Upcoming seminars

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.

Coherence power of quantum evolutions

Seminar date and time: 
2015-12-18 14:30
Author: 
María García Díaz
Affiliation: 
Ulm

The structure of the environment in which an open system is embedded determines its coherence capabilities. Whether these can result in any functional advantage remains an open question. The resource theory of coherence is a convenient framework to investigate these issues. Through the definition of the coherence power we will explore the ability of unitary operators to generate coherence. We will also introduce non-unitary time evolutions as quantum channels whose coherence capabilities it would be of interest to compute.

 

Criticality and general quantum correlations:
 Reasons to study quantum discord

Seminar date and time: 
2015-12-02 14:30
Author: 
Steve Campbell
Affiliation: 
School of Mathematics and Physics, Queen's University Belfast

The study of quantum correlations has significantly progressed in recent years. An interesting measure proposed, and one that still proves divisive, is the quantum discord. In this talk I will show some advantages that arise when discord and discord inspired measures of general quantum correlations are carefully put to good use. In particular when examining inherently quantum mechanical phenomena, i.e. quantum phase transitions in simple spin models.

Ultimate Limits of quantum metrology assisted by error correction and fast control

Seminar date and time: 
2015-11-24 14:30
Author: 
Michalis Skotiniotis
Affiliation: 
Institute for Theoretical Physics, University of Innsbruck

We consider ultimate limits on how precise a parameter, such as frequency or magnetic field strength, can be estimated in the presence of general noise.  We show that the usage of full quantum control, in particular of auxiliary systems and fast continuous quantum error correction, allows one to improve the achievable accuracy. When an overall Hamiltonian description is appropriate, we find that a quadratic improvement (Heisenberg scaling) is achievable for all kinds of noise except noise generated by the Hamiltonian to be estimated.

Non-local order in a fermionic chain with extended correlated hopping

Seminar date and time: 
2015-11-19 14:30
Author: 
Julia Stasińska
Affiliation: 
Postdoctoral Researcher ICFO - The Institute of Photonic Sciences

I will discuss a non-standard Hubbard model with next-nearest-neighbour correlated hopping which describes ultracold fermions in a one-dimensional, spin-dependent, optical lattice. We provide an exact non-trivial, solution to this many-body model, which is independent of known exact solutions in 1-d systems. The solution reveals the general properties of this system for arbitrary filling: exact and asymmetric spin-charge separation, a gapless spectrum of lowest energy excitations, a spin-gap and a non-vanishing string correlator, which signals the presence of the non-local order.

Location: 
(Sala de Graus II to be confirmed)
Contact: 
julia.stasinska@icfo.es

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