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Author |
Usmani, Imam; Clausen, Christoph; Bussières, Félix; Sangouard, Nicolas; Afzelius, Mikael; Gisin, Nicolas |
Title |
Heralded quantum entanglement between two crystals |
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Journal Article |
Year |
2012 |
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Nature Photonics |
Abbreviated Journal |
Nat. Photon. |
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6 |
Issue |
4 |
Pages |
234-237 |
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fromIPMRAS |
Abstract |
Quantum networks must have the crucial ability to entangle quantum nodes. A prominent example is the quantum repeater, which allows the distance barrier of direct transmission of single photons to be overcome, provided remote quantum memories can be entangled in a heralded fashion. Here, we report the observation of heralded entanglement between two ensembles of rare-earth ions doped into separate crystals. A heralded single photon is sent through a 50/50 beamsplitter, creating a single-photon entangled state delocalized between two spatial modes. The quantum state of each mode is subsequently mapped onto a crystal, leading to an entangled state consisting of a single collective excitation delocalized between two crystals. This entanglement is revealed by mapping it back to optical modes and by estimating the concurrence of the retrieved light state. Our results highlight the potential of crystals doped with rare-earth ions for entangled quantum nodes and bring quantum networks based on solid-state resources one step closer. |
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RPLAB @ gujma @ |
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793 |
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Hase, Muneaki; Katsuragawa, Masayuki; Constantinescu, Anca Monia; Petek, Hrvoje |
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 |
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Pages |
243–247 |
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fromIPMRAS |
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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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794 |
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Lu, Chao-Yang; Zhou, Xiao-Qi; Gühne, Otfried; Gao, Wei-Bo; Zhang, Jin; Yuan, Zhen-Sheng; Goebel, Alexander; Yang, Tao; Pan, Jian-Wei |
Title |
Experimental entanglement of six photons in graph states |
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Journal Article |
Year |
2007 |
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Nature Physics |
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Nat. Phys. |
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3 |
Issue |
2 |
Pages |
91-95 |
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fromIPMRAS |
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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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796 |
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Ursin, R.; Tiefenbacher, F.; Schmitt-Manderbach, T.; Weier, H.; Scheidl, T.; Lindenthal, M.; Blauensteiner, B.; Jennewein, T.; Perdigues, J.; Trojek, P.; Ömer, B.; Fürst, M.; Meyenburg, M.; Rarity, J.; Sodnik, Z.; Barbieri, C.; Weinfurter, H.; Zeilinger, A. |
Title |
Entanglement-based quantum communication over 144km |
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Journal Article |
Year |
2007 |
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Nature Physics |
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Nat. Phys. |
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3 |
Issue |
7 |
Pages |
481-486 |
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fromIPMRAS |
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Quantum entanglement is the main resource to endow the field of quantum information processing with powers that exceed those of classical communication and computation. In view of applications such as quantum cryptography or quantum teleportation, extension of quantum-entanglement-based protocols to global distances is of considerable practical interest. Here we experimentally demonstrate entanglement-based quantum key distribution over 144km. One photon is measured locally at the Canary Island of La Palma, whereas the other is sent over an optical free-space link to Tenerife, where the Optical Ground Station of the European Space Agency acts as the receiver. This exceeds previous free-space experiments by more than an order of magnitude in distance, and is an essential step towards future satellite-based quantum communication and experimental tests on quantum physics in space. |
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RPLAB @ gujma @ |
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797 |
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Pirandola, Stefano; Mancini, Stefano; Lloyd, Seth; Braunstein, Samuel L. |
Title |
Continuous-variable quantum cryptography using two-way quantum communication |
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Journal Article |
Year |
2008 |
Publication |
Nature Physics |
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Nat. Phys. |
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4 |
Issue |
9 |
Pages |
726-730 |
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fromIPMRAS |
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Quantum cryptography has recently been extended to continuous-variable systems, such as the bosonic modes of the electromagnetic field possessing continuous degrees of freedom. In particular, several cryptographic protocols have been proposed and experimentally implemented using bosonic modes with Gaussian statistics. These protocols have shown the possibility of reaching very high secret key rates, even in the presence of strong losses in the quantum communication channel. Despite this robustness to loss, their security can be affected by more general attacks where extra Gaussian noise is introduced by the eavesdropper. Here, we show a `hardware solution' for enhancing the security thresholds of these protocols. This is possible by extending them to two-way quantum communication where subsequent uses of the quantum channel are suitably combined. In the resulting two-way schemes, one of the honest parties assists the secret encoding of the other, with the chance of a non-trivial superadditive enhancement of the security thresholds. These results should enable the extension of quantum cryptography to more complex quantum communications. |
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RPLAB @ gujma @ |
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798 |
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