31 research outputs found
Experimental Test of Two-way Quantum Key Distribution in Presence of Controlled Noise
We describe the experimental test of a quantum key distribution performed
with a two-way protocol without using entanglement. An individual incoherent
eavesdropping is simulated and induces a variable amount of noise on the
communication channel. This allows a direct verification of the agreement
between theory and practice.Comment: 4 pages, 3 figure
Football history: a German perspective on current research fields
In the last 25 years, German football has experienced several turning points. First, the collapse of communism in 1989 rendered necessary a complete reorganisation of the sport and football landscape in eastern Germany. Second, in parallel with the award in the year 2000 of the right to host the 2006 FIFA World Cup in the Federal Republic of Germany, a significant upturn took place in academic research on football. The reappraisal of the National Socialist era, in particular, has experienced a noticeable upswing since the year 2000. The present article focuses on several key thematic areas that shape current research and will shape research in the future. They include, first, the question of the character of the Vereine (here: football clubs) under the conditions of a communist dictatorship, and second, an increased interest in the biographical component of the history of the development of football. At the same time, it is clear that by now the question of a memory culture in football is no longer limited to national perspectives such as the reappraisal of the "Miracle of Bern". Rather, the dynamic development of European football renders possible the emergence of European realms of shared memory. At the same time, a boom in public engagement with football history can be observed in Germany and elsewhere. This holds true for both the social commemoration of footballers who were victims of war and tyranny and for popular cultural publications. In recent years, therefore, there has not only been an increase in the “museumisation” but also in the media marketing of football history. Thus, football history itself has become a market that is served by various stakeholders, such as clubs, companies, and the media
Bright filter-free source of indistinguishable photon pairs
We demonstrate a high-brightness source of pairs of indistinguishable photons
based on a type-II phase-matched doubly-resonant optical parametric oscillator
operated far below threshold. The cavity-enhanced down-conversion output of a
PPKTP crystal is coupled into two single-mode fibers with a mode coupling
efficiency of 58%. The high degree of indistinguishability between the photons
of a pair is demonstrated by a Hong-Ou-Mandel interference visibility of higher
than 90% without any filtering at an instantaneous coincidence rate of 450 000
pairs/s per mW of pump power per nm of down-conversion bandwidth. For the
degenerate spectral mode with a linewidth of 7 MHz at 795 nm a rate of 70
pairs/(s mW MHz) is estimated, increasing the spectral brightness for
indistinguishable photons by two orders of magnitude compared to similar
previous sources.Comment: 7 pages, 3 figure
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
Polarization entanglement and quantum beats of photon pairs from four-wave mixing in a cold 87Rb ensemble
10.1088/1367-2630/17/9/093034New Journal of Physics1799303
Probing the quantum-classical boundary with compression software
10.1088/1367-2630/18/3/035011New Journal of Physics1833501