Kawakami, A., Saito, S., & Hyodo, M. (2011). Fabrication of nano-antennas for superconducting Infrared detectors. IEEE Trans. Appl. Supercond., 21(3), 632–635.
Abstract: To improve the response performance of superconducting infrared detectors, we have developed a fabrication process for nano-antennas. A nano-antenna consists of a dipole antenna, and a superconducting thin film strip placed in the antenna's center. By measuring the transition temperature of the superconducting strips, we confirmed that their superconductivity maintained a good condition after the nano-antenna fabrication process. We also evaluated nano-antenna characteristics using Fourier transform infrared spectroscopy. The evaluated antenna length and width were respectively set at around 2400 nm and 400 nm, and the antennas were placed at intervals of several micrometers around the area of 1 mm2 . In an evaluation of spectral transmission characteristics, clear absorption caused by antenna effects was observed at around 1400 cm-1. High polarization dependencies were also observed.
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Lobanov, Y. V., Tong, C. - Y. E., Hedden, A. S., Blundell, R., Voronov, B. M., & Gol'tsman, G. N. (2011). Direct measurement of the gain and noise bandwidths of HEB mixers. IEEE Trans. Appl. Supercond., 21(3), 645–648.
Abstract: The intermediate frequency (IF) bandwidth of a hot electron bolometer (HEB) mixer is an important parameter of the mixer, in that it helps to determine its suitability for a given application. With the availability of wideband low noise amplifiers, it is simple to measure the performance of an HEB mixer over a wide range of IF at a fixed LO frequency using the standard Y-factor method. This in-situ method allows us to measure both the gain and noise bandwidths simultaneously. We have also measured mixer output impedance with a vector network analyser. Intrinsic time constant has been extracted from the impedance data and compared to the mixer's bandwidths determined from receiver Y-factor measurement.
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Dada, A. C., Leach, J., Buller, G. S., Padgett, M. J., & Andersson, E. (2011). Experimental high-dimensional two-photon entanglement and violations of generalized Bell inequalities. Nat. Phys., 7(9), 677–680.
Abstract: Quantum entanglement plays a vital role in many quantum-information and communication tasks. Entangled states of higher-dimensional systems are of great interest owing to the extended possibilities they provide. For example, they enable the realization of new types of quantum information scheme that can offer higher-information-density coding and greater resilience to errors than can be achieved with entangled two-dimensional systems (see ref. and references therein). Closing the detection loophole in Bell test experiments is also more experimentally feasible when higher-dimensional entangled systems are used. We have measured previously untested correlations between two photons to experimentally demonstrate high-dimensional entangled states. We obtain violations of Bell-type inequalities generalized to d-dimensional systems up to d=12. Furthermore, the violations are strong enough to indicate genuine 11-dimensional entanglement. Our experiments use photons entangled in orbital angular momentum, generated through spontaneous parametric down-conversion, and manipulated using computer-controlled holograms.
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Grinolds, M. S., Maletinsky, P., Hong, S., Lukin, M. D., Walsworth, R. L., & Yacoby, A. (2011). Quantum control of proximal spins using nanoscale magnetic resonance imaging. Nat. Phys., 7(9), 687–692.
Abstract: Quantum control of individual spins in condensed-matter systems is an emerging field with wide-ranging applications in spintronics, quantum computation and sensitive magnetometry. Recent experiments have demonstrated the ability to address and manipulate single electron spins through either optical or electrical techniques. However, it is a challenge to extend individual-spin control to nanometre-scale multi-electron systems, as individual spins are often irresolvable with existing methods. Here we demonstrate that coherent individual-spin control can be achieved with few- nanometre resolution for proximal electron spins by carrying out single-spin magnetic resonance imaging (MRI), which is realized using a scanning-magnetic-field gradient that is both strong enough to achieve nanometre spatial resolution and sufficiently stable for coherent spin manipulations. We apply this scanning-field-gradient MRI technique to electronic spins in nitrogen-vacancy (NV) centres in diamond and achieve nanometre resolution in imaging, characterization and manipulation of individual spins. For NV centres, our results in individual-spin control demonstrate an improvement of nearly two orders of magnitude in spatial resolution when compared with conventional optical diffraction-limited techniques. This scanning-field-gradient microscope enables a wide range of applications including materials characterization, spin entanglement and nanoscale magnetometry.
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Capmany, J., Gasulla, I., & Sales, S. (2011). Microwave photonics: Harnessing slow light. Nat. Photon., 5(12), 731–733.
Abstract: Slow-light techniques originally conceived for buffering high-speed digital optical signals now look set to play an important role in providing broadband phase and true time delays for microwave signals.
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Hannay, T. (2011). A new kind of science? Nat. Phys., 7, 742.
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Prevedel, R., Hamel, D. R., Colbeck, R., Fisher, K., & Resch, K. J. (2011). Experimental investigation of the uncertainty principle in the presence of quantum memory and its application to witnessing entanglement. Nat. Phys., 7(10), 757–761.
Abstract: Heisenberg's uncertainty principle provides a fundamental limitation on the ability of an observer holding classical information to predict the outcome when one of two measurements is performed on a quantum system. However, an observer with access to a particle (stored in a quantum memory) which is entangled with the system generally has a reduced uncertainty: indeed, if the particle and system are maximally entangled, the observer can perfectly predict the outcome of whichever measurement is chosen. This effect has recently been quantified in a new entropic uncertainty relation. Here we experimentally investigate this relation, showing its effectiveness as an efficient entanglement witness. We use entangled photon pairs, an optical delay line serving as a simple quantum memory and fast, active feed-forward. Our results quantitatively agree with the new uncertainty relation. Our technique acts as a witness for almost all entangled states in our experiment as we obtain lower uncertainties than would be possible without the entangled particle.
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Fuchs, G. D., Burkard, G., Klimov, P. V., & Awschalom, D. D. (2011). A quantum memory intrinsic to single nitrogen–vacancy centres in diamond. Nat. Phys., 7(10), 789–793.
Abstract: A quantum memory, composed of a long-lived qubit coupled to each processing qubit, is important to building a scalable platform for quantum information science. These two qubits should be connected by a fast and high-fidelity operation to store and retrieve coherent quantum states. Here, we demonstrate a room-temperature quantum memory based on the spin of the nitrogen nucleus intrinsic to each nitrogen–vacancy (NV) centre in diamond. We perform coherent storage of a single NV centre electronic spin in a single nitrogen nuclear spin using Landau–Zener transitions across a hyperfine-mediated avoided level crossing. By working outside the asymptotic regime, we demonstrate coherent state transfer in as little as 120 ns with total storage fidelity of 88±6%. This work demonstrates the use of a quantum memory that is compatible with scaling as the nitrogen nucleus is deterministically present in each NV centre defect.
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Hosseini, M., Campbell, G., Sparkes, B. M., Lam, P. K., & Buchler, B. C. (2011). Unconditional room-temperature quantum memory. Nat. Phys., 7(10), 794–798.
Abstract: Just as classical information systems require buffers and memory, the same is true for quantum information systems. The potential that optical quantum information processing holds for revolutionizing computation and communication is therefore driving significant research into developing optical quantum memory. A practical optical quantum memory must be able to store and recall quantum states on demand with high efficiency and low noise. Ideally, the platform for the memory would also be simple and inexpensive. Here, we present a complete tomographic reconstruction of quantum states that have been stored in the ground states of rubidium in a vapour cell operating at around 80 °C. Without conditional measurements, we show recall fidelity up to 98% for coherent pulses containing around one photon. To unambiguously verify that our memory beats the quantum no-cloning limit we employ state-independent verification using conditional variance and signal-transfer coefficients.
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Rasulova, G. K., Brunkov, P. N., Pentin, I. V., Kovalyuk, V. V., Gorshkov, K. N., Kazakov, A. Y., et al. (2011). Mutual synchronization of two coupled self-oscillators based on GaAs/AlGaAs superlattices. Tech. Phys., 56(6), 826–830.
Abstract: The interaction of self-oscillators based on 30-period weakly coupled GaAs/AlGaAs superlattices is studied. The action of one self-oscillator on the other was observed for a constant bias voltage in the absence of generation of self-sustained oscillations in one of the oscillators. It is shown that induced oscillations in a forced oscillator appear due to excitation of oscillations in the system of coupled oscillators forming the electric-field domain wall at the frequency of one of the higher harmonics of a forcing oscillation.
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