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Chinese Physics B 2021年第6期30卷 154-163页

作者： Faustin Blaise Migueu Mercel Vubangsi martin tchoffo Lukong Cornelius Fai Unitéde Recherche de Matière Condensée d'Électronique et de Traitement du SignalDépartement de PhysiqueFacultédes SciencesUniversitéde DschangB.P:67DschangCameroon Computational Material Science Laboratory Higher Technical Teachers'Training College BambiliUniversity of BamendaPO Box 39BamendaCameroon Centre d'Études et de Recherches en Agronomie et en Biodiversité Universitéde DschangDschangCameroon

AD = 1 position-dependent mass approach to constructing nonlinear quantum states for a modified Coulomb potential is used to generate Gazeau–Klauder coherent states. It appears that their energy eigenvalues are scaled down by the quantum number and the nonlinearity coefficient. We study the basic properties of these states, which are found to be undefined on the whole complex plane, and some details of their revival structure are discussed.

关键词： deformed Coulomb potential energy spectrum coherent states photon number distribution quantum revivals

Enhancement of the group delay in quadratic coupling optomechanical systems subjected to an external force

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Chinese Physics B 2023年第12期32卷 325-331页

作者： Jimmi HervéTalla Mbé Ulrich Chancelin Tiofack Demanou Christian Kenfack-Sadem martin tchoffo Research Unit of Condensed Matter Electronics and Signal ProcessingDepartment of PhysicsUniversity of DschangP.O.Box 67DschangCameroon African Institute for Mathematical Sciences P.O.Box 608LimbeCameroon

We theoretically study the effect of the quadratic coupling strength on optomechanical systems subjected to a continuous external force. Quadratic coupling strength originates from strong coupling between the optical and the mechanical degrees of freedom. We show that the quadratic coupling strength reduces the amplitude of the dispersion spectra at the resonance in both blue-and red-sideband regimes. However, it increases(decreases) the amplitude of the absorption spectrum in the blue-(red-)sideband regime. Furthermore, in both sideband regimes, the effective detuning between the pump and the cavity deviates with the quadratic coupling strength. Thereby, appropriate selection of the quadratic coupling strength results in an important magnification(in absolute value) of the group delay for both slow and fast light exiting from the optomechanical cavity.

关键词： slow and fast light optomechanical systems group delay quadratic coupling

Effects of colored noise on the dynamics of quantum entanglement of a one-parameter qubit-qutrit system

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Chinese Physics B 2022年第5期31卷 141-149页

作者： Odette Melachio Tiokang Fridolin Nya Tchangnwa Jaures Diffo Tchinda Arthur Tsamouo Tsokeng martin tchoffo Research Unit of Condensed Matter Electronic and Signal ProcessingDepartment of PhysicsDschang School of Sciences and TechnologyUniversity of DschangPO Box:67 DschangCameroon Material Science Research Group Physics LaboratoryDepartment of PhysicsPost Graduate SchoolUniversity of MarouaPO Box:814 MarouaCameroon Centre d’Etudes et de Recherches en Agronomie et en Biodiversite Faculte d’Agronomie et des Sciences AgricolesUniversite de DschangCameroun

We analyzed the effect of colored noise on the negativity dynamics of a hybrid system consisting of a qubit-qutrit and not interacting,prepared from the start in an entangled one-parameter state and acting with noise in local and non-local *** this pink and brown noise we investigated two different situations:in the first situation,the noise is produced by a bistable oscillator with an unknown exchange rate;however,in the second situation,the noise is generated by a set of bistable *** found that entanglement decreases with time to zero,and undergoes the phenomenon of sudden death and *** pink noise is more prone to entanglement than the brown noise and the non-local environment is more prone to entanglement than the local *** the number of fluctuators is increased,entanglement decays faster and finally,for certain parameters of the initial state,the subsystems are not affected by the noise.

关键词： entanglement hybrid system qutrit colored noise

Effects of classical random external field on the dynamics of entanglement in a four-qubit system

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Chinese Physics B 2021年第11期30卷 240-252页

作者： Edwige Carole Fosso Fridolin Tchangnwa Nya Lionel Tenemeza Kenfack martin tchoffo Research Unit of Condensed Matter Electronic and Signal ProcessingDepartment of PhysicsDschang School of Sciences and TechnologyUniversity of DschangPO Box:67 DschangCameroon Material Science Research Group Physics LaboratoryDepartment of PhysicsPost Graduate SchoolUniversity of MarouaPO Box:814 MarouaCameroon Centre d’Etudes et de Recherches en Agronomie et en Biodiversite Faculte d’Agronomie et des Sciences AgricolesUniversite de DschangCameroun

We investigate the dynamics of entanglement through negativity and witness operators in a system of four noninteracting qubits driven by a classical phase noisy laser characterized by a classical random external field(CREF).The qubits are initially prepared in the GHZ-type and W-type states and interact with the CREF in two different qubit-field configurations,namely,common environment and independent environments in which the cases of equal and different field phase probabilities are *** find that entanglement exhibits different decaying behavior,depending on the input states of the qubits,the qubit-field coupling configuration,and field phase *** the one hand,we demonstrate that the coupling of the qubits in a common environment is an alternative and more efficient strategy to completely shield the system from the detrimental impacts of the decoherence process induced by a CREF,independent of the input state and the field phase probabilities ***,we show that GHZ-type states have strong dynamics under CREF as compared to W-type *** the other hand,we demonstrate that in the model investigated the system robustness’s can be greatly improved by increasing the number of qubits constituting the system.

