From: Anders Sandberg (asa@nada.kth.se)
Date: Mon May 26 2003 - 10:14:35 MDT
Some good news for spacetime engineers and high bandwidth quantum
channels:
Physical Review Letters
23 May 2003
Phys. Rev. Lett. 90, 201102 (2003)
Traversable Wormholes with Arbitrarily Small Energy Condition
Violations
Matt Visser
School of Mathematical and Computing Sciences, Victoria University of
Wellington, PO Box 600, Wellington, New Zealand
Sayan Kar
Department of Physics and Centre for Theoretical Studies, Indian
Institute of Technology, Kharagpur 721 302, WB, India
Naresh Dadhich
Inter-University Centre for Astronomy and Astrophysics, Post Bag 4,
Ganeshkhind, Pune 411 007, India
Traversable wormholes necessarily require violations of the averaged
null energy condition, this being the definition of "exotic matter."
However, the theorems which guarantee the energy condition violation
are remarkably silent when it comes to making quantitative statements
regarding the "total amount" of energy condition violating matter in
the spacetime. We develop a suitable measure for quantifying this
notion and demonstrate the existence of spacetime geometries
containing traversable wormholes that are supported by arbitrarily
small quantities of exotic matter. ©2003 The American Physical
Society
URL: http://link.aps.org/abstract/PRL/v90/e201102
Physical Review Letters
25 April 2003
Phys. Rev. Lett. 90, 167906 (2003)
Exceeding the Classical Capacity Limit in a Quantum Optical Channel
Mikio Fujiwara, Masahiro Takeoka, Jun Mizuno, and Masahide Sasaki
Communications Research Laboratory, Koganei, Tokyo 184-8795, Japan
The amount of information transmissible through a communications
channel is determined by the noise characteristics of the channel and
by the quantities of available transmission resources. In classical
information theory, the amount of transmissible information can be
increased twice at most when the transmission resource is doubled for
fixed noise characteristics. In quantum information theory, however,
the amount of information transmitted can increase even more than
twice. We present a proof-of-principle demonstration of this
superadditivity of classical capacity of a quantum channel by using
the ternary symmetric states of a single photon, and by event
selection from a weak coherent light source. We also show how the
superadditive coding gain, even in a small code length, can boost the
communication performance of the conventional coding technique. ©2003
The American Physical Society
URL: http://link.aps.org/abstract/PRL/v90/e167906
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