Karl Kraus (physicist)

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Karl Kraus, 1984

Karl Kraus (born March 21, 1938 in Vrchlabí (German Hohenelbe / Riesengebirge); † June 9, 1988 in Würzburg ) was a German theoretical physicist who made important contributions to the fundamentals of quantum physics .

Live and act

Kraus was born in 1938 in Hohenelbe / Giant Mountains, today's Vrchlabí . After the war he grew up in Elsterwerda and attended schools there. From 1955 to 1960 he studied physics at the Humboldt University Berlin (East) and the Free University Berlin (West). There he received his doctorate in 1962 with a thesis under Kurt Just on the subject of Lorentz's variant of gravitation theory . Kraus then switched to Günther Ludwig at the University of Marburg as an assistant , where he completed his habilitation in 1966. In 1971 he accepted a position at the Physics Institute at the University of Würzburg , where he founded a mathematical-physical working group on the subject of the fundamentals of quantum theory . In 1980 Kraus spent a research year at the University of Austin with John Archibald Wheeler , Arno Böhm , George Sudarshan , William Wootters and Wojciech Zurek .

Throughout his entire academic life, Kraus dealt with the question of the connection between the nonlocality of the quantum world and the obvious locality of our classical world. In this context, he researched and published on the Einstein-Podolsky-Rosen effect and repeatedly on questions of the measurement process in quantum theory , the problems of which, in his opinion , had been largely ignored by the founders of quantum theory in the context of the Copenhagen interpretation .

Important publications on the measurement process in Kraus' quantum theory were:

  • Measuring processes in quantum mechanics I. Continuous observation and the watchdog effect.
  • Measuring processes in quantum mechanics II. The classical behavior of measuring instruments.
  • States, Effects, and Operations.

In the aforementioned book States, Effects, and Operations , Kraus first introduced the term and mathematical formalism of quantum operation , a special mapping of density matrices, to describe the measurement process in quantum mechanics . The representation he used in this context is known today as the Kraus representation , Kraus operator formalism or operator-sum formalism and is now frequently used in connection with developments in the field of quantum information . The Kraus representation is based on a theorem by WF Stinespring about completely positive maps of finite-dimensional C * -algebras . For a modern proof of the Kraus representation, which instead of Stinespring's theorem is based on a theorem by M.-D. Choi supports, see e.g. M. Nielsen, I. Chuang.

The questions on the fundamentals of quantum theory dealt with by Kraus are still a topical research area today. New theoretical advances are discussed in E. Joos, HD Zeh , C. Kiefer , D. Giulini, J. Kupsch, I.-O. Stamatescu. The connection of these decoherence theories with modern experiments, such as those started in particular by the working groups of Serge Haroche (Paris) and Anton Zeilinger (Innsbruck, Vienna), can perhaps help to improve the measurement process in quantum theory and thus the connection between the quantum world and the classical To understand the world better in the future.

In addition to mathematics and physics, Kraus had a special interest in biology, acquired extensive knowledge in it and even published some biological works. Karl Kraus died in 1988 at the age of 50 as a result of a tumor disease.

Individual evidence

  1. ↑ Karl Kraus: Lorentzine variant gravitation theory , dissertation, Free University of Berlin, 1962.
  2. ^ Karl Kraus: Quantum Theory, Causality and EPR Experiments , in Proceedings of the Joensuu Symposium on the Foundations of Modern Physics: 50 Years of the EPR Thought Experiment , p. 138, World Scientific, Singapore, 1986.
  3. ^ Karl Kraus: Measuring processes in quantum mechanics I. Continuous observation and the watchdog effect . Foundations of Physics, Vol. 11, pp. 547-576, 1981.
  4. ^ Karl Kraus: Measuring processes in quantum mechanics. II. The classical behavior of measuring instruments . Foundations of Physics, Vo. 15, pp. 717-730, 1985.
  5. ^ Karl Kraus: States, Effects, and Operations . Lecture Notes in Physics, vol. 190.1983.
  6. ^ WF Stinespring, Positive Functions on C * -algebras, Proceedings of the American Mathematical Society, 211-216, 1955.
  7. ↑ M. Choi, Completely Positive Linear Maps on Complex matrices, Linear Algebra and Its Applications, 285-290, 1975.
  8. ↑ M. Nielsen and I. Chuang, Quantum Computation and Quantum Information, Cambridge University Press, 2000.
  9. ↑ E. Joos, HD Zeh, C. Kiefer, D. Giulini, J. Kupsch, I.-O. Stamatescu: Decoherence and the Appearance of a Classical World in Quantum Theory , 2nd ed., 2003, Springer, Berlin.
  10. ^ MA Schlosshauer: Decoherence - and the Quantum-To-Classical Transition , 2007, Springer, Berlin.
  11. ↑ see below: G. Reents, B. Schiekel: In memoriam Karl Kraus .
  12. ^ Georg Reents: Obituary for Karl Kraus , Foundations of Physics Letters, Vol. 2, p. 7, 1989.

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personal data
SURNAME Kraus, Karl (physicist)
BRIEF DESCRIPTION German theoretical physicist
DATE OF BIRTH March 21, 1938
PLACE OF BIRTH Vrchlabí
DATE OF DEATH June 9, 1988
Place of death Wurzburg