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We present a network consisting of quantum gates that produces two imperfect copies of an arbitrary qubit. The quality of the copies does not depend on the input qubit. We also show that for a restricted class of inputs it is possible to use a very similar network to produce three copies instead of two. For qubits in this class, the copy quality is again… (More)

- Vladimír R. Buzek, Mark Hillery
- QCQC
- 1998

We review our recent work on the universal (i.e. input state independent) optimal quantum copying (cloning) of qubits. We present unitary transformations which describe the optimal cloning of a qubit, and we present the corresponding quantum logic network. We also present a network for an optimal quantum copying " machine " (transformation) which produces N… (More)

- Mário Ziman, Peter Stelmachovic, Vladimír R. Buzek
- Open Syst. Inform. Dynam.
- 2005

- Vladimír Buzek, Miguel Orszag, Marián Rosko
- Physical review letters
- 2005

Using tools of quantum information theory we show that the ground state of the Dicke model exhibits an infinite sequence of instabilities (quantum-phase-like transitions). These transitions are characterized by abrupt changes of the bi-partite entanglement between atoms at critical values kappa(j) of the atom-field coupling parameter kappa and are… (More)

- Jan Bouda, Vladimír R. Buzek
- Int. J. Found. Comput. Sci.
- 2003

- F De Martini, V Buzek, F Sciarrino, C Sias
- Nature
- 2002

In classical computation, a 'bit' of information can be flipped (that is, changed in value from zero to one and vice versa) using a logical NOT gate; but the quantum analogue of this process is much more complicated. A quantum bit (qubit) can exist simultaneously in a superposition of two logical states with complex amplitudes, and it is impossible to find… (More)

- M Koniorczyk, V Bužek, J Janszky
- 2001

We present a unified approach to quantum teleportation in arbitrary dimensions based on the Wigner-function formalism. This approach provides us with a clear picture of all manipulations performed in the telepor-tation protocol. In addition within the framework of the Wigner-function formalism all the imperfections of the manipulations can be easily taken… (More)

We show that the distribution of information at the output of the quantum cloner can be efficiently controlled via preparation of the quantum cloner. We present a universal cloning network with the help of which asymmetric cloning can be performed.

- Martin Plesch, Mário Ziman, Vladimír R. Buzek, Peter Stelmachovic
- Open Syst. Inform. Dynam.
- 2006

When standard methods of process (black-box) estimation are applied straightforwardly then it may happen that some sets of experimental data result in unphysical estimations of the corresponding channels (maps) describing the process. To prevent this problem, one can use the method of maximum likelihood (MML), which provides an efficient scheme for… (More)

- Vladimír R. Buzek, Mark Hillery, Mário Ziman, Marián Rosko
- Quantum Information Processing
- 2006