Prof. Vladimír Bužek Profile

Prof. Vladimír Bužek

at Slovak Academy of Sciences

SPIE Involvement:

Author

Proceedings Article | 22 July 2002 Paper

Quantum safe with classical key: physics of open systems from the point view of information theory

Mario Ziman, P. Stelmachovic, Vladimir Buzek, Mark Hillery, Valerio Scarani, Nicolas Gisin

Proceedings Volume 4888, (2002) https://doi.org/10.1117/12.475875

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Proceedings Article | 19 July 1999 Paper

Quantum state reconstruction and optimal manipulations with quantum information (1996 IOC Prize Winner)

Vladimir Buzek

Proceedings Volume 3749, (1999) https://doi.org/10.1117/12.354814

KEYWORDS: Quantum information, Quantum physics, Probability theory, Quantum efficiency, Quality measurement, Physics, Information science, Particles, Data analysis, Bayesian inference

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The concept of a quantum state represents one of the most fundamental pillars of the paradigm of quantum theory.'3 Contrary to its mathematical elegance and convenience in calculations, the physical interpretation of a quantum state is not so transparent. The problem is that the quantum state (described either by a state vector, or density operator or a phase-space probability density distribution) does not have a well defined objective status, i.e. a state vector is not an objective property of a particle. According to Peres (see,1 p. 374): "There is no physical evidence whatsoever that every physical system has at every instant a well defined state. .. In strict interpretation of quantum theory these mathematical symbols [i.e., state vectorsi represent statistical information enabling us to compute the probabilities of occurrence of specific events." Once this point of view is adopted then it becomes clear that any "measurement" or a reconstruction of a density operator (or its mathematical equivalent) can be understood exclusively as an expression of our knowledge about the quantum mechanical state based on a certain set of measured data. To be more specific, any quantum-mechanical reconstruction scheme is nothing more than an a posteriori estimation of the density operator of a quantum-mechanical (microscopic) system based on data obtained with the help of a macroscopic measurement apparatus.3 The quality of the reconstruction depends on the "quality" of the measured data and the efficiency of the reconstruction procedure with the help of which the data analysis is performed. In particular, we can specify three different situations. Firstly, when all system observables are precisely measured. In this case the complete reconstruction of an initially unknown state can be performed (we will call this the reconstruction on the complete observation level) . Secondly, when just part of the system observables is precisely measured then one cannot perform a complete reconstruction of the measured state. Nevertheless, the reconstructed density operator still uniquely determines mean values of the measured observables (we will denote this scheme as reconstruction on incomplete observation levels) . Finally, when measurement does not provide us with sufficient information to specify the exact mean values (or probability distributions) but only the frequencies of appearances of eigenstates of the measured observables, then one can perform an estimation (e.g. reconstruction based on quantum Bayesian inference) which is the "best" with respect to the given measured data and the a priori knowledge about the state of the measured system.

Proceedings Article | 14 July 1999 Paper

Optimal manipulations with qubits: universal quantum cloning and universal logical NOT operation

Vladimir Buzek, Mark Hillery

Proceedings Volume 3820, (1999) https://doi.org/10.1117/12.353044

KEYWORDS: Quantum communications, Quantum information, Quantum networks, Quantum physics, Poincaré sphere, Adaptive optics, Physics, Superposition, Quantum information processing, Quantum efficiency

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