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Чулкова, Г. М., Корнеев, А. А., Смирнов, К. В., & Окунев, О. В. (2012). Энергетическая релаксация в примесных металлах, двумерном электронном газе в AlGaAs-GaAs, сверхпроводниковых пленках NbN и детекторы субмиллиметрового и ик излучения на их основе. Прометей, МПГУ.
Abstract: Монография посвящена обзору исследований влияния эффектов электронного беспорядка на электронное взаимодействие в металлах, сверхпроводниках, полупроводниках, а также в различных низкоразмерных структурах. Актуальность поднятых в монографии вопросов определяется интенсивным развитием нанотехнологий, созданием новых наноструктурированных материалов и уникальных наноэлементов для электроники и фотоники. Упругое электронное рассеяние на границах наноструктур качественно меняет взаимодействие электронов с фонолами, что, безусловно, должно учитываться при проектировании соответствующей элементной базы. Прикладная часть работы посвящена контролируемой модификации электронных процессов для оптимизации новых наносенсоров на основе электронного разогрева в сверхпроводниковых и полупроводниковых структурах. Монография предназначена для студентов старших курсов, аспирантов и начинающих следователей, работающих в области сверхпроводниковой наноэлектроники.
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Казаков, А. Ю., Кардакова, А. И., Селиверстов, С. В., Горшков, К. Н., Дивочий, А. В., Финкель, М. И., et al. (2012). Возможность применения сверхпроводниковых материалов в качестве отражающего покрытия холодного зеркала телескопа субмиллиметрового диапазона. Совр. проб. науки и обр., (3), 1–5.
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Pile, D. (2012). How many bits can a photon carry. Nat. Photon., 6(1), 14–15.
Abstract: Quantum physics offers a way to enhance the amount of information a photon can carry, with potential applications in optical communication, lithography, metrology and imaging.
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Swetz, D. S., Bennett, D. A., Irwin, K. D., Schmidt, D. R., & Ullom, J. N. (2012). Current distribution and transition width in superconducting transition-edge sensors. Appl. Phys. Lett., 101, 242603.
Abstract: Present models of the superconducting-to-normal transition in transition-edge sensors (TESs) do not describe the current distribution within a biased TES. This distribution is complicated by normal-metal features that are integral to TES design. We present a model with one free parameter that describes the evolution of the current distribution with bias. To probe the current distribution experimentally, we fabricated TES devices with different current return geometries. Devices where the current return geometry mirrors current flow within the device have sharper transitions, thus allowing for a direct test of the current-flow model.Measurements from these devices show that current meanders through a TES low in the resistivetransition but flows across the normal-metal features by 40% of the normal-state resistance. Comparison of transition sharpness between device designs reveals that self-induced magnetic fields play an important role in determining the width of the superconducting transition.
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Pernice, W. H. P., Schuck, C., Minaeva, O., Li, M., Goltsman, G. N., Sergienko, A. V., et al. (2012). High-speed and high-efficiency travelling wave single-photon detectors embedded in nanophotonic circuits. Nat. Commun., 3, 1325 (1 to 10).
Abstract: Ultrafast, high-efficiency single-photon detectors are among the most sought-after elements in modern quantum optics and quantum communication. However, imperfect modal matching and finite photon absorption rates have usually limited their maximum attainable detection efficiency. Here we demonstrate superconducting nanowire detectors atop nanophotonic waveguides, which enable a drastic increase of the absorption length for incoming photons. This allows us to achieve high on-chip single-photon detection efficiency up to 91% at telecom wavelengths, repeatable across several fabricated chips. We also observe remarkably low dark count rates without significant compromise of the on-chip detection efficiency. The detectors are fully embedded in scalable silicon photonic circuits and provide ultrashort timing jitter of 18 ps. Exploiting this high temporal resolution, we demonstrate ballistic photon transport in silicon ring resonators. Our direct implementation of a high-performance single-photon detector on chip overcomes a major barrier in integrated quantum photonics.
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Sclafani, M., Marksteiner, M., Keir, F. M. L., Divochiy, A., Korneev, A., Semenov, A., et al. (2012). Sensitivity of a superconducting nanowire detector for single ions at low energy. Nanotechnol., 23(6), 065501 (1 to 5).
