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Sep 23, 2013
09/13

by
Ch. Silberhorn; N. Korolkova; G. Leuchs

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We suggest a quantum cryptographic scheme using continuous EPR-like correlations of bright optical beams. For binary key encoding, the continuous information is discretized in a novel way by associating a respective measurement, amplitude or phase, with a bit value "1" or "0". The secure key distribution is guaranteed by the quantum correlations. No pre-determined information is sent through the quantum channel contributing to the security of the system.

Source: http://arxiv.org/abs/quant-ph/0109009v3

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38

Sep 19, 2013
09/13

by
K. Laiho; K. N. Cassemiro; Ch. Silberhorn

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Parametric down-conversion (PDC) offers the possibility to control the fabrication of non-Gaussian states such as Fock states. However, in conventional PDC sources energy and momentum conservation introduce strict frequency and photon number correlations, which impact the fidelity of the prepared state. In our work we optimize the preparation of single-photon Fock states from the emission of waveguided PDC via spectral filtering. We study the effect of correlations via photon number resolving...

Source: http://arxiv.org/abs/0910.0152v2

3
3.0

Jun 30, 2018
06/18

by
G. Harder; D. Mogilevtsev; N. Korolkova; Ch. Silberhorn

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We present an efficient and robust method for the reconstruction of photon number distributions by using solely thermal noise as a probe. The method uses a minimal number of pre-calibrated quantum devices, only one on/off single-photon detector is sufficient. Feasibility of the method is demonstrated by the experimental inference of single-photon, thermal and two-photon states. The method is stable to experimental imperfections and provides a direct, user-friendly quantum diagnostics tool.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1409.8076

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36

Sep 22, 2013
09/13

by
K Laiho; M Avenhaus; K N Cassemiro; Ch Silberhorn

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We investigate the capabilities of loss-tolerant quantum state characterization using a photon-number resolving, time-multiplexed detector (TMD). We employ the idea of probing the Wigner function point-by-point in phase space via photon parity measurements and displacement operations, replacing the conventional homodyne tomography. Our emphasis lies on reconstructing the Wigner function of non-Gaussian Fock states with highly negative values in a scheme that is based on a realistic experimental...

Source: http://arxiv.org/abs/0811.0284v3

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41

Sep 20, 2013
09/13

by
Ch. Silberhorn; T. C. Ralph; N. Lütkenhaus; G. Leuchs

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We demonstrate that secure quantum key distribution systems based on continuous variables implementations can operate beyond the apparent 3 dB loss limit that is implied by the beam splitting attack . The loss limit was established for standard minimum uncertainty states such as coherent states. We show that by an appropriate postselection mechanism we can enter a region where Eve's knowledge falls behind the information shared between Alice and Bob even in the presence of substantial losses.

Source: http://arxiv.org/abs/quant-ph/0204064v3

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33

Sep 23, 2013
09/13

by
S. Lorenz; Ch. Silberhorn; N. Korolkova; R. S. Windeler; G. Leuchs

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Amplitude squeezed pulsed light has been produced using a microstructured silica fibre. By spectrally filtering after the nonlinear propagation in the fibre a squeezing value of -1.7dB has been measured. A quantum key distribution scheme based on squeezed light from such microstructured fibres is proposed.

Source: http://arxiv.org/abs/quant-ph/0109018v2

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39

Sep 23, 2013
09/13

by
N. Korolkova; Ch. Silberhorn; O. Gloeckl; S. Lorenz; Ch. Marquardt; G. Leuchs

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We present schemes for the generation and evaluation of continuous variable entanglement of bright optical beams and give a brief overview of the variety of optical techniques and quantum communication applications on this basis. A new entanglement-based quantum interferometry scheme with bright beams is suggested. The performance of the presented schemes is independent of the relative interference phase which is advantageous for quantum communication applications.

Source: http://arxiv.org/abs/quant-ph/0109011v3

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40

Sep 22, 2013
09/13

by
A. Schreiber; K. N. Cassemiro; V. Potoček; A. Gábris; I. Jex; Ch. Silberhorn

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We investigate the impact of decoherence and static disorder on the dynamics of quantum particles moving in a periodic lattice. Our experiment relies on the photonic implementation of a one-dimensional quantum walk. The pure quantum evolution is characterized by a ballistic spread of a photon's wave packet along 28 steps. By applying controlled time-dependent operations we simulate three different environmental influences on the system, resulting in a fast ballistic spread, a diffusive...

