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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) 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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  Notes Approved no  
  Call Number RPLAB @ gujma @ Serial 806  
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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) Korotkov, Alexander N. openurl 
  Title Entanglement preservation: The Sleeping Beauty approach Type Journal Article
  Year 2012 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 8 Issue 2 Pages 107-108  
  Keywords fromIPMRAS  
  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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  Call Number RPLAB @ gujma @ Serial 814  
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Author (up) Kumar, Sushil; Chan, Chun Wang I.; Hu, Qing; Reno, John L. openurl 
  Title A 1.8-THz quantum cascade laser operating significantly above the temperature of hw/k Type Journal Article
  Year 2011 Publication Nature Physics Abbreviated Journal  
  Volume 7 Issue Pages 166-171  
  Keywords QCL, 2 mW at 155 K and 1.8 THz  
  Abstract Several competing technologies continue to advance the field of terahertz science; of particular importance has been the development of a terahertz semiconductor quantum cascade laser (QCL), which is arguably the only solid-state terahertz source with average optical power levels of much greater than a milliwatt. Terahertz QCLs are required to be cryogenically cooled and improvement of their temperature performance is the single most important research goal in the field. Thus far, their maximum operating temperature has been empirically limited to ~planckω/kB, a largely inexplicable trend that has bred speculation that a room-temperature terahertz QCL may not be possible in materials used at present. Here, we argue that this behaviour is an indirect consequence of the resonant-tunnelling injection mechanism employed in all previously reported terahertz QCLs. We demonstrate a new scattering-assisted injection scheme to surpass this limit for a 1.8-THz QCL that operates up to ~1.9planckω/kB (163 K). Peak optical power in excess of 2 mW was detected from the laser at 155 K. This development should make QCL technology attractive for applications below 2 THz, and initiate new design strategies for realizing a room-temperature terahertz semiconductor laser.  
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  Notes Approved no  
  Call Number Serial 631  
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Author (up) Kumar, Sushil; Wang I. Chan, Chun; Hu, Qing; Reno, John L. openurl 
  Title A 1.8-THz quantum cascade laser operating significantly above the temperature of ω/kB Type Journal Article
  Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 7 Issue Pages  
  Keywords fromIPMRAS  
  Abstract Several competing technologies continue to advance the field of terahertz science; of particular importance has been the development of a terahertz semiconductor quantum cascade laser (QCL), which is arguably the only solid-state terahertz source with average optical power levels of much greater than a milliwatt. Terahertz QCLs are required to be cryogenically cooled and improvement of their temperature performance is the single most important research goal in the field. Thus far, their maximum operating temperature has been empirically limited to ~ω/kB, a largely inexplicable trend that has bred speculation that a room-temperature terahertz QCL may not be possible in materials used at present. Here, we argue that this behaviour is an indirect consequence of the resonant-tunnelling injection mechanism employed in all previously reported terahertz QCLs. We demonstrate a new scattering-assisted injection scheme to surpass this limit for a 1.8-THz QCL that operates up to ~1.9ω/kB (163 K). Peak optical power in excess of 2 mW was detected from the laser at 155 K. This development should make QCL technology attractive for applications below 2 THz, and initiate new design strategies for realizing a room-temperature terahertz semiconductor laser.  
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  Notes Approved no  
  Call Number RPLAB @ gujma @ Serial 836  
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Author (up) Lu, Chao-Yang; Zhou, Xiao-Qi; Gühne, Otfried; Gao, Wei-Bo; Zhang, Jin; Yuan, Zhen-Sheng; Goebel, Alexander; Yang, Tao; Pan, Jian-Wei openurl 
  Title Experimental entanglement of six photons in graph states Type Journal Article
  Year 2007 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 3 Issue 2 Pages 91-95  
  Keywords fromIPMRAS  
  Abstract Graph states-multipartite entangled states that can be represented by mathematical graphs-are important resources for quantum computation, quantum error correction, studies of multiparticle entanglement and fundamental tests of non-locality and decoherence. Here, we demonstrate the experimental entanglement of six photons and engineering of multiqubit graph states. We have created two important examples of graph states, a six-photon Greenberger-Horne-Zeilinger state, the largest photonic Schrödinger cat so far, and a six-photon cluster state, a state-of-the-art `one-way quantum computer'. With small modifications, our method allows us, in principle, to create various further graph states, and therefore could open the way to experimental tests of, for example, quantum algorithms or loss- and fault-tolerant one-way quantum computation.  
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  Call Number RPLAB @ gujma @ Serial 796  
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Author (up) Lupascu, Adrian openurl 
  Title Nonlinear dynamics: Quantum pendula locked in Type Journal Article
  Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 7 Issue 2 Pages 100-101  
  Keywords fromIPMRAS  
  Abstract A study of the autoresonant behaviour of a superconducting pendulum reveals that quantum fluctuations determine only the initial oscillator motion and not its subsequent dynamics. This could be important in the development of more efficient methods for reading solid-state qubits.  
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  Notes Approved no  
  Call Number RPLAB @ gujma @ Serial 840  
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