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Research Center for Quantum Information
Institute of Physics, Slovak Academy of Sciences
Dúbravská cesta 9, 84511 Bratislava, Slovakia
Tel: (+421 +2) 20910701
Fax: (+421 +2) 54776085

N E W S  old news 
14.09.2017 Research publication
Divisibility of quantum dynamical maps and collision models
The divisibility of dynamical maps is visualized by trajectories in the parameter space and analyzed within the framework of collision models. We introduce ultimate completely positive (CP) divisible processes, which lose CP divisibility under infinitesimal perturbations, and characterize Pauli dynamical semigroups exhibiting such a property. We construct collision models with factorized environment particles, which realize additivity and multiplicativity of generators of CP divisible maps. A mixture of dynamical maps is obtained with the help of correlated environment. The mixture of ultimate CP divisible processes is shown to result in a class of eternal CP indivisible evolutions. We explicitly find collision models leading to weakly and essentially nonMarkovian Pauli dynamical maps.
by
S. N. Filippov, J. Piilo, S. Maniscalco, and M. Ziman
Phys. Rev. A 96, 032111 (2017)
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APVV140878 (QETWORK), VEGA 2/0173/17 (MAXAP), GACR GA1622211S

13.09.2017 Research publication
Finding paths with quantum walks or quantum walking through a maze
We show that it is possible to use a quantum walk to find a path from one marked vertex to another. In the specific case of M stars connected in a chain, one can find the path from the first star to the last one in O(M√N) steps, where N is the number of spokes of each star. First we provide an analytical result showing that by starting in a phasemodulated highly superposed initial state we can find the path in O(M√N logM) steps. Next, we improve this efficiency by showing that the recovery of the path can also be performed by a series of successive searches when we start at the last known position and search for the next connection in O(√N) steps leading to the overall efficiency of O(M√N). For this result we use the analytical solution that can be obtained for a ring of stars of double the length of the chain.
by
Daniel Reitzner, Mark Hillery, and Daniel Koch
Phys. Rev. A 96, 032323 (2017)
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SASPRO, APVV140878 (QETWORK), VEGA 2/0151/15 (QWIN)


S E M I N A R S
 more 
12/09 11:00
Mario Ziman (Bratislava)
PR box implementation in process theories
20/09 13:30
Seth Lloyd (MIT)
Quantum machine learning
21/09 11:00
Tomáš Rybár (Bratislava)
Incompatibility for Pauli channels and measurements

V I S I T O R S
 history 
20.0920.09 Seth Lloyd
(MIT)


