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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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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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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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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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De Luca, M., Gupta, H., Neufeld, D., Gerin, M., Teyssier, D., Drouin, B. J., et al. (2012). Herschel/HIFI discovery of HCL+ in the interstellar medium. Astrophys. J. Lett., 751(2), L37.
Abstract: The radical ion HCl+, a key intermediate in the chlorine chemistry of the interstellar gas, has been identified for the first time in the interstellar medium with the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared. The ground-state rotational transition of H35Cl+, 2Π3/2 J = 5/2-3/2, showing Λ-doubling and hyperfine structure, is detected in absorption toward the Galactic star-forming regions W31C (G10.6-0.4) and W49N. The complex interstellar absorption features are modeled by convolving in velocity space the opacity profiles of other molecular tracers toward the same sources with the fine and hyperfine structure of HCl+. This structure is derived from a combined analysis of optical data from the literature and new laboratory measurements of pure rotational transitions, reported in the accompanying Letter by Gupta et al. The models reproduce well the interstellar absorption, and the frequencies inferred from the astronomical observations are in exact agreement with those calculated using spectroscopic constants derived from the laboratory data. The detection of H37Cl+ toward W31C, with a column density consistent with the expected 35Cl/37Cl isotopic ratio, provides additional evidence for the identification. A comparison with the chemically related molecules HCl and H2Cl+ yields an abundance ratio of unity with both species (HCl+ : H2Cl+ : HCl ~ 1). These observations also yield the unexpected result that HCl+ accounts for 3%-5% of the gas-phase chlorine toward W49N and W31C, values several times larger than the maximum fraction (~1%) predicted by chemical models.
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Korneev, A., Korneeva, Y., Florya, I., Voronov, B., & Goltsman, G. (2012). NbN nanowire superconducting single-photon detector for mid-infrared. Phys. Procedia, 36, 72–76.
Abstract: Superconducting single-photon detectors (SSPD) is typically 100 nm-wide supercondiucting strip in a shape of meander made of 4-nm-thick film. To reduce response time and increase voltage response a parallel connection of the strips was proposed. Recently we demonstrated that reduction of the strip width improves the quantum effciency of such a detector at wavelengths longer than 1.5 μm. Being encourage by this progress in quantum effciency we improved the fabrication process and made parallel-wire SSPD with 40-nm-wide strips covering total area of 10 μm x 10 μm. In this paper we present the results of the characterization of such a parallel-wire SSPD at 10.6 μm wavelength and demonstrate linear dependence of the count rate on the light power as it should be in case of single-photon response.
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Xu, X. A., & Wong, C. W. (2012). Quantum optics: Correlations on a chip. Nat. Photon., 6, 75–76.
Abstract: Researchers have developed a semiconductor structure capable of supporting quantum correlations between photons and strong single-photon nonlinearities, thus paving the way for the development of chip-based devices for quantum secure communications and quantum information processing.
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Akalin, T. (2012). Terahertz sources: Powerful photomixers. Nat. Photon., 6(2), 81.
Abstract: An efficient continuous-wave source of terahertz radiation that combines the outputs from two near-infrared semiconductor lasers in a novel photomixer looks set to benefit applications in spectroscopy and imaging.
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Tuchak, A. N., Gol’tsman, G. N., Kitaeva, G. K., Penin, A. N., Seliverstov, S. V., Finkel, M. I., et al. (2012). Generation of nanosecond terahertz pulses by the optical rectification method. JETP Lett., 96(2), 94–97.
Abstract: The possibility of the generation of quasi-cw terahertz radiation by the optical rectification method for broad-band Fourier unlimited nanosecond laser pulses has been experimentally demonstrated. The broadband radiation of a LiF dye-center laser is used as a pump source of a nonlinear optical oscillator. The energy efficiency of terahertz optical frequency conversion in a periodically polarized lithium niobate crystal is 4 × 10−9 at a pump power density of 7 MW/cm2.
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Korotkov, A. N. (2012). Entanglement preservation: The Sleeping Beauty approach. Nat. Phys., 8(2), 107–108.
Abstract: Two-qubit entanglement can be preserved by partially measuring the qubits to leave them in a 'lethargic' state. The original state is restored using quantum measurement reversal after the qubits have travelled through a decoherence channel.
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Смирнов, А. В., Карманцов, М. С., Смирнов, К. В., Вахтомин, Ю. Б., Мастеров, Д. В., Тархов, М. А., et al. (2012). Терагерцовый отклик болометров на основе тонких пленок YBCO. ЖТФ, 82(12), 108–111.
Abstract: Представлены первые результаты измерения болометрического отклика высокотемпературных сверхпроводниковых детекторов на основе тонких пленок YBCO на электромагнитное излучение с частотой 2.5 THz. Минимальное значение оптической мощности, эквивалентной шуму созданных детекторов, составило 3.5· 10-9 W/sqrt(Hz)sqrt. Обсуждена возможность дальнейшего увеличения чувствительности исследуемых детекторов.
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Hollenberg, L. C. L. (2012). Quantum control: Through the quantum chicane. Nat. Phys., 8(2), 113–114.
Abstract: In quantum control there is an inherent tension between high fidelity requirements and the need for speed to avoid decoherence. A direct comparison of quantum control protocols at these two extremes indicates where the sweet spot may lie.
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Kim, Y. - S., Lee, J. - C., Kwon, O., & Kim, Y. - H. (2012). Protecting entanglement from decoherence using weak measurement and quantum measurement reversal. Nat. Phys., 8(2), 117–120.
Abstract: Decoherence, often caused by unavoidable coupling with the environment, leads to degradation of quantum coherence. For a multipartite quantum system, decoherence leads to degradation of entanglement and, in certain cases, entanglement sudden death. Tackling decoherence, thus, is a critical issue faced in quantum information, as entanglement is a vital resource for many quantum information applications including quantum computing, quantum cryptography, quantum teleportation and quantum metrology. Here, we propose and demonstrate a scheme to protect entanglement from decoherence. Our entanglement protection scheme makes use of the quantum measurement itself for actively battling against decoherence and it can effectively circumvent even entanglement sudden death.
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