Showing papers by "Ping Koy Lam published in 2011"
TL;DR: In this paper, the authors demonstrate the squeezed-light enhancement of GEO600, which will be the GW observatory operated by the LIGO Scientific Collaboration in its search for GWs for the next 3-4 years.
Abstract: Around the globe several observatories are seeking the first direct detection of gravitational waves (GWs). These waves are predicted by Einstein’s general theory of relativity1 and are generated, for example, by black-hole binary systems2. Present GW detectors are Michelson-type kilometre-scale laser interferometers measuring the distance changes between mirrors suspended in vacuum. The sensitivity of these detectors at frequencies above several hundred hertz is limited by the vacuum (zero-point) fluctuations of the electromagnetic field. A quantum technology—the injection of squeezed light3—offers a solution to this problem. Here we demonstrate the squeezed-light enhancement of GEO 600, which will be the GW observatory operated by the LIGO Scientific Collaboration in its search for GWs for the next 3–4 years. GEO 600 now operates with its best ever sensitivity, which proves the usefulness of quantum entanglement and the qualification of squeezed light as a key technology for future GW astronomy4.
810 citations
TL;DR: Results show that simple warm atomic vapour systems have clear potential as a platform for quantum memory, and show 87% efficient recall of light pulses, the highest efficiency measured to date for any coherent optical memory suitable for quantum information applications.
Abstract: By harnessing aspects of quantum mechanics, communication and information processing could be radically transformed. Promising forms of quantum information technology include optical quantum cryptographic systems and computing using photons for quantum logic operations. As with current information processing systems, some form of memory will be required. Quantum repeaters, which are required for long distance quantum key distribution, require quantum optical memory as do deterministic logic gates for optical quantum computing. Here, we present results from a coherent optical memory based on warm rubidium vapour and show 87% efficient recall of light pulses, the highest efficiency measured to date for any coherent optical memory suitable for quantum information applications. We also show storage and recall of up to 20 pulses from our system. These results show that simple warm atomic vapour systems have clear potential as a platform for quantum memory.
295 citations
TL;DR: In this article, the authors presented a random number generation scheme that uses broadband measurements of the vacuum field contained in the radiofrequency sidebands of a single-mode laser, even though the measurements may contain technical noise.
Abstract: We present a random number generation scheme that uses broadband measurements of the vacuum field contained in the radio-frequency sidebands of a single-mode laser. Even though the measurements may contain technical noise, we show that suitable algorithms can transform the digitized photocurrents into a string of random numbers that can be made arbitrarily correlated with a subset of the quantum fluctuations (high quantum correlation regime) or arbitrarily immune to environmental fluctuations (high environmental immunity). We demonstrate up to 2 Gbps of real time random number generation that were verified using standard randomness tests.
211 citations
TL;DR: In this paper, the quantum state is stored in a vapour of rubidium atoms and then recalled with a fidelity in excess of 98% with the help of optical quantum memories.
Abstract: Optical quantum memories—storage devices for the data encoded in light pulses—will be vital for buffering the flow of quantum information. Researchers now demonstrate such a device that can operate at room temperature. The quantum state is stored in a vapour of rubidium atoms and then recalled with a fidelity in excess of 98%.
171 citations
TL;DR: In this paper, a low-latency analysis pipeline was used to identify and localize GW event candidates and to request images of targeted sky locations, where a catalog of nearby galaxies and Milky Way globular clusters were used to select the most promising sky positions to be imaged.
Abstract: Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations.
Methods. During two observing periods (Dec 17 2009 to Jan 8 2010 and Sep 2 to Oct 20 2010), a low-latency analysis pipeline was used to identify GW event candidates and to reconstruct maps of possible sky locations. A catalog of nearby galaxies and Milky Way globular clusters was used to select the most promising sky positions to be imaged, and this directional information was delivered to EM observatories with time lags of about thirty minutes. A Monte Carlo simulation has been used to evaluate the low-latency GW pipeline's ability to reconstruct source positions correctly.
Results. For signals near the detection threshold, our low-latency algorithms often localized simulated GW burst signals to tens of square degrees, while neutron star/neutron star inspirals and neutron star/black hole inspirals were localized to a few hundred square degrees. Localization precision improves for moderately stronger signals. The correct sky location of signals well above threshold and originating from nearby galaxies may be observed with ~50% or better probability with a few pointings of wide-field telescopes.
