15th CEQIP workshop, June 13-16 2018, Smolenice, Slovakia

Wednesday, 13.6.2018
17:30-19:00 EVENING SESSION (chaired by)
17:30-18:10 I Matthias Kleinmann: Methods for a conclusive verification of bipartite bound entanglement   ΞΞΞ Bipartite bound entangled states form a class of states with a small volume within the quantum states. Also, this class of states is particularly difficult to prepare experimentally, because bound entangled states are both, entangled and mixed. Even if data has been taken successfully, yet another challenge is the actual verification that such a preparation was successful, since all states compatible with the data have to be verified to be bound entangled. In this talk I will present a method to find states which are most suitable for preparation and verification and I detail the statistical methods for verifying that the experimental state was indeed bound entangled. [ pdf ]
18:10-18:35 C Sergey Filippov: Lower and upper bounds on classical capacity of nonunital channels[ pdf ]
18:35-19:00 C Stefan Baeuml: Fundamental limitations on the capacities of bipartite quantum interactions [ pdf ]

Thursday, 14.6.2018
08:00-08:45 Breakfast
09:00-12:30 MORNING SESSION (chaired by)
09:00-09:40 I Tamás Vértesi: Useful correlations from bound entangled states   ΞΞΞ Bound entangled states are very weakly entangled states. In fact they are so weakly entangled that given an infinite number of copies, no pure state entanglement can be distilled from them. Nevertheless, they are useful in certain applications such as quantum key distribution. Here we show that bipartite bound entangled states are also useful in metrology and Bell nonlocality. In particular they can outperform separable states in linear interferometers and can give rise to Bell inequality violation. [ pdf ]
09:40-10:05 C Andreas Bluhm: Quantum compression relative to a set of measurements [ pdf ]
10:05-10:30 C Frédéric Dupuis: Secure Certification of Mixed Quantum States with Application to Two-Party Randomness Generation [ pdf ]
10:30-11:00 Coffee & Refreshment
11:00-11:40 I Sergii Strelchuk: Learning hard quantum distributions with variational autoencoders ΞΞΞStudying general quantum many-body systems is one of the major challenges in modern physics because it requires computational resources that scale exponentially with the size of the system. Simulating the evolution of a state, or even storing its description, rapidly becomes intractable for exact classical algorithms. Recently, machine learning techniques, in the form of restricted Boltzmann machines, have been proposed as a way to efficiently represent certain quantum states with applications in state tomography and ground state estimation. In my talk, I will introduce a new representation of states based on variational autoencoders. Variational autoencoders are a type of generative model in the form of a neural network. We probe the power of this representation by encoding probability distributions associated with states from different classes. We focus on two questions: (i) Are deeper networks better at learning quantum states? (ii) How well can we learn "hard" states? I will review recent mathematical results which explore how depth improves the representational capability of networks for classical problems and discuss our results for the quantum case.
11:40-12:05 C Daniel Nagaj: Shorter unentangled proofs for Ground State Connectivity [ pdf ]
12:05-12:30 C Vilasini Venkatesh: Composable security in relativistic quantum cryptography [ pdf ]
12:30-13:30 Lunch
14:00-15:30 AFTERNOON SESSION (chaired by)
14:00-14:40 I Marcus Huber: Thermodynamic limitations to quantum measurements   ΞΞΞ Projective measurements and the Born rule are centerpieces of the foundation of quantum information theory. They do, however, seem to violate the third law of thermodynamics. We show that in a self-contained description, quantum measurements are indeed strictly speaking impossible and can only be approximated at a work cost that diverges with the desired quality of the measurement approaching perfection. We then build an explicit model for a self contained measurement and show that reasonable measurements of quantum systems require macroscopic units of energy in order to be realised.
14:40-15:05 C Chris Perry: Elementary Thermal Operations
15:05-15:30 C Aleksandra Krawiec: Vertices cannot be hidden from quantum spatial search for almost all random graphs [ pdf ]
15:30-16:00 Coffee & Refreshment
16:00-18:30 POSTER SESSION
18:30 DINNER
19:00-23:00 CIPHER GAME (18:30 registration)

Friday, 15.6.2018
08:00-08:45 Breakfast
09:00-12:30 MORNING SESSION (chaired by)
09:00-09:40 I Robert Koenig: Quantum advantage with shallow circuits   ΞΞΞ We prove that constant-depth quantum circuits are more powerful than their classical counterparts. To this end we introduce a non-oracular version of the Bernstein-Vazirani problem which we call the 2D Hidden Linear Function problem. An instance of the problem is specified by a quadratic form q that maps n-bit strings to integers modulo four. The goal is to identify a linear boolean function which describes the action of q on a certain subset of n-bit strings. We prove that any classical probabilistic circuit composed of bounded fan-in gates that solves the 2D Hidden Linear Function problem with high probability must have depth logarithmic in n. In contrast, we show that this problem can be solved with certainty by a constant-depth quantum circuit composed of one- and two-qubit gates acting locally on a two-dimensional grid. This is joint work with Sergey Bravyi and David Gosset.
09:40-10:05 C Miguel Navascues: Resetting uncontrolled quantum systems [ pdf ]
10:05-10:30 C Remigiusz Augusiak: Bell inequalities for maximally entangled states [ pdf ]
10:30-10:35 Group photo
10:35-11:00 Coffee & Refreshment
11:00-11:40 I Alessandro Bisio: Higher order quantum computation   ΞΞΞ Higher order quantum computation is an extension of quantum computation where input and output of transformations can be transformations themselves. This idea leads to the notion of higher order maps, which generalise channels and quantum operations. Such a generalisation goes recursively, with the construction of a full hierarchy of maps of increasingly higher order. The analysis of special cases already showed that higher order maps, exhibit features that cannot be tracked down to the usual circuits, such as indefinite causal structures, providing provable advantages over circuital maps. The present treatment provides a general framework where this kind of analysis can be carried out in full generality. Higher order quantum computation is introduced axiomatically with a formulation based on the language of types of transformations. Complete positivity of higher order maps is derived from the general admissibility conditions instead of being postulated as in previous approaches. The recursive characterization of convex sets of maps of a given type is used to prove equivalence relations between different types. The axioms for higher order computation do not refer to the specific mathematical structure of quantum theory, and can be therefore exported in the context of any general operational probabilistic theory.
11:40-12:05 C Jedrzej Kaniewski: Self-testing of qutrit systems [ pdf ]
12:05-12:30 C Zbigniew Puchała: Coherifying quantum channels [ pdf ]
12:30-13:30 Lunch

Saturday, 16.6.2018
09:00-09:30 Breakfast
09:30-10:45 MORNING SESSION (chaired by)
09:30-09:55 C Marti Perarnau-Llobet: Quantum metrology with one-dimensional superradiant photonic states
09:55-10:20 C Libor Caha: Feynman-Kitaev computer's clock: bias, gaps, idling and pulse tuning
10:20-10:45 C Wieslaw Laskowski: Multipartite nonlocality and random measurement
10:45-10:50 Take Away Refreshment
11:00-13:30 Conference bus
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