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Publication Date: 2022/02/20
Iranian Journal of Physics Research (16826957) 21(4)pp. 735-747
The study of many-body quantum systems, that fail to thermalize in the presence of disorder, has recently attracted lots of interests. This is due to the appearance of the many-body localized phase and breakdown of eigenstate thermalization hypothesis in such systems which can be described by the local integrals of motion. In this paper, we consider a disordered spin chain in the many-body localized phase and try to study the dynamics of entanglement generation in this system using the local integrals of motion. To this end, we, first, solve the non-interacting system analytically to describe the mechanism of entanglement generation for different kinds of initial states, exactly. Then, we generalize this approach to the interacting system to learn the dynamics of entanglement generation. Finally, we discuss the physical meaning of different behaviors in the dynamics of entanglement generation in the presence and absence of interaction.
Publication Date: 2024
Physica Scripta (00318949) 99(8)
In this paper, we investigate the Kane-Mele model and endeavor to demonstrate, through analytical calculations, how the presence of topological edge states influences the RKKY interaction. We illustrate that the effect diminishes as one moves away from the edges. To facilitate our analytical approach, we initially utilize a one-dimensional wire exhibiting linear dispersion for each spin as an approximation to the Kane-Mele model. We examine its impact on the RKKY interaction. Subsequently, we establish a correspondence between the edge states of the Kane-Mele model and a one-dimensional quantum wire model, wherein the coupling strength diminishes with increasing distance from the edges. Finally, we compare the analytical results with numerical findings obtained using the Landauer-Buttiker formulation. © 2024 IOP Publishing Ltd.
Publication Date: 2024
Physical Review B (24699950) 109(2)
The quantization of conductance in the presence of nonmagnetic point defects is a consequence of topological protection and the spin-momentum locking of helical edge states in two-dimensional topological insulators. This protection ensures the absence of backscattering of helical edge modes in the quantum Hall phase of the system. However, in this paper, we focus on exploring an approach to spoil such conductance quantization. We propose that a linear arrangement of (nonmagnetic) on-site impurities can effectively cause deviations from the conductance quantization of the edge states in the Kane-Mele model. To investigate this phenomenon, we consider an armchair ribbon containing a line defect spanning its width. Utilizing the tight-binding model and nonequilibrium Green's function method, we calculate the transmission coefficient of the system. Our results reveal a suppression of conductance at energies near the lower edge of the bulk gap for positive on-site potentials. To further comprehend this behavior, we perform analytical calculations and discuss the formation of an impurity channel. This channel arises due to the overlap of in-gap bound states, linking the bottom edge of the ribbon to its top edge, consequently facilitating backscattering. Our explanation is supported by the analysis of the local density of states at sites near the position of impurities. © 2024 American Physical Society.
Soltani renani, M. ,
Jalilvand, S. ,
Sodagar, S. ,
Noorinejad z., Z. ,
Karbaschi, H. ,
Soltani M. Publication Date: 2024
Physica Scripta (00318949) 99(6)
We examine an armchair bilayer phosphorene connected to two leads, one hot and one cold, on both sides, investigating the thermoelectric properties of this system with periodic vacancies along the armchair direction and at the center of the nanoribbon. Initially, we analytically demonstrate that the creation of a vacancy results in the generation of a localized state around it. Subsequently, we illustrate that the presence of periodic vacancies leads to the formation of a new energy band in the energy bandstructure. Our calculations reveal that by varying the distance between vacancies, one can tune the width of the corresponding transmission channel, the generated electric power, and the thermoelectric efficiency. © 2024 IOP Publishing Ltd.
