
Inducing nontrivial qubit coherence through a controlled dispersive environment
Wallace S. Teixeira, Fernando Nicacio, Fernando L. SemiãoWe show how the dispersive regime of the JaynesCummings model may serve as a valuable tool to the study of open quantum systems. We employ it in a bottomup approach to build an environment that preserves qubit energy and induces varied coherence dynamics. We then present the derivation of a compact expression for the qubit coherence, applied here to the case of a finite number of thermally populated modes in the environment. We also discuss how the model parameters can be adjusted to facilitate the production of shorttime monotonic decay (STMD) of the qubit coherence. Our results provide a broadly applicable platform for the investigation of energyconserving open system dynamics which is fully within the grasp of current quantum technologies.

Experimental characterization of a spin quantum heat engine
John P. S. Peterson, Tiago B. Batalhão, Marcela Herrera, Alexandre M. Souza, Roberto S. Sarthour, Ivan S. Oliveira, Roberto M. SerraarXiv:1803.06021 (2018)Developments in the thermodynamics of small quantum systems envisage nonclassical 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 spin1/2 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 proofofconcept quantum heat engine is able to reach an efficiency for work extraction (η≈42%) very close to its thermodynamic limit (η=44%).

Workinduced constrained quantum dynamics
André M. Timpanaro, Sascha Wald, Fernando Semião, Gabriel T. LandiarXiv:1807.04374 (2018)In classical mechanics, external constraints on the dynamical variables can be easily implemented within the Lagrangian formulation and form the basis for several interesting mechanical phenomena and devices. Conversely, the extension of this idea to the quantum realm, which dates back to Dirac, has proven notoriously difficult due to the noncommutativity of observables. Motivated by recent progress in the experimental control of quantum systems, we propose here an implementation of quantum constraints based on the idea of work protocols, which are dynamically engineered to enfore the constraints. As a proof of principle, we consider a quantum harmonic oscillator and show how the combination of two work protocols can be used to implement nontrivial constraints in quantum phase space which couple together the first and second moments of the quadrature operators. We find that such constraints affect the equations of motion for the system in a nontrivial way, inducing nonlinear behavior and even classical chaos, although Gaussianity is preserved at all times. A discussion concerning the robustness of this approach to possible experimental errors is also presented.

Investigating nonclassicality in nonlinear electronic spectroscopy
Saulo V. Moreira, Fernando L. SemiãoIn this work, we establish a connection between nonlinear electronic spectroscopy and quantum information protocols for the nondisturbance condition. The nonfulfillment of the later is a witness of nonclassicality. Our approach permits us to express the nondisturbance condition in terms of common observables in the context of electronic spectroscopy experiments, such as the induced polarization. We then provide the theoretical framework allowing one to infer nonclassicality from the detected signals in these experiments. A prominent feature of our proposal is then the model independence. In particular, for thirdorder nonlinear spectroscopies, such as the widely used twodimensional electronic spectroscopy, we find that the induction of thirdorder polarization in systems satisfying inversion symmetry automatically implies nonclassicality.

Pulse engineering for population control under dephasing and dissipation
I. Medina, F. L. SemiãoWe apply reverseengineering to find electromagnetic pulses that allow for the control of populations in quantum systems under dephasing and thermal noises. In particular, we discuss twolevel systems given their importance in the description of several molecular systems as well as quantum computing. Such an investigation naturally finds applications in a multitude of physical situations involving the control of quantum systems. We present an analytical description of the pulse which solves a constrained dynamics where the initial and final populations are fixed a priori. This constrained dynamics is sometimes impossible and we precisely spot the conditions for that. One of our main results is the presentation of analytical conditions for the establishment of steady states for finite coherence in the presence of noise. This might naturally find applications in quantum memories.

Reversing the thermodynamic arrow of time using quantum correlations
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 LutzarXiv:1711.03323 (2017)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 spins1/2, 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 informationtheoretical quantities.

Coupled harmonic systems as quantum buses in thermal environments
F Nicacio, F L Semião 
Nonequilibrium properties of trapped ions under sudden application of a laser
A. A. Cifuentes, F. Nicacio, M. Paternostro, F. L. Semião 
Thermal transport in outofequilibrium quantum harmonic chains
F. Nicacio, A. Ferraro, A. Imparato, M. Paternostro, F. L. Semião 
Transport of correlations in a harmonic chain
F. Nicacio, F. L. Semião 
Motional entanglement with trapped ions and a nanomechanical resonator
F. Nicacio, K. Furuya, F. L. Semião
1 a 11 de 11 Preprints encontradas Grupo(s): GIQUFABC