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847 results on '"Walmsley, I. A."'

551. Towards a quantum Zeno tomography

Author

Facchi, P., Krenn, G., Pascazio, S., Hradil, Z., Řeháček, J., Bigelow, N. P., editor, Eberly, J. H., editor, Stroud, C. R., editor, and Walmsley, I. A., editor

Published
2003
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597. Enhancing Multiphoton Rates with Quantum Memories.

Author

Nunn, J., Langford, N. K., Kolthammer, W. S., Champion, T. F. M., Sprague, M. R., Michelberger, P. S., Jin, X.-M., England, D. G., and Walmsley, I. A.

Subjects
*MULTIPHOTON ionization, *QUANTUM theory, *CATASTROPHE modeling, *BANDWIDTHS, *PHOTONS
Abstract

Single photons are a vital resource for optical quantum information processing. Efficient and deterministic single photon sources do not yet exist, however. To date, experimental demonstrations of quantum processing primitives have been implemented using nondeterministic sources combined with heralding and/or postselection. Unfortunately, even for eight photons, the data rates are already so low as to make most experiments impracticable. It is well known that quantum memories, capable of storing photons until they are needed, are a potential solution to this "scaling catastrophe." Here, we analyze in detail the benefits of quantum memories for producing multiphoton states, showing how the production rates can be enhanced by many orders of magnitude. We identify the quantity ηB as the most important figure of merit in this connection, where η and B are the efficiency and time-bandwidth product of the memories, respectively. [ABSTRACT FROM AUTHOR]

Published
2013
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598. High-fidelity polarization storage in a gigahertz bandwidth quantum memory.

Author

England, D. G., Michelberger, P. S., Champion, T. F. M., Reim, K. F., Lee, K. C., Sprague, M. R., Jin, X-M, Langford, N. K., Kolthammer, W. S., Nunn, J., and Walmsley, I. A.

Subjects
*OPTICAL polarization, *LIGHT sources, *BANDWIDTHS, *QUANTUM information science, *INTERFEROMETERS, *PERFORMANCE evaluation
Abstract

We demonstrate a dual-rail optical Raman memory inside a polarization interferometer; this enables us to store polarization-encoded information at GHz bandwidths in a room-temperature atomic ensemble. By performing full process tomography on the system, we measure up to 97 ± 1% process fidelity for the storage and retrieval process. At longer storage times, the process fidelity remains high, despite a loss of efficiency. The fidelity is 86 ± 4% for 1.5 µs storage time, which is 5000 times the pulse duration. Hence, high fidelity is combined with a large time-bandwidth product. This high performance, with an experimentally simple setup, demonstrates the suitability of the Raman memory for integration into large-scale quantum networks. [ABSTRACT FROM AUTHOR]

Published
2012
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599. Multipulse Addressing of a Raman Quantum Memory: Configurable Beam Splitting and Efficient Readout.

Author

Reim, K. F., Nunn, J., Jin, X.-M., Michelberger, P. S., Champion, T. F. M., England, D. G., Lee, K. C., Kolthammer, W. S., Langford, N. K., and Walmsley, I. A.

Subjects
*QUANTUM information theory, *BEAM splitters, *PHOTONS, *QUANTUM communication, *METROLOGY, *OPTICAL communications
Abstract

Quantum memories are vital to the scalability of photonic quantum information processing (PQIP), since the storage of photons enables repeat-until-success strategies. On the other hand, the key element of all PQIP architectures is the beam splitter, which allows us to coherently couple optical modes. Here, we show how to combine these crucial functionalities by addressing a Raman quantum memory with multiple control pulses. The result is a coherent optical storage device with an extremely large time bandwidth product, that functions as an array of dynamically configurable beam splitters, and that can be read out with arbitrarily high efficiency. Networks of such devices would allow fully scalable PQIP, with applications in quantum computation, long distance quantum communications and quantum metrology. [ABSTRACT FROM AUTHOR]

Published
2012
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600. Macroscopic non-classical states and terahertz quantum processing in room-temperature diamond.

Author

Lee, K. C., Sussman, B. J., Sprague, M. R., Michelberger, P., Reim, K. F., Nunn, J., Langford, N. K., Bustard, P. J., Jaksch, D., and Walmsley, I. A.

Subjects
*QUASIPARTICLES, *LATTICE dynamics, *PHONONS, *RAMAN effect, *PHOTONICS
Abstract

The nature of the transition between the familiar classical, macroscopic world and the quantum, microscopic one continues to be poorly understood. Expanding the regime of observable quantum behaviour to large-scale objects is therefore an exciting open problem. In macroscopic systems of interacting particles, rapid thermalization usually destroys any quantum coherence before it can be measured or used at room temperature. Here, we demonstrate quantum processing in the vibrational modes of a macroscopic diamond sample under ambient conditions. Using ultrafast Raman scattering, we create an extended, highly non-classical state in the optical phonon modes of bulk diamond. Direct measurement of phonon coherence and correlations establishes the non-classical nature of the crystal dynamics. These results show that optical phonons in diamond provide a unique opportunity for the study of large-scale quantum behaviour, and highlight the potential for diamond as a micro-photonic quantum processor capable of operating at terahertz rates. [ABSTRACT FROM AUTHOR]

Published
2012
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