Upcoming seminars

On Landau-Zener transitions for dephasing Lindbladians

Seminar date and time: 
2018-02-15 15:00
Author: 
On Landau-Zener transitions for dephasing Lindbladians
Affiliation: 
ETH, Zurich

We consider a driven open system whose evolution is described by a Lindbladian. The Lindbladian is assumed to be dephasing and its Hamiltonian part to be given by the Landau-Zener Hamiltonian. We derive a formula for the transition probability which, unlike previous results, extends the Landau-Zener formula to open systems

Location: 
GIQ Seminar Room C5/262
Contact: 
michail.skoteiniotis@uab.cat

Estimating the decoherence time using quantum functional inequalities

Seminar date and time: 
2018-02-15 12:00
Author: 
Ivan Bardet
Affiliation: 
Institut des Hautes Études Scientifiques, Université Paris-Saclay, France

Environment Induced Decoherence is a physical concept which provides a dynamical explanation to the disappearance of quantum phenomenon in the real world. Intuitively, it states that a quantum system is never per- fectly isolated, so that quantum correlations disappear due to the action of the environment on the system. Focusing on finite-dimensional quantum systems undergoing Markovian evolutions, we propose natural generaliza- tions of certain non-commutative functional inequalities that are adapted to the study of decoherence.

Location: 
GIQ Seminar Room C5/262
Contact: 
michail.skoteiniotis@uab.cat

Lower bounds on the quantum Fisher information based on the variance and various types of entropies

Seminar date and time: 
2018-01-10 12:00
Author: 
Geza Toth
Affiliation: 
University of the Basque Country

We examine important properties of the difference between the variance
and the quantum Fisher information over four, i.e., (ΔA)2−FQ[ϱ,A]/4.
We find that it is equal to a generalized variance defined in Petz [J.
Phys. A 35, 929 (2002)] and Gibilisco, Hiai, and Petz [IEEE Trans.
Inf. Theory 55, 439 (2009)]. We present an upper bound on this
quantity that is proportional to the linear entropy. As expected, our
relations show that for states that are close to being pure, the
quantum Fisher information over four is close to the variance. We also

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Matrix Product States: Irreducible forms and Continuum limits

Seminar date and time: 
2017-12-18 12:00
Author: 
Gemma de las Cuevas
Affiliation: 

This talk will consist of two parts. In the first part, 
I will present the irreducible form of a Matrix Product States (MPS),
which is a generalization of the canonical form of an MPS in the 
sense that it is also defined for states with periodicity. I will 
then present a fundamental theorem for MPS in irreducible form, 
namely one that specifies how two tensors in irreducible form are 
related if they give rise to the same MPS. Finally, I will present
two applications of this result: an equivalence between the 

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Generalized entanglement entropies of quantum designs

Seminar date and time: 
2017-11-15 12:00
Author: 
Zi-Wen Liu
Affiliation: 
Massachusetts Institute of Technology USA

The entanglement properties of random quantum states or dynamics are important to the study of a broad spectrum of disciplines of physics, ranging from quantum information to condensed matter to high energy. Ensembles of quantum states or unitaries that reproduce the first t moments of completely random states or unitary channels (drawn from the Haar measure) are called t-designs.  Entropic functions of the t-th power of a density operator are called t-entropies (e.g. Renyi and Tsallis).

Location: 
GIQ Seminar Room C5/262
Contact: 
michail.skoteniotis@uab.cat

Classical Simulation of Bosonic Circuits

Seminar date and time: 
2017-11-14 12:00
Author: 
Saleh Rahimi-Keshari
Affiliation: 
Leibniz University (Germany)

It is generally believed that quantum computers can perform certain tasks faster than their classical counterparts. Identifying the resource that potentially enables this speedup is of particular interest in quantum information science. In this talk, by using the well-developed theory of phase-space quasiprobability distributions, I present two sufficient conditions for efficient classical simulation of quantum-optics experiments. These conditions show that the negativity of the phase-space quasiprobability distributions is an essential resource for quantum speedup.

Location: 
GIQ Seminar Room C5/262
Contact: 
michail.skoteniotis@uab.cat

Non-classical correlations in quantum mechanics and beyond

Seminar date and time: 
2017-10-31 10:30
Author: 
Ludovico Lami
Affiliation: 
UAB, Barcelona

This thesis is concerned with a seemingly naive question: what happens when you separate two physical systems that were previously together? One of the greatest discovery of the last century is that systems that obey quantum mechanical instead of classical laws remain inextricably linked even after they are physically separated, a phenomenon known as entanglement. This leads immediately to another, deep question: is entanglement an exclusive feature of quantum systems, or is it common to all non-classical theories?

Location: 
GIQ Seminar Room
Contact: 
michail.skoteiniotis@uab.cat

Quantum estimation of unknown parameters

Seminar date and time: 
2017-10-25 14:30
Author: 
Esteban Martínez Vargas
Affiliation: 
GIQ

There seems to be a persistent problem in the field of Quantum Metrology: Quantum Fisher Information is well defined only for an infinite amount of resources, via an adaptive measurement scheme. We state a theoretical framework that avoids this issue, which is based on a Bayesian parameter estimation scheme. Although the Bayesian approach have already been made in the field, we introduced a modified bound which entails taking the maximization over all POVMs for the Van Trees Information instead of the Fisher Information (i.e.

Location: 
GIQ Seminar Room
Contact: 
michail.skoteiniotis@uab.cat

How to gauge general quantum processes?

Seminar date and time: 
2017-10-16 16:00
Author: 
Cristina Cirstoiu
Affiliation: 
Imperial College

Gauge theories are fundamental in our understanding of the laws of nature. The formalism emerges from the concept of symmetry and exploits redundant degrees of freedom. One can easily gauge Lagrangians by extending the global invariance to a local one at the expense of introducing gauge fields with suitable transformation properties. More recently in the context of many body theory it has been shown how to gauge pure quantum states. How can we gauge general quantum processes?

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