New article: Reversing the thermodynamic arrow of time using quantum correlations

Title: Reversing the thermodynamic arrow of time using quantum correlations

Authors: Kaonan Micadei, John P. S. Peterson, Alexandre M. Souza, Roberto S. Sarthour, Ivan S. Oliveira, Gabriel T. Landi, Tiago B. Batalhão, Roberto M. Serra, Eric Lutz

Link: https://arxiv.org/abs/1711.03323

Abstract: The second law permits the prediction of the direction of natural processes, thus defining a thermodynamic arrow of time. However, standard thermodynamics presupposes the absence of initial correlations between interacting systems. We here experimentally demonstrate the reversal of the arrow of time for two initially quantum correlated spins-1/2, prepared in local thermal states at different temperatures, employing a Nuclear Magnetic Resonance setup. We observe a spontaneous heat flow from the cold to the hot system. This process is enabled by a trade off between correlations and entropy that we quantify with information-theoretical quantities.

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QM Talks@CBPF: Yelena Guryanova — 30.11, 16h00

Title: Thermodynamics of quantum systems with multiple conserved quantities

Speaker: Yelena Guryanova (IQOQI- Institute for Quantum Optics and Quantum Information)

Coordinates: room 601D, CBPF. 30.11, 16h00

Abstract: We consider a generalisation of thermodynamics that deals with multiple conserved quantities at the level of individual quantum systems. Each conserved quantity, which, importantly, need not commute with the rest, can be extracted and stored in its own battery. Unlike in standard thermodynamics, where the second law places a constraint on how much of the conserved quantity (energy) that can be extracted, here, on the contrary, there is no limit on how much of any individual conserved quantity that can be extracted. However, other conserved quantities must be supplied, and the second law constrains the combination of extractable quantities and the trade-offs between them which are allowed. We present explicit protocols which allow us to perform arbitrarily good trade-offs and extract arbitrarily good combinations of conserved quantities from individual quantum systems.

QM Talks@CBPF: David Jennings – 30.08, 16h00

The Olympic games are over, but Rio is still receiving many visitors. Among them, next week, we welcome David Jennings, from Imperial College London. David’s interests are really broad, ranging from foundational issues in quantum mechanics up to cosmology. From the micro up to the macro, his research also crosses quantum thermodynamics, and this is the subject he’ll tell us about in our next QM Talks@CBPF. See the description below, and see you there!

Title: Thermodynamics and quantum information theory

Speaker: David Jennings (Imperial College London)

Coordinates: room 601D (tentative), CBPF. 30.08, 16h00

Abstract: How do we separate finite-sized effects and stochasticity from genuinely non-classical features in thermodynamics? In the past two decades, quantum information science has developed a range of results designed to perform precisely this type of separation. While these results were originally motivated by computational, information-processing and foundational concerns, more recently there is increasing work that applies such techniques to thermodynamics.
Here I will describe such approaches and discuss their strengths and weaknesses. I will argue that present approaches are poorly suited to handling such topics as quantum phase transitions, however I will also argue that such approaches do provide new perspectives on the interplay between coherence and time-dependent processes, shed light on the role of non-commutativity and emphasize structural relations between thermodynamics and the theory of entanglement.

New Article: Experimental rectification of entropy production by a Maxwell’s Demon in a quantum system

Our NMR “quantum computer” is once again used to probe the foundations of quantum thermodynamics. The qig@CBPF, in collaboration with the quantum information group from the UFABC, were now able to create a quantum Maxwell’s Demon! See the details below, and check the full article here.

Title: Experimental rectification of entropy production by a Maxwell’s Demon in a quantum system

Authors: P. A. Camati, J. P. S. Peterson, T. B. Batalhão, K. Micadei, A. M. Souza, R. S. Sarthour, I. S. Oliveira, R. M. Serra

Abstract: Maxwell’s demon explores the role of information in physical processes. Employing information about microscopic degrees of freedom, this “intelligent observer” is capable of compensating entropy production (or extracting work), apparently challenging the second law of thermodynamics. In a modern standpoint, it is regarded as a feedback control mechanism and the limits of thermodynamics are recast incorporating information-to-energy conversion. We derive a trade-off relation between information-theoretic quantities empowering the design of an efficient Maxwell’s demon in a quantum system. The demon is experimentally implemented as a spin-1/2 quantum memory that acquires information, and employs it to control the dynamics of another spin-1/2 system, through a natural interaction. Noise and imperfections in this protocol are investigated by the assessment of its effectiveness. This realization provides experimental evidence that the irreversibility on a non-equilibrium dynamics can be mitigated by assessing microscopic information and applying a feed-forward strategy at the quantum scale.