Publication Date: 2023
Physical Review B (24699950) 107(20)
Although one of the most important and intriguing features of the topological insulators is the presence of edge states, the closed-form expressions for the edge states of some famous topological models are still lacking. Here, we focus on the Kane-Mele model with and without Rashba spin-orbit coupling as a well-known model to describe a two-dimensional version of the Z2 topological insulator to study the properties of its edge states analytically. By considering the tight-binding model on a honeycomb lattice with zigzag boundaries and introducing a perturbative approach, we derive explicit expressions for the wave functions, energy dispersion relations, and the spin rotations of the (generic) helical edge states. To this end, we first map the edge states of the ribbon geometry into an effective two-leg ladder model with momentum-dependent energy parameters. Then, we split the Hamiltonian of the system into an unperturbed part and a perturbation. The unperturbed part has a flat-band energy spectrum and can be solved exactly, which allows us to consider the remaining part of the Hamiltonian perturbatively. The resulting energy dispersion relation within the first-order perturbation, surprisingly, is in excellent agreement with the numerical spectra over a very wide range of wave numbers. Our perturbative framework also allows deriving an explicit form for the rotation of the spins of the momentum edge states in the absence of axial spin symmetry due to the Rashba spin-orbit interaction. © 2023 American Physical Society.
Publication Date: 2023
Iranian Journal of Physics Research (16826957) 23(1)pp. 73-78
In this research, firstly, the structure of a double-layer phosphorene nanoribbon is introduced. Then, for the simplified structure of this system in the presence of a void, the substituted wave function which has a topological origin is analyzed analytically and the analytical results are compared with the numerical method. The Landauer-Buttiker approach is used in the numerical calculation of the substituted probability density (LDOS). Finally, for bilayer phosphorene, by considering more parameters, the wave function and the energy of the substituted state in the presence of a vacancy have been reported numerically. © 2023, Isfahan University of Technology. All rights reserved.
Publication Date: 2023
Physica Scripta (00318949) 98(1)
We have theoretically investigated strain-induced thermoelectric power generation properties of zigzag bilayer phosphorene nanoribbon. Since energy bandgap size and edge state dispersion play a significant role in the thermoelectric properties of such a structure, we have investigated the effect of strain in different directions on these two quantities. We have shown that by applying both tensile and compressive strains in different directions, it is possible to properly tune the energy bandgap size and adjust the edge state dispersion. We have also selected strain combinations in different directions that simultaneously increase the size of the energy bandgap and decrease the dispersion of the edge state. It has shown that with such combinations of strains, the maximal figure of merit has been improved by about two times compared to the pristine case. © 2022 IOP Publishing Ltd.
Publication Date: 2023
Scientific Reports (20452322) 13(1)
Studying the edge states of a topological system and extracting their topological properties is of great importance in understanding and characterizing these systems. In this paper, we present a novel analytical approach for obtaining explicit expressions for the edge states in the Kane-Mele model within a ribbon geometry featuring armchair boundaries. Our approach involves a mapping procedure that transforms the system into an extended Su–Schrieffer–Heeger model, specifically a two-leg ladder, in momentum space. Through rigorous derivation, we determine various analytical properties of the edge states, including their wave functions and energy dispersion. Additionally, we investigate the condition for topological transition by solely analyzing the edge states, and we elucidate the underlying reasons for the violation of the bulk-edge correspondence in relatively narrow ribbons. Our findings shed light on the unique characteristics of the edge states in the quantum spin Hall phase of the Kane–Mele model and provide valuable insights into the topological properties of such systems. © 2023, Springer Nature Limited.
Publication Date: 2023
Nanotechnology (09574484) 34(46)
We have studied a 5-terminal system consisting of three single level quantum dots (QDs) that are in contact with their respective reservoirs. In addition to the intra-dot Coulomb interaction, the electron in the dot affected by an inter-dot Coulomb repulsion from its adjacent QD. We describe this system by an Anderson type model Hamiltonian and apply the Greens function method to study the transport properties of the system. Since we are interested in temperatures higher than the Kondo temperature, we use the equations of motion technique to calculate Green’s functions. Numerical analysis shows that there is a correlation between the transport characteristics of the lower and upper dot and we can change the conductivity of the lower dot only by varying the parameters of the upper dot and vice versa. We demonstrated that the middle dot play the role of the switch on/off of this correlation. Also, we investigated the effect of thermoelectric properties. We found that the inter-dot Coulomb interaction can improve the thermoelectric performance of the system. © 2023 IOP Publishing Ltd.
