Title: Experimental characterization of a spin quantum heat engine
Authors: John P. S. Peterson, Tiago B. Batalhão, Marcela Herrera, Alexandre M. Souza, Roberto S. Sarthour, Ivan S. Oliveira, Roberto M. Serra
Abstract: Developments in the thermodynamics of small quantum systems envisage non-classical thermal machines. In this scenario, energy fluctuations play a relevant role in the description of irreversibility. We experimentally implement a quantum heat engine based on a spin-1/2 system and nuclear magnetic resonance techniques. Irreversibility at microscope scale is fully characterized by the assessment of energy fluctuations associated with the work and heat flows. We also investigate the efficiency lag related to the entropy production at finite time. The implemented heat engine operates in a regime where both thermal and quantum fluctuations (associated with transitions among the instantaneous energy eigenstates) are relevant to its description. Performing a quantum Otto cycle at maximum power, the proof-of-concept quantum heat engine is able to reach an efficiency for work extraction (η≈42%) very close to its thermodynamic limit (η=44%).
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
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.
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.
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.
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.
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.
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!