QM Talks@CBPF: Roberto M. Serra – 18.05, 16h00

This week we have many guests visiting the qig@CBPF: Roberto Serra (UFABC), Thiago Batalhão (UFABC), and Cristhiano Duarte (UFMG). Serra and Thiago are here to fine tune some details about an experiment our NMR crew is performing; while Cristhiano is here to work in a project on quantum channels from coarse-grained dynamics in collaboration with Fernando de Melo (that’s me).

We take this chance and asked Serra to deliver a talk on his latest results (which by the way involve some collaboration with the qig@CBPF). See the details below. See you there.

Title: Irreversibility and Maxwell’s Demons in quantum systems

Speaker: Roberto M. Serra – UFABC

Coordinates: Auditorium 6th floor, CBPF. 18.05, 16h00

Abstract: Maxwell’s demon explores the role of information in physical processes. Employing information about microscopic degrees of freedom, this “intelligent observer” is capable of compensating entropy production (or extracting work), apparently challenging the second law of thermodynamics. In a modern standpoint, it is regarded as a feedback control mechanism and the limits of thermodynamics are recast incorporating information-to-energy conversion into fluctuation theorems. Endeavors to incorporate information into thermodynamics acquire a pragmatic applicability within the recent technological progress, where information just started to be manipulated at the micro and nano-scale. In this seminar, we will discuss the panorama of the Thermodynamics of Information at Quantum Scales. We will introduce a trade-off relation between information-theoretic quantities empowering the design of an efficient Maxwell’s demon in a quantum system. Moreover, an experimental implementation of the Demon will also be presented. Such a creature is materialised as a spin-1/2 quantum memory that acquires information, and employs it to control the dynamics of another spin-1/2 system, through a natural interaction in a NMR setup. This realisation provides experimental evidence that assessing microscopic information and applying a feed-forward strategy at the quantum scale can mitigate the irreversibility on a non-equilibrium dynamics.

Um dos primeiros experimentos na área de termodinâmica quântica

Resumo por Alexandre Martins de Souza (qig@CBPF)
Publicado no Informe CBPF

A termodinâmica é um ramo da física que permite a investigação de propriedades de equilíbrio de objetos macroscópicos. Com base em quantidades mensuráveis, como calor e trabalho, ela fornece uma estrutura universal para estudar a conversão de diferentes formas de energia. A termodinâmica foi introduzida há mais de um século, no início da revolução industrial, para analisar e melhorar o desempenho da máquina a vapor recém-inventada, e tem sido aplicada com sucesso desde então para projetar uma grande variedade de dispositivos tais como motores de automóveis e refrigeradores.

Atualmente, pesquisadores procuram entender a termodinâmica em objetos muitos pequenos, milhões de vezes menores que um centímetro, onde efeitos quânticos são relevantes.

Em estudo publicado na revista Physical Review Letters, pesquisadores do CBPF e colaboradores observaram pela primeira vez o trabalho realizado por um sistema quântico durante sua evolução. Como a mecânica quântica é inerentemente probabilística, não existe um único valor bem definido para o trabalho realizado por um sistema. Pelo contrário, teremos uma distribuição estatística dos possíveis valores de trabalho. Cada valor está associado a uma possível “trajetória” seguida pelo sistema quântico em sua evolução.

Leia o artigo: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.140601
O artigo foi escolhido como sugestão do editor!

Colloquium @CBPF: Paulo Henrique Souto Ribeiro — 30.09, 16h

Paulo H. S. Ribeiro, known to everyone as Paulão, is one of the most important figures for the quantum information community in Brazil. Paulão is the head (the arm, the leg, the heart!) of the Quantum Optics Laboratory at Federal University of Rio de Janeiro. His lab draws from close collaboration with the theoretical part of the quantum information group at UFRJ to be one of most well known groups in Brazil and worldwide.

