Minicourse on Quantum Entanglement: From Quantum Information to Many-Body Physics and Beyond (20-24/08 @ ICTP/SAIFR-UNESP, São Paulo)

From 20 to 24 of August, 2018, at ICTP/SAIFR-UNESP, in São Paulo.

Professor Fernando Brandão (CalTech) and Dr. Burak Sahinoglu (Caltech, USA) will deliver a one-week mini-course on quantum many-body entanglement.

Mini-course on quantum entanglement and many-body physics

The course will be open (no registration fee) to post-graduate students (or postdocs) working on quantum information, or connected areas (e.g., condensed matter physics, statistical mechanics, and high energy physics).

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New paper & talk @UFF: Witnessing genuine multi-photon indistinguishability

Daniel Brod and I (Ernesto Galvão) have recently posted a new preprint on the arxiv, the latest result of our long-standing collaboration with the experimental group of Fabio Sciarrino at Sapienza University of Rome. I’ll be giving a talk about it next Friday, April 20th, at 11.00 in room A5-01, come if you can!

The paper describes a way to test whether a set of single-photon sources is producing a state of n genuinely indistinguishable photons, as opposed to some convex combination of states in which effectively less than n photons interfere. As it turns out, this question can be motivated by a simple logic problem, as I explain below. Then I briefly describe how the Rome lab experimentally tested our idea. Read the rest of this entry »


Work on semi-quantum instrumental causal networks in PRL Editor´s suggestion

Joint theoretical-experimental work of researchers Ranieri V. Neri and Marcio M. Taddei (both at Federal University of Rio de Janeiro), Rafael Chaves (IIP-Natal), and Leandro Aolita (Federal University of Rio de Janeiro & ICTP/SAIFR-São Paulo) published in PRL as Editor´s Suggestion:

Quantum Steering Beyond Instrumental Causal Networks

We theoretically predict, and experimentally verify with entangled photons, that outcome communication is not enough for hidden-state models to reproduce quantum steering. Hidden-state models with outcome communication correspond, in turn, to the well-known instrumental processes of causal inference but in the one-sided device-independent scenario of one black-box measurement device and one well-characterized quantum apparatus. We introduce one-sided device-independent instrumental inequalities to test against these models, with the appealing feature of detecting entanglement even when communication of the black box’s measurement outcome is allowed. We find that, remarkably, these inequalities can also be violated solely with steering, i.e., without outcome communication. In fact, an efficiently computable formal quantifier—the robustness of noninstrumentality—naturally arises, and we prove that steering alone is enough to maximize it. Our findings imply that quantum theory admits a stronger form of steering than known until now, with fundamental as well as practical potential implications.


Work on quantum violation of an instrumental test in Nature Physics.

Quantum weirdness alters basic cause-effect relations

Joint Brazilian-Italian work, reported in Nature Physics, demonstrates unexpected quantum effects in the simplest causal-inference scenario.

https://www.nature.com/articles/s41567-017-0008-5

Why do things happen? What causes Nature to behave the way we observe it to? These are among the most fundamental questions in science and philosophy. The instrumental causal structure is the simplest one where causal influences can be detected in the presence of hidden common causes and without interventions, i.e. from observations alone. All classical instrumental causal models satisfy fundamental constraints known as instrumental inequalities. Up to now, it was believed that the violation of such inequalities unambiguously certified that the causal model is not an instrumental one. Defying this well established paradigm, a young team of physicists has shown that the presence of quantum entanglement in instrumental causal models can both fake causal influences as well as lead to violations of instrumental inequalities, something impossible classically.

Brazilian-based Profs. Rafael Chaves, from the International Institute of Physics at Natal, and Leandro Aolita, from the Federal University of Rio de Janeiro and ICTP/SAIFR São Paulo, together with an Italian-based team led by Prof. Fabio Sciarrino, from Sapienza University Rome, studied quantum instrumental causal models. The Brazilian-Italian team theoretically predicted and experimentally confirmed that entanglement can not only enhance the descriptive power of instrumental models but also even lead to violations of instrumental inequalities. The discovery shakes fundamental pillars of the field of causal inference. In addition, it is also relevant to the foundations of quantum theory itself, since the instrumental scenario is simpler than the paradigmatic Bell scenario commonly used to observe the mismatch between quantum and classical predictions. In fact, the instrumental causal structure is the simplest one where a gap between classical and quantum predictions is possible, as the team has now confirmed.

