Almost regular weekly seminar.

[PHOTO] 20/11 11:00
Andras Bodor (Pecs)
Receiver operation characteristics of quantum state discrimination
We provide a description of the problem of the discrimination of two quantum states in terms of receiver operation characteristics analysis, a prevalent approach in classical statistics. Receiveroperation characteristics diagrams provide an expressive representation of the problem, in which quantities such as the fidelity and the trace distance also appear explicitly. In addition we introduce an alternative quantum generalization of the classical Bhattacharyya coefficient. We evaluate our quantum Bhattacharyya coefficient for certain situations and describe some of its properties. These properties make it applicable as another possible quantifier of the similarity of quantum states.
[PHOTO] 23/11 11:00
Errka Haapasalo (Kjoto)
The unavoidable information flow to environment in quantum measurements
One of the basic lessons of quantum theory is that one cannot obtain information on an unknown quantum state without disturbing it. Hence, by performing a certain measurement, we limit the other possible measurements that can be effectively implemented on the original input state. It has been recently shown that one can implement sequentially any device, either channel or observable, which is compatible with the first measurement [T. Heinosaari and T. Miyadera: Phys. Rev. A Vol 91 (2015), 022110]. In this work we prove that this can be done, apart from some special cases, only when the succeeding device is implemented on a larger system than just the input system. This means that some part of the still available quantum information has been flown to the environment and cannot be gathered by accessing the input system only. We characterize the size of the post-measurement system by determining the class of measurements for the observable in question that allow the subsequent realization of any measurement process compatible with the said observable. We also study the class of measurements that allow the subsequent realization of any observable jointly measurable with the first one and show that these two classes coincide when the first observable is extreme.
[PHOTO] 24/11 10:00
Pavol Zajac (Bratislava)
Postquantum cryptography
[PHOTO] 07/12 11:00
Roope Uola (Siegen)
A unified picture for spatial, temporal and channel steering
Quantum steering describes how local actions on a quantum system can affect another, space-like separated, quantum state. Lately, quantum steering has been formulated also for time-like scenarios and for quantum channels. We approach all the three scenarios as one using tools from Stinespring dilations of quantum channels. By applying our technique we link all three steering problems one-to-one with the incompatibility of quantum measurements, a result formerly known only for spatial steering. We exploit this connection by showing how measurement uncertainty relations can be used as tight steering inequalities for all three scenarios. Moreover, we show that certain notions of temporal and spatial steering are fully equivalent and prove a hierarchy between temporal steering and macrorealistic hidden variable models.
[PHOTO] slovakia.gif
14/12 11:00
Martin Plavala (Bratislava)
Conditions on the compatibility of channels in General Probabilistic Theory and their connection to steering and Bell nonlocality
Place: RCQI, Institute of Physics, Dúbravská cesta 9, Bratislava | map |

Specialized lecture courses. Currently no lectures are scheduled.

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Joint quantum scientific gathering of groups from Wien, Brno and Bratislava.

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