Actually, one of the “secrets” of the quantum info group at UFRJ is that there is no such sharp distinction between theory and experiment. Of course at the end of the day there are those who will go align the mirrors and detectors, and those who will solve integrals and apply Cauchy-Schwartz whereever they can, but most of the times they are all mingled together, and the discussions fly high!

I can say that from first eye witness, as I did my PhD in this group. It was really exciting for a kid like me (at that time, at least) to be able to take part and contribute to the design of an experiment where we saw for the first time the dynamics of entanglement in an open quantum system in a very controlled way (article here). I still remember one day when I was showing Paulão the results we were getting for a two-qubits tomography and which were giving strange results. Paulão, without caring too much about my fancy Mathematica program for tomography, asked me to see the raw data file. These were just a bunch of numbers, I thought, with no real meaning… but for Paulão these numbers are the real thing, and he immediately realized that those results were not possible and suggested to swap two columns. When I did what he suggested, the reconstruction just popped out exactly as we expected. I couldn’t hold my self and shouted at Paulão: “Vai tomar no %$#” (something like “go f#$% yourself”), to which I immediately apologized, but that was out of a profound feeling of respect (and envy, I must confess) for his knowledge and understanding how things really work (this repeated many times, and still does, but I can hold myself better nowadays). We went back to the lab with Marcelo and Stephen and realized that we indeed had mixed up the label of some basis elements. After performing the experiment again, all results were perfect. Below is a picture I got during the realization of this experiment.

From left to right:  Stephen Walborn, Marcelo P. Almeida, Paulão, and Luiz Davidovich. Experimental setup to measure the entanglement dynamics for an open quantum system.

From left to right: Stephen Walborn, Marcelo P. Almeida, Paulão, and Luiz Davidovich. Experimental setup to measure the entanglement dynamics for an open quantum system.

I should emphasize that Paulão didn’t get the lab ready for him to “just” work out his ideas. He built everything from scratch. And I have the feeling that this is what he likes to do: to get a lab just starting and build it into a world class research facility. That might explain why he’s now moving from Rio (leaving the Lab at Steve’s very capable hands) to Florianópolis. I’m sure we won’t stop hearing from Paulão and his accomplishments… and we have a great excuse to go to Floripa every now and then!

It is thus more than timing that we invite Paulão for a colloquium at CBPF. It’s both an opportunity to learn once more from Paulão, and to thank him for being such unstoppable force pushing the Physics of (all) Brazil to ever better levels. See the information about Paulão’s colloquium below, and be sure to show up!

Thank you Paulão!!
(P.s.: If you have any story involving Paulão that you want/can share, or just want to thank him, please leave a comment below!)

Palestrante: Paulo Henrique Souto Ribeiro (UFRJ)

Título: Experimentos com Fótons Gêmeos: dos Fundamentos da Mecânica Quântica à Termodinâmica Quântica

Coordenadas: 30.09, 16h no auditório do 6º andar – CBPF

Resumo: Os fótons gêmeos produzidos na conversão paramétrica descendente espontânea foram produzidos pela primeira vez no início dos anos 1970. Inicialmente foram observadas correlações entre eles, das quais a correlação temporal é a mais marcante e leva à denominação “gêmeos” para o par de fótons. Eles possuem correlações quânticas naturais em seus graus de liberdade espaciais e de energia e tempo, podendo ser também preparados em estados emaranhados de polarização. Esta é a fonte de estados emaranhados mais simples e versátil que se conhece até hoje. Com estes pares de fótons e suas propriedades quânticas sem análogo clássico, foram feitos experimentos para estudar os fundamentos da Mecânica Quântica, testar algoritmos quânticos, implementar esquemas de computação e comunicação quântica e mais recentemente para a simulação de outros sistemas quânticos. Neste caso, eles começam a ter utilidade para o estudo da chamada Termodinâmica Quântica. Neste seminário, será feito um breve resumo das principais aplicações de fótons gêmeos e discutiremos experimentos recentes realizados na UFRJ para estudar correlações quânticas e para simulação de sistemas quânticos, abordando alguns aspectos termodinâmicos.