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Work Done on a Coherently Driven Quantum System

Journal of Quantum Information Science 2015年第3期5卷 89-102页

作者： issofa nsangou Lukong Cornelius Fai Mesoscopic and Multilayer Structures Laboratory Faculty of Science Department of Physics University of Dschang Yaounde Cameroon

We calculate the work done by a Landau-Zener-like dynamical field on two- and three-level quantum system by constructing a quantum power operator. We elaborate a general theory applicable to a wide range of closed-quantum system. We consider the dynamics of the system in the time domain ]-tLZ,tLZ[ (where is the LZ transition time in the sudden limit) where the external pulse changes its sign and its action becomes relevant. The statistical work is evaluated in a period [0,T] where T ≤tLZ. Our results are observed to be in good qualitative agreement with known results.

关键词： Power Operator Statistical Work Landau-Zener Model Level Crossing

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Thermodynamic Parameters of Central Spin Coupled to an Antiferromagnetic Bath: Path Integral Formalism

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Journal of Applied Mathematics and Physics 2021年第1期9卷 133-145页

作者： Christian Platini Fogang Kuetche nsangou issofa Mathurin Esouague Ateuafack Lukong Cornelius Fai Research Unity of Condensed Matter Electronics and Signal Processing Department of Physics Faculty of Science University of Dschang Dschang Cameroon Department of Research Development Innovation and Training SpaceKola Yaounde Cameroon Department of Electrical and Electronic Engineering College of Technology University of Buea Buea Cameroon

A path-integral representation of central spin system immersed in an antiferromagnetic environment was investigated. To carry out this study, we made use of the discrete-time propagator method associated with a basic set involving coherent states of Grassmann variables which made it possible to obtain the analytical propagator which is the centerpiece of the study. In this study, we considered that the environment was in the low-temperature and low-excitation limit and was split into 2 subnets that do not interact with each other. The evaluation of our system was made by considering the first neighbor approximation. From the formalism of the path integrals, it is easy to evaluate the partition function and thermodynamic properties followed from an appropriate tracing over Grassmann variables in the imaginary time domain. We show that the energy of the system depends on the number of sites n when β → 0.

关键词： Path Integral Grassmann Algebra Antiferromagnetic Environment Partition Function

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Decoherence of a Damped Anisotropic Harmonic Oscillator under Magnetic Field Effects in a Two-Dimensional Noncommutative Phase-Space

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Journal of Applied Mathematics and Physics 2020年第12期8卷 2801-2823页

作者： Martin Tcoffo Germain Yinde Deuto issofa nsangou Armel Azangue Koumetio Lylyane S. Yonya Tchapda Alain G. Tene Research Unit of Condensed Matter Electronics and Signal Processing University of Dschang Dschang Cameroon Centre d’Etude et de Recherche en Agronomie et en Biodiversité FASA Université de Dschang Dschang Cameroun

In this paper, decoherence of a damped anisotropic harmonic oscillator in the presence of a magnetic field is studied in the framework of the Lindblad theory of open quantum systems in noncommutative phase-space. General fundamental conditions that should follow our quantum mechanical diffusion coefficients appearing in the master equation are kindly derived. From the master equation, the expressions of density operator, the Wigner distribution function, the expectation and variance with respect to coordinates and momenta are obtained. Based on these quantities, the total energy of the system is evaluated and simulations show its dependency to phase-space structure and its improvement due to noncommutativity effects and the environmental temperature as well. In addition, we also evaluate the decoherence time scale and show that it increases with noncommutativity phase-space effects as compared to the commutative case. It turns out from simulations that this time scale is significantly improved under magnetic field effects.

关键词： Decoherence Noncommutative Phase-Space Lindblad Theory Wigner Distribution

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Effect of the Variable B-Field on the Dynamic of a Central Electron Spin Coupled to an Anti-Ferromagnetic Qubit Bath

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World Journal of Condensed Matter Physics 2012年第4期2卷 246-256页

作者： Martin Tchoffo Georges Collince Fouokeng Siaka Massou Ngwa Engelbert Afuoti issofa nsangou Lukong Cornelius Fai Alex Ghislain Tchouadeu Jean-Pierre Kenné De- partment of Physics Faculty of Sciences and Technics University of Abomey-Calavi Cotonou Benin Department of Mechanical Engineering Laboratory of Integrated Production Technologies University of Québec Québec Canada Department of Physics Laboratory of Mesoscopic and Multilayer Structures University of Dschang Dschang Cameroon Department of Physics Laboratory of Mesoscopic and Multilayer Structures University of Dschang Dschang Cameroon Department of Thermal Engineering and Energetics Douala University Institute of Technology Douala Cameroun

This present issue is an extension of the work of Y. Xiao-Zhong et al. who investigated the influence of constant external magnetic field on the decoherence of a central electron spin of atom coupled to an anti-ferromagnetic environment. We have shown in this work that the character variability of the field induces oscillations amongst the eigen modes of the environment. This observation is made via the derivation of the transition probability density of state, a manner by which critical parameters (parameters where transition occur) of the system could be obtained as it shows resonance peak. We equally observed that the two different magnons modes resulting from the frequency splitting via the application of the time-varying external B-Field, exhibit each a resonant peak of similar amplitude at different temperature ranges. This additional information shows that the probability for the central spin system to remain in its initially prepared diabatic state is enhanced for some temperature ranges for the corresponding two magnon modes. Hence, these temperature ranges where the probability density is maximum could save as decoherence free environment;an important requirement for the implementation of quantum computation and information processing in solid state circuitry. The theoretical and numerical results presented for the decoherence time and the probability density are that of a decohered central electron spin coupled to an anti-ferromagnetic spin bath. The theory is based on a spin wave approximation and on the density matrix using both transformations of Bloch, Primakov and Bogoliobuv in the adiabatic limit.

关键词： Decoherence Spin Wave Anti-Ferromagnetic Environment Central Spin Variable B-Field

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