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tayefeh-rezakhani--ali
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Quantum Process Tomography: A New Approach Based on Moments
, M.Sc. Thesis Sharif University of Technology ; Tayefeh Rezakhani, Ali (Supervisor)
Abstract
In this report, we have formulated a new technique for characterizing quantum optical processes based on probing unknown processes only with coherent states and simply by measuring normally-ordered moments of output states. Our method has two substantial advantages in comparison with previous methods.First, for practical purposes of uantum-optical communications and information, predicting of the classicality or nonclassicality of output states from an unknown quantum process is generally important. Because of truncation of the Hilbert space in the Fock basis and/or exploiting Klauder theorem, antecedent methods failed to carry out foretelling the [non]classicality features of the process’...
Characterization of topological phases in the compass ladder model
, Article Journal of Physics Condensed Matter ; Volume 28, Issue 17 , 2016 ; 09538984 (ISSN) ; Langari, A ; Tayefeh Rezakhani, A ; Sharif University of Technology
Institute of Physics Publishing
2016
Abstract
The phase diagram of the quantum compass ladder model is investigated through numerical density matrix renormalization group based on infinite matrix product state algorithm and analytic effective perturbation theory. For this model we obtain two symmetry-protected topological phases, protected by a Z2 × Z2 symmetry, and a topologically-trivial Z2-symmetry-breaking phase. The symmetry-protected topological phases - labeled by symmetry fractionalization - belong to different topological classes, where the complexconjugate symmetry uniquely distinguishes them. An important result of this classification is that, as revealed by the nature of the Z2-symmetry-breaking phase, the associated quantum...
Fluctuation relation for heat exchange in Markovian open quantum systems
, Article Physical Review E ; Volume 97, Issue 4 , April , 2018 ; 24700045 (ISSN) ; Golshani, M ; Tayefeh Rezakhani, A ; Sharif University of Technology
American Physical Society
2018
Abstract
A fluctuation relation for the heat exchange of an open quantum system under a thermalizing Markovian dynamics is derived. We show that the probability that the system absorbs an amount of heat from its bath, at a given time interval, divided by the probability of the reverse process (releasing the same amount of heat to the bath) is given by an exponential factor which depends on the amount of heat and the difference between the temperatures of the system and the bath. Interestingly, this relation is akin to the standard form of the fluctuation relation (for forward-backward dynamics). We also argue that the probability of the violation of the second law of thermodynamics in the form of the...
Pressure effects on the carbon nano-tube embedded Y-123 superconductors
, Article Physica B: Condensed Matter ; Volume 487 , 2016 , Pages 42-46 ; 09214526 (ISSN) ; Manivannan, N ; Daadmehr, Vahid ; Tayefeh Rezakhani, A ; Hoon Kim, K ; Sharif University of Technology
Elsevier
2016
Abstract
It has been known that applying pressure and doping carbon nano-tubes (CNTs) can each affect the behavior of high temperature superconductors. Here, bridging these two effects in order to see how they can interplay, we investigate how the dc resistivity varies in both pure and CNT-doped polycrystalline YBa2Cu3O7-δ (Y-123) compounds under hydrostatic pressure. We demonstrate that the broadening of the resistivity transition in the CNT-doped samples (of 0.7 wt%) is smaller than the undoped samples. In addition, by increasing applied pressure, the doped samples exhibit a higher rate of the increase of the transition temperatures Tcon and Tcmid than the undoped samples. Interestingly as well,...
Quantum detailed balance conditions and fluctuation relations for thermalizing quantum dynamics
, Article Physical Review E ; Volume 98, Issue 5 , 2018 ; 24700045 (ISSN) ; Benatti, F ; Floreanini, R ; Marcantoni, S ; Golshani, M ; Tayefeh Rezakhani, A ; Sharif University of Technology
American Physical Society
2018
Abstract
Quantum detailed balance conditions and quantum fluctuation relations are two important concepts in the dynamics of open quantum systems: both concern how such systems behave when they thermalize because of interaction with an environment. We prove that for thermalizing quantum dynamics the quantum detailed balance conditions yield validity of a quantum fluctuation relation (where only forward-time dynamics is considered). This implies that to have such a quantum fluctuation relation (which in turn enables a precise formulation of the second law of thermodynamics for quantum systems) it suffices to fulfill the quantum detailed balance conditions. We, however, show that the converse is not...
Quantum Estimation: Properties and Calculation of the Quantum Fisher Information and Adaptive Scheme
, Ph.D. Dissertation Sharif University of Technology ; Rezakhani, Ali (Supervisor)
Abstract
In this thesis , we study quantum estimation , its primary tools and different approaches . To this end , along with reviewing the main concepts of classical and quantum estimation , the Cramer-Rao inequlity which establishes a lower bound on the precision of estimation has been used . This lower bound can be calculated using the quantum Fisher information . In order to explore properties of the quantum Fisher information , we study the continuity relation of this quantity in the most general case and we calculate it for different quantum states . To underline the importance of the continuity relation , one can demonstrate an estimate of the value of the quantum Fisher information...
