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  12.02.2024 Publication
Gravitational quantum switch on a superposition of spherical shells
In the absence of a complete theory of quantum gravity, phenomenological models built upon minimal assumptions have been explored for the analysis of possible quantum effects in gravitational systems. Implications of a superposition of geometries have been considered in such models, including the occurrence of processes with indefinite order. In a gravitational quantum switch, in particular, the order of operations applied by two agents on a target system is entangled with the state of the geometry. We consider a model describing the superposition of geometries produced by distinct arrangements of spherical mass shells, and show that a protocol for the implementation of a gravitational quantum switch can be formulated in such a system. The geometries in superposition are identical in an exterior region outside a given radius, and differ within such a radius. The exterior region provides a classical frame from which the superposition of geometries in the interior region can be probed. One of the agents crosses the interior region and becomes entangled with the geometry, which is explored as a resource for the implementation of the quantum switch. Novel features of the protocol include the superposition of nonisometric geometries, the existence of a region with a definite geometry, and the fact that the agent that experiences the superposition of geometries is in free fall, preventing information on the global geometry to be obtained from within its laboratory.
by Natália S. Móller, Bruna Sahdo, Nelson Yokomizo
Quantum 8, 1248 (2024) | +++ |
Schwarz stipend, APVV-22-0570 (DeQHOST), VEGA 2/0183/21 (DESCOM), VEGA 2/0156/22 (QuaSiModo), JTF-61466 (QISS)
  12.02.2024 Publication
Incompatibility of quantum instruments
Quantum instruments describe outcome probability as well as state change induced by measurement of a quantum system. Incompatibility of two instruments, i. e. the impossibility to realize them simultaneously on a given quantum system, generalizes incompatibility of channels and incompatibility of positive operator-valued measures (POVMs). We derive implications of instrument compatibility for the induced POVMs and channels. We also study relation of instrument compatibility to the concept of non-disturbance. Finally, we prove equivalence between instrument compatibility and postprocessing of certain instruments, which we term complementary instruments. We illustrate our findings on examples of various classes of instruments.
by Leevi Leppäjärvi, Michal Sedlák
Quantum 8, 1246 (2024) | +++ |
SASPRO-2-945478, APVV-22-0570 (DeQHOST), VEGA 2/0183/21 (DESCOM)
  04.02.2024 Job opening
Looking for PhD in quantum technologies and foundations ΞΞΞ
Are you a master/engineer student fascinated by quantum physics or future of quantum technologies? Want to understand quantum foundations, run quantum computers, build quantum systems, use quantum networks, or encrypt quantum messages? Interested to join our research team for four years of you life? That is the time it takes to do the research and become expert (with PhD title) in quantum simulations, or optical quantum communication networks, or quantum security, or foundations of quantum phenomena. All of these fields are waiting for your contribution. Currently, we have open several PhD positions at our Institute. We are open for your email ideally before 29/02/2024. As for the first step please get in contact with a potential PhD advisor (send him 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. If you are uncertain who to contact, just choose any of us. We are all happy to help. \ΞΞΞ
  01.02.2024 Job opening
IPSAS fellowship call - seeking for a colleague
Within the call for IPSAS fellowship we are looking for motivated postdoc, or a colleague willing to spent his/her sabbatical time with us. If interested please send your CV before February 29th (the sooner the better) directly to one of us. Choose the one who matches the best with your experience and interests. Making the right choice is part of the preselection process. If undecided email to ziman@savba.sk. Final interviews will happen in the second week of March.