New article: Experimental characterization of a spin quantum heat engine

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

link: https://arxiv.org/abs/1803.06021

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%).

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New article: Quantum Walks via Quantum Cellular Automata


Title: Quantum Walks via Quantum Cellular Automata

Authors: Pedro C.S. Costa (CBPF), Renato Portugal (LNCC), Fernando de Melo (CBPF)

Link: https://arxiv.org/abs/1803.02176

Abstract: Very much as its classical counterpart, quantum cellular automata are expected to be a great tool for simulating complex quantum systems. Here we introduce a partitioned model of quantum cellular automata and show how it can simulate, with the same amount of resources (in terms of effective Hilbert space dimension), various models of quantum walks. All the algorithms developed within quantum walk models are thus directly inherited by the quantum cellular automata. The latter, however, has its structure based on local interactions between qubits, and as such it can be more suitable for present (and future) experimental implementations.

QM Talks@CBPF: Ivan de Oliveira, HOJE, 16h

Title: ‘Q-bits supercondutores’

Speaker: Ivan de Oliveira (CBPF)

Coordinates: room 601C, CBPF. 28.02, 16h00

Abstract: O ano de 2017 pode entrar para a história da computação e da tecnologia (e também da física!) como aquele em que os computadores quânticos superaram as possibilidades computacionais das máquinas clássicas, um marco que está sendo chamado ‘supremacia quântica’.

A razão para isso foi o anúncio feito pela empresa IBM, em novembro do ano passado, da construção de um chip quântico contendo 50 q-bits (50 bits quânticos), baseado na tecnologia de supercondutores.

A despeito de um inevitável grau de sensacionalismo midiático, os esforços, agora, concentram-se, por um lado, em se demonstrar que, de fato, tal supremacia ocorreu e, por outro, tornar essa tecnologia acessível ao usuário comum.

Neste seminário, serão apresentados os três tipos de q-bits supercondutores, como eles se acoplam em um chip passível de escalonamento, bem como a plataforma da IBM.

New article: Quantum Algorithm for Simulating the Wave Equation

Title: Quantum Algorithm for Simulating the Wave Equation

Authors: Pedro C.S. Costa (CBPF), Stephen Jordan (NIST/Maryland), Aaron Ostrander (Maryland)

Link: https://scirate.com/arxiv/1711.05394

Abstract: We present a quantum algorithm for simulating the wave equation under Dirichlet and Neumann boundary conditions. The algorithm uses Hamiltonian simulation and quantum linear system algorithms as subroutines. It relies on factorizations of discretized Laplacian operators to allow for improved scaling in truncation errors and improved scaling for state preparation relative to general purpose linear differential equation algorithms. We also consider using Hamiltonian simulation for Klein-Gordon equations and Maxwell’s equations.

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.

QM Talks@CBPF: Pedro C. da Silva — 11.10, 16h00

Next in our series QM Talks@CBPF is a talk by Pedro C. da Silva, PhD student here at CBPF. In this talk Pedro will show some interesting results he got during his stay in Maryland, collaborating with the group of Prof. Stephen P. Jordan. Be sure to be there! Details follow.

Title: Quantum Algorithm for Simulating the Wave Equation

Speaker: Pedro C. da Silva (CBPF)

Coordinates: room 601C, CBPF. 11.10, 16h00

Abstract: We present a quantum algorithm for simulating the wave equation under Dirichlet and Neumann boundary conditions. The algorithm uses Hamiltonian simulation and quantum linear system algorithms as subroutines. It relies on factorizations of discretized Laplacian operators to allow for improved scaling in truncation errors and improved scaling in state preparation relative to general purpose linear differential equation algorithms. We also consider using Hamiltonian simulation for Klein-Gordon equations and Maxwell’s equations.

New article: Emerging Dynamics Arising From Quantum Mechanics

Title: Emerging Dynamics Arising From Quantum Mechanics

Authors: Cristhiano Duarte (UFMG), Gabriel Dias Carvalho (CBPF), Nadja K. Bernades (UFMG), Fernando de Melo (CBPF)

Link: https://arxiv.org/abs/1705.01604

Abstract: Physics dares to describe Nature from elementary particles all the way up to cosmological objects like cluster of galaxies and black holes. Although a unified description for all this spectrum of events is desirable, an one-theory-fits-all would be highly impractical. To not get lost in unnecessary details, effective descriptions are mandatory. Here we analyze what are the dynamics that may emerge from a fully quantum description when one does not have access to all the degrees of freedom of a system. More concretely, we describe the properties of the dynamics that arise from Quantum Mechanics if one has only access to a coarse grained description of the system. We obtain that the effective channels are not necessarily of Kraus form, due to correlations between accessible and non-accessible degrees of freedom, and that the distance between two effective states may increase under the action of the effective channel. We expect our framework to be useful for addressing questions such as the thermalization of closed quantum systems, and the description of measurements in quantum mechanics.