A Review of Quantum Uncertainty Principle and Some of Its Consequences
, M.Sc. Thesis Sharif University of Technology ; Rezakhani, Ali (Supervisor)
Abstract
In quantum mechanics, every system is described by a state function. The state function determines the probability of different outcomes of a certain measurement which is performed on the physical system. The connection between uncertainties about different measurements is presented by inequalities best known as Heisenberg’s uncertainty inequality. In face, the uncertainty relations state that there exist incompatible measurements, to which the outcomes of measurements cannot be predicted simultaneously. Although the uncertainty relations can be inferred from mathematical formalism of quantum mechanics, there is a profound relationship with other aspects of physics. Here we investigate the...
Review of Thermalization in Closed Quantum Systems
, M.Sc. Thesis Sharif University of Technology ; Rezakhani, Ali (Supervisor)
Abstract
For a physical system, equilibrium is defined as a state in which the values of macroscopic quantities describing the system do not change in time. We observe systems around us reaching equilibrium every day. Describing such a seemingly simple phenomena has remained as one of the important challenges in theoretical physics. So far, various explanations for thermalization (approach to equilibrium) have been offered within classical and quantum thermodynamics. In classical statistical mechanics, the microcanonical ensemble provides a suitable prediction of the thermal behavior of a closed system. In this ensemble, using ergodic hypothesis and chaos theory one can assume that all microstates...
Optimal Coherent Control of Quantum Dynamics: Process-Based Approach
, Ph.D. Dissertation Sharif University of Technology ; Rezakhani, Ali (Supervisor)
Abstract
One of the main tools of the developing quantum technology is making the desired quantum gates and processes in the presence of the environmental noises. In this thesis, we first derive a Markovian master equation which defines purely the time evolution of the dynamics (process matrix) of the open system rather than its state (density matrix). This master equation indeed describes the time evolution of the Choi-Jamiolkowsli matrix which is independent of the state of the system at all times including the initial state. The n, by using this master equation we provide a scheme to manipulate optimally and locally the dynamics of the open system by external coherent agents. Such scheme...
Dynamical Behavior in Statistical Mechanics of Open Quantum Systems
, M.Sc. Thesis Sharif University of Technology ; Rezakhani, Ali (Supervisor)
Abstract
A fundamental question in investigating decoherence and equilibrium of a system in contact with a bath is how its entropy changes in time. Normally, von Neumann’s entropy is used in such studies to quantize degree of decoherence. Recently, certain researches have been conducted addressing entropy rate and various bounds have been achieved for this quantity, utilizing which one can discuss decoherence rate and equilibrium state of open systems.In this thesis, we introduce these bounds and try to improve them. Using improved bound we will show that for almost all conceivable initial states of the system and the bath, average of entropy rate will be negligible. This result is obtained under...
Effects of Non-Markovian dynamics on the Energy Transport Processes in a Quantum Network
, M.Sc. Thesis Sharif University of Technology ; Rezakhani, Ali (Supervisor)
Abstract
In this thesis we are going to study the effects of Non-Markovianity on the excitation energy transport(EET) and compare it with Markovian effects. We will see that the shape of a network affects its efficiency. The speed of EET in linear networks is slowed down as Non-Markovianity is increased and this in turn lowers the efficiency of linear networks in Non-Markovian regime. Finally, we compare the efficiency of different networks
Review of the Range of Validity of Markovian Master Equations for Harmonic Oscillators
, M.Sc. Thesis Sharif University of Technology ; Rezakhani, Ali (Supervisor)
Abstract
Quantum mechanics, in the first place, investigates systems by introducing some principals about Hilbert space, Schrodinger equation etc. which are recognized as closed quantum systems. In principal, this is not possible to separate a system from its surrounding environment. Thus, the implications of the environment on the evolution of the system must be taken into consideration. As a matter of fact, all systems are considered open in a sense that, it is interacting with another system called the environment. In such circumstances, we tend to represent a description of open quantum systems in a way that following the evolution of the total system, i.e. system and the environment, is not...
Efficiency of Excitonic Energy Transfer Phenomenon in Multi-Levels Quantum Systems
, Ph.D. Dissertation Sharif University of Technology ; Rezakhani, Ali (Supervisor)
Abstract
The process of energy transfer in quantum systems is an interesting phenomenon due to the emergence of quantum effects . This phenomena can be studied in one of two possible spaces : real space and energy space of the system . In addition , to evaluate how this process is successful , one can define an efficiency as the population of a target state . Finding the approaches to increase this quantity takes into account one of the main objectives of the current researches . On the other hand , isolating the quantum systems from the surrounding environment (bath) in practice is impossible and then interaction between them is inevitable . In this research , we provide a comprehensive...
An Investigation into Entanglement in Electrical Transport in a One-dimensional Model Using Transfer Matrix Method
, M.Sc. Thesis Sharif University of Technology ; Rezakhani, Ali (Supervisor) ; Shokri, Ali Asghar (Co-Supervisor)
Abstract
This thesis analyzes the scattering of a propagating electron from a single bound electron .The study demonstrates how the scattering of the propagating electron from the bound electron causes entanglement between two electrons. The study then considers the impact of spin-dependent scattering in the presence of Hartree and exchange potentials. In the first step, only an exchange potential is studied. Transmission coefficients are calculated for spin-flip and non-spin-flip states by solving the Hamiltonian equation in different regions, applying the continuity boundary conditions for the wave function and its derivative in each region, and using the transfer matrix method. Transmission...