Publication Date: 2022
Physica E: Low-Dimensional Systems and Nanostructures (13869477) 139
In this paper, the scattering from a spin impurity for the edge state of the Kane–Mele model has been calculated via the Lippmann–Schwinger approach. To solve this problem analytically, we first approximately calculate the edge states of the Kane–Mele model and use it to obtain Green's function. We then calculate the scattering matrix of an electron from a spin impurity with Heisenberg interaction. Finally, we generalize this method to a double impurity model and use it to calculate the entanglement between two spins of two impurities. © 2022 Elsevier B.V.
Publication Date: 2022
European Physical Journal Plus (21905444) 137(6)
Zigzag Phosphorene nanoribbon supports topological edge states in the gap region near the Ferm level. We consider a bilayer system consisting of two coupled Phosphorene layers with zigzag edges and investigate the thermoelectric properties of the system by engineering its corresponding edge modes. To this end, we first map the edge states of zigzag bilayer phosphorene nanoribbon (ZBPNR) into an effective Su-Schrieffer-Heeger (SSH) ladder model with momentum dependent hopping probabilities which allow us to obtain their corresponding band dispersion and wave functions analytically. Then, by applying the energy filtering method and employing non-equilibrium Green’s function approach, we show that the electric power and thermoelectric efficiency of the ZBPNRs can be improved remarkably in the presence of mid-gap edge states. We also argue how to engineer the edge modes to further optimize thermoelectric power and efficiency of the system by applying periodic point potentials at the boundaries © 2022, The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2022
Physical Review B (24699950) 106(5)
Many-body localization (MBL) is a novel prototype of ergodicity breaking due to the emergence of local integrals of motion (LIOMs) in a disordered interacting quantum system. To better understand the role played by the existence of such LIOMs, we explore and study some of their structural properties across the MBL transition. We first consider a one-dimensional XXZ spin chain in a disordered magnetic field and introduce and implement a nonperturbative, fast, and accurate method of constructing LIOMs. In contrast to already existing methods, our scheme allows obtaining LIOMs not only in the deep MBL phase but, rather, near the transition point too. Then, we take the matrix representation of LIOM operators as an adjacency matrix of a directed graph whose elements describe the connectivity of ordered eigenbasis in the Hilbert space. Our cluster-size analysis for this graph shows that the MBL transition coincides with a percolation transition in the Hilbert space. By performing finite-size scaling, we compare the critical disorder and correlation exponent ν both in the presence and absence of interactions. Finally, we also discuss how the distribution of diagonal elements of LIOM operators in a typical cluster signals the transition. © 2022 American Physical Society.
Publication Date: 2021
Physics Letters, Section A: General, Atomic and Solid State Physics (03759601) 387
Double-level quantum systems are good candidates for revealing coherent quantum transport properties. Here, we consider quantum interference effects due to the formation of a two-level system (TLS) coupled to the edge channel of a zigzag Phosphorene nanoribbon (ZPNR). Using the tight-binding approach, we first demonstrate the formation of a TLS in bulk Phosphorene sheet due to the existence of two nearby vacancy impurities. Then, we show that such a TLS can couple to the quasi-one-dimensional continuum of the edge states in a ZPNR which results in the appearance of two-dip Fano-type line shapes. To this end, we generalize the Lippmann–Schwinger approach to study the scattering of edge electrons in a ZPNR by two coupled impurity defects. We obtain an analytical expression of the transmission coefficient which shows that the positions and widths of the antiresonances can be controlled by changing the intervacancy distance as well as their distance from the edge of the ribbon. This work constitutes a clear example of the multiple Fano resonances in mesoscopic transport. © 2020 Elsevier B.V.
Soltani renani, M. ,
Rezaei, M. ,
Karbaschi, H. ,
Amini, M. ,
Soltani M. ,
Rashedi g., Publication Date: 2021
Nanotechnology (09574484) 32(37)
Armchair phosphorene nanoribbons (APNRs) are known to be semiconductors with an indirect bandgap. Here, we propose to introduce new states in the gap of APNRs by creating a periodic structure of vacancies (antidots). Based on the tight-binding model, we show that a periodic array of vacancies or nanopores leads to the formation of an impurity band inside the gap region. We first present an analytical expression for the dispersion relation of an impurity band induced by hybridization of bound states associated with each single vacancy defect. Then, we increase the size of vacancy defects to include a bunch of atoms and theoretically investigate the effect of nanopores size and their spacing on electronic band structure, carrier transmission function, and thermoelectric properties. Our analysis of the power generation rate and thermoelectric efficiency of these structures reveals that an ANPR can be used as a superb thermoelectric power generation module. © 2021 IOP Publishing Ltd.
