Institute For Quantenoptik Und Quanteninformation

Innsbruck, Austria

Institute For Quantenoptik Und Quanteninformation

Innsbruck, Austria
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Aikawa K.,University of Innsbruck | Frisch A.,University of Innsbruck | Mark M.,University of Innsbruck | Baier S.,University of Innsbruck | And 4 more authors.
Physical Review Letters | Year: 2012

We report on the achievement of Bose-Einstein condensation of erbium atoms and on the observation of magnetic Feshbach resonances at low magnetic fields. By means of evaporative cooling in an optical dipole trap, we produce pure condensates of Er168, containing up to 7×104 atoms. Feshbach spectroscopy reveals an extraordinary rich loss spectrum with six loss resonances already in a narrow magnetic-field range up to 3 G. Finally, we demonstrate the application of a low-field Feshbach resonance to produce a tunable dipolar Bose-Einstein condensate and we observe its characteristic d-wave collapse. © 2012 American Physical Society.

Northup T.E.,University of Innsbruck | Blatt R.,Institute For Quantenoptik Und Quanteninformation
Nature Photonics | Year: 2014

Optical communication channels have redefined the scope and applications of classical computing; similarly, photonic transfer of quantum information promises to open new horizons for quantum computing. The implementation of light-matter interfaces that preserve quantum information is technologically challenging, but key building blocks for such devices have recently been demonstrated by several research groups. Here, we outline the theoretical framework for information transfer between the nodes of a quantum network, review the current experimental state of the art and discuss the prospects for hybrid systems currently in development. © 2014 Macmillan Publishers Limited. All rights reserved.

Aikawa K.,University of Innsbruck | Frisch A.,University of Innsbruck | Mark M.,University of Innsbruck | Baier S.,University of Innsbruck | And 3 more authors.
Physical Review Letters | Year: 2014

We report on the creation of a degenerate dipolar Fermi gas of erbium atoms. We force evaporative cooling in a fully spin-polarized sample down to temperatures as low as 0.2 times the Fermi temperature. The strong magnetic dipole-dipole interaction enables elastic collisions between identical fermions even in the zero-energy limit. The measured elastic scattering cross section agrees well with the predictions from the dipolar scattering theory, which follow a universal scaling law depending only on the dipole moment and on the atomic mass. Our approach to quantum degeneracy proceeds with very high cooling efficiency and provides large atomic densities, and it may be extended to various dipolar systems. © 2014 American Physical Society.

Zwerger M.,University of Innsbruck | Briegel H.J.,University of Innsbruck | Briegel H.J.,Institute For Quantenoptik Und Quanteninformation | Dur W.,University of Innsbruck
Physical Review Letters | Year: 2013

We investigate measurement-based entanglement purification protocols (EPP) in the presence of local noise and imperfections. We derive a universal, protocol-independent threshold for the required quality of the local resource states, where we show that local noise per particle of up to 24% is tolerable. This corresponds to an increase of the noise threshold by almost an order of magnitude, based on the joint measurement-based implementation of sequential rounds of few-particle EPP. We generalize our results to multipartite EPP, where we encounter similarly high error thresholds. © 2013 American Physical Society.

Brownnutt M.,University of Innsbruck | Brownnutt M.,University of Hong Kong | Kumph M.,University of Innsbruck | Rabl P.,Vienna University of Technology | And 2 more authors.
Reviews of Modern Physics | Year: 2015

Electric-field noise near surfaces is a common problem in diverse areas of physics and a limiting factor for many precision measurements. There are multiple mechanisms by which such noise is generated, many of which are poorly understood. Laser-cooled, trapped ions provide one of the most sensitive systems to probe electric-field noise at MHz frequencies and over a distance range 30-3000 μm from a surface. Over recent years numerous experiments have reported spectral densities of electric-field noise inferred from ion heating-rate measurements and several different theoretical explanations for the observed noise characteristics have been proposed. This paper provides an extensive summary and critical review of electric-field noise measurements in ion traps and compares these experimental findings with known and conjectured mechanisms for the origin of this noise. This reveals that the presence of multiple noise sources, as well as the different scalings added by geometrical considerations, complicates the interpretation of these results. It is thus the purpose of this review to assess which conclusions can be reasonably drawn from the existing data, and which important questions are still open. In so doing it provides a framework for future investigations of surface-noise processes. © 2015 American Physical Society.

