Q-ESSENCE

High speed optical quantum random number generation

Date: 
2010-06-02
Reference: 

Martin Fürst, Henning Weier, Sebastian Nauerth, Davide G. Marangon, Christian Kurtsiefer, and Harald Weinfurter
Optics Express, Vol. 18, Issue 12, pp. 13029-13037 (2010)
doi:10.1364/OE.18.013029

We present a fully integrated, ready-for-use quantum random number generator (QRNG) whose stochastic model is based on the randomness of detecting single photons in attenuated light. We show that often annoying deadtime effects associated with photomultiplier tubes (PMT) can be utilized to avoid postprocessing for bias or correlations. The random numbers directly delivered to a PC, generated at a rate of up to 50 Mbit/s, clearly pass all tests relevant for (physical) random number generators.

Experimental Extraction of Secure Correlations from a Noisy Private State

Date: 
2011-01-18
Reference: 

K. Dobek, M. Karpiński, R. Demkowicz-Dobrzański, K. Banaszek, and P. Horodecki
Phys. Rev. Lett. 106, 030501 (2011)
http://link.aps.org/doi/10.1103/PhysRevLett.106.030501

We report experimental generation of a noisy entangled four-photon state that exhibits a separation between the secure key contents and distillable entanglement, a hallmark feature of the recently established quantum theory of private states. The privacy analysis, based on the full tomographic reconstruction of the prepared state, is utilized in a proof-of-principle key generation. The inferiority of distillation-based strategies to extract the key is exposed by an implementation of an entanglement distillation protocol for the produced state.

Coherent frequency-down-conversion interface for quantum repeaters

Date: 
2010-10-04
Reference: 

Noé Curtz, Rob Thew, Christoph Simon, Nicolas Gisin, and Hugo Zbinden
Optics Express, Vol. 18, Issue 21, pp. 22099-22104 (2010)
doi:10.1364/OE.18.022099

We report a coherence-preserving photon frequency down-conversion experiment based on difference-frequency generation in a periodically poled Lithium niobate waveguide, at the single-photon level. The coherence of the process has been demonstrated by measuring the phase coherence of pseudo single-photon time-bin qubits after frequency conversion with an interference visibility of >96 %. This interface could be of interest for quantum repeater based hybrid networks.

Simulation of noise-assisted transport via optical cavity networks

Date: 
2011-01-11
Reference: 

Filippo Caruso, Nicolò Spagnolo, Chiara Vitelli, Fabio Sciarrino, and Martin B. Plenio
Phys. Rev. A 83, 013811 (2011)
http://link.aps.org/doi/10.1103/PhysRevA.83.013811

Efficient quantum state tomography

Date: 
2010-12-21
Author(s): 

Marcus Cramer, Martin B. Plenio, Steven T. Flammia, Rolando Somma, David Gross, Stephen D. Bartlett, Olivier Landon-Cardinal, David Poulin and Yi-Kai Liu

Reference: 

Nat. Commun. 1, 149 (2010)
doi:10.1038/ncomms1147

Quantum state tomography—deducing quantum states from measured data—is the gold standard for verification and benchmarking of quantum devices. It has been realized in systems with few components, but for larger systems it becomes unfeasible because the number of measurements and the amount of computation required to process them grows exponentially in the system size. Here, we present two tomography schemes that scale much more favourably than direct tomography with system size.

Tensor Rank and Stochastic Entanglement Catalysis for Multipartite Pure States

Date: 
2010-11-08
Author(s): 

Lin Chen, Eric Chitambar, Runyao Duan, Zhengfeng Ji, and Andreas Winter

Reference: 

Phys. Rev. Lett. 105, 200501 (2010)

Quantum networks reveal quantum nonlocality

Date: 
2011-02-08
Author(s): 

Daniel Cavalcanti, Mafalda L. Almeida, Valerio Scarani and Antonio Acín

Reference: 

Nat. Commun. 2 , 184 (2011)
doi:10.1038/ncomms1193 (2011)

The results of local measurements on some composite quantum systems cannot be reproduced classically. This impossibility, known as quantum nonlocality, represents a milestone in the foundations of quantum theory. Quantum nonlocality is also a valuable resource for information-processing tasks, for example, quantum communication, quantum key distribution, quantum state estimation or randomness extraction. Still, deciding whether a quantum state is nonlocal remains a challenging problem.

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