Upcoming seminars

Beating the shot-noise limit at finite temperatures with many-body systems

Seminar date and time: 
2016-03-16 14:30
Author: 
Mohammad Mehboudi
Affiliation: 
GIQ - UAB

Parameter estimation in strongly correlated systems is gaining an increasing attention, due to the crucial role of the value of such parameters in determining the (phase) behaviour of many body systems. In this work we deal with the estimation of coupling constants of such systems at finite temperatures. To this end we use tools from quantum metrology and find the ultimate precision of estimation allowed by quantum mechanics.

Markovianization of tripartite quantum states and its application to distributed quantum computation

Seminar date and time: 
2016-03-11 15:30
Author: 
Eyuri Wakakuwa
Affiliation: 
The University of Electro-Communications, Chofu (Japan)

We introduce a task that we call Markovianization, in which a tripartite quantum state is transformed to an approximate quantum Markov chain by a random unitary operation on one of the three subsystems. We consider an asymptotic limit of infinite copies and vanishingly small error, and define the Markovianizing cost as the minimum cost of randomness per copy required for the task.

The second law of quantum thermodynamics as an equality

Seminar date and time: 
2016-03-11 14:30
Author: 
Jonathan Oppenheim
Affiliation: 
University College London

The traditional second law of thermodynamics says that the average amount of work required to change one state into another while in contact with a heat reservoir,  must be at least as large as the change in free energy of the system. Here, we consider a fine-grained notion of the free energy, and show that in terms of it, the second law can be written as an equality. We also obtain a generalisation of the Jarzynski fluctuation theorem which holds for arbitrary initial states, not just the case of an initial thermal state. These can be derived from a fully quantum parent identity.

Channel adapted decoding strategies based on complementarity

Seminar date and time: 
2016-02-25 15:30
Author: 
Alvaro Piedrafita
Affiliation: 
ETH

Focus on recovering classical and phase information is a structured way of decoding. This complementarity decoder has shown high performance when tested with different kinds of codes, outperforming strategies based on recovering from errors. We hope that the structured nature of the recovery operation might lead to implementable decoding schemes.

Heisenberg-Weyl basis observables and their application in entanglement detection

Seminar date and time: 
2016-02-25 14:30
Author: 
Claudio Kloeckl
Affiliation: 
UAB - GIQ

Bloch vectors provide a very useful geometrical representation of quantum states for characterizing their properties. We establish a new basis of observables constructed by a suitable combination of the non-Hermitian generalization of the Pauli matrices, the Heisenberg-Weyl operators. This allows us to identify a (Hermitian) Bloch representation for an arbitrary density operator of finite, as well as infinite dimensional systems in terms of complete set of Heisenberg-Weyl observables.

Lecture on asymptotic geometric analysis

Seminar date and time: 
2016-02-24 14:30
Author: 
Cécilia Lancien
Affiliation: 
UAB - GIQ and Institut Camille Jordan, Université Claude Bernard Lyon 1

This lecture will revolve round some applications of asymptotic geometric analysis (fancy name, but don't worry it's not so terrible as it sounds!) in quantum information theory. Depending on the preferences of the audience, the main focus of the lecture could be on one of the following topics:

Detecting nonlocality in symmetric many-body systems

Seminar date and time: 
2016-02-17 14:30
Author: 
Rubén Quesada
Affiliation: 
GIQ - UAB

Intensive studies of entanglement properties have proven essential for our understanding of quantum many-body systems. In contrast, much less is known about the role of quantum nonlocality in these systems because the available multipartite Bell inequalities involve correlations among many particles, which are difficult to access experimentally. We will review multipartite Bell inequalities that involve only two-body correlations and show how they reveal the nonlocality in symmetric many-body systems relevant for nuclear and atomic physics.

Multiqubit Clifford groups are unitary 3-designs

Seminar date and time: 
2016-02-10 14:30 to 15:30
Author: 
Huangjun Zhu
Affiliation: 
Perimeter Institute for Theoretical Physics and Institute for Theoretical Physics, University of Cologne

We show that the multiqubit (including qubit) Clifford group in any even prime power dimension is not only a unitary 2-design, but also a unitary 3-design. Moreover, it is a minimal unitary 3-design except for dimension 4. As an immediate consequence, any orbit of pure states of the multiqubit Clifford group forms a complex projective 3-design; in particular, the set of stabilizer states forms a 3-design. By contrast, the Clifford group in any odd prime power dimension is only a unitary 2-design.

Location: 
GIQ seminar room

Necessity of Eigenstate Thermalization

Seminar date and time: 
2016-01-27 14:30
Author: 
Yoshifumi Nakata
Affiliation: 
UAB - GIQ

Understanding thermalization process is one of the central issues in the foundation of statistical mechanics. In recent years, several microscopic mechanisms of thermalization have been proposed such as canonical typicality and the eigenstate thermalization hypothesis (ETH). In this talk, I review PRL 115, 220401 (2015) by G. De Palma, A. Serafini, V. Giovannetti, and M. Cramer, which shows that the ETH is necessary and sufficient for thermalization (in some sense).

Identification of a quantum change point

Seminar date and time: 
2016-01-13 14:30
Author: 
Ramon Muñoz Tapia
Affiliation: 
UAB - GIQ

A source  assumed to prepare identical copies of a state suffers some internal alteration that makes it to start producing a different type of state.  We are interested in knowing when the change occurred assuming that it happens with equal probability at any point  of a string of N states. This an instance of multi-hypoteses discrimination for which very few results are known. I will review the optimality conditions and apply them for this task. I will compute the optimal asymptotic solution, and obtain a closed expression, which involve the use of some nice tricks.

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