11th Central European Quantum Information Processing Workshop
5-8 June 2014, Znojmo, Czech Republic

PROGRAM (preliminary plan)
I = invited (7x), C = contributed (17x)

THURSDAY, 05/06/2014
16:00-17:30 Registration and refreshment
Afternoon session (chaired by Jan Bouda)
17:30-18:15 I Fernando Brandao: Limitations for quantum PCPS   ΞΞΞAn interesting current open problem in quantum complexity theory is the quantum PCP conjecture. In analogy with the PCP theorem, the conjecture states that it is QMA-hard to tell whether a quantum constraint satisfaction problem (aka a local quantum Hamiltonian) is satisfiable or far from satisfiable, with a constant fraction of the constraints being violated in any assignment.

In this talk I will discuss limitations for quantum PCPs due to one of the most distinguishing features of quantum entanglement: its monogamous character. The monogamy of entanglement is the principle that the more entangled a system is with another one, the less entangled it can be with anything else. I will show how a quantitative understanding of entanglement monogamy leads both to limitations on the parameters that a potential quantum analogue of the PCP theorem might have, and to potential approaches to proving such an analogue (for instance by attempting to quantize the main steps of Dinur’s proof of the PCP theorem).

The talk will be mostly based on joint work with Aram Harrow (arXiv:1310.0017).
18:15-18:40 C Martin Schwarz: Simulating Quantum Circuits with Sparse Output Distributions ΞpdfΞ
18:40-19:05 C Alexander Müller-Hermes: Quantum Subdivision Capacities and Continuous Quantum Coding ΞpdfΞ
19:30 TAKE-ME-OUT-FOR-DINNER TRAIN, in front of the Loucky monanstery (conference venue)
20:00 WELCOME DINNER Pivnice u Šneka, Zelenářská 1 (GPS 48°51'17.205"N, 16°2'55.892"E)

FRIDAY, 06/06/2014
08:00 Breakfast (in your hotel)
Morning session (chaired by Fernando Brandao)
09:00-09:45 I Andreas Winter: Weak locking capacity of quantum channels can be much larger than private capacity   ΞΞΞWe show that it is possible for the so-called weak locking capacity of a quantum channel [Guha et al., PRX 4:011016, 2014] to be much larger than its private capacity. Both reflect different ways of capturing the notion of reliable communication via a quantum system while leaking almost no information to an eavesdropper; the difference is that the latter imposes an intrinsically quantum security criterion whereas the former requires only a weaker, classical condition. The channels for which this separation is most straightforward to establish are the complementary channels of classical-quantum (cq-)channels, and hence a subclass of Hadamard channels. We also prove that certain symmetric channels (related to photon number splitting) have positive weak locking capacity in the presence of a vanishingly small pre-shared secret, whereas their private capacity is zero.
These findings are powerful illustrations of the difference between two apparently natural notions of privacy in quantum systems, relevant also to quantum key distribution (QKD): the older, naive one based on accessible information, contrasting with the new, composable one embracing the quantum nature of the eavesdropper's information.
Assuming an additivity conjecture for constrained minimum output Renyi entropies, the techniques of the first part demonstrate a single-letter formula for the weak locking capacity of complements to cq-channels, coinciding with a general upper bound of Guha et al. for these channels. Furthermore, still assuming this additivity conjecture, this upper bound is given an operational interpretation for general channels as the maximum weak locking capacity of the channel activated by a suitable noiseless channel​. [arXiv:1403.6361]​
09:45-10:10 C Juan Bermejo-Vega: The computational power of normalizer circuits over ∞ Abelian groups ΞpdfΞ
10:10 Break and refreshment
10:40-11:25 I Valerio Scarani: Randomness from quantum systems: a guided tour   ΞΞΞWhat are randomness generation, expansion, and amplification? Under which assumptions does quantum physics provide "better" randomness than classical? Do Bell inequalities really allow us to buy our cryptographic apparatus from the enemy? Are all "experimental demonstrations" of randomness meaningful? This talk will review these questions.
References: arXiv:1303.3081 (lecture notes on device-independence), arXiv:1401.4243v2
11:25-11:50 C David Reeb: Trace-norm contraction under tensor product channels ΞpdfΞ
11:50-12:15 C Marcus Huber: Inequalities for the Ranks of Quantum States ΞpdfΞ
12:15 Lunch
Afternoon Session (chaired by Valerio Scarani*)
13:45-14:30 I Frédéric Dupuis: Bounding the uncertainty of constrained adversaries   ΞΞΞIn many cryptographic protocols, the main ingredient of the security proof involves showing that a dishonest party has a limited amount of information about a particular string or quantum system of interest. This bound on the adversary's information often comes from a physical constraint, such as a limited or noisy quantum memory, which must then be harnessed by the security proof. In this talk, I will present a general technique for making use of this type of constraint in security proofs, and will give concrete applications to cryptography in the bounded storage model and to bounds on random-access codes. For more information, see arXiv:1305.1316. (Joint work with Omar Fawzi and Stephanie Wehner) ΞpdfΞ
14:30-14:55 C Julio De Vicente: The maximally entangled set of multipartite quantum states ΞpdfΞ
14:55-15:20 C Sergey N. Filippov: Dissociation and annihilation of multi-partite entanglement structures ΞpdfΞ
15:20 Break and refreshment
15:50-16:15 C Daniela Frauchiger: True Randomness from Realistic Quantum Devices ΞpdfΞ
16:15-16:40 C Matej Pivoluska: Device-independent randomness extraction for arbitrarily weak min-entropy source ΞpdfΞ
16:40-17:05 C Marcin Pawlowski: Dimension Witness Networks ΞpdfΞ
17:05-19:00 Poster session

