes including fringe tracking, fast and sensitive detection, Fourier spectral reconstruction and also to manage a large number of incoming beams. The paper presents three practical implementations, two dealing with pair-wise integrated optics beam combinations and the third one with an all-in-one 8 beam combination. In all cases the principles turned into a pair wise baseline coding after proper data processing. |
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RPLAB @ gujma @ |
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650 |
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Yang, J.K.W.; Kerman, A.J.; Dauler, E.A.; Cord, B.; Anant, V.; Molnar, R.J.; Berggren, K.K. |
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Suppressed critical current in superconducting nanowire single-photon detectors with high fill-factors |
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2009 |
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IEEE Trans. Appl. Supercond. |
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19 |
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3 |
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318-322 |
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SNSPD |
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In this work we present a new fabrication process that enabled the fabrication of superconducting nanowire single photon detectors SNSPD with fill-factors as high as 88% with gaps between nanowires as small as 12 nm. This fabrication process combined high-resolution electron-beam lithography with photolithography. Although this work was motivated by the potential of increased detection efficiency with higher fill-factor devices, test results showed an unexpected systematic suppression in device critical currents with increasing fill-factor. |
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RPLAB @ gujma @ |
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677 |
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Ожегов, Р.В.; Окунев, О.В.; Гольцман, Г.Н. |
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Флуктуационная чувствительность сверхпроводящего болометрического смесителя на эффекте разогрева электронного газа |
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Journal Article |
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2009 |
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Радиотехника |
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3 |
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120-124 |
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смеситель на горячих электронах; флуктуационная чувствительность; тепловизор терагерцевого диапазона частот; hot-electron bolometer mixer; Imaging system; Noise equivalent temperature difference; Heterodyne receiver; Terahertz range |
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Interest in research in the terahertz range is driven by a great number of various applications, where terahertz instruments may play a leading role. To name just a few, such applications include study of the cosmic microwave background radiation and the distribution of the dark matter, medicine, navigation, fire alarm, security systems and environmental monitoring. The paper discusses the possibility of using a receiver based on the hot-electron effect in superconducting films as an imaging system. We present the results of the noise equivalent temperature difference (NETD) measurements performed with a hot-electron bolometer mixer made from a thin superconducting film. The receiver with a noise temperature of ~ 3800 K at a local oscillator frequency of 300 GHz a bandwidth of 500 MHz and an integration time of 1 s has offered an NETD of 0.5 K. We have also developed a technique that enabled us to reduce the contribution of the mixer gain fluctuations to the overall system instability. As of this writing, the above value of the NETD is the lowest value offered for this type of receiver, which indicates the possibility to use such receivers in real-time imaging systems. The technique offered in the paper for achieving the limiting value of the NETD offers an alternative to the phase-locking scheme.
Представены результаты измерения флуктуационной чувствительности (NETD – noise equivalent temperature difference) болометрического смесителя на эффекте разогрева электронного газа в тонких сверхпроводящих пленках. Получено предельное значение NETD, равное 0,5 К, при шумовой температуре приемника 3800 К, ширине полосы преобразования 500 МГц, постоянной времени 1 с и частоте гетеродина 300 ГГц. Разработана методика достижения предельной флуктуационной чувствительности, позволяющая избежать влияния нестабильности коэффициента преобразования смесителя. |
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RPLAB @ gujma @ |
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728 |
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Zurek, Wojciech Hubert |
| Title |
Quantum Darwinism |
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Journal Article |
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2009 |
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Nature Physics |
Abbreviated Journal |
Nat. Phys. |
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5 |
Issue |
3 |
Pages |
181-188 |
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fromIPMRAS |
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Quantum Darwinism describes the proliferation, in the environment, of multiple records of selected states of a quantum system. It explains how the quantum fragility of a state of a single quantum system can lead to the classical robustness of states in their correlated multitude; shows how effective `wave-packet collapse' arises as a result of the proliferation throughout the environment of imprints of the state of the system; and provides a framework for the derivation of Born's rule, which relates the probabilities of detecting states to their amplitudes. Taken together, these three advances mark considerable progress towards settling the quantum measurement problem. |
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