10th Central European Quantum Information Processing Workshop
5-9 June 2013, Valtice, Czech Republic

I = invited (7x), C = contributed (22x)

WEDNESDAY, 05/06/2013
16:00-17:00 Registration and refreshment
Afternoon session (chaired by Mario Ziman)
17:00-17:45 I Marcus Cramer: Quantification of entanglement using simple measurements   ΞΞΞI will report on some recent results concerning ways to quantify entanglement in many-body systems. At the hand of experimentally available systems, I will demonstrate how already available measurements can suffice to quantify the amount of entanglement: Given a set of observables, we consider all density matrices that are compatible with measured expectation values of these observables. Amongst these density matrices, we find the one with the least amount of entanglement as quantified by a suitable entanglement measure. In this way, we determine a lower bound on the entanglement that must have been present in the state that gave rise to the observations. Examples will include results on a recent experimental quantification of the entanglement of bosons in optical lattices.
17:45-18:10 C Tomáš Rybár: Propagation and spectral properties of quantum walks in electric fields
18:15-18:40 C Miguel Navascues: How energy conservation limits our measurements

THURSDAY, 06/06/2013
08:00 Breakfast
Morning session (chaired by Andreas Winter)
09:00-09:45 I Fernando Brandao: Product-state approximations to quantum ground states   ΞΞΞCANCELLED. In the talk I will present recent results showing new bounds on the usefulness of product states for approximating the groundenergy of quantum local Hamiltonians. I will show applications of the bounds to the quantum PCP conjecture and to obtaining new algorithms for computing the mean-energy of certain classes of Hamiltonians (such as planar and dense models). Based on joint work with Aram Harrow.
09:15-09:40 C Daniel Reitzner: Fault-ignorant Quantum Search
09:45-10:10 C Mark Howard: Negativity, Contextuality and Universal Quantum Computation
10:15-10:45 Break and refreshment
10:45-11:10 C David Reeb: (Im-)Proving Landauer's Principle Ξ pdf Ξ
11:15-11:40 C Lea Kraemer: Generalized Entropies
11:45-12:10 C Lídia Del Rio: Relative thermalization
12:15 Lunch

FRIDAY, 07/06/2013
08:00 Breakfast
Morning session (chaired by David Reeb)
09:00-09:45 I Andris Ambainis: The power of exact quantum algorithms   ΞΞΞA quantum algorithm is exact if, on any input data, it outputs the correct answer with certainty (probability 1). We present the first example of a Boolean function f(x_1, ..., x_N) for which exact quantum algorithms have superlinear advantage over the deterministic algorithms. Any deterministic algorithm that computes our function must use N queries but an exact quantum algorithm can compute it with O(N^{0.8675...}) queries. We also present two other new exact quantum algorithms for EXACT_k and THRESHOLD_k functions (i.e. determining whether the number of input bits that are equal to 1 is equal to k or at least k) which are faster than any classical algorithm. Based on arxivs: 1211.0721 and 1302.1235. The second part is joint work with Jānis Iraids and Juris Smotrovs.
09:45-10:10 C Valerio Scarani: Super-polynomial complex quantum states Ξ pdf Ξ
10:15-10:45 Break and refreshment
10:45-11:10 C Marcin Pawlowski: Amplification of arbitrarily weak randomness
11:15-11:40 C Gonzalo de La Torre: Certifying that a process is as intrinsically random as it is observed to be
11:45-12:10 C Phuc Thinh Le: Properties of the random seed input to Bell tests
12:30 Lunch
Afternoon Session (chaired by Matyas Koniorczyk)
14:30-15:30 T Jan Bouda: Classical zero-error communication over classical and quantum channel   ΞΞΞOne of the main questions of information theory is whether it is possible to communicate information through a (particular) noisy channel with a zero probability of error, and what is the bit rate one can achieve. In this tutorial I’ll present the basic analysis of the scenario, namely the communication of classical information through a noisy channel (memoryless, both classical and quantum), without feedback or entanglement.
15:30-15:55 C Marcin Jarzyna: Matrix product states for quantum metrology
16:00-16:30 Break and Refreshemnt
16:30-17:15 I Andreas Winter: Zero-error quantum communication - the role of non-local resources   ΞΞΞEntanglement, and more generally non-local correlations, are among the most fascinating aspects of quantum theory. Their fundamental manifestation is in the violation of Bell inequalities, but it is well-known that they also enhance the communication capabilities of channels. In particular zero-error communication (originally developed by Shannon in 1956, it continues to inspire work in combinatorics) offers a rich field of study of different non-local effects: The zero-error capacity of classical channels is enhanced by entanglement, and even more by general no-signalling correlations. This is in contrast to the ordinary, Shannon, capacity of the channel, and can be related to so-called pseudo-telepathy games. I will report on recent developments in the zero-error information theory of quantum channels, assisted by entanglement, feedback and general no-signalling correlations. [Joint work Runyao Duan and Simone Severini.] Ξ pdf Ξ
17:15-17:45 C Stefan Baeuml: Limitations on quantum privacy swapping
18:00 MUSEUM of TORTURE excursion