104 citations
Posted Content•
TL;DR: In this article, the authors demonstrate cross phase modulation (XPM) between two optical pulses; one stored and one freely propagating through the memory medium, and explain how this idea can be extended to enable substantial nonlinear interaction between two single photons that are both stored in memory.
Abstract: Using a gradient echo memory, we experimentally demonstrate cross phase modulation (XPM) between two optical pulses; one stored and one freely propagating through the memory medium. We explain how this idea can be extended to enable substantial nonlinear interaction between two single photons that are both stored in the memory. We present semi-classical and quantum simulations along with a proposed experimental scheme to demonstrate the feasibility of achieving large XPM at single photon level.
82 citations
TL;DR: In this paper, the authors present the first direct search for the gravitational-wave emission associated with oscillations of the fundamental quadrupole mode excited by a pulsar timing glitch.
Abstract: The physical mechanisms responsible for pulsar timing glitches are thought to excite quasinormal mode oscillations in their parent neutron star that couple to gravitational-wave emission. In August 2006, a timing glitch was observed in the radio emission of PSR B0833-45, the Vela pulsar. At the time of the glitch, the two colocated Hanford gravitational-wave detectors of the Laser Interferometer Gravitational wave observatory (LIGO) were operational and taking data as part of the fifth LIGO science run (S5). We present the first direct search for the gravitational-wave emission associated with oscillations of the fundamental quadrupole mode excited by a pulsar timing glitch. No gravitational-wave detection
candidate was found. We place Bayesian 90% confidence upper limits of 6.3 x 10^(-21) to 1.4 x 10^(-20) on the peak intrinsic strain amplitude of gravitational-wave ring-down signals, depending on which spherical harmonic mode is excited. The corresponding range of energy upper limits is 5.0 x 10^(-44) to 1.3 x 10^(-45) erg.
65 citations
TL;DR: This work reports on the performance of a dual-wavelength resonant, traveling-wave optical parametric oscillator to generate squeezed light for application in advanced gravitational-wave interferometers, and demonstrates that the traveled-wave design has excellent intracavity backscattered light suppression and incident backscattering light suppression, which is a crucial design issue forApplication in advanced interferometer.
Abstract: We report on the performance of a dual-wavelength resonant, traveling-wave optical parametric oscillator to generate squeezed light for application in advanced gravitational-wave interferometers. Shot noise suppression of 8.6±0.8 dB was measured across the detection band of interest to Advanced LIGO, and controlled squeezing measured over 5900 s. Our results also demonstrate that the traveling-wave design has excellent intracavity backscattered light suppression of 47 dB and incident backscattered light suppression of 41 dB, which is a crucial design issue for application in advanced interferometers.
54 citations
TL;DR: A digital control system, freely available for download online, specifically designed for quantum optics experiments that allows for automatic and sequential re-locking of optical components, and how the inbuilt locking analysis tools can be used to help optimize individual locks is shown.
Abstract: Digital control of optics experiments has many advantages over analog control systems, specifically in terms of the scalability, cost, flexibility, and the integration of system information into one location. We present a digital control system, freely available for download online, specifically designed for quantum optics experiments that allows for automatic and sequential re-locking of optical components. We show how the inbuilt locking analysis tools, including a white-noise network analyzer, can be used to help optimize individual locks, and verify the long term stability of the digital system. Finally, we present an example of the benefits of digital locking for quantum optics by applying the code to a specific experiment used to characterize optical Schrodinger cat states.
28 citations
TL;DR: In this article, the authors compare three nonlinear materials, two of which have not been well characterized for squeezed state production, and also investigate the viability of doubly-resonant optical parametric oscillator cavities in achieving these requirements.