Abstract: We report on the characterization of a superconducting nanowire detector for ions at low kinetic energies. We measure the absolute single-particle detection efficiency eta and trace its increase with energy up to eta = 100%. We discuss the influence of noble gas adsorbates on the cryogenic surface and analyze their relevance for the detection of slow massive particles. We apply a recent model for the hot-spot formation to the incidence of atomic ions at energies between 0.2 and 1 keV. We suggest how the differences observed for photons and atoms or molecules can be related to the surface condition of the detector and we propose that the restoration of proper surface conditions may open a new avenue for SSPD-based optical spectroscopy on molecules and nanoparticles.
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Семенов, А. В., Корнеев, А. А., Лобанов, Ю. В., Корнеева, Ю. П., Рябчун, С. А., Лаврова, О. С., et al. (2012). Поляризация электромагнитной волны вблизи фокуса зеркала и системы зеркал в субтерагерцовом диапазоне частот. Современные проблемы науки и образования, (2).
Abstract: Рассмотрено влияние оптической системы телескопа на поляризацию принимаемого электромагнитного сигнала. Описано изменение поляризации луча при отражении от произвольно ориентированной поверхности зеркала. Учтены искажения поляризации, обусловленные как отклонением лучей от первоначального направления, так и различием в коэффициентах отражения для разных поляризаций в случае неидеального отражения. В рамках метода Френеля получены оценочные формулы, дающие отношение амплитуд поля с исходной поляризацией и с поляризацией, перпендикулярной исходной, вблизи фокальной точки оптической системы. Формулы выведены для нескольких практически важных случаев, в том числе для параболического зеркала и системы двух зеркал. Оценена верхняя граница поляризационных искажений в пределах кружка Эйри. Полученные оценки согласуются с результатами численного расчёта для двухзеркального радиотелескопа субтерагерцового диапазона.
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Semenov, A. V., Devyatov, I. A., Korneev, A. A., Smirnov, K. V., Goltsman, G. N., & Melnikov, A. P. (2012). Derivation of expression for thermodynamic potential of “dirty” superconductor. Rus. J. Radio Electron., (4).
Abstract: We derive a formula for thermodynamic potential of dirty superconductor which express it via isotropic quasiclassical Green functions of Usadel theory. Our result allows unify description of dynamic processes and fluctuations in superconducting nano-electronic devices.
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Bulaevskii, L. N., Graf, M. J., & Kogan, V. G. (2012). Vortex-assisted photon counts and their magnetic field dependence in single-photon superconducting detectors. Phys. Rev. B, 85(1), 9.
Abstract: We argue that photon counts in a superconducting nanowire single-photon detector (SNSPD) are caused by the transition from a current-biased metastable superconducting state to the normal state. Such a transition is triggered by vortices crossing the thin and narrow superconducting strip from one edge to another due to the Lorentz force. Detector counts in SNSPDs may be caused by three processes: (a) a single incident photon with sufficient energy to break enough Cooper pairs to create a normal-state belt across the entire width of the strip (direct photon count), (b) thermally induced single-vortex crossing in the absence of photons (dark count), which at high-bias currents releases the energy sufficient to trigger the transition to the normal state in a belt across the whole width of the strip, and (c) a single incident photon of insufficient energy to create a normal-state belt but initiating a subsequent single-vortex crossing, which provides the rest of the energy needed to create the normal-state belt (vortex-assisted single-photon count). We derive the current dependence of the rate of vortex-assisted photon counts. The resulting photon count rate has a plateau at high currents close to the critical current and drops as a power law with high exponent at lower currents. While the magnetic field perpendicular to the film plane does not affect the formation of hot spots by photons, it causes the rate of vortex crossings (with or without photons) to increase. We show that by applying a magnetic field one may characterize the energy barrier for vortex crossings and identify the origin of dark counts and vortex-assisted photon counts.
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Knee, G. C., Simmons, S., Gauger, E. M., Morton, J. J. L., Riemann, H., Abrosimov, N. V., et al. (2012). Violation of a Leggett–Garg inequality with ideal non-invasive measurements. Nat. Comm., 3(606), 6.
