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Author (up) Gustafsson, Martin V.; Santos, Paulo V.; Johansson, Göran; Delsing, Per openurl 
  Title Local probing of propagating acoustic waves in a gigahertz echo chamber Type Journal Article
  Year 2012 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 8 Issue 4 Pages 338-343  
  Keywords fromIPMRAS  
  Abstract In the same way that micro-mechanical resonators resemble guitar strings and drums, surface acoustic waves resemble the sound these instruments produce, but moving over a solid surface rather than through air. In contrast with oscillations in suspended resonators, such propagating mechanical waves have not before been studied near the quantum mechanical limits. Here, we demonstrate local probing of surface acoustic waves with a displacement sensitivity of 30amRMSHz-1/2 and detection sensitivity on the single-phonon level after averaging, at a frequency of 932MHz. Our probe is a piezoelectrically coupled single-electron transistor, which is sufficiently fast, non-destructive and localized to enable us to track pulses echoing back and forth in a long acoustic cavity, self-interfering and ringing the cavity up and down. We project that strong coupling to quantum circuits will enable new experiments, and hybrids using the unique features of surface acoustic waves. Prospects include quantum investigations of phonon-phonon interactions, and acoustic coupling to superconducting qubits for which we present favourable estimates.  
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  Call Number RPLAB @ gujma @ Serial 813  
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Author (up) Hadfield, Robert H. doi  openurl
  Title Single-photon detectors for optical quantum information applications Type Journal Article
  Year 2009 Publication Nature Photonics Abbreviated Journal Nature Photonics  
  Volume 3 Issue Pages 696-705  
  Keywords SPD  
  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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  Call Number RPLAB @ gujma @ Serial 678  
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Author (up) Hannay, Timo openurl 
  Title A new kind of science? Type Journal Article
  Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 7 Issue Pages 742  
  Keywords fromIPMRAS  
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  Call Number RPLAB @ gujma @ Serial 818  
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Author (up) Hanneke, D.; Home, J. P.; Jost, J. D.; Amini, J. M.; Leibfried, D.; Wineland, D. J. openurl 
  Title Realization of a programmable two-qubit quantum processor Type Journal Article
  Year 2010 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 6 Issue 1 Pages 13-16  
  Keywords fromIPMRAS  
  Abstract The universal quantum computer is a device capable of simulating any physical system and represents a major goal for the field of quantum information science. In the context of quantum information, `universal' refers to the ability to carry out arbitrary unitary transformations in the system's computational space. Combining arbitrary single-quantum-bit (qubit) gates with an entangling two-qubit gate provides a set of gates capable of achieving universal control of any number of qubits, provided that these gates can be carried out repeatedly and between arbitrary pairs of qubits. Although gate sets have been demonstrated in several technologies, they have so far been tailored towards specific tasks, forming a small subset of all unitary operators. Here we demonstrate a quantum processor that can be programmed with 15 classical inputs to realize arbitrary unitary transformations on two qubits, which are stored in trapped atomic ions. Using quantum state and process tomography, we characterize the fidelity of our implementation for 160 randomly chosen operations. This universal control is equivalent to simulating any pairwise interaction between spin-1/2 systems. A programmable multiqubit register could form a core component of a large-scale quantum processor, and the methods used here are suitable for such a device.  
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  Call Number RPLAB @ gujma @ Serial 801  
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Author (up) Hase, Muneaki; Katsuragawa, Masayuki; Constantinescu, Anca Monia; Petek, Hrvoje openurl 
  Title Frequency comb generation at terahertz frequencies by coherent phonon excitation in silicon Type Journal Article
  Year 2012 Publication Nature Photonics Abbreviated Journal Nat. Photon.  
  Volume 6 Issue Pages 243–247  
  Keywords fromIPMRAS  
  Abstract High-order nonlinear light–matter interactions in gases enable the generation of X-ray and attosecond light pulses, metrology and spectroscopy1. Optical nonlinearities in solid-state materials are particularly interesting for combining optical and electronic functions for high-bandwidth information processing2. Third-order nonlinear optical processes in silicon have been used to process optical signals with bandwidths greater than 1 GHz (ref. 2). However, fundamental physical processes for a silicon-based optical modulator in the terahertz bandwidth range have not yet been explored. Here, we demonstrate ultrafast phononic modulation of the optical index of silicon by irradiation with intense few-cycle femtosecond pulses. The anisotropic reflectivity modulation by the resonant Raman susceptibility at the fundamental frequency of the longitudinal optical phonon of silicon (15.6 THz) generates a frequency comb up to seventh order. All-optical >100 THz frequency comb generation is realized by harnessing the coherent atomic motion of the silicon crystalline lattice at its highest mechanical frequency.  
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  Call Number RPLAB @ gujma @ Serial 794  
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Author (up) Haviland, David openurl 
  Title Superconducting circuits: Quantum phase slips Type Journal Article
  Year 2010 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 6 Issue Pages 565–566  
  Keywords fromIPMRAS  
  Abstract Coulomb interactions can cause a rapid change in the phase of the wavefunction along a very narrow superconducting system. Such a phase slip at the quantum level is now measured in a chain of Josephson junctions.  
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  Call Number RPLAB @ gujma @ Serial 807  
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Author (up) He, Rongrui; Sazio, Pier J. A.; Peacock, Anna C.; Healy, Noel; Sparks, Justin R.; Krishnamurthi, Mahesh; Gopalan, Venkatraman; Badding, John V. openurl 
  Title Integration of gigahertz-bandwidth semiconductor devices inside microstructured optical fibres Type Journal Article
  Year 2012 Publication Nature Photonics Abbreviated Journal Nat. Photon.  
  Volume 6 Issue 3 Pages 174-179  
  Keywords fromIPMRAS  
  Abstract The prospect of an all-fibre optical communications network in which light can be generated, modulated and detected within the fibre itself without the need for discrete optoelectronic devices is an appealing one. However, to become a reality, this approach requires the incorporation of optoelectronic materials and functionalities into silica fibres to create a new breed of semiconductor-fibre hybrid devices for performing various tasks. Here, we report the integration of precisely doped semiconductor materials and high-quality rectifying semiconductor junctions into microstructured optical fibres, enabling high-speed, in-fibre functionalities such as photodetection at telecommunications wavelengths. These semiconductor-fibre hybrid devices exhibit a bandwidth of up to 3 GHz and seamless coupling to standard single-mode optical fibres.  
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  Call Number RPLAB @ gujma @ Serial 783  
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Author (up) Hollenberg, Lloyd C. L. openurl 
  Title Quantum control: Through the quantum chicane Type Journal Article
  Year 2012 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 8 Issue 2 Pages 113-114  
  Keywords fromIPMRAS  
  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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  Call Number RPLAB @ gujma @ Serial 812  
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Author (up) Home, Jonathan openurl 
  Title Quantum entanglement: Watching correlations disappear Type Journal Article
  Year 2010 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 6 Issue 12 Pages 938-939  
  Keywords fromIPMRAS  
  Abstract Engineered decoherence enables tracking of multipartite entanglement as a quantum state decays.  
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  Call Number RPLAB @ gujma @ Serial 832  
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Author (up) Hosseini, M.; Campbell, G.; Sparkes, B. M.; Lam, P. K.; Buchler, B. C. openurl 
  Title Unconditional room-temperature quantum memory Type Journal Article
  Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 7 Issue 10 Pages 794-798  
  Keywords fromIPMRAS  
  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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  Call Number RPLAB @ gujma @ Serial 824  
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Author (up) Ikuta, Rikizo; Kusaka, Yoshiaki; Kitano, suyoshi; Kato, Hiroshi; Yamamoto, Takashi; Koashi, Masato; Imoto, Nobuyuki openurl 
  Title Wide-band quantum interface for visible-totelecommunication wavelength conversion Type Journal Article
  Year 2011 Publication Nature Communications Abbreviated Journal Nat. Comm.  
