Atom chip based generation of entanglement for quantum metrology

Atom chips provide a versatile `quantum laboratory on a microchip' for experiments with ultracold atomic gases. They have been used in experiments on diverse topics such as low-dimensional quantum gases, cavity quantum electrodynamics, atom-surface interactions, and chip-based atomic clocks and interferometers. A severe limitation of atom chips, however, is that techniques to control atomic interactions and to generate entanglement have not been experimentally available so far. Such techniques enable chip-based studies of entangled many-body systems and are a key prerequisite for atom chip applications in quantum simulations, quantum information processing, and quantum metrology. Here we report experiments where we generate multi-particle entanglement on an atom chip by controlling elastic collisional interactions with a state-dependent potential. We employ this technique to generate spin-squeezed states of a two-component Bose-Einstein condensate and show that they are useful for quantum metrology. The observed 3.7 dB reduction in spin noise combined with the spin coherence imply four-partite entanglement between the condensate atoms and could be used to improve an interferometric measurement by 2.5 dB over the standard quantum limit. Our data show good agreement with a dynamical multi-mode simulation and allow us to reconstruct the Wigner function of the spin-squeezed condensate. The techniques demonstrated here could be directly applied in chip-based atomic clocks which are currently being set up

Entanglement-enhanced probing of a delicate material system

Quantum metrology uses entanglement and other quantum effects to improve the sensitivity of demanding measurements. Probing of delicate systems demands high sensitivity from limited probe energy and has motivated the field's key benchmark-the standard quantum limit. Here we report the first entanglement-enhanced measurement of a delicate material system. We non-destructively probe an atomic spin ensemble by means of near-resonant Faraday rotation, a measurement that is limited by probe-induced scattering in quantum-memory and spin-squeezing applications. We use narrowband, atom-resonant NOON states to beat the standard quantum limit of sensitivity by more than five standard deviations, both on a per-photon and per-damage basis. This demonstrates quantum enhancement with fully realistic loss and noise, including variable-loss effects. The experiment opens the way to ultra-gentle probing of single atoms, single molecules, quantum gases and living cells.Comment: 7 pages, 8 figures; Nature Photonics, advance online publication, 16 December 201

Oekosystemforschung Niedersaechsisches Wattenmeer. T. B: ELAWAT -Elastizitaet des Oekosystems Wattenmeer. Projektsynthese Abschlussbericht

The aim of the basic research part of the Ecosystem Research Lower Saxonian Wadden Sea was to detect fundamental ecological properties of this ecosystem. Therefore, the concept of ELAWAT (Resilience of the Wadden Sea Ecosystem) realized, for the first time in the history of ecosystem research, an approach based on stability properties. Processes and mechanisms relevant for a long-term preservation of the Wadden Sea were investigated. 12 projects were involved in this interdisciplinary approach. Field investigations and experiments were carried out in the back barrier tidal flat behind the island of Spiekeroog to detect temporal and spatial patterns and effects of disturbances. Most parameters revealed high variability. Therefore no reference situation can be named for the Wadden Sea. Instead, the 'state' of the Wadden Sea is its dynamic. Several abiotic components showed a resilience on intermediate scales, e.g. a return of basic morphological features of the tidal flats 6 months after a severe ice winter. Stability properties could also be named for biotic components of the Wadden Sea, being specific for the studied variables and scales. Mechanisms to react to disturbance events include a high functional morphology, high reproductive output and high mobility of the Wadden Sea biota. These stability mechanisms can only function in a natural system with an undisturbed tidal regime. To preserve this ecosystem, entire tidal basins shoule be protected to ensure a variety of habitats, source populations for recolonization and undisturbed dispersion. (orig.)SIGLEAvailable from TIB Hannover: F98B1440 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman