Collins, M. J., Xiong, C., Rey, I. H., Vo, T. D., He, J., Shahnia, S., et al. (2013). Integrated spatial multiplexing of heralded single-photon sources. Nature Communications, .
Abstract: The non-deterministic nature of photon sources is a key limitation for single-photon quantum processors. Spatial multiplexing overcomes this by enhancing the heralded single-photon yield without enhancing the output noise. Here the intrinsic statistical limit of an individual source is surpassed by spatially multiplexing two monolithic silicon-based correlated photon pair sources in the telecommunications band, demonstrating a 62.4% increase in the her- alded single-photon output without an increase in unwanted multipair generation. We further demonstrate the scalability of this scheme by multiplexing photons generated in two waveguides pumped via an integrated coupler with a 63.1% increase in the heralded photon rate. This demonstration paves the way for a scalable architecture for multiplexing many photon sources in a compact integrated platform and achieving efficient two-photon inter- ference, required at the core of optical quantum computing and quantum communication protocols.
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Wei, J., Olaya, D., Karasik, B. S., Pereverzev, S. V., Sergeev, A. V., & Gershenson, M. E. (2008). Ultrasensitive hot-electron nanobolometers for terahertz astrophysics. Nature Nanotech, 3(8), 496–500.
Abstract: 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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Bonifas, A. P., & McCreery, R. L. (2010). ‘Soft’ Au, Pt and Cu contacts for molecular junctions through surface-diffusion-mediated deposition. Nat. Nanotech., 5(8), 612–617.
Abstract: Virtually all types of molecular electronic devices depend on electronically addressing a molecule or molecular layer through the formation of a metallic contact. The introduction of molecular devices into integrated circuits will probably depend on the formation of contacts using a vapour deposition technique, but this approach frequently results in the metal atoms penetrating or damaging the molecular layer. Here, we report a method of forming 'soft' metallic contacts on molecular layers through surface-diffusion-mediated deposition, in which the metal atoms are deposited remotely and then diffuse onto the molecular layer, thus eliminating the problems of penetration and damage. Molecular junctions fabricated by this method exhibit excellent yield (typically >90%) and reproducibility, and allow examination of the effects of molecular-layer structure, thickness and contact work function.
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Freer, E. M., Grachev, O., Duan, X., Martin, S., & Stumbo, D. P. (2010). High-yield self-limiting single-nanowire assembly with dielectrophoresis. Nat. Nanotech., 5(7), 525–530.
Abstract: Single-crystal nanowire transistors and other nanowire-based devices could have applications in large-area and flexible electronics if conventional top-down fabrication techniques can be integrated with high-precision bottom-up nanowire assembly. Here, we extend dielectrophoretic nanowire assembly to achieve a 98.5% yield of single nanowires assembled over 16,000 patterned electrode sites with submicrometre alignment precision. The balancing of surface, hydrodynamic and dielectrophoretic forces makes the self-assembly process controllable, and a hydrodynamic force component makes it self-limiting. Our approach represents a methodology to quantify nanowire assembly, and makes single nanowire assembly possible over an area limited only by the ability to reproduce process conditions uniformly.
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Konstantatos, G., & Sargent, E. H. (2010). Nanostructured materials for photon detection. Nat. Nanotech., 5(6), 391–400.
Abstract: The detection of photons underpins imaging, spectroscopy, fibre-optic communications and time-gated distance measurements. Nanostructured materials are attractive for detection applications because they can be integrated with conventional silicon electronics and flexible, large-area substrates, and can be processed from the solution phase using established techniques such as spin casting, spray coating and layer-by-layer deposition. In addition, their performance has improved rapidly in recent years. Here we review progress in light sensing using nanostructured materials, focusing on solution-processed materials such as colloidal quantum dots and metal nanoparticles. These devices exhibit phenomena such as absorption of ultraviolet light, plasmonic enhancement of absorption, size-based spectral tuning, multiexciton generation, and charge carrier storage in surface and interface traps.
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Kawano, Y., & Ishibashi, K. (2008). An on-chip near-field terahertz probe and detector. Nature Photon, 2(10), 618–621.
Abstract: The advantageous properties of terahertz waves, such as their transmission through objects opaque to visible light, are attracting attention for imaging applications. A promising approach for achieving high spatial resolution is the use of near-field imaging. Although this method has been well established in the visible and microwave regions, it is challenging to perform in the terahertz region. In the terahertz techniques investigated to date, detectors have been located remotely from the probe, which degrades sensitivity, and the influence of far-field waves is unavoidable. Here we present a new integrated detection device for terahertz near-field imaging in which all the necessary detection components — an aperture, a probe and a terahertz detector — are integrated on one semiconductor chip, which is cryogenically cooled. This scheme allows highly sensitive, high-resolution detection of the evanescent field alone and promises new capabilities for high-resolution terahertz imaging.
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Takesue, H., Nam, S. W., Zhang, Q., Hadfield, R. H., Honjo, T., Tamaki, K., et al. (2007). Quantum key distribution over a 40-dB channel loss using superconducting single-photon detectors. Nat. Photon., 1, 343–348.
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Williams, B. S. (2007). Terahertz quantum-cascade lasers. Nature Photonics, 1, 517–525.
Abstract: Six years after their birth, terahertz quantum-cascade lasers can now deliver milliwatts or more of continuous-wave coherent radiation throughout the terahertz range — the spectral regime between millimetre and infrared wavelengths, which has long resisted development. This paper reviews the state-of-the-art and future prospects for these lasers, including efforts to increase their operating temperatures, deliver higher output powers and emit longer wavelengths.
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Lydersen, L., Wiechers, C., Wittmann, C., Elser, D., Skaar, J., & Makarov, V. (2010). Hacking commercial quantum cryptography systems by tailored bright illumination. Nat. Photon., 4(10), 686–689.
Abstract: The peculiar properties of quantum mechanics allow two remote parties to communicate a private, secret key, which is protected from eavesdropping by the laws of physics. So-called quantum key distribution (QKD) implementations always rely on detectors to measure the relevant quantum property of single photons. Here we demonstrate experimentally that the detectors in two commercially available QKD systems can be fully remote-controlled using specially tailored bright illumination. This makes it possible to tracelessly acquire the full secret key; we propose an eavesdropping apparatus built of off-the-shelf components. The loophole is likely to be present in most QKD systems using avalanche photodiodes to detect single photons. We believe that our findings are crucial for strengthening the security of practical QKD, by identifying and patching technological deficiencies.
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Hadfield, R. H. (2009). Single-photon detectors for optical quantum information applications. Nature Photonics, 3, 696–705.
Abstract: The past decade has seen a dramatic increase in interest in new single-photon detector technologies. A major cause of this trend has undoubtedly been the push towards optical quantum information applications such as quantum key distribution. These new applications place extreme demands on detector performance that go beyond the capabilities of established single-photon detectors. There has been considerable effort to improve conventional photon-counting detectors and to transform new device concepts into workable technologies for optical quantum information applications. This Review aims to highlight the significant recent progress made in improving single-photon detector technologies, and the impact that these developments will have on quantum optics and quantum information science.
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