SATURDAY, 08/06/2013
08:00 Breakfast
Morning session (chaired by Andris Ambainis)
09:00-09:45 I Daniel Nagaj: Quantum 3-SAT is QMA_1-complete   ΞΞΞTogether with David Gosset we finally managed to prove that Q-3-SAT is a quantumly-tough nut to crack (and not only NP-complete). The talk will be about basic clocks, more involved clocks, and complicated clocks consisting each of several clocks, with all of them running in parallell (in 2D). We will also discuss how hard it is to bring something 1-epsilon to exactly 1, which is why we have to keep writing the annoying subscript in QMA_1 for now.
09:45-10:10 C Piotr Cwiklinski: The Power of Noisy Fermionic Quantum Computation
10:15 Break and refreshment
10:45-11:30 I Ramon Munoz Tapia: Improve your estimation by abstaining...   ΞΞΞKnowing the state of a system is a key task in quantum information processing. An unknown quantum state can only be unveiled by means of measurements. The aim is then to find the measurement protocol that yields the best estimate of a family of input states. I will analyse the effects of introducing the possibility of giving an inconclusive estimate or abstain. This approach can be of interest when the standard protocol fails to achieve the minimum standard of performance required for some specific task, but some number of inconclusive responses, or abstentions, is affordable. I first discuss the discrimination problem with abstention, where it is somehow a natural ingredient. I then present the issue of parameter estimation (phase and direction) with general pure states of an arbitrary number N of qubits. For large N the problem is formulated in the continuous as a minimisation of certain action for which analytical expressions can be obtained. I will show that abstention enable drastic improvements, up to the extent of attaining the Heisenberg limit. I finally discuss the estimation in noisy settings and show that abstention does not enable to surpass the recent bounds on the unattainability of the Heisenberg scaling. This talk is based on the papers: Phys. Rev. A 86, 040303 (2012), New J. Phys. 14 105015 (2012), Phys. Rev. Lett. 110, 100501 (2013).
11:30-11:55 C Michal Sedlák: Optimal discrimination of quantum measurements Ξ pdf Ξ
12:00 Lunch
Afternoon Session (chaired by Valerio Scarani)
14:00-14:45 I Marcus Huber: On the role of entanglement in quantum thermodynamics   ΞΞΞUnderstanding the thermodynamics of quantum systems is of fundamental importance, from both theoretical and experimental perspectives. We will introduce and analyze two exemplary model systems that provide an ideal test-bed for exploring quantum thermodynamics. So far, however, the importance of quantum effects in these systems has remained elusive. We first briefly review a framework of entanglement quantification and use it to show that entanglement, the paradigmatical quantum effect, is connected to the task of extracting work from quantum batteries. More importantly we reveal that it plays a fundamental role in small self-contained quantum refrigerators, as it can enhance cooling and energy transport -- except notably when the efficiency is close to the Carnot limit. Hence a truly quantum refrigerator can outperform a classical one. Furthermore, the amount of entanglement alone quantifies the enhancement in cooling. More generally, our work shows that entanglement opens new possibilities in thermodynamics.
14:45-15:10 C Margherita Zuppardo: Experimental distribution of entanglement via separable states
15:15-15:45 Break and Refreshemnt
15:45-16:10 C Marcin Zwierz: Universality of the Heisenberg Limit Ξ pdf Ξ
16:15-16:40 C Janek Kolodynski: Efficient tools for quantum metrology with decoherence Ξ pdf Ξ
16:45 Group photo
17:00-19:00 Poster session
19:00-23:00 CIPHER GAME

SUNDAY, 09/06/2013
08:00 Breakfast
Morning session (chaired by Ramon Munoz Tapia)
09:00-09:25 C Teiko Heinosaari: Qualitative Noise-Disturbance Relation for Quantum Measurements
09:30-09:55 C Peter Rapčan: Direct estimation of decoherence parameters
10:00-10:30 Break and refreshment
10:30-10:55 C Alex Monras: Learning Quantum Markov Chains: The Completely-Positive Realization Problem
11:00-11:25 C Mária Kieferová: Quantum Walks on Necklaces and Mixing
11:30-11:55 C Nikolay Nahimov: Grover's algorithm with faulty and non-faulty marked items Ξ pdf Ξ
12:00 Lunch
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