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Physical accessibility of non-completely positive maps
Hilary Carteret, Daniel R. Terno, Karol Zyczkowski
Maps that are not completely positive (CP) are often useful to describe the dynamics of open systems. An apparent violation of complete positivity can occur because there are prior…
A concise guide to complex Hadamard matrices
Wojciech Tadej, Karol Zyczkowski
Complex Hadamard matrices, consisting of unimodular entries with arbitrary phases, play an important role in the theory of quantum information. We review basic properties of comple…
Quantum Error Correcting Codes From The Compression Formalism
Man-Duen Choi, David W. Kribs, Karol Zyczkowski
We solve the fundamental quantum error correction problem for bi-unitary channels on two-qubit Hilbert space. By solving an algebraic compression problem, we construct qubit codes…
On the structure of the body of states with positive partial transpose
Stanislaw Szarek, Ingemar Bengtsson, Karol Zyczkowski
We show that the convex set of separable mixed states of the 2 x 2 system is a body of constant height. This fact is used to prove that the probability to find a random state to be…
Scalable Noise Estimation with Random Unitary Operators
Joseph Emerson, Robert Alicki, Karol Zyczkowski
We describe a scalable stochastic method for the experimental measurement of generalized fidelities characterizing the accuracy of the implementation of a coherent quantum transfor…