Upcoming seminars

Reversing unknown quantum transformations: A universal protocol for inverting general unitary operations

Seminar date and time: 
2019-07-10 12:00
Author: 
Marco Túlio Quintino
Affiliation: 
University of Tokyo

Given a general d-dimensional unitary operation for which, apart from the dimension, its description is unknown, is it possible to implement its inverse operation with a universal protocol that works for every unitary? How does the situation change when k uses of unitary operation  are allowed? In this paper we show that any universal protocol implementing the inverse of a general unitary with a positive heralded probability requires at least d−1 uses of this unitary.

Symmetries and inference in quantum information processing

Seminar date and time: 
2019-07-02 12:00
Author: 
Marco Fanizza
Affiliation: 
Scuola Normale Superiore, Pisa

I will present new results on the problem of estimating the overlap of two arbitrary quantum states in any finite dimension, given any number of copies of each of them. This problem is of wide interest for applications in quantum technologies and our study provides a full characterization of the optimal strategy, as well as several natural (sub-optimal) strategies including the widely used swap-test. I will also review a powerful graphical method based on the recoupling theory of SU(2), which proved very useful for our study. 

Location: 
Contact: 

Qubit channel parameter estimation with very noisy initial states

Seminar date and time: 
2019-06-21 12:00
Author: 
David Collins
Affiliation: 
Colorado Mesa University

The issue of optimally estimating parameters associated with quantum channels has been thoroughly studied in various contexts, yielded an enhancement of accuracy using resources such as entangled states. For various qubit channels, using the quantum Fisher information per channel invocation as a measure of the estimation accuracy, optimal estimation protocols and the possible advantages that they might yield are well understood. However, these resulting optimal estimation protocols usually require pure initial states.

Location: 
GIQ Seminar Room
Contact: 
dacollin@coloradomesa.edu

Contextual advantage for state-dependent cloning

Seminar date and time: 
2019-05-27 12:00
Author: 
Gabriel Senno
Affiliation: 
ICFO, Barcelona

A number of noncontextual models exist which reproduce different subsets of quantum theory and admit a no-cloning theorem. Therefore, if one chooses noncontextuality as one's notion of classicality, no-cloning cannot be regarded as a nonclassical phenomenon. However, in the work that I'll present in this talk, we show that the phenomenology of quantum state cloning is indeed nonclassical, but not for the reasons usually given.

Location: 
GIQ Seminar Room (C5/262)
Contact: 
Gabriel.Senno@icfo.eu

Introduction to Blockchain

Seminar date and time: 
2019-05-02 12:00
Author: 
Luis Muñoz-Tapia
Affiliation: 
Universitat Politécnica de Catalunya

Blockchain technologies are beginning to mature and  are triggering great interest both in academic and industrial fields. At the technical level, the Blockchain
incorporates concepts from different areas of knowledge such as computer networks, distributed systems, consensus algorithms, security and cryptography,
programming and game theory to create a state machine equally shared among many entities. In this talk I will start by describing a classical centralized

Location: 
GIQ Seminar Room
Contact: 
jose.munoz@entel.upc.edu

Entanglement negativity as a universal non-Markovianity witness

Seminar date and time: 
2019-04-25 12:00
Author: 
Janek Kolodynski
Affiliation: 
University of Warsaw

In order to engineer an open quantum system and its evolution, it is essential to identify and control the memory effects. These are formally attributed to the non-Markovianity of dynamics that manifests itself by the evolution being indivisible in time, a property which can be witnessed by a non-monotonic behavior of contractive functions or correlation measures. We show that by monitoring directly the entanglement behavior of a system in a tripartite setting it is possible to witness all invertible non-Markovian dynamics, as well as all (also non-invertible) qubit evolutions.

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