SATURDAY, 07/06/2014
08:00 Breakfast (in your hotel)
Morning session (chaired by David Reeb)
09:00-09:45 I Daniel Burgarth: Quantum Computing in Plato's Cave   ΞΞΞWe show that mere observation of a quantum system can turn its dynamics from a very simple one into a universal quantum computation. This effect, which occurs if the system is regularly observed at short time intervals, can be rephrased as a modern version of Plato's Cave allegory. More precisely, while in the original version of the myth, the reality perceived within the Cave is described by the projected shadows of some more fundamental dynamics which is intrinsically more complex, we found that in the quantum world the situation changes drastically as the "projected" reality perceived through sequences of measurements can be more complex than the one that originated it. After discussing examples we go on to show that this effect is generally to be expected: almost any quantum dynamics will become universal once "observed" as outlined above. Conversely, we show that any complex quantum dynamics can be "purified" into a simpler one in larger dimensions. ΞpdfΞ
09:45-10:10 C Mária Kieferová: On The Power Of Coherently Controlled Quantum Adiabatic Evolutions ΞpdfΞ
10:10 Break and refreshment
10:40-11:25 I Giannicola Scarpa: Graphs, classical channels and nonlocality: the interplay   ΞΞΞCertain graph parameters, like the independence number and the chromatic number, can be redefined as nonlocal games. When the players of the game are allowed to share entanglement, we obtain the notion of quantum graph parameters. There are graphs for which such quantities exhibit a different behaviour. Interestingly, this property is reflected in zero-error information theory, where noisy classical channels are studied through their confusability graphs. We will see an application of this idea, but there is more: quantum graph parameters also help us in the study of nonlocality in general. We will see how every nonlocal game has a characteristic "game graph" and how different parameters provide information about the winning probability of quantum and classical strategies. ΞpdfΞ
11:25-11:50 C Rafael Chaves: An Entropic Approach to Causal Inference and Applications to Nonlocality and Machine Learning ΞpdfΞ
11:50-12:15 C Erkka Haapasalo: Boundariness and minimum-error discrimination ΞpdfΞ
12:20 Group photo
12:30 Lunch
15:00 CIPHER GAME (downtown part)
20:00 CIPHER GAME (monastery part)

SUNDAY, 08/06/2014
08:00 Breakfast (in your hotel)
Morning session (chaired by Mario Ziman)
09:00-09:45 I Ciara Morgan: Additivity and quantum channel capacity: an old problem revisited   ΞΞΞOne of the fundamental tasks in quantum information theory is to establish the capacity of noisy quantum channels, that is, the maximum rate at which information can be transmitted from one party to another over the channel with vanishing error. In this talk we focus on the task of classical information transmission and revisit the additivity problem, providing an overview of the current state and presenting new results involving the amplitude damping channel. Based on joint work with Tony Dorlas. ΞpdfΞ
09:45-10:10 C Tomáš Rybár: Estimation in presence of memory effects ΞpdfΞ
10:10 Break and refreshment
10:40-11:05 C Alessandro Tossini: The Feynman problem and Fermionic entanglement: Fermionic theory versus qubit theory ΞpdfΞ
11:05-11:30 C Richard Kueng: Stabilizer states are complex projective 3-designs ΞpdfΞ
11:30-11:55 C John Lapeyre: The role of local and global geometry in quantum entanglement percolation ΞpdfΞ
12:00 Lunch
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