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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 
06.10.2020 Interview
Slovaks tests unbreakable cryptosystem aiming to connect Bratislava and Vienna
interview with prof. Vladimír Bužek for online IT technology journal http://zive.aktuality.sk/ by Jan Trangel and Filip Hanker (in Slovak)
Slováci testujú neprelomiteľný spôsob šifrovania, idú spojiť Bratislavu a Viedeň. Pri súčasnej vedomosti o tom, ako vyzerá fyzika a svet, nie je kvantovú šifru možné zlomiť, hovorí o prevratnej technológii profesor Vladimír Bužek, jeden z najcitovanejších slovenských fyzikov ...  pdf 

20.11.2019 Publication
Probabilistic storage and retrieval of qubit phase gates
Probabilistic storage and retrieval (PSR) of unitary quantum dynamics is possible with exponentially small failure probability with respect to the number of systems used as a quantum memory [M. Sedlák, A. Bisio, and M. Ziman, Phys. Rev. Lett. 122, 170502 (2019)]. Here we study improvements due to a priori knowledge about the unitary transformation to be stored. In particular, we study N→1 PSR of qubit phase gates, i.e., qubit rotations around the Z axis with an unknown angle, and show that if we access the gate only N times the optimal probability of perfect retrieving of its single use is N/(N+1). We propose a quantum circuit realization for the optimal protocol and show that a programmable phase gate [G. Vidal, L. Masanes, and J. I. Cirac, Phys. Rev. Lett. 88, 047905 (2002)] can be turned into a (2k−1)→1 optimal PSR of phase gates and requires only k controllednot gates, while having exponentially small failure probability in k.
by
Michal Sedlák and Mário Ziman
Phys. Rev. A 102, 032618 (2020)
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OPTIQUTE APVV180518, HOQIT VEGA 2/0161/19,
QuantERA project HIPHOP, QISS

01.07.2020 Conference
Informal quantum symposium 2020
Informal quantum symposium (IQUAS) aims to bring together experts working in the area of quantum information science and technologies and to create a motivating environment full of scientific interactions and discussions (while keeping the regulation of safe distance :). Conceptually, IQUAS stands somewhere between workshops and unconferences, thus, its goal is not only to present new results, but also to discuss research problems in the areas of interests of participants. Except of either presenting their recent results (as short talks and posters), or give a tutorial on recent scientific topics, participants are expected to actively discuss their current research interests with other participants. The number of participants is limited.
Dates: 2428/08/2020
Place: Smolenice, Slovakia
Meeting website http://qute.sk/iquas/

14.08.2020 Publication
Easing the Monte Carlo sign problem
Quantum Monte Carlo (QMC) methods are the gold standard for studying equilibrium properties of quantum manybody systems. However, in many interesting situations, QMC methods are faced with a sign problem, causing the severe limitation of an exponential increase in the runtime of the QMC algorithm. In this work, we develop a systematic, generally applicable, and practically feasible methodology for easing the sign problem by efficiently computable basis changes and use it to rigorously assess the sign problem. Our framework introduces measures of nonstoquasticity that—as we demonstrate analytically and numerically—at the same time provide a practically relevant and efficiently computable figure of merit for the severity of the sign problem. Complementing this pragmatic mindset, we prove that easing the sign problem in terms of those measures is generally an NPcomplete task for nearestneighbor Hamiltonians and simple basis choices by a reduction to the MAXCUTproblem.
by
Dominik Hangleiter, Ingo Roth, Daniel Nagaj and Jens Eisert
Science Advances 6, eabb8341 (2020)
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QETWORK APVV140878, VEGA MAXAP 2/0173/17


S E M I N A R S
 more 
30/06 11:00
Hamed Mohammady (Bratislava)
Stochastic quantum thermodynamics of projective measurements via coarsegrained trajectories
23/06 11:00
Sazim Sheikh (Bratislava)
Classical Communications with Indefinite Causal Order for N completely depolarizing channels

V I S I T O R S
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