Hauke P.,Institute For Quantenoptik Und Quanteninformation | Hauke P.,University of Innsbruck | Lewenstein M.,Institute Of Ciencies Fotoniques | Lewenstein M.,Catalan Institution for Research and Advanced Studies | Eckardt A.,Max Planck Institute For Physik Komplexer Systeme
Physical Review Letters | Year: 2014

We propose a simple scheme for tomography of band-insulating states in one- and two-dimensional optical lattices with two sublattice states. In particular, the scheme maps out the Berry curvature in the entire Brillouin zone and extracts topological invariants such as the Chern number. The measurement relies on observing - via time-of-flight imaging - the time evolution of the momentum distribution following a sudden quench in the band structure. We consider two examples of experimental relevance: the Harper model with π flux and the Haldane model on a honeycomb lattice. Moreover, we illustrate the performance of the scheme in the presence of a parabolic trap, noise, and finite measurement resolution. © 2014 American Physical Society.

Blatt R.,University of Innsbruck | Blatt R.,Institute For Quantenoptik Und Quanteninformation | Roos C.F.,University of Innsbruck | Roos C.F.,Institute For Quantenoptik Und Quanteninformation
Nature Physics | Year: 2012

In the field of quantum simulation, methods and tools are explored for simulating the dynamics of a quantum system of interest with another system that is easier to control and measure. Systems of trapped atomic ions can be accurately controlled and manipulated, a large variety of interactions can be engineered with high precision and measurements of relevant observables can be obtained with nearly 100% efficiency. Here, we discuss prospects for quantum simulations using systems of trapped ions, and review the available set of quantum operations and first proof-of-principle experiments for both analog and digital quantum simulations with trapped ions. © 2012 Macmillan Publishers Limited. All rights reserved.

Curty M.,University of Vigo | Moroder T.,Institute For Quantenoptik Und Quanteninformation
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

Device-independent quantum key distribution does not need a precise quantum mechanical model of employed devices to guarantee security. Despite its beauty, it is still a very challenging experimental task. We compare a recent proposal by Gisin to close the detection loophole problem with that of a simpler quantum relay based on entanglement swapping with linear optics. Our full-mode analysis for both schemes confirms that, in contrast to recent beliefs, the second scheme can indeed provide a positive key rate which is even considerably higher than that of the first alternative. The resulting key rates and required detection efficiencies of approximately 95% for both schemes, however, strongly depend on the underlying security proof. © 2011 American Physical Society.

Hein S.M.,TU Berlin | Schulze F.,TU Berlin | Carmele A.,Institute For Quantenoptik Und Quanteninformation | Knorr A.,TU Berlin
Physical Review Letters | Year: 2014

In a solid-state platform for quantum information science, the biexciton cascade is an important source of entangled photons. However, the entanglement is usually reduced considerably by the fine-structure splitting of the exciton levels. We show how to counteract this loss of entanglement by applying optical feedback. Substantial control and enhancement of photon entanglement can be achieved by coherently feeding back a part of the emitted signal, e.g., by a mirror, and by tuning the feedback phase and delay time. We present full quantum-mechanical calculations, which include the external photon mode continuum, and discuss the mechanisms leading to the above effects. © 2014 American Physical Society.

Jungnitsch B.,Institute For Quantenoptik Und Quanteninformation | Moroder T.,Institute For Quantenoptik Und Quanteninformation | Guhne O.,Institute For Quantenoptik Und Quanteninformation | Guhne O.,University of Siegen
Physical Review Letters | Year: 2011

We present an approach to characterize genuine multiparticle entanglement by using appropriate approximations in the space of quantum states. This leads to a criterion for entanglement which can easily be calculated by using semidefinite programing and improves all existing approaches significantly. Experimentally, it can also be evaluated when only some observables are measured. Furthermore, it results in a computable entanglement monotone for genuine multiparticle entanglement. Based on this, we develop an analytical approach for the entanglement detection in cluster states, leading to an exponential improvement compared with existing schemes. © 2011 American Physical Society.

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