An Approach for Dynamic Selection of Virtual Machines for Migration in Cloud Data Centers
, M.Sc. Thesis Sharif University of Technology ; Movaghar Rahimabadi, Ali (Supervisor)
Abstract
Increasing the workload of physical machines in data centers, performance of the system decreases and energy consumption increases. Various methods have been proposed to overcome this challenge and solve the problem. One of these solutions is the migration of virtual machines (VMs) from the over-loaded physical machine (PM) to another one, namely the under-loaded PM, in the clouds, which is effective in increasing the performance of the system and improving energy consumption When the performance of a PM is less than a certain threshold, due to overload, migration of the selected VM to a candidate PM can improve performance, if it is done in an intelligent way. Choosing the best suitable VM...
Synthesis and Characterization of a Novel Hydrogel Wound Dressing based on Silk Fibroin and Zinc Oxide Nanoparticles
, M.Sc. Thesis Sharif University of Technology ; Nemati, Ali (Supervisor) ; Shokrgozar, Mohammad Ali (Supervisor) ; Farokhi, Mehdi (Co-Supervisor)
Abstract
Recently, some wound dressings have been designed that are expected to enhance the wound healing process and prevent blood bleeding and infection. Polymeric dressings have attracted attention due to their biocompatibility, biodegradability, lack of toxicity, and non-allergenic nature. There is widespread interest in using silk fibroin (SF) for this purpose because of its unique properties. Given these points, we have designed an injectable antioxidant hydrogel wound dressing based on SF and Polydopamine(PDA) modified ZnO nanoparticles. First, ZnO nanoparticles were doped with Cu and then modified with PDA (ZnCuO@PDA). XRD, FTIR, SEM, and TEM characterizations were carried out to confirm the...
Binding Energy of Multi-Partite Quantum Systems based on Quantum Thermodynamics Viewpoint
, Ph.D. Dissertation Sharif University of Technology ; Bahrampour, Alireza (Supervisor) ; Rezakhani, Ali (Supervisor)
Abstract
Examining composite quantum systems through quantum thermodynamics, we face the new concept of binding energy. In this thesis, we are going to present a general definition for binding energy in quantum systems which covers any kind of interactions. First of all, we examine the possibility of energy exchange in a quantum system using quantum thermodynamics. In this theory, energy exchanges of an open quantum system may be divided in to two portions: heat and work; due to an accepted definition, heat is the portion of energy that is supposed to change entropy, while work has no influence on that. In this research, we restrict our calculations to the systems which are thermally closed and...
Analysis of Entanglement in Ladder Lattices
, M.Sc. Thesis Sharif University of Technology ; Jafari, Akbar (Supervisor) ; Rezakhani, Ali (Supervisor)
Abstract
Since concepts in quantum information theory has recently been applied to characterize states in many-body systems, we survey entanglement of the ground states in the S = 1/2 antiferromagnetic Heisenberg ladder systems and 2D square lattices. The Lancz¨os method for exact diagonalization of quantum spin models are used to find the ground states. Moreover, effect of defect in ladder on entanglement and ground state energy are studied
Quantum Estimation of Open Systems Using Extended Cramer-Rao Bounds
, M.Sc. Thesis Sharif University of Technology ; Rezakhani, Ali (Supervisor) ; Alipour, Sahar (Co-Advisor)
Abstract
Any physical system is characterized with some set of quantities or parameters, knowing which, is equivalent to estimation of the system. Evaluating such parameters is usually done using tomography methods. An important question to ask, is how to increase the precision of measurement, being able to do some specific set of physical operations, say, measurement?
this question is more important in parameter estimation in quantum meanical systems. It has been shown that, quantum meanics causes a fundamental limit, on precision of estimating su parameters, escribed by the so called “antum Cramér-Rao bound”.We must note that almost all quantum meanical systems are interacting with the...
this question is more important in parameter estimation in quantum meanical systems. It has been shown that, quantum meanics causes a fundamental limit, on precision of estimating su parameters, escribed by the so called “antum Cramér-Rao bound”.We must note that almost all quantum meanical systems are interacting with the...
The Role of Quantum Coherence and Geometry on the Excitonic Energy Transfer in Photosynthetic Structures
, M.Sc. Thesis Sharif University of Technology ; Karimipour, Vahid (Supervisor) ; Rezakhani, Ali (Supervisor)
Abstract
It has been of great interest to know whether quantum effects can play an essential role in the biological processes. Considering that quantum features, such as coherence and entanglement,can be harnessed to perform quantum information processing tasks, which are believed to be hard classically, the question is whether nature has also exploited these features in order to enhance the performance of biological systems. Although the presence of warm and wet environment around the biological systems results in the rapid destruction of quantum effects, recent experiments reported the existence of quantum coherence in light-harvesting complexes of some photosynthetic systems.This coherence lasts...