Abstract: A squeezed light source requires properties such as high squeezing amplitude, high bandwidth and stability over time, ideally using as few resources, such as laser power, as possible. We compare three nonlinear materials, two of which have not been well characterized for squeezed state production, and also investigate the viability of doubly-resonant optical parametric oscillator cavities in achieving these requirements. A model is produced that provides a new way of looking at the construction of an optical parametric oscillator/optical parametric amplifier setup where second harmonic power is treated as a limited resource. The well-characterized periodically poled potassium titanyl phosphate (PPKTP) is compared in an essentially identical setup to two relatively new materials, periodically poled stoichiometric lithium tantalate (PPSLT) and 1.7% magnesium oxide doped periodically poled stoichiometric lithium niobate (PPSLN). Although from the literature PPSLT and PPSLN present advantages such as a higher damage threshold and a higher nonlinearity, respectively, PPKTP was still found to have the most desirable properties. With PPKTP, 5.8 dB of squeezing below the shot noise limit was achieved. With PPSLT, 5.0 dB of squeezing was observed but the power required to see this squeezing was much higher than expected. A technical problem with the PPSLN limited the observed squeezing to around 1.0 dB. This problem is discussed.
26 citations
01 Mar 2011
TL;DR: A.J. Abadie, B. Abbott, R. Adhikari, P. Allen, E. Barriga, L. Barsotti, M. Bock, T. Blair, D. Donovan, K. Frei, A. Freisinger, C. Freise, S. Fricke, J. Friedrich, P Fritschel, V. Fairhurst, Y.
Journal Article•
TL;DR: In this article, the authors present a survey of the state-of-the-art work in this area: A.A. Adhikari, P. A. Ajith, B. Barriga, S.A., A.B. Bennett, J.C. Dooley, E.M. Brandt, J-C. Hohenberger, M.E.Charlton, N.C., C.Chua, C.C, T.Chung, D.Chakrabarty, D-C., D.
Abstract: J. Abadie, B. P. Abbott, R. Abbott, R. Adhikari, P. Ajith, B. Allen, G. Allen, E. Amador Ceron, R. S. Amin, S. B. Anderson, W.G. Anderson, M.A. Arain, M. Araya, Y. Aso, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, P. Baker, S. Ballmer, D. Barker, B. Barr, P. Barriga, L. Barsotti, M.A. Barton, I. Bartos, R. Bassiri, M. Bastarrika, B. Behnke, M. Benacquista, M. F. Bennett, J. Betzwieser, P. T. Beyersdorf, I. A. Bilenko, G. Billingsley, R. Biswas, E. Black, J. K. Blackburn, L. Blackburn, D. Blair, B. Bland, O. Bock, T. P. Bodiya, R. Bondarescu, R. Bork, M. Born, S. Bose, P. R. Brady, V. B. Braginsky, J. E. Brau, J. Breyer, D.O. Bridges, M. Brinkmann, M. Britzger, A. F. Brooks, D.A. Brown, A. Bullington, A. Buonanno, O. Burmeister, R. L. Byer, L. Cadonati, J. Cain, J. B. Camp, J. Cannizzo, K. C. Cannon, J. Cao, C. Capano, L. Cardenas, S. Caudill, M. Cavaglià, C. Cepeda, T. Chalermsongsak, E. Chalkley, P. Charlton, S. Chatterji, S. Chelkowski, Y. Chen, N. Christensen, S. S. Y. Chua, C. T. Y. Chung, D. Clark, J. Clark, J. H. Clayton, R. Conte, D. Cook, T. R. C. Corbitt, N. Cornish, D. Coward, D. C. Coyne, J. D. E. Creighton, T. D. Creighton, A.M. Cruise, R.M. Culter, A. Cumming, L. Cunningham, K. Dahl, S. L. Danilishin, K. Danzmann, B. Daudert, G. Davies, E. J. Daw, T. Dayanga, D. DeBra, J. Degallaix, V. Dergachev, R. DeSalvo, S. Dhurandhar, M. Dı́az, F. Donovan, K. L. Dooley, E. E. Doomes, R.W. P. Drever, J. Driggers, J. Dueck, I. Duke, J.