Publication Date: 2020
Physical Review B (24699950) 101(11)
The existence of robust chiral edge states in a finite topologically nontrivial Chern insulator is a consequence of the bulk-boundary correspondence. In this paper, we present a theoretical framework based on lattice Green's function to study the scattering of such chiral edge electrons by a single localized impurity. To this end, in the first step, we consider the standard topological Haldane model on a honeycomb lattice with strip geometry. We obtain analytical expressions for the wave functions and their corresponding energy dispersion of the low-energy chiral states localized at the edge of the ribbon. Then, we employ the T-matrix Lippmann-Schwinger approach to explicitly show the robustness of chiral edge states against the impurity scattering. This backscattering-free process has an interesting property that the transmitted wave function acquires an additional phase factor. Although this additional phase factor does not affect quantum transport through the chiral channel, it can carry quantum information. As an example of such quantum information transport, we investigate the entanglement of two magnetic impurities in a Chern insulator through the dissipationless scattering of chiral electrons. © 2020 American Physical Society.
Publication Date: 2019
Journal of Physics Condensed Matter (09538984) 31(21)
Zigzag phosphorene nanoribbons have quasi-flat band edge modes entirely detached from bulk states. We analytically study the electronic transport through such edge states in the presence of a localized defect for semi-infinite and finite ribbon widths. Using the tight-binding model, we derive analytical expressions for the Green's function and transmission amplitude of both pristine and defective nanoribbons. We find that the transmission of ribbons with both semi-infinite and finite width is sensitive to the location of a single impurity defect with respect to the edge. By the presence of an impurity on the outermost edge site of the ribbon, the transmission through the edge channel, similar to a one-dimensional chain, strongly suppresses for the entire energy spectrum of the quasi-flat band. In contrast, the transmission of low-energy (E ≈ 0) states, is robust as the impurity is moved one position far away from the edge on the same sub-lattice. The analytical calculations are also complemented by exact numerical transport computations using the Landauer approach. © 2019 IOP Publishing Ltd Printed in the UK.
Publication Date: 2019
Physical Review B (24699950) 99(8)
Motivated by recent scanning tunneling microscopy and spectroscopy experiments on probing single vacancies in black phosphorus, we present a theory for Fano antiresonances induced by coupling between vacancy states and edge states of zigzag phosphorene nanoribbons (zPNRs). To this end, in the first step, using the tight-binding Hamiltonian, we obtain an analytic solution on the lattice for the state associated with a single vacancy located in the bulk phosphorene which shows a highly anisotropic localization in real space. For a finite zigzag ribbon, in the absence of particle-hole symmetry, the localized state induced by vacancies can couple with the wave functions of the edge states, which results in the formation of a new bound state. The energy of the vacancy bound state lies inside the quasiflat band composed of edge states when the vacancy locates sufficiently far away from the edge. Then, we employ the T-matrix Lippmann-Schwinger approach to obtain an explicit analytical expression for the scattering amplitude of the edge electrons of a zPNR through the presence of a single vacancy which shows a Fano resonance profile with a tunable dip. We demonstrate that varying the position of the vacancy produces substantially different effects on the resonance width, the resonance energy position, and the asymmetry parameter of the Fano line shape. Furthermore, the validity of the theoretical descriptions is verified numerically by using the Landauer approach. © 2019 American Physical Society.
Publication Date: 2017
European Physical Journal D (14346060) 71(1)
Abstract: Motivated by the problem of Casimir energy, we investigate the idea of usinginhomogeneity of surfaces instead of their corrugation, which leads to Casimir interactionbetween two inhomogeneous semi-transparent concentric cylinders. Using the multiplescattering method, we study the Casimir energy and torque between the cylinders withdifferent potentials subjected to Dirichlet boundary conditions, both in weak and strongcoupling regimes. We also extend our formalism to the case of two inhomogeneousdielectrics in a weak coupling regime. Graphical abstract: [Figure not available: see fulltext.] © 2017, EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.