Source: http://arxiv.org/abs/1101.2638v1

123
123

Jul 19, 2013
07/13

by
O. Glöckl; U. L. Andersen; S. Lorenz; Ch. Silberhorn; N. Korolkova; G. Leuchs

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We present a setup to perform sub shot noise measurements of the phase quadrature for intense pulsed light without the use of a separate local oscillator. A Mach--Zehnder interferometer with an unbalanced arm length is used to detect the fluctuations of the phase quadrature at a single side band frequency. Using this setup, the non--separability of a pair of quadrature entangled beams is demonstrated experimentally.

Source: http://arxiv.org/abs/quant-ph/0406087v1

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34

Sep 24, 2013
09/13

by
Ch. Silberhorn; P. K. Lam; O. Weiss; F. Koenig; N. Korolkova; G. Leuchs

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We report on the generation of a continuous variable Einstein-Podolsky-Rosen (EPR) entanglement using an optical fibre interferometer. The Kerr nonlinearity in the fibre is exploited for the generation of two independent squeezed beams. These interfere at a beam splitter and EPR entanglement is obtained between the output beams. The correlation of the amplitude (phase) quadratures are measured to be 4.0+-0.2 (4.0+-0.4) dB below the quantum noise limit. The sum criterion for these squeezing...

Source: http://arxiv.org/abs/quant-ph/0103002v1

2
2.0

Jun 29, 2018
06/18

by
G. Harder; Ch. Silberhorn; J. Rehacek; Z. Hradil; L. Motka; B. Stoklasa; L. L. Sanchez-Soto

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We report the experimental point-by-point sampling of the Wigner function for nonclassical states created in an ultrafast pulsed type-II parametric down-conversion source. We use a loss-tolerant time-multiplexed detector based on a fiber-optical setup and a pair of photon-number-resolving avalanche photodiodes. By capitalizing on an expedient data-pattern tomography, we assess the properties of the light states with outstanding accuracy. The method allows us to reliably infer the squeezing of...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1603.06938

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32

Sep 19, 2013
09/13

by
A. Schreiber; K. N. Cassemiro; V. Potocek; A. Gabris; P. J. Mosley; E. Andersson; I. Jex; Ch. Silberhorn

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We present the first robust implementation of a coined quantum walk over five steps using only passive optical elements. By employing a fiber network loop we keep the amount of required resources constant as the walker's position Hilbert space is increased. We observed a non-Gaussian distribution of the walker's final position, thus characterizing a faster spread of the photon wave-packet in comparison to the classical random walk. The walk is realized for many different coin settings and...

Source: http://arxiv.org/abs/0910.2197v2

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48

Sep 21, 2013
09/13

by
H. B. Coldenstrodt-Ronge; J. S. Lundeen; A. Feito; B. J. Smith; W. Mauerer; Ch. Silberhorn; J. Eisert; M. B. Plenio; I. A. Walmsley

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Measurement is the only part of a general quantum system that has yet to be characterized experimentally in a complete manner. Detector tomography provides a procedure for doing just this; an arbitrary measurement device can be fully characterized, and thus calibrated, in a systematic way without access to its components or its design. The result is a reconstructed POVM containing the measurement operators associated with each measurement outcome. We consider two detectors, a single-photon...

Source: http://arxiv.org/abs/0902.4384v1

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43

Jul 22, 2013
07/13

by
J. S. Lundeen; A. Feito; H. Coldenstrodt-Ronge; K. L. Pregnell; Ch. Silberhorn; T. C. Ralph; J. Eisert; M. B. Plenio; I. A. Walmsley

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Measurement connects the world of quantum phenomena to the world of classical events. It plays both a passive role, observing quantum systems, and an active one, preparing quantum states and controlling them. Surprisingly - in the light of the central status of measurement in quantum mechanics - there is no general recipe for designing a detector that measures a given observable. Compounding this, the characterization of existing detectors is typically based on partial calibrations or elaborate...

Source: http://arxiv.org/abs/0807.2444v1