-C. Dumas, S. Dwyer, M. Edgar, M. Edwards, A. Effler, P. Ehrens, T. Etzel, M. Evans, T. Evans, S. Fairhurst, Y. Faltas, Y. Fan, D. Fazi, H. Fehrmann, L. S. Finn, K. Flasch, S. Foley, C. Forrest, N. Fotopoulos, M. Frede, M. Frei, Z. Frei, A. Freise, R. Frey, T. T. Fricke, D. Friedrich, P. Fritschel, V. V. Frolov, P. Fulda, M. Fyffe, J. A. Garofoli, S. Ghosh, J. A. Giaime, S. Giampanis, K.D. Giardina, E. Goetz, L.M. Goggin, G. González, S. Goßler, A. Grant, S. Gras, C. Gray, R. J. S. Greenhalgh, A.M. Gretarsson, R. Grosso, H. Grote, S. Grunewald, E. K. Gustafson, R. Gustafson, B. Hage, J.M. Hallam, D. Hammer, G. D. Hammond, C. Hanna, J. Hanson, J. Harms, G.M. Harry, I.W. Harry, E. D. Harstad, K. Haughian, K. Hayama, T. Hayler, J. Heefner, I. S. Heng, A. Heptonstall, M. Hewitson, S. Hild, E. Hirose, D. Hoak, K. A. Hodge, K. Holt, D. J. Hosken, J. Hough, E. Howell, D. Hoyland, B. Hughey, S. Husa, S. H. Huttner, D. R. Ingram, T. Isogai, A. Ivanov, W.W. Johnson, D. I. Jones, G. Jones, R. Jones, L. Ju, P. Kalmus, V. Kalogera, S. Kandhasamy, J. Kanner, E. Katsavounidis, K. Kawabe, S. Kawamura, F. Kawazoe, W. Kells, D. G. Keppel, A. Khalaidovski, F. Y. Khalili, R. Khan, E. Khazanov, H. Kim, P. J. King, J. S. Kissel, S. Klimenko, K. Kokeyama, V. Kondrashov, R. Kopparapu, S. Koranda, D. Kozak, V. Kringel, B. Krishnan, G. Kuehn, J. Kullman, R. Kumar, P. Kwee, P. K. Lam, M. Landry, M. Lang, B. Lantz, N. Lastzka, A. Lazzarini, P. Leaci, M. Lei, N. Leindecker, I. Leonor, H. Lin, P. E. Lindquist, T. B. Littenberg, N.A. Lockerbie, D. Lodhia, M. Lormand, P. Lu, M. Lubinski, A. Lucianetti, H. Lück, A. Lundgren, B. Machenschalk, M. MacInnis, M. Mageswaran, K. Mailand, C. Mak, I. Mandel, V. Mandic, S. Márka, Z. Márka, A. Markosyan, J. Markowitz, E. Maros, I.W. Martin, R.M. Martin, J. N. Marx, K. Mason, F. Matichard, L. Matone, R. A. Matzner, N. Mavalvala, R. McCarthy, D. E. McClelland, S. C. McGuire, G. McIntyre, D. J. A. McKechan, M. Mehmet, A. Melatos, A. C. Melissinos, G. Mendell, D. F. Menéndez, R. A. Mercer, L. Merrill, S. Meshkov, C. Messenger, M. S. Meyer, H. Miao, J. Miller, Y. Mino, S. Mitra, V. P. Mitrofanov, G. Mitselmakher, R. Mittleman, O. Miyakawa, B. Moe, S. D. Mohanty, S. R. P. Mohapatra, G. Moreno, K. Mors, K. Mossavi, C. MowLowry, G. Mueller, H. Müller-Ebhardt, S. Mukherjee, A. Mullavey, J. Munch, P. G. Murray, T. Nash, R. Nawrodt, J. Nelson, G. Newton, E. Nishida, A. Nishizawa, J. O’Dell, B. O’Reilly, R. O’Shaughnessy, E. Ochsner, G.H. Ogin, R. Oldenburg, D. J. Ottaway, R. S. Ottens, H. Overmier, B. J. Owen, A. Page, Y. Pan, C. Pankow, M.A. Papa, P. Patel, D. Pathak, M. Pedraza, L. Pekowsky, S. Penn, C. Peralta, A. Perreca, M. Pickenpack, I.M. Pinto, M. Pitkin, H. J. Pletsch, M.V. Plissi, F. Postiglione, M. Principe, R. Prix, L. Prokhorov, O. Puncken, V. Quetschke, F. J. Raab, D. S. Rabeling, H. Radkins, P. Raffai, Z. Raics, M. Rakhmanov, V. Raymond, C.M. Reed, T. Reed, H. Rehbein, S. Reid, D.H. Reitze, R. Riesen, K. Riles, P. Roberts, N.A. Robertson, C. Robinson, E. L. Robinson, S. Roddy, C. Röver, J. Rollins, J. D. Romano, J. H. Romie, S. Rowan, A. Rüdiger, K. Ryan, S. Sakata, L. Sammut, L. Sancho de la Jordana, V. Sandberg, V. Sannibale, L. Santamarı́a, G. Santostasi, S. Saraf, P. Sarin, B. S. Sathyaprakash, S. Sato, M. Satterthwaite, P. R. Saulson, R. Savage, R. Schilling, R. Schnabel, R. Schofield, B. Schulz, B. F. Schutz, P. Schwinberg, J. Scott, S.M. Scott, A. C. Searle, F. Seifert, D. Sellers, A. S. Sengupta, A. Sergeev, B. Shapiro, PHYSICAL REVIEW D 83, 042001 (2011)
TL;DR: In this article, a technique for photon-number resolution using homodyne detection was proposed, which can be used to reconstruct the statistics of the non-Gaussian one-and two-photon subtracted squeezed vacuum states.