Publication Date: 2017
Physical Review A (24699934) 95(2)
The normal and the lateral Casimir interactions between corrugated ideal metallic plates in the presence of an amplifying or an absorptive dielectric slab is studied by the path-integral quantization technique. The effect of the amplifying slab, which is located between corrugated conductors, is to increase the normal and lateral Casimir interactions, while the presence of the absorptive slab diminishes the interactions. These effects are more pronounced if the thickness of the slab increases and, also, if the slab comes closer to one of the bounding conductors. When both bounding ideal conductors are flat, the normal Casimir force is nonmonotonic in the presence of the amplifying slab and the system has a stable mechanical equilibrium state, while the force is attractive and is weakened by intervening the absorptive dielectric slab in the cavity. Upon replacing one of the flat conductors with a flat ideal permeable plate the force becomes nonmonotonic and the system has an unstable mechanical equilibrium state in the presence of either an amplifying or an absorptive slab. When the left-side plate is a conductor and the right one is permeable, the force is nonmonotonic in the presence of a double-layer dissipative-amplifying dielectric slab with a stable mechanical equilibrium state, while it is purely repulsive in the presence of a double-layer amplifying-dissipative dielectric slab. © 2017 American Physical Society.
Publication Date: 2016
European Physical Journal D (14346060) 70(12)
Abstract: Electromagnetic field quantization, in the presence of two semi-infinite dielectrics withmoving interface, is investigated in 1 +1-dimensional space-time. The moving interface is modelled for smalldisplacements and the field equation is solved perturbatively. Input-output relations andspectral distribution of emitted photons are obtained and the effect of small transitionsthrough the interface discussed. Graphical abstract: [Figure not available: see fulltext.] © 2016, EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.
Soltani renani, M. ,
Jalali j., J. ,
Soltani M. ,
Rashedi g., ,
Azizi e., E. ,
Ezatabadipour h., H. Publication Date: 2015
European Physical Journal D (14346060) 69(7)
Abstract We propose a method to generate stationary entanglement between two macroscopic vibrating elements (micro-mechanical resonators (MRs)), via a transmission line resonator (TLR) field mode, where the MRs are coupled to the TLR capacitively. In this paper two situations are studied; (i) a driving on TLR field with an external microwave pulse, (ii) driving on TLR field and simultaneous driving on two MRs. Here, the entanglement is quantified by the logarithmic negativity. As our proposed system is a continuous variable system, the logarithmic negativity is defined in terms of covariance matrix. We have shown that the second case leads to much stronger entanglement, even at a few milli Kelvin temperatures. © 2015 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.
Publication Date: 2015
Iranian Journal of Physics Research (16826957) 15(3)pp. 317-335
In this work, we generalize the entanglement of three-qbit Bosonic systems beyond the single-mode approximation when one of the observers is accelerated. For this purpose, we review the effects of acceleration on field modes and quantum states. The single-mode approximation and beyond the single-mode approximation methods are introduced. After this brief introduction, the main problem of this paper, tripartite entanglement of bosonic systems in a noninertial frame beyond the single- mode approximation is investigated. The tripartite entangled states have different classes with GHZ and W states being most important. Here, we choose π-tangle as a measure of tripartite entanglement. If the three parties share GHZ state, the corresponding π-tangle will increase by increasing acceleration for some Unruh modes. This phenomenon, increasing entanglement, has never been observed in the single-mode approximation for bosonic case. Moreover, the π-tangle dose not exhibit a monotonic behavior with increasing acceleration. In the infinite acceleration limit, the π-tangle goes to different nonzero values for distinct Unruh modes. Unlike GHZ state, the entanglement of the W state shows only monotonically increasing and decreasing behaviors with increasing acceleration. Also, the entanglement for all possible choices of Unruh modes approaches only 0.176 in the high acceleration limit. Therefore, according to the quantum entanglement, there is no distinction between the single-mode approximation and beyond the single-mode approximation methods in this limit. © 2015, Iranian Journal of Physics Research. All rights reserved.
