12 research outputs found
Atmospheric Channel Characteristics for Quantum Communication with Continuous Polarization Variables
We investigate the properties of an atmospheric channel for free space
quantum communication with continuous polarization variables. In our
prepare-and-measure setup, coherent polarization states are transmitted through
an atmospheric quantum channel of 100m length on the roof of our institute's
building. The signal states are measured by homodyne detection with the help of
a local oscillator (LO) which propagates in the same spatial mode as the
signal, orthogonally polarized to it. Thus the interference of signal and LO is
excellent and atmospheric fluctuations are autocompensated. The LO also acts as
spatial and spectral filter, which allows for unrestrained daylight operation.
Important characteristics for our system are atmospheric channel influences
that could cause polarization, intensity and position excess noise. Therefore
we study these influences in detail. Our results indicate that the channel is
suitable for our quantum communication system in most weather conditions.Comment: 6 pages, 4 figures, submitted to Applied Physics B following an
invitation for the special issue "Selected Papers Presented at the 2009
Spring Meeting of the Quantum Optics and Photonics Section of the German
Physical Society
Spectral function and quasiparticle weight in the generalized t-J model
We extend to the spectral function an approach which allowed us to calculate
the quasiparticle weight for destruction of a real electron Z_c sigma (k) (in
contrast to that of creation of a spinless holon Z_h(k) in a generalized
model, using the self-consistent Born approximation (SCBA). We compare our
results with those obtained using the alternative approach of Sushkov et al.,
which also uses the SCBA. The results for Z_c sigma (k) are also compared with
results obtained using the string picture and with exact diagonalizations of a
32-site square cluster. While on a qualitative level, all results look similar,
our SCBA approach seems to compare better with the ED one. The effect of
hopping beyond nearest neighbors, and that of the three-site term are
discussed.Comment: 7 pages, 6 figure
Electrical transport properties of a CNT/C60/CNT hybrid junction with closed end CNT leads using Greenâs function method
Guy Hocquenghem
In our continuous variable quantum key distribution (QKD) scheme, the
homodyne detection set-up requires balancing the intensity of an incident beam
between two photodiodes. Realistic lens systems are insufficient to provide a
spatially stable focus in the presence of large spatial beam-jitter caused by
atmospheric transmission. We therefore present an improved geometry for optical
tapers which offer up to four times the angular tolerance of a lens. The
effective area of a photodiode can thus be increased, without decreasing its
bandwidth. This makes them suitable for use in our free space QKD experiment
and in free space optical communication in general.Comment: 8 pages, 4 figures. Version 2: references added, minor content
revisions. To appear in QuantumComm 2009, LNICST 36, Springer (2010
Habitat use and population structure of four native minnows (family Cyprinidae) in the upper Missouri and lower Yellowstone rivers, North Dakota (USA)
The evolutionary ecology of fatty-acid variation : Implications for consumer adaptation and diversification
The nutritional diversity of resources can affect the adaptive evolution of consumer metabolism and consumer diversification. The omega-3 long-chain polyunsaturated fatty acids eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) have a high potential to affect consumer fitness, through their widespread effects on reproduction, growth and survival. However, few studies consider the evolution of fatty acid metabolism within an ecological context. In this review, we first document the extensive diversity in both primary producer and consumer fatty acid distributions amongst major ecosystems, between habitats and amongst species within habitats. We highlight some of the key nutritional contrasts that can shape behavioural and/or metabolic adaptation in consumers, discussing how consumers can evolve in response to the spatial, seasonal and community-level variation of resource quality. We propose a hierarchical trait-based approach for studying the evolution of consumers' metabolic networks and review the evolutionary genetic mechanisms underpinning consumer adaptation to EPA and DHA distributions. In doing so, we consider how the metabolic traits of consumers are hierarchically structured, from cell membrane function to maternal investment, and have strongly environment-dependent expression. Finally, we conclude with an outlook on how studying the metabolic adaptation of consumers within the context of nutritional landscapes can open up new opportunities for understanding evolutionary diversification