关键词： entanglement qubit and classical random external field

Nonlinear resonances phenomena in a modified Josephson junction model

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Chinese Physics B 2020年第12期29卷 162-173页

作者： Pernel Nguenang Sandrine Takam Mabekou Patrick Louodop Arthur Tsamouo Tsokeng martin tchoffo Research Unit Condensed Matter Electronics and Signal ProcessingThe University of DschangP.O.Box 67 DschangCameroon Unitède Recherche de Mècanique et de Modèlisation des Systemes Physiques(UR-2MSP) Facultèdes SciencesUniversitède DschangBP 69 DschangCameroun Sao Paulo State University(UNESP) Instituto de Fìsica TeóricaRua Dr.BentoTeobaldo Ferraz 271Bloco IIBarra Funda01140-070 Sao PauloBrazil

In this paper,the equivalent circuit of the non-autonomous Josephson junction(JJ)is presented and the effect of the proper frequency on the phaseφis *** also study nonlinear resonance phenomena in the oscillations of a modified Josephson junction(MJJ).These oscillations are probed through a system of nonlinear differential equations and the multiple time scale method is employed to investigate all different types of resonance that *** results of primary,superharmonic and subharmonic resonances are obtained *** show that the system exhibits hardening and softening behaviors,as well as hysteresis and amplitude hopping phenomena in primary and superharmonic resonances,and only the hysteresis phenomenon in subharmonic *** addition,the stabilities and the steady state solutions in each type of resonances are kindly *** number of equilibrium points that evolve with time and their stabilities are also ***,the equations of motion are numerically integrated to check the correctness of analytical *** further show that the dynamics of the MJJ is strongly influenced by its parameters.

关键词： nonlinear resonances hysteresis and jump phenomena modified Josephson junction

Generalized Van der Waals Equation for Liquid-Vapor Equilibria in a Stationary Gravitational Field

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World Journal of Condensed Matter Physics 2021年第1期11卷 1-11页

作者： Makokiyu Godlove Akumbom Georges Collince Fouokeng martin tchoffo Lukong Cornelius Fai Unité de Recherche de Matiere Condensée d’Electronique et de Traitement de Signal (URMACETS) Department of Physics Faculty of Science University of Dschang Dschang Cameroon Centre d’Etudes et de Recherche en Agronomie et en Biodiversité Faculté d’Agronomie et des Sciences Agricoles (FASA) Université de Dschang Dschang Cameroon

The behavior of liquids undergoing phase transition in the gravitational field is studied by considering the generalized Van der Waals equation. Considering the two simple models for liquid-vapor boundary of a pure classical fluid, the generalized Van der Waals equation shows how the three critical parameters (critical temperature, critical volume and critical pressure), suffice to describe the reduced state parameters (reduced temperature, reduced volume and reduced pressure), the concentration profile and the liquid-vapor boundary position, which can be used to observe transition phenomenon. This model shows how the form of the equation can influence the vertical phase separation induced by the stationary gravitational field, and on the gas condensation effects.

关键词： Liquid-Vapor Phase Transition Gravitational Field Classical Fluid Concentration Profile

Electron Auto-Localization Tailored by Its Thermal Energy: Dynamic Matrix Approach (DMA)

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Journal of Applied Mathematics and Physics 2021年第3期9卷 515-527页

作者： Idriss Fomadjo Fokou Michael Nana Jipdi martin tchoffo Lukong Cornelius Fai Research Unit Condensed Matter Electronics and Signal Processing Université de Dschang Dschang Cameroon Department of Physics Higher Teacher Training College University of Bamenda Bambili Cameroon Centre d’études et de Recherches en Agronomie et en Biodiversité Faculté d’Agronomie et des Sciences Agricoles University of Dschang Dschang Cameroon

This paper investigates the thermal energy effect on electron auto-localization. The polaron characteristics (self-action potential and effective mass) are observed to be expressed via the renormalized electron-phonon coupling constant tailored by the thermal energy. Low temperatures are observed to favour auto-localization of the carrier while high temperatures favour polaron undressing and subsequent quenching of the quantum behaviour thereby rendering the system classical. The critical (transition) temperature τc expressed via the critical coupling constant ϒC is found to be the separating boundary between the quantum and the classical phases. Therefore, the polaron undergoes phase transition (from self-tapped to quasi free states) when the temperature of the medium is enhanced.