Abstract: The nonlinearity of a conditional photon-counting measurement can be used to "de-Gaussify" a Gaussian state of light. Here we present and experimentally demonstrate a technique for photon-number resolution using only homodyne detection. We then apply this technique to inform a conditional measurement, unambiguously reconstructing the statistics of the non-Gaussian one- and two-photon-subtracted squeezed vacuum states. Although our photon-number measurement relies on ensemble averages and cannot be used to prepare non-Gaussian states of light, its high efficiency, photon-number- resolving capabilities, and compatibility with the telecommunications band make it suitable for quantum-information tasks relying on the outcomes of mean values.
17 Oct 2011
TL;DR: In this paper, the authors reported the generation of entangled states of light between the wavelengths 810 and 1550 nm in the continuous variable regime by type I optical parametric oscillation in a standing wave cavity built around a periodically poled potassium titanyl phosphate crystal, operated above threshold.
Abstract: We report on the generation of entangled states of light between the wavelengths 810 and 1550 nm in the continuous variable regime. The fields were produced by type I optical parametric oscillation in a standing‐wave cavity build around a periodically poled potassium titanyl phosphate crystal, operated above threshold. Balanced homodyne detection was used to detect the non‐classical noise properties, while filter cavities provided the local oscillators by separating carrier fields from the entangled sidebands. We were able to obtain an inseparability of F= 0.82, corresponding to about —0.86 dB of non‐classical quadrature correlation.
Book•
28 Dec 2011
TL;DR: The conference proceedings will be of interest to physicists, engineers and mathematicians working with quantum mechanical systems and frontier technologies.
Abstract: The conference proceedings will be of interest to physicists, engineers and mathematicians working with quantum mechanical systems and frontier technologies The QCMC series of conferences provides a forum for the presentation and discussion of new results from the field of quantum information Quantum information is the study of information stored in quantum systems The unique properties of quantum mechanics lead to the ability to perform information tasks that are hard or impossible for classical systems
TL;DR: In this article, experimental observations of interference between an atomic spin coherence and an optical field in a gradient echo memory are presented. But the interference is mediated by a strong classical field that couples a weak probe field to the atomic coherence through a resonant Raman transition.
Abstract: We present experimental observations of interference between an atomic spin coherence and an optical field in a {\Lambda}-type gradient echo memory. The interference is mediated by a strong classical field that couples a weak probe field to the atomic coherence through a resonant Raman transition. Interference can be observed between a prepared spin coherence and another propagating optical field, or between multiple {\Lambda} transitions driving a single spin coherence. In principle, the interference in each scheme can yield a near unity visibility.
TL;DR: In this paper, a measurement of the covariance matrix was performed and a violation of the Reid and Drummond EPR-criterion at a value of only 0.36 ± 0.03 compared to the threshold of 1.
Abstract: We report on the preparation of entangled two mode squeezed states of yet unseen quality. Based on a measurement of the covariance matrix we found a violation of the Reid and Drummond EPR-criterion at a value of only 0.36 ± 0.03 compared to the threshold of 1. Furthermore, quantum state tomography was used to extract a single photon Fock state solely based on homodyne detection, demonstrating the strong quantum features of this pair of laser-beams. The probability for a single photon in this ensemble measurement exceeded 2/3.