Abstract: The quantum superposition principle states that an entity can exist in two different states simultaneously, counter to our 'classical' intuition. Is it possible to understand a given system's behaviour without such a concept? A test designed by Leggett and Garg can rule out this possibility. The test, originally intended for macroscopic objects, has been implemented in various systems. However to date no experiment has employed the 'ideal negative result' measurements that are required for the most robust test. Here we introduce a general protocol for these special measurements using an ancillary system, which acts as a local measuring device but which need not be perfectly prepared. We report an experimental realization using spin-bearing phosphorus impurities in silicon. The results demonstrate the necessity of a non-classical picture for this class of microscopic system. Our procedure can be applied to systems of any size, whether individually controlled or in a spatial ensemble.
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Smith, D. H., Gillett, G., de Almeida, M. P., Branciard, C., Fedrizzi, A., Weinhold, T. J., et al. (2012). Conclusive quantum steering with superconducting transition-edge sensors. Nat. Comm., 3(625), 6.
Abstract: Quantum steering allows two parties to verify shared entanglement even if one measurement device is untrusted. A conclusive demonstration of steering through the violation of a steering inequality is of considerable fundamental interest and opens up applications in quantum communication. To date, all experimental tests with single-photon states have relied on post selection, allowing untrusted devices to cheat by hiding unfavourable events in losses. Here we close this 'detection loophole' by combining a highly efficient source of entangled photon pairs with superconducting transition-edge sensors. We achieve an unprecedented ~62% conditional detection efficiency of entangled photons and violate a steering inequality with the minimal number of measurement settings by 48 s.d.s. Our results provide a clear path to practical applications of steering and to a photonic loophole-free Bell test.
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Ghali, M., Ohtani1, K., Ohno, Y., & Ohno, H. (2012). Generation and control of polarization-entangled photons from GaAs island quantum dots by an electric field. Nat. Comm., 3(661), 6.
Abstract: Semiconductor quantum dots are potential sources for generating polarization-entangled photons efficiently. The main prerequisite for such generation based on biexciton-exciton cascaded emission is to control the exciton fine-structure splitting. Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices. Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field. In contrast to previous studies, which were limited to In(Ga)As quantum dots, GaAs island quantum dots formed by a thickness fluctuation were used because they exhibit a larger oscillator strength and emit light with a shorter wavelength. A forward voltage was applied to a Schottky diode to control the fine-structure splitting. We observed a decrease and suppression in the fine-structure splitting of the studied single quantum dot with the field, which enabled us to generate polarization-entangled photons with a high fidelity of 0.72 ± 0.05.
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Grotz, B., Hauf, M. V., Dankerl, M., Naydenov, B., Pezzagna, S., Meijer, J., et al. (2012). Charge state manipulation of qubits in diamond. Nat. Comm., 3(729), 6.
Abstract: The nitrogen-vacancy (NV) centre in diamond is a promising candidate for a solid-state qubit. However, its charge state is known to be unstable, discharging from the qubit state NV- into the neutral state NV0 under various circumstances. Here we demonstrate that the charge state can be controlled by an electrolytic gate electrode. This way, single centres can be switched from an unknown non-fluorescent state into the neutral charge state NV0, and the population of an ensemble of centres can be shifted from NV0 to NV-. Numerical simulations confirm the manipulation of the charge state to be induced by the gate-controlled shift of the Fermi level at the diamond surface. This result opens the way to a dynamic control of transitions between charge states and to explore hitherto inaccessible states, such as NV+.
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Gao, J., McMillan, J. F., & Wong, C. W. (2012). Nanophotonics: Remote on-chip coupling. Nat. Photon., 6(1), 7–8.
Abstract: Scientists have demonstrated strongly coupled photon states between two distant high-Q photonic crystal cavities connected by a photonic crystal waveguide. Remote dynamic control over the coupled states could aid the development of delay lines, optical buffers and qubit operations in both classical and quantum information processing.
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Santori, C., & Beausoleil, R. G. (2012). Quantum memory: Phonons in diamond crystals. Nat. Photon., 6, 10–12.
Abstract: The demonstration that quantum information can be stored in a bulk-diamond crystal in the form of an optically excited phonon gives researchers a new type of mechanical solid-state quantum memory to explore.
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