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03.03.2021 Job opening
PhD positions available
Interested to join our research team for four years of you life? That is
exactly the time the PhD study takes. Currently, we have open several
PhD positions at our Institute. We are open for submissions until
31/03/2020) with PhD starting in September 2020. If interested,
as the first step, please get in contact with a
potential PhD advisor
(send them your cv, motivation letter and contacts to potential references),
discuss the subject and follow his/her instructions. Do not wait until
the submission deadline and do this as soon as possible.
03.03.2021 Job opening
Open for student internships
Are you a high-school, or an university student seeking for a research experience in our group? Do not hesitate to contact us in advance (at least two months before the intended internship) via email to email@example.com. In your email shortly explain your motivation (at most 1 page), potential dates (preferences for May/June/September/October), duration (2-6 weeks) and whether you request financial support. We have (limited) resources to cover living expenses for you for several weeks. For undergraduate and graduate students we are ready to support your applications at scholarships.sk offering research stays of several months (deadlines are at the end of April and end of October). There is no strict deadline for applications and we are reviewing them every monthly. In order to get our support we recommend to apply before the end of March. This year the possibility of internship strongly depends on the unpredictable COVID situation. So far we are restricting plans for internships for August/September and later dates.
Postprocessing of quantum instruments
Studying sequential measurements is of the utmost importance to both the foundational aspects of quantum theory and the practical implementations of quantum technologies, with both of these applications being abstractly described by the concatenation of quantum instruments into a sequence of a certain length. In general, the choice of instrument at any given step in the sequence can be conditionally chosen based on the classical results of all preceding instruments. For two instruments in a sequence we consider the conditional second instrument as an effective way of postprocessing the first instrument into a new one. This is similar to how a measurement described by a positive operator-valued measure (POVM) can be postprocessed into another by way of classical randomization of its outcomes using a stochastic matrix. In this work we study the postprocessing relation of instruments and the partial order it induces on their equivalence classes. We characterize the greatest and the least element of this order, give examples of postprocessings between different types of instruments, and draw connections between postprocessings of some of these instruments and their induced POVMs.
Leevi Leppäjärvi and Michal Sedlák
Phys. Rev. A 103, 022615 (2021)
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OPTIQUTE (APVV-18-0518), HOQIP (VEGA 2/0161/19), HIPHOP (QuantERA project), QISS (JTF No. 61466)
Three kings conference / Trojkáľová konferencia
Annual one day meeting of Czech and Slovak physicists will be held on
January 27th online. More information and registration form are available
on the meeting website http://unix12.fzu.cz/3KK-2021/.
Pinned quantum Merlin-Arthur: The power of fixing a few qubits in proofs
What could happen if we pinned a single qubit of a system and fixed it in a particular state? First, we show that this leads to difficult static questions about the ground-state properties of local Hamiltonian problems with restricted types of terms. In particular, we show that the pinned commuting and pinned stoquastic Local Hamiltonian problems are quantum-Merlin-Arthur–complete. Second, we investigate pinned dynamics and demonstrate that fixing a single qubit via often repeated measurements results in universal quantum computation with commuting Hamiltonians. Finally, we discuss variants of the ground-state connectivity (GSCON) problem in light of pinning, and show that stoquastic GSCON is quantum-classical Merlin-Arthur–complete.
Daniel Nagaj, Dominik Hangleiter, Jens Eisert and Martin Schwarz
Physical Review A 103, 012604 (2021)
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OPTIQUTE (APVV-18-0518), HIPHOP (Quantera project 731473)