28 Aug 2011
TL;DR: In this paper, the authors present experimental results of high efficiency quantum state storage in a warm rubidium vapour cell using the gradient echo memory (GEM) technique, and show recall fidelity up to 98% for coherent pulses containing around one photon.
Abstract: We present experimental results of high efficiency quantum state storage in a warm rubidium vapour cell using the gradient echo memory (GEM) technique. Without conditional measurements, we show recall fidelity up to 98% for coherent pulses containing around one photon.
TL;DR: In this article, the authors briefly review squeezing and plans for its implementation into advanced ground-based gravitational wave detectors, which will be operating at power levels close to the tolerance of the optical components, significant further improvement in sensitivity will require the use of quantum optical techniques such as the injection of squeezed states.
Abstract: Second generation ground-based gravitational wave detectors, scheduled to be operating by the middle of this decade, will be limited in sensitivity over much of their detection range by optical quantum noise. As they will be operating at power levels close to the tolerance of the optical components, significant further improvement in sensitivity will require the use of quantum optical techniques such as the injection of squeezed states. In this paper we briefly review squeezing and plans for its implementation into advanced gravitational wave detectors.
Posted Content•
TL;DR: In this paper, the authors extend the security proof for continuous variable quantum key distribution protocols using post selection to account for arbitrary eavesdropping attacks by employing the concept of an equiv-alent protocol where the post-selection is implemented as a projective quantum measurement.
Abstract: We extend the security proof for continuous variable quantum key distribution protocols using post selection to account for arbitrary eavesdropping attacks by employing the concept of an equiv- alent protocol where the post-selection is implemented as a projective quantum measurement. We demonstrate that the security can be calculated using only experimentally accessible quantities and finally explicitly evaluate the performance for the case of a noisy Gaussian channel in the limit of unbounded key length.
22 May 2011
TL;DR: In this article, two mode quantum state tomography was used to extract single photon Fock states solely based on homodyne detection, demonstrating the strong quantum features of this entangled pair of laser beams.
Abstract: We report on the preparation of entangled two mode squeezed states of yet unseen quality. Based on a measurement of the covariance matrix we found for the famous EPR-variance a value of 0.36. Furthermore, two mode quantum state tomography was used to extract single photon Fock states solely based on homodyne detection, demonstrating the strong quantum features of this entangled pair of laser beams. The probability for a single photon in this ensemble measurement exceeded 2/3.
Posted Content•
04 Jul 2011
TL;DR: In this paper, the authors present experimental observations of interference between an atomic spin coherence and an optical field in a Λ-type gradient echo memory, where the interference is mediated by a strong classical field that couples a weak probe field to the atomic coherence through a resonant Raman transition.
Abstract: We present experimental observations of interference between an atomic spin coherence and an optical field in a Λ-type gradient echo memory. The interference is mediated by a strong classical field that couples a weak probe field to the atomic spin coherence through a resonant Raman transition. Interference can be observed between a prepared spin coherence and another propagating optical field, or between multiple Λ transitions driving a single spin coherence. In principle, the interference in each scheme can yield a near unity visibility and could be used as a coherent all-optical switch.
01 May 2011
TL;DR: This work analyses the security and performance of a continuous variable quantum key distribution protocol using post selection, deriving results that are unconditionally secure in the sense of no longer restricting the eavesdroppers attack.
Abstract: We analyse the security and performance of a continuous variable quantum key distribution protocol using post selection, deriving results that are unconditionally secure in the sense of no longer restricting the eavesdroppers attack.
06 Jun 2011
TL;DR: In this article, a quantum memory based on warm Rb atoms surpassing the no-cloning limit for optical coherent states down to single photon level was demonstrated, and state reconstruction reveals a fidelity up to 93% with an average efficiency of 78%
Abstract: We demonstrate a quantum memory based on warm Rb atoms surpassing the no-cloning limit for optical coherent states down to single photon level The state reconstruction reveals a fidelity up to 93% with an average efficiency of 78%
28 Aug 2011
TL;DR: In this paper, the authors show that quantum discord can quantify the information advantage of a quantum processing over an optimal classical processing and experimentally extract a lower bound on the quantum discord of a non-entangled continuous-variable quantum system.
