State preparation for quantum information science and metrology

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Iterative Entanglement Distillation: Approaching full Elimination of Decoherence

The distribution and processing of quantum entanglement form the basis of quantum communication and quantum computing. The realization of the two is difficult because quantum information inherently has a high susceptibility to decoherence, i.e. to uncontrollable information loss to the environment. For entanglement distribution, a proposed solution to this problem is capable of fully eliminating decoherence; namely iterative entanglement distillation. This approach builds on a large number of distillation steps each of which extracts a number of weakly decohered entangled states from a larger number of strongly decohered states. Here, for the first time, we experimentally demonstrate iterative distillation of entanglement. Already distilled entangled states were further improved in a second distillation step and also made available for subsequent steps.Our experiment displays the realization of the building blocks required for an entanglement distillation scheme that can fully eliminate decoherence

Two Color Entanglement

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 I=0.82, corresponding to about -0.86 dB of non-classical quadrature correlation.Comment: 4 pages, 2 figure

Towards Einstein-Podolsky-Rosen quantum channel multiplexing

A single broadband squeezed field constitutes a quantum communication resource that is sufficient for the realization of a large number N of quantum channels based on distributed Einstein-Podolsky-Rosen (EPR) entangled states. Each channel can serve as a resource for, e.g. independent quantum key distribution or teleportation protocols. N-fold channel multiplexing can be realized by accessing 2N squeezed modes at different Fourier frequencies. We report on the experimental implementation of the N=1 case through the interference of two squeezed states, extracted from a single broadband squeezed field, and demonstrate all techniques required for multiplexing (N>1). Quantum channel frequency multiplexing can be used to optimize the exploitation of a broadband squeezed field in a quantum information task. For instance, it is useful if the bandwidth of the squeezed field is larger than the bandwidth of the homodyne detectors. This is currently a typical situation in many experiments with squeezed and two-mode squeezed entangled light.Comment: 4 pages, 4 figures. In the new version we cite recent experimental work bei Mehmet et al., arxiv0909.5386, in order to clarify the motivation of our work and its possible applicatio

Markov Chain Monte Carlo Estimation of Quantum States

We apply a Bayesian data analysis scheme known as the Markov Chain Monte Carlo (MCMC) to the tomographic reconstruction of quantum states. This method yields a vector, known as the Markov chain, which contains the full statistical information concerning all reconstruction parameters including their statistical correlations with no a priori assumptions as to the form of the distribution from which it has been obtained. From this vector can be derived, e. g. the marginal distributions and uncertainties of all model parameters and also of other quantities such as the purity of the reconstructed state. We demonstrate the utility of this scheme by reconstructing the Wigner function of phase-diffused squeezed states. These states posses non-Gaussian statistics and therefore represent a non-trivial case of tomographic reconstruction. We compare our results to those obtained through pure maximum-likelihood and Fisher information approaches.Comment: 8 pages, 8 figures. Accepted for publication in Phys. Rev.

Der Lifter - Ein Flugobjekt mit Ionenantrieb -

Der in diesem Artikel vorgestellte Lifter ist ein faszinierendes Flugobjekt, das ohne bewegliche Elemente, stattdessen durch einen Ionenantrieb zum Schweben gebracht werden kann. Obwohl oder gerade weil der Lifter aus so einfachen Materialien wie Draht, Strohhalmen und Aluminiumfolie gebaut werden kann, zieht er viel Aufmerksamkeit auf sich und ruft immer wieder Staunen und fragende Gesichter hervor. Im Folgenden wird eine Bauanleitung des Lifters sowie eine einfache Theorie zur Funktionsweise vorgestellt. Die theoretischen Ergebnisse werden durch verschiedene Experimentiervorschläge ergänzt und durch die entsprechenden Messergebnisse gestütz

Der Lifter - Ein Flugobjekt mit Ionenantrieb -

Der in diesem Artikel vorgestellte Lifter ist ein faszinierendes Flugobjekt, das ohne bewegliche Elemente, stattdessen durch einen Ionenantrieb zum Schweben gebracht werden kann. Obwohl oder gerade weil der Lifter aus so einfachen Materialien wie Draht, Strohhalmen und Aluminiumfolie gebaut werden kann, zieht er viel Aufmerksamkeit auf sich und ruft immer wieder Staunen und fragende Gesichter hervor. Im Folgenden wird eine Bauanleitung des Lifters sowie eine einfache Theorie zur Funktionsweise vorgestellt. Die theoretischen Ergebnisse werden durch verschiedene Experimentiervorschläge ergänzt und durch die entsprechenden Messergebnisse gestütz

Preparation of distilled and purified continuous variable entangled states

The distribution of entangled states of light over long distances is a major challenge in the field of quantum information. Optical losses, phase diffusion and mixing with thermal states lead to decoherence and destroy the non-classical states after some finite transmission-line length. Quantum repeater protocols, which combine quantum memory, entanglement distillation and entanglement swapping, were proposed to overcome this problem. Here we report on the experimental demonstration of entanglement distillation in the continuous-variable regime. Entangled states were first disturbed by random phase fluctuations and then distilled and purified using interference on beam splitters and homodyne detection. Measurements of covariance matrices clearly indicate a regained strength of entanglement and purity of the distilled states. In contrast to previous demonstrations of entanglement distillation in the complementary discrete-variable regime, our scheme achieved the actual preparation of the distilled states, which might therefore be used to improve the quality of downstream applications such as quantum teleportation