International Journal of Theoretical Physics

, Volume 46, Issue 4, pp 860–876 | Cite as

Quantum Information and Entropy

  • Subhash KakEmail author


Thermodynamic entropy is not an entirely satisfactory measure of information of a quantum state. This entropy for an unknown pure state is zero, although repeated measurements on copies of such a pure state do communicate information. In view of this, we propose a new measure for the informational entropy of a quantum state that includes information in the pure states and the thermodynamic entropy. The origin of information is explained in terms of an interplay between unitary and non-unitary evolution. Such complementarity is also at the basis of the so-called interaction-free measurement.


Quantum information quantum entropy interaction-free measurement origin of information 


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Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  1. 1.Department of Electrical & Computer EngineeringLouisiana State University, Baton RougeBaton RougeUSA

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