Abstract: We show that quantum discord can quantify the information advantage of a quantum processing over an optimal classical processing We experimentally extract a lower bound on the quantum discord of a non-entangled continuous-variable quantum system
28 Aug 2011
TL;DR: In this paper, the authors report on the production of diffractive mirrors, which generate high-order optical vortices using direct machining with a diamond tool and are shown to generate high quality optical vortsices ranging in charge from 1 to 1000 at a wavelength of 532 nm.
Abstract: We report on the production of diffractive mirrors, which generate high-order optical vortices. The mirrors are produced by direct machining with a diamond tool and are shown to generate high-quality optical vortices ranging in charge from 1 to 1000 at a wavelength of 532 nm.
28 Aug 2011
TL;DR: In this article, the ability of gradient echo memory (GEM) to spectrally manipulate light pulses stored in the memory was investigated, and both theoretical and experimental results demonstrated the ability to shift the frequency, as well as compress or expand a pulse.
Abstract: The burgeoning fields of quantum computing and quantum key distribution have created a demand for a quantum memory. The gradient echo memory (GEM) is one such scheme that can boast efficiencies approaching unity. Here we investigate the ability of GEM to spectrally manipulate light pulses stored in the memory. Spectral manipulation is important for pulse compression sideband extraction, and matching of pulse spectra to resonant and spectroscopic systems, as well as the potential to increase qubit rates in quantum communications networks. We present both theoretical and experimental results demonstrating the ability to shift the frequency, as well as spectrally compress or expand a pulse. Also the ability of GEM to recall different frequency components of a pulse at different times, and interfere two initially time separated pulses that are stored in the memory, are shown.
22 May 2011
TL;DR: In this article, the authors present an alternative set of tools for flexible, computer reconfigurable, multi-mode entanglement using beam-splitters of defined ratios and relative phases.
Abstract: New continuous variable quantum protocols such as cluster state computation [1] and quantum error correction [2] require an increasing number of modes to be entangled in a specific way. Conventionally, the entangled modes are carried by as many single mode beams [3, 4]. In order to produce entanglement, each beam of classical light first goes through a single mode optical parametric amplifier (OPA). This OPA reduces the variance of one of the quadratures of one mode of the electromagnetic field below the quantum noise limit (the mode is then called squeezed). The squeezed modes are then mixed together using a specific sequence of beam-splitters of defined ratios. For each beamsplitter, the relative phase of the two input modes is also defined and controlled. To each sequence of beam-splitting ratios and relative phases corresponds a unitary transformation between the input modes and the output modes. This unitary transformation gives a set of sub quantum noise relationships between the output modes quadratures with each protocol defined by a different set of relationships. After the desired entanglement has been produced, homodyne detections are performed on the output modes to implement the protocol. Using one beam per mode is resource heavy and inflexible. We present and characterize an alternative set of tools for flexible, computer reconfigurable, multi-mode entanglement.
06 Jun 2011
TL;DR: In this article, a continuous variable quantum key distribution protocol using post selection against non-Gaussian eavesdropper attacks was proposed and proved secure in the presence of non-inertial, relativistic observers.
Abstract: We prove security of a continuous variable quantum key distribution protocol using post selection against non-Gaussian eavesdropper attacks. We discuss CV repeater protocols based on noiseless amplification. We analyze CV QKD between non-inertial, relativistic observers.
TL;DR: In this paper, a measurement of the covariance matrix was performed and a violation of the Reid and Drummond EPR-criterion at a value of only 0.36 ± 0.03 compared to the threshold of 1.
Abstract: We report on the preparation of entangled two mode squeezed states of yet unseen quality. Based on a measurement of the covariance matrix we found a violation of the Reid and Drummond EPR-criterion at a value of only 0.36\pm0.03 compared to the threshold of 1. Furthermore, quantum state tomography was used to extract a single photon Fock state solely based on homodyne detection, demonstrating the strong quantum features of this pair of laser-beams. The probability for a single photon in this ensemble measurement exceeded 2/3.