关键词： Autolocalization Quantum Phase Transition Self-Trapping Critical Temperature

Thermodynamic Properties and Decoherence of a Central Electron Spin of Atom Coupled to an Anti-Ferromagnetic Spin Bath

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Journal of Quantum Information Science 2013年第1期3卷 10-15页

作者： martin tchoffo Georges Collince Fouokeng Lukong Cornelius Fai Mathurin Esouague Ateuafack Mesoscopic and Multilayer Structures Laboratory Department of Physics Faculty of Science University of Dschang Dschang Cameroon

The decoherence of a central electron spin of an atom coupled to an anti-ferromagnetic spin bath in the presence of a time varying B-Field (VBF) is investigated applying the Holstein-Primak off and Bloch transformations approaches. The Boltzmann entropy and the specific heat capacity at a given temperature are obtained and show the correlation of the coupling of the spin bath and the electron spin of the central atom. At low frequencies the coherence of the coupled system is dominated by the magnetic field intensity. At low VBF intensity, there is decrease in entropy and heat capacity at increase external magnetic field that show the decoherence suppression of the central electron spin atom. The crossing observed in the specific heat capacity corresponds to the critical field point Bc of the system which represents the point of transition from the anti-ferromagnetic system to the ferromagnetic one.

关键词： Entropy Specific Heat Capacity Varying B-Field Decoherence

Quantum Interferometry for Different Energy Landscapes in a Tuneable Josephson Junction Circuit

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Journal of Applied Mathematics and Physics 2020年第11期8卷 2569-2600页

作者： Pernel Nguenang Michael Nana Jipdi Patrick Louodop martin tchoffo Lukong Cornelius Fai Hilda A. Cerdeira Research Unit Condensed Matter Electronics and Signal Processing Université de Dschang Dschang Cameroon Department of Physics Higher Teacher Training College University of Bamenda Bambili Cameroon Sã o Paulo State University (UNESP) Instituto de Física Teórica Barra Funda S&#227 o Paulo Brazil Centre d’études et de Recherches en Agronomie et en Biodiversité Faculté d’Agronomie et des Sciences Agricoles University of Dschang Dschang Cameroon

This paper presents a simple Josephson-junction circuit with two parameters (inductance and capacitance) which can be tuned to represent different energy landscapes with different physical properties. By tuning this quantum circuit through external accessible elements we can move from two to three and more energy levels depending on the parameter setting. The inductance, the capacitance as well as the external voltage (driving terms) condition the number of relevant energy levels as well as the model to be used. We show that the quantized circuit represents a multi-state system with tunneling induced by the Landau-Zener and Landau-Zener-Stückelberg transition. The special cases of single crossing and multi-crossing models are thoroughly studied and the transition probability is obtained in each case. It is proven that, the crossing time as well as the relaxation time affect drastically the transition probability;the system mimics a single passage for short relaxation and a multiple passage problem for large relaxation. The nonlinearity of energy levels modifies the transition probability and the derived adiabatic parameters help to redefine the Landau-Zener probability. The observed constructive and destructive interferences are parametrically conditioned by the initial condition set by the inductive branch. Moreover, the total population transfers as well as the complete blockage of the system are obtained in a permissible range of parameters only by changing the values of the inductance. Therefore, the system models a controllable level-crossing where the additional branches (inductive and capacitive) help in designing the number of states, the type of interferometry as well as the control of states occupation.

关键词： Josephson Junction Tuneable Josephson Junction Energy Landscapes Quantum Interferometry

Revival of Order in the Chaotic Dynamics with Position and Time Dependent Perturbed System

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Journal of Applied Mathematics and Physics 2020年第11期8卷 2658-2670页

作者： Lylyane S. Yonya Tchapda martin tchoffo Mercel Vubangsi Faustin B. Migueu Lukong C. Fai Condensed Matter and Nanomaterials Department of Physics Faculty of Science University of Dschang Dschang Cameroon

Studying quantum properties of a system has been quite popular in quantum mechanics. One of the most important systems that are very crucial to the framework of quantum mechanics is the system of harmonic oscillator a system whose classical evolution is known to exhibit peculiar chaotic dynamics. We are motivated to investigate the behavior of quantum properties for a system with position and time dependent perturbed. Starting with Hamiltonian, we determined the equation of motion and obtained the wave function. The energy of the whole system using the operator ordering method was found. We show that the quantum mechanical picture alludes to a chaotic dynamics as expected. This is evidenced through the appearance of energy level crossings. An additional signature to this chaotic dynamics is observed in the transition of Eigen values from real to imaginary. We also show numerically that one can give the behavior of the system is Poincare section. By so doing we confirmed that increasing and decreasing the perturbation amplitude of the system becomes chaotic.

关键词： Schrödinger Equation Crossing Chaotic Dynamics Perturbed System Harmonic Oscillator