Publication Date: 2014
International Journal of Theoretical Physics (15729575) 53(7)pp. 2141-2154
In this work the Hawking-Unruh effect on the quantum entanglement of bosonic field in background of a spherically symmetric black hole of Gauss-Bonnet gravity is investigated beyond the single mode approximation. The entanglement decreases due to Hawking-Unruh effect. However, it has been shown that the dimensions of space time, Gauss-Bonnet term and the parameter β of initial entangled state would be influenced on this degradation. In our investigation, we consider the accelerated observer either near or far from the event horizon and inspect entanglement degradation for them. The mutual information of this bosonic system is also calculated in beyond the single mode approximation and we show that the mutual information will have different behavior when the Hawking temperature increases. © 2013, Springer Science+Business Media New York.
Soltani renani, M. ,
Soltani M. ,
Ezatabadipour h., H. ,
Jalali j., J. ,
Darabi, P. ,
Azizi e., E. ,
Rashedi g., Publication Date: 2013
European Physical Journal D (14346060) 67(12)
In this paper,we introduce a system containing of two qubits interacting with a cavity which interacted with a reservoir. Using the Fano technique we will show this system is equivalent with two qubits which are interacting with a common heat bath. We also add a laser field and the behavior of this system is investigated when the qubits are dissipative. In this way we show that the presence of laser field can generate a high entanglement in this system, in other word the pump of energy using the laser field can compensate for the lose of dissipation of qubits. We also show that our system is almost insensible to temperature. © 2013 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.
Publication Date: 2013
International Journal of Theoretical Physics (15729575) 52(12)pp. 4403-4411
The entanglement generation in a two-qubit system interacting with electromagnetic vacuum field and an external local magnetic field is investigated in the framework of the master equation. The time-evolution for the most general density matrix of the two-qubit system is obtained and solved. It is shown that the two-qubit system ends up in an entangled stationary state independent on the initial separable state. © 2013 Springer Science+Business Media New York.
Publication Date: 2012
International Journal of Theoretical Physics (15729575) 51(3)pp. 787-804
Entanglement degradation caused by the Unruh effect is discussed for the tripartite GHZ or W states constructed by modes of a non-interacting quantum field viewed by one inertial observer and two uniformly accelerated observers. For fermionic states, the Unruh effect even for infinite accelerations cannot completely remove the entanglement. However, for the bosonic states, the situation is different and the entanglement vanishes asymptotically. Also, the entanglement is studied for the bipartite subsystems. While for the GHZ states all the bipartite subsystems are identically disentangled, for the W states the bipartite subsystems are somewhat entangled, though, this entanglement can be removed for appropriately accelerated observers. Interestingly, logarithmic negativity as a measure for determining the entanglement of one part of the system relative to the other two parts, is not generally the same for different parts. This means that we encounter tripartite systems where each part is differently entangled to the other two parts. © 2011 Springer Science+Business Media, LLC.
Publication Date: 2012
Physical Review A - Atomic, Molecular, and Optical Physics (10502947) 86(2)
We investigate the lateral Casimir interaction between two corrugated conductors when they enclose a dielectric slab. The magnitude of the lateral Casimir force can be changed due to the presence of a dielectric slab between them, and it strongly depends on the thickness (d) and dielectric function of the slab and also on the position of the slab with respect to the conductors. In addition, the distance between the conductors (H) and their corrugation wavelengths play important roles in tuning the lateral Casimir interaction. For fixed d and H, quite interestingly, the magnitude of the lateral Casimir force varies when the position of the slab with respect to conductors changes, and it has a maximum when the slab is positioned precisely at the center of the space between the conductors. We find that the interaction decreases when the dielectric constant of the slab increases. © 2012 American Physical Society.
Publication Date: 2011
Annals of Physics (00034916) 326(3)pp. 657-667
By using the path-integral formalism, electromagnetic field in the presence of some linear, isotropic magnetodielectric slabs is quantized and related correlation functions are found. In the framework of path-integral techniques, Casimir force between two infinitely large, parallel and ideal conductors, with a different number of magnetodielectric slabs in between, is obtained by calculating the Green's function corresponding to each geometry. © 2011 Elsevier Inc.
