113,842 research outputs found
Free-space quantum key distribution by rotation-invariant twisted photons
Twisted photons are photons carrying a well-defined nonzero value of orbital
angular momentum (OAM). The associated optical wave exhibits a helical shape of
the wavefront (hence the name) and an optical vortex at the beam axis. The OAM
of light is attracting a growing interest for its potential in photonic
applications ranging from particle manipulation, microscopy and
nanotechnologies, to fundamental tests of quantum mechanics, classical data
multiplexing and quantum communication. Hitherto, however, all results obtained
with optical OAM were limited to laboratory scale. Here we report the
experimental demonstration of a link for free-space quantum communication with
OAM operating over a distance of 210 meters. Our method exploits OAM in
combination with optical polarization to encode the information in
rotation-invariant photonic states, so as to guarantee full independence of the
communication from the local reference frames of the transmitting and receiving
units. In particular, we implement quantum key distribution (QKD), a protocol
exploiting the features of quantum mechanics to guarantee unconditional
security in cryptographic communication, demonstrating error-rate performances
that are fully compatible with real-world application requirements. Our results
extend previous achievements of OAM-based quantum communication by over two
orders of magnitudes in the link scale, providing an important step forward in
achieving the vision of a worldwide quantum network
Deep Space Network information system architecture study
The purpose of this article is to describe an architecture for the Deep Space Network (DSN) information system in the years 2000-2010 and to provide guidelines for its evolution during the 1990s. The study scope is defined to be from the front-end areas at the antennas to the end users (spacecraft teams, principal investigators, archival storage systems, and non-NASA partners). The architectural vision provides guidance for major DSN implementation efforts during the next decade. A strong motivation for the study is an expected dramatic improvement in information-systems technologies, such as the following: computer processing, automation technology (including knowledge-based systems), networking and data transport, software and hardware engineering, and human-interface technology. The proposed Ground Information System has the following major features: unified architecture from the front-end area to the end user; open-systems standards to achieve interoperability; DSN production of level 0 data; delivery of level 0 data from the Deep Space Communications Complex, if desired; dedicated telemetry processors for each receiver; security against unauthorized access and errors; and highly automated monitor and control
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