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Mohan, N.; Minaeva, O.; Gol'tsman, G. N.; Nasr, M. B.; Saleh, B. E.; Sergienko, A. V.; Teich, M. C. |
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Photon-counting optical coherence-domain reflectometry using superconducting single-photon detectors |
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Journal Article |
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2008 |
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Opt. Express |
Abbreviated Journal |
Opt. Express |
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16 |
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22 |
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18118-18130 |
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Keywords |
SSPD, SNSPD |
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We consider the use of single-photon counting detectors in coherence-domain imaging. Detectors operated in this mode exhibit reduced noise, which leads to increased sensitivity for weak light sources and weakly reflecting samples. In particular, we experimentally demonstrate the possibility of using superconducting single-photon detectors (SSPDs) for optical coherence-domain reflectometry (OCDR). These detectors are sensitive over the full spectral range that is useful for carrying out such imaging in biological samples. With counting rates as high as 100 MHz, SSPDs also offer a high rate of data acquisition if the light flux is sufficient. |
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Department of Biomedical Engineering, Boston University, Boston, MA 02215, USA. nm82@bu.edu |
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1094-4087 |
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PMID:18958090 |
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1407 |
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Nasr, M. B.; Minaeva, O.; Goltsman, G. N.; Sergienko, A. V.; Saleh, B. E.; Teich, M. C. |
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Title |
Submicron axial resolution in an ultrabroadband two-photon interferometer using superconducting single-photon detectors |
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Journal Article |
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Year |
2008 |
Publication |
Opt. Express |
Abbreviated Journal |
Opt. Express |
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16 |
Issue |
19 |
Pages |
15104-15108 |
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Keywords |
SSPD, SNSPD |
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We generate ultrabroadband biphotons via the process of spontaneous parametric down-conversion in a quasi-phase-matched nonlinear grating that has a linearly chirped poling period. Using these biphotons in conjunction with superconducting single-photon detectors (SSPDs), we measure the narrowest Hong-Ou-Mandel dip to date in a two-photon interferometer, having a full width at half maximum (FWHM) of approximately 5.7 fsec. This FWHM corresponds to a quantum optical coherence tomography (QOCT) axial resolution of 0.85 µm. Our results indicate that a high flux of nonoverlapping biphotons may be generated, as required in many applications of nonclassical light. |
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Departments of Electrical & Computer Engineering and Physics, Quantum Imaging Laboratory, Boston University, Boston, MA 02215, USA. boshra@bu.edu |
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1094-4087 |
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PMID:18795048 |
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1408 |
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Bryant, Garnett W.; García de Abajo, F. Javier; Aizpurua, Javier |
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Title |
Mapping the Plasmon Resonances of Metallic Nanoantennas |
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2008 |
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Nano Letters |
Abbreviated Journal |
Nano Lett. |
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5 |
Issue |
2 |
Pages |
631-636 |
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Keywords |
optical antennas |
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We study the light scattering and surface plasmon resonances of Au nanorods that are commonly used as optical nanoantennas in analogy to dipole radio antennas for chemical and biodetection field-enhanced spectroscopies and scanned-probe microscopies. With the use of the boundary element method, we calculate the nanorod near-field and far-field response to show how the nanorod shape and dimensions determine its optical response. A full mapping of the size (length and radius) dependence for Au nanorods is obtained. The dipolar plasmon resonance wavelength λ shows a nearly linear dependence on total rod length L out to the largest lengths that we study. However, L is always substantially less than λ/2, indicating the difference between optical nanoantennas and long-wavelength traditional λ/2 antennas. Although it is often assumed that the plasmon wavelength scales with the nanorod aspect ratio, we find that this scaling does not apply except in the extreme limit of very small, spherical nanoparticles. The plasmon response depends critically on both the rod length and radius. Large (500 nm) differences in resonance wavelength are found for structures with different sizes but with the same aspect ratio. In addition, the plasmon resonance deduced from the near-field enhancement can be significantly red-shifted due to retardation from the resonance in far-field scattering. Large differences in near-field and far-field response, together with the breakdown of the simple scaling law must be accounted for in the choice and design of metallic λ/2 nanoantennas. We provide a general, practical map of the resonances for use in locating the desired response for gold nanoantennas. |
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RPLAB @ gujma @ |
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737 |
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Pirandola, Stefano; Mancini, Stefano; Lloyd, Seth; Braunstein, Samuel L. |
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Title |
Continuous-variable quantum cryptography using two-way quantum communication |
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Journal Article |
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2008 |
Publication |
Nature Physics |
Abbreviated Journal |
Nat. Phys. |
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4 |
Issue |
9 |
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726-730 |
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Keywords |
fromIPMRAS |
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Quantum cryptography has recently been extended to continuous-variable systems, such as the bosonic modes of the electromagnetic field possessing continuous degrees of freedom. In particular, several cryptographic protocols have been proposed and experimentally implemented using bosonic modes with Gaussian statistics. These protocols have shown the possibility of reaching very high secret key rates, even in the presence of strong losses in the quantum communication channel. Despite this robustness to loss, their security can be affected by more general attacks where extra Gaussian noise is introduced by the eavesdropper. Here, we show a `hardware solution' for enhancing the security thresholds of these protocols. This is possible by extending them to two-way quantum communication where subsequent uses of the quantum channel are suitably combined. In the resulting two-way schemes, one of the honest parties assists the secret encoding of the other, with the chance of a non-trivial superadditive enhancement of the security thresholds. These results should enable the extension of quantum cryptography to more complex quantum communications. |
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RPLAB @ gujma @ |
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798 |
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Author |
Wei, Jian; Olaya, David; Karasik, Boris S.; Pereverzev, Sergey V.; Sergeev, Andrei V.; Gershenson, Michael E. |
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Title |
Ultrasensitive hot-electron nanobolometers for terahertz astrophysics |
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Journal Article |
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2008 |
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Nature Nanotechnology |
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Nature Nanotech |
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3 |
Issue |
8 |
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496-500 |
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HEB, Ti/NbN, single terahertz photons, detection |
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The submillimetre or terahertz region of the electromagnetic spectrum contains approximately half of the total luminosity of the Universe and 98% of all the photons emitted since the Big Bang. This radiation is strongly absorbed in the Earth's atmosphere, so space-based terahertz telescopes are crucial for exploring the evolution of the Universe. Thermal emission from the primary mirrors in these telescopes can be reduced below the level of the cosmic background by active cooling, which expands the range of faint objects that can be observed. However, it will also be necessary to develop bolometers – devices for measuring the energy of electromagnetic radiation—with sensitivities that are at least two orders of magnitude better than the present state of the art. To achieve this sensitivity without sacrificing operating speed, two conditions are required. First, the bolometer should be exceptionally well thermally isolated from the environment;
second, its heat capacity should be sufficiently small. Here we demonstrate that these goals can be achieved by building a superconducting hot-electron nanobolometer. Its design eliminates the energy exchange between hot electrons and the leads by blocking electron outdiffusion and photon emission. The thermal conductance between hot electrons and the thermal bath, controlled by electron–phonon interactions, becomes very small at low temperatures (10-16 WK-1 at 40 mK). These devices, with a heat capacity of 10-19 J K-1, are sufficiently sensitive to detect single terahertz photons in submillimetre astronomy and other applications based on quantum calorimetry and photon counting. |
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1748-3387 |
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576 |
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