7 research outputs found
Hamiltonians for one-way quantum repeaters
Quantum information degrades over distance due to the unavoidable
imperfections of the transmission channels, with loss as the leading factor.
This simple fact hinders quantum communication, as it relies on propagating
quantum systems. A solution to this issue is to introduce quantum repeaters at
regular intervals along a lossy channel, to revive the quantum signal. In this
work we study unitary one-way quantum repeaters, which do not need to perform
measurements and do not require quantum memories, and are therefore
considerably simpler than other schemes. We introduce and analyze two methods
to construct Hamiltonians that generate a repeater interaction that can beat
the fundamental repeaterless key rate bound even in the presence of an
additional coupling loss, with signals that contain only a handful of photons.
The natural evolution of this work will be to approximate a repeater
interaction by combining simple optical elements.Comment: 8 pages, 3 figure
Zero-Error Attacks and Detection Statistics in the Coherent One-Way Protocol for Quantum Cryptography
This is a study of the security of the Coherent One-Way (COW) protocol for
quantum cryptography, proposed recently as a simple and fast experimental
scheme. In the zero-error regime, the eavesdropper Eve can only take advantage
of the losses in the transmission. We consider new attacks, based on
unambiguous state discrimination, which perform better than the basic
beam-splitting attack, but which can be detected by a careful analysis of the
detection statistics. These results stress the importance of testing several
statistical parameters in order to achieve higher rates of secret bits
Space-QUEST: Experiments with quantum entanglement in space
The European Space Agency (ESA) has supported a range of studies in the field
of quantum physics and quantum information science in space for several years,
and consequently we have submitted the mission proposal Space-QUEST (Quantum
Entanglement for Space Experiments) to the European Life and Physical Sciences
in Space Program. We propose to perform space-to-ground quantum communication
tests from the International Space Station (ISS). We present the proposed
experiments in space as well as the design of a space based quantum
communication payload.Comment: 4 pages, 1 figure, accepted for the 59th International Astronautical
Congress (IAC) 200