Besides the fundamental relevance, the results may also find applications in practical information-processing tasks. This is due to the fact that the discovered quantum violations of instrumental inequalities define a novel form of quantum nonlocality, stronger than nonlocal hidden-variable models that include one-way communication of measurement outomes between the parties involved. This may be relevant, e.g., in cryptographic or randomness-generation protocols without the need for experimentally ensuring large spatial separations. A brand-new venue for theoretical and experimental exploration in a relatively simple scenario is opened.

To end up with, it is important to highlight that the research was carried out during one of the worst science-budget cuts in Brazil’s recent history. The collaboration with the Italian experimental team was crucial in this sense. This is a story of success in difficult times, and shows that it is still possible to produce top-quality science in Brazil if resources are given. Unfortunately, the Brazilian government has proposed to deepen the budget cut even more. If the current situation is not reverted, this type of success stories is in serious danger.

 

 

 

 

 

 

 

 

 

 

 


Work on resource theory of quantum contextuality in PRL

Joint work of Profs. Barbara Amaral (Federal University of Ouro Preto & IIP-Natal), Adán Cabello (University of Sevilla), Marcelo T. Acunha (UNICAMP-Campinas), and Leandro Aolita (Federal University of Rio de Janeiro & ICTP/SAIFR-São Paulo) published in PRL:

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.130403

Contextuality is a fundamental feature of quantum theory and is necessary for quantum computation and communication. Serious steps have therefore been taken towards a formal framework for contextuality as an operational resource. However, the most important component for a resource theory – a concrete, explicit form for the free operations of contextuality – was still missing. Here we provide such a component by introducing noncontextual wirings: a physically-motivated class of contextuality-free operations with a friendly parametrization. We characterize them completely for the general case of black-box measurement devices with arbitrarily many inputs and outputs. As applications, we show that the relative entropy of contextuality is a contextuality monotone and that maximally contextual boxes that serve as contextuality bits exist for a broad class of scenarios. Our results complete a unified resource-theoretic framework for contextuality and Bell nonlocality.


Talk @UFRJ, Celso Villas Boas, Monday 16/04, 15H30

The Quantum Optics and Information Group (UFRJ) is proud to announce next week’s seminar, which will be given by Celso Villas Boas (UFSCar). We invite all to come!

See the details of the talk below:

MONDAY, April 16th, at 15H30
in room 343 (3rd floor of block A of the Technology Center building)

“Transparência eletromagneticamente induzida e suas aplicações em teoria da informação quântica”
Celso Villas Boas (UFSCar)

Abstract:
Neste seminário vou abordar recentes estudos desenvolvidos em nosso grupo sobre transparência eletromagneticamente induzida (EIT) [1], isto é, a capacidade de se tornar transparente um meio inicialmente opaco a um certo campo via algum agente controlador externo, por exemplo um campo laser. Vou discutir alguns aspectos fundamentais como os análogos clássicos da EIT [2,3], embora nem todos os aspectos possam ser reproduzidos classicamente [3], e como o decaimento assimétrico do estado excitado em experimentos com sistemas de três níveis em configuração Lambda [4] influencia as propriedades ópticas do meio. Também vou discutir aplicações da EIT em teoria da informação quântica, por exemplo memórias quânticas [5] e implementação de portas lógicas [6].

[1] M. Fleischhauer, A. Imamoglu, and J. P. Marangos, Reviews of Modern Physics 77, 633 (2005).
[2] C. L. Garrido-Alzar, M. A. G. Martinez, and P. Nussenzveig, American Journal of Physics 70, 37 (2002).
[3] J. A. Souza, L. Cabral, R. R. Oliveira, and C. J. Villas-Boas, Physical Review A 92, 023818 (2015).
[4] H. S. Borges, M. H. Oliveira, and C. J. Villas-Boas, Scientific Reports 7, 7132 (2017).
[5] H. P. Specht, C. Nolleke, A. Reiserer, M. Uphoff, E. Figueroa, S. Ritter, and G. Rempe, Nature 473, 190 (2011).
[6] H. S. Borges and C. J. Villas-Boas, Physical Review A 94, 052337 (2016).
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You can incorporate our calendar to your Google Calendar and have information about all the confirmed seminars using this link.


Talk @UFF, Allan Tosta, Friday April 13th, 11.00

This week’s talk at the Infoptics group at UFF will be given by Allan David Tosta, who’ll be talking about “Origem conceitual da estatística fracionária”. The seminar will take place next Friday, April 13th at 11.00 in room A5-01, and all are welcome to attend! For an abstract, please see below. Read the rest of this entry »