A wavelength-tunable fiber-coupled source of narrowband entangled photons

We demonstrate a wavelength-tunable, fiber-coupled source of polarization-entangled photons with extremely high spectral brightness and quality of entanglement. Using a 25 mm PPKTP crystal inside a polarization Sagnac interferometer we detect a spectral brightness of 273000 pairs/(s mW nm), a factor of 28 better than comparable previous sources while state tomography showed the two-photon state to have a tangle of T=0.987. This improvement was achieved by use of a long crystal, careful selection of focusing parameters and single-mode fiber coupling. We demonstrate that, due to the particular geometry of the setup, the signal and idler wavelengths can be tuned over a wide range without loss of entanglement.Comment: 10 pages, 5 figures. Article rewritten, added Fig.(1a-1b). Published in Optics Express, comments welcom

Quantum erasure with causally disconnected choice

The counterintuitive features of quantum physics challenge many common-sense assumptions. In an interferometric quantum eraser experiment, one can actively choose whether or not to erase which-path information, a particle feature, of one quantum system and thus observe its wave feature via interference or not by performing a suitable measurement on a distant quantum system entangled with it. In all experiments performed to date, this choice took place either in the past or, in some delayed-choice arrangements, in the future of the interference. Thus in principle, physical communications between choice and interference were not excluded. Here we report a quantum eraser experiment, in which by enforcing Einstein locality no such communication is possible. This is achieved by independent active choices, which are space-like separated from the interference. Our setup employs hybrid path-polarization entangled photon pairs which are distributed over an optical fiber link of 55 m in one experiment, or over a free-space link of 144 km in another. No naive realistic picture is compatible with our results because whether a quantum could be seen as showing particle- or wave-like behavior would depend on a causally disconnected choice. It is therefore suggestive to abandon such pictures altogether

Experimental quantum teleportation over a high-loss free-space channel

We present a high-fidelity quantum teleportation experiment over a high-loss free-space channel between two laboratories. We teleported six states of three mutually unbiased bases and obtained an average state fidelity of 0.82(1), well beyond the classical limit of 2/3. With the obtained data, we tomographically reconstructed the process matrices of quantum teleportation. The free-space channel attenuation of 31 dB corresponds to the estimated attenuation regime for a down-link from a low-earth-orbit satellite to a ground station. We also discussed various important technical issues for future experiments, including the dark counts of single-photon detectors, coincidence-window width etc. Our experiment tested the limit of performing quantum teleportation with state-of-the-art resources. It is an important step towards future satellite-based quantum teleportation and paves the way for establishing a worldwide quantum communication network

Unterstützung informellen Lernens Studierender. Möglichkeiten studentischen Arbeitens mit Social Software

Innerhalb des Projektes „Learner Communities of Practice“ (LCP) wurde mit Förderung durch das Sächsische Staatsministerium für Wissenschaft und Kunst ein Schulungskonzept entwickelt, welches das informelle Lernen Studierender in der Studieneingangsphase mittels Social-Software-Tools unterstützt. Der Beitrag beschreibt die didaktische und technische Umsetzung des Schulungskonzeptes, stellt die Ergebnisse einer testweisen Durchführung dar und skizziert generelle Herausforderungen beim Einsatz von Social Software in der akademischen Aus- und Weiterbildung. (DIPF/Orig.

Side effects of angiotensin converting enzyme inhibitor (captopril) in newborns and young infants

Aim: To analyze the side effects of captopril, an angiotensin converting enzyme inhibitor (ACEI) in newborn and young infants. Methods: Retrospective analysis of side effects in 43 patients with congenital heart disease after cardiac surgery treated with captopril for heart failure during a two-year period. Results: Median age of the patients was 26days (range 6-310days), median weight 3.5kg (range 1.9-7.9kg). Initial median dose of captopril was 0.17 mg/kg/day (range 0.05-0.55mg/kg/day), slowly increased over 3-33days to a maximal median dose of 1.86 mg/kg/day (range 0.2-2.3mg/kg/day). All patients were additionally treated with diuretics. Side effects occurred in 17 patients (renal impairment or failure in 6, low blood pressure in 8, and oxygen saturation deficit in 3) requiring cessation or interruption in seven patients with renal impairment/failure (n=4), hypotension (n=1) and aorto-pulmonary shunting with low pulmonary perfusion (n=2). The six children who developed renal impairment or failure did so following a median delay of nine days after reaching the final dose and weighed on average 500g less than the other patients (P=0.046). All side effects were fully reversible. Conclusion: Side effects due to captopril were not dose-related in newborns and infants in this study. However, renal side effects occurred more often in smaller infants. Routine monitoring of infants on ACEI should include renal function tests, blood pressure and transcutaneous oxygen saturation measurement

High-fidelity transmission of entanglement over a high-loss freespace channel

Quantum entanglement enables tasks not possible in classical physics. Many quantum communication protocols require the distribution of entangled states between distant parties. Here we experimentally demonstrate the successful transmission of an entangled photon pair over a 144 km free-space link. The received entangled states have excellent, noise-limited fidelity, even though they are exposed to extreme attenuation dominated by turbulent atmospheric effects. The total channel loss of 64 dB corresponds to the estimated attenuation regime for a two-photon satellite quantum communication scenario. We confirm that the received two-photon states are still highly entangled by violating the CHSH inequality by more than 5 standard deviations. From a fundamental point of view, our results show that the photons are virtually not subject to decoherence during their 0.5 ms long flight through air, which is encouraging for future world-wide quantum communication scenarios.Comment: 5 pages, 3 figures, replaced paper with published version, added journal referenc