  Volume 2 Issue Pages 5  
  Keywords fromIPMRAS  
  Abstract Although near-infrared photons in telecommunication bands are required for long-distance quantum communication, various quantum information tasks have been performed by using visible photons for the past two decades. Recently, such visible photons from diverse media including atomic quantum memories have also been studied. Optical frequency down-conversion from visible to telecommunication bands while keeping the quantum states is thus required for bridging such wavelength gaps. Here we report demonstration of a quantum interface of frequency down-conversion from visible to telecommunication bands by using a nonlinear crystal, which has a potential to work over wide bandwidths, leading to a high-speed interface of frequency conversion. We achieved the conversion of a picosecond visible photon at 780 nm to a 1,522-nm photon, and observed that the conversion process retained entanglement between the down-converted photon and another photon.  
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  Call Number RPLAB @ gujma @ Serial 764  
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Author (up) Johnson, B. R.; Reed, M. D.; Houck, A. A.; Schuster, D. I.; Bishop, Lev S.; Ginossar, E.; Gambetta, J. M.; Dicarlo, L.; Frunzio, L.; Girvin, S. M.; Schoelkopf, R. J. openurl 
  Title Quantum non-demolition detection of single microwave photons in a circuit Type Journal Article
  Year 2010 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 6 Issue 9 Pages 663-667  
  Keywords fromIPMRAS  
  Abstract Thorough control of quantum measurement is key to the development of quantum information technologies. Many measurements are destructive, removing more information from the system than they obtain. Quantum non-demolition (QND) measurements allow repeated measurements that give the same eigenvalue. They could be used for several quantum information processing tasks such as error correction, preparation by measurement and one-way quantum computing. Achieving QND measurements of photons is especially challenging because the detector must be completely transparent to the photons while still acquiring information about them. Recent progress in manipulating microwave photons in superconducting circuits has increased demand for a QND detector that operates in the gigahertz frequency range. Here we demonstrate a QND detection scheme that measures the number of photons inside a high-quality-factor microwave cavity on a chip. This scheme maps a photon number, n, onto a qubit state in a single-shot by means of qubit-photon logic gates. We verify the operation of the device for n=0 and 1 by analysing the average correlations of repeated measurements, and show that it is 90% QND. It differs from previously reported detectors because its sensitivity is strongly selective to chosen photon number states. This scheme could be used to monitor the state of a photon-based memory in a quantum computer.  
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  Call Number RPLAB @ gujma @ Serial 806  
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Author (up) Kawano, Yukio; Ishibashi, Koji url  doi
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  Title An on-chip near-field terahertz probe and detector Type Journal Article
  Year 2008 Publication Nature Photonics Abbreviated Journal Nature Photon  
  Volume 2 Issue 10 Pages 618-621  
  Keywords single molecule, terahertz, THz, near-field, microscopy, imaging, 2DEG, GaAs/AlGaAs, detector, applications  
  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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  ISSN 1749-4885 ISBN Medium  
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  Call Number Serial 570  
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Author (up) Kim, Yong-Su; Lee, Jong-Chan; Kwon, Osung; Kim, Yoon-Ho openurl 
  Title Protecting entanglement from decoherence using weak measurement and quantum measurement reversal Type Journal Article
  Year 2012 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 8 Issue 2 Pages 117-120  
  Keywords fromIPMRAS  
  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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  Call Number RPLAB @ gujma @ Serial 815  
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Author (up) Knee, George C.; Simmons, Stephanie; Gauger, Erik M.; Morton, John J. L.; Riemann, Helge; Abrosimov, Nikolai V.; Becker, Peter; Pohl, Hans-Joachim; Itoh, Kohei M.; Thewalt, Mike L. W.; Briggs, G. Andrew D.; Benjamin, Simon C. openurl 
  Title Violation of a Leggett–Garg inequality with ideal non-invasive measurements Type Journal Article
  Year 2012 Publication Nature Communications Abbreviated Journal Nat. Comm.  
  Volume 3 Issue 606 Pages 6  
  Keywords fromIPMRAS  
  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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  Call Number RPLAB @ gujma @ Serial 767  
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