Quantum information theory
Nowadays the foundations of quantum mechanics become relevant for information
transfer. In our group several new directions of this field have been discovered.
[P52] A.E. Allahverdyan
and Th.M. N., Breakdown of the Landauer bound for information erasure in
the quantum regime, Phys. Rev. E 64, 056117 (2001) (9 pages)
Many experiments have shown violation of Bell inequalities, the first ones were
by the Clauser and the Aspect groups. There are several loopholes, which to date have
not been closed simultaneously in a single experiment.
If one believes in the applicability of quantum mechanics, the loophole issue
should be solvable one day. But even then one may wonder whether Bell made the
proper connection to absence of local realism.
On the basis of a physical reasoning we argue that this connection is based on
a misconception:
[C44] Th. M. Nieuwenhuizen,
Where Bell went wrong ,
AIP Conf. Proc. 1101: Foundations of Probability and Physics - 5,
Luigi Accardi, Guillaume Adenier, Christopher A. Fuchs, Gregg Jaeger, Andrei Yu. Khrennikov,
Jan-Ake Larsson and Stig Stenholm, eds,
(Am. Inst. Phys., Melville, NY, 2009), pp 127-133.
Determining a quantum state by means of a single apparatus has been believed to be forbidden
by the principles of quantum mechanics, because of the non-commutativity of quantum operators.
We showed that is is possible, however, by coupling each member of the ensemble
of systems to an assistant, the ensemble of which is described by some known density matrix.
After letting the pairs evolve for a given period, a large enough number of commuting
variables of the combined system can be measured to fix the information about initial
state of the test system. Optimal setups are considered [L43].
The Landauer bound for information
erasure, sometimes said to be another formulation of the second law,
has founded a whole field in computation science. We showed that it
can be violated in the quantum regime [P52].