Publication Date: 2011
Physical Review A - Atomic, Molecular, and Optical Physics (10502947) 83(3)
Starting from a Lagrangian, the electromagnetic field in the presence of a nonlinear dielectric medium is quantized using path-integral techniques, and correlation functions of different fields are calculated. The susceptibilities of the nonlinear medium are obtained, and their relations to coupling functions are determined. Finally, the Casimir energy and force in the presence of a nonlinear medium at finite temperature are calculated. © 2011 American Physical Society.
Publication Date: 2011
Physical Review A - Atomic, Molecular, and Optical Physics (10502947) 84(6)
Starting from a Lagrangian, an electromagnetic field is quantized in the presence of a medium in thermal equilibrium and also in a medium with time-varying temperature. The vector potential for both equilibrium and nonequilibrium cases is obtained and vacuum fluctuations of the fields are calculated. As an illustrative example, the finite-temperature decay rate and level shift of an atom in a polarizable medium are calculated in this approach. © 2011 American Physical Society.
Publication Date: 2011
Physical Review D - Particles, Fields, Gravitation and Cosmology (15502368) 84(2)
Bipartite entanglement for states of a noninteracting bosonic or fermionic field in the spacetime of a spherically symmetric black hole of Einstein-Gauss-Bonnet gravity is investigated. Although the initial state is chosen to be maximally entangled as the Bell states, the Hawking-Unruh effect causes the state to be mixed and the entanglement degrades, but with different asymptotic behaviors for the fermionic and bosonic fields. The Gauss-Bonnet term with positive α can play an antigravitation role and so this causes a decrease in the Hawking-Unruh effect and consequently reduces the entanglement degradation. On the other hand, the suggested higher dimensions for the spacetime lead to increased entanglement degradation by increasing the dimension. There is a dramatic difference between the behaviors of the entanglement in terms of the radius of the horizon for a five-dimensional black hole and that for higher dimensional black holes. Both bosonic and fermionic fields entanglements are treated beyond the single-mode approximation. Also, the cases where the accelerating observers located at regions near and far from the event horizon of black hole are studied separately. © 2011 American Physical Society.
Publication Date: 2010
Physical Review A - Atomic, Molecular, and Optical Physics (10502947) 81(5)
We investigate the Casimir effect in the presence of a medium by quantizing the electromagnetic field in the presence of a magnetodielectric medium using the path-integral technique. For a given medium with definite electric and magnetic susceptibilities, explicit expressions for the Casimir force are obtained. The Lifshitz formula is recovered and in the absence of a medium the results tend to the original Casimir force between two conducting parallel plates immersed in the quantum electromagnetic vacuum. © 2010 The American Physical Society.
Publication Date: 2010
Physical Review A - Atomic, Molecular, and Optical Physics (10502947) 82(4)
Path-integral formalism is employed to study normal and lateral Casimir interactions in a system composed of a dispersive medium surrounded by two semi-infinite ideal conductors. The dispersive medium is modeled by a continuum of harmonic oscillators, and it is shown that for smooth conductors, the normal force at small distances in the presence of a dispersive medium coincides with the original Casimir force, while at large distances, it tends to the original form with a renormalized coefficient. The correction to the normal force because of the roughness on one of the conductors is calculated. When the inner surfaces of both conductors have roughness, the lateral Casimir interaction occurs because of translational symmetry breaking, which is studied. It is shown that both normal and lateral Casimir forces in the presence of a dispersive medium are weaker in comparison with the original one and are proportional to the roughness amplitude squared. The dependence of the normal and lateral interactions on the memory and strength of the dispersive medium is considered. © 2010 The American Physical Society.
Publication Date: 2008
Physical Review A - Atomic, Molecular, and Optical Physics (10502947) 78(1)
The Huttner-Barnett model is extended to a magnetodielectric medium by adding a matter field to this model. The eigenoperators for the coupled system are calculated and electromagnetic field is written in terms of these operators. The electric and magnetic susceptibilities of the medium are explicitly derived and shown to satisfy the Kramers-Kronig relations. It is shown that the results obtained in this extended model are equivalent to their counterparts obtained in the phenomenological methods. © 2008 The American Physical Society.
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