Sharif Digital Repository

In this investigation has been tried to indagate the Bell’s inequality both theoretically and experimentally. This inequality published by John Bell in 1964 on the EPR argument. In the EPR argument they reasonably deduced that quantum mechanics with the wave function interpretation is incomplete (but proposing correct results), so we must looking for a deterministic and more fundamental and underlying theory than common quantum mechanics, the alternative theory shall contain Reality and Locality assumptions and also could produce current quantum mechanics results. Afterward, scientific probation started for finding a deterministic theory that including hidden variables, infact supplement... 

Entanglement plays a major role in quantum communication as the main resource of the network and makes it possible to perform protocols such as quantum teleportation and quantum cryptography which are not achievable in classical networks. Yet, being a very fragile resource against noise, which inevitably is more destructive as the distance increases and as time passes, makes it a very hard to share entangled pairs between two points at a long distance. This discouraging result for linear networks, has prompted investigation of entanglement percolation and entanglement distribution in regular one- and two-dimensional networks with various (i.e rectangular, triangular and hexagonal)... 

To answer the explanabilty of consciousness, we have first clarified the terms “consciousness”, “explanation”, and “physic”, concluding that consciousness and physics should be integrated in a single unified explanatory system. The common problem we have targeted in this work is “direct observation”. Then, inspired by Bergson, we have suggested that ,in direct observation, there is a unity between observer and the observed, out of which the qualitative characteristic of experience or qualia is constructed. Following computer graphic courses, this unity is called “rendering unity”. In the next scientific step, by analyzing the Wigner’s friend paradox, we have stipulated that, in direct... 

In this thesis, we study two important quantum effects at deSitter spacetime and using the Schrödinger field theory, the power spectrum of massive non-interacting, minimally coupled scalars in a fixed de Sitter background would be obtained. To calculate the N-point function in Schrödinger field theory, the ”in-in” formalism is extended in the Friedmann- Lemaître-Robertson-Walker (FLRW) universe. This formalism in such picture would have a crucial role for evaluating the correlation functions of those quantum states naturally written in Schrödinger picture. We compute the three-point function for primordial scalar field fluctuation in the single field inflation by this in-in formalism. The... 

Behind almost all of the communication protocols and quantum information processing tasks, there is the assumption of existence of a shared reference frame between the parties. However, it is interesting to ask whether it is really necessitated to have a shared reference frame in order to succeed in these tasks. In this thesis, after investigating the effect of the absence of shared reference frame, classical and quantum communication in the absence of shared frame via spin ./5 particles are reviewed.Then, the concepts of relative and collective parameters of composite systems are discussed and the relative parameters of a general pure two qubit state are characterized.Finally, certain... 

In the last decade, the developement of Quantum Information theory have created new concepts and methods in the study of quantum many-body systems, that previously weren’t available to physicist involved in areas such as condensed matter and field theory. One of the most important steps is the insight provided by structure of the many body system’s Hilbert space. Although, it is not completed, it leads us to deep results.In fact, we have found out that with high probability, the state of a many-body system is located in a very small corner of the Hilbert space, which requires only a small number of parameteres to describe it, that with respect to the number of particles, it grows linearly... 

Entanglement is one of the key resources of quantum information science which makes identification of entangled states essential to a wide range of quantum technologies and phenomena.This problem is however both computationally and experimentally challenging.Here we use autoencoder neural networks to find semi-optimal measurements for detection of entangled states. We show that it is possible to find high-performance entanglement detectors with as few as three measurements. Also, with the complete information of the state, we develop a neural network that can identify all two-qubits entangled states almost perfectly.This result paves the way for automatic development of efficient... 

Entanglement is one of the unique phenomena in quantum systems that does not have any similar phenomena in classical systems. Entanglement has been used in many protocols of quantum information theory, and there is agreement on its key role in quantum computations and quantum communication protocols. Therefore, studying its dynamics as well as preventing its degradation is important for us. Extensive studies have been done in this field, including the study of entanglement evolution in a situation where all parts of the system are entangled with one of its sub-system has irreversible dynamics due to interaction with its environment [1], [2], [3], [4], [5], [6], [7], [8]. However, the study... 

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... 

Achievements in the synthesis of polycatenanes promise new opportunities for having and designing new smart materials. However, the out-of-equilibrium dynamic of polycate-nane is largely unstudied. This research studies the interplay of poly[2]catenane topology and hydrodynamic interactions in pure shear flow using the MPCD method. To question the effect of topological interaction, we simulated systems with bonded rings alongside systems with poly[2]catenane. In order to investigate the effect of hydrodynamic interaction, each system was examined using the random solvent method as well. Our study shows the poly[2]catenane structure can control the shear and stress by twist and rotation... 

Entanglement is a defining characteristic distinguishing quantum systems from their classical counterparts. Since previous research has proven this phenomenon is the main reason for supremacy of quantum information processing protocols over classical information processing, the study of quantum entanglement has increasingly garnered more importance. On the other hand, our comprehension of multi-body and many-body systems continues to evolve. To understand these systems better, it is necessary to research their crucial feature, entanglement. In this study, after introducing multipartite absolutely maximally entangled states, their statistical distribution will be explored. This task will be... 

In this thesis, we will examine quantum state and entanglement transfer. Quantum state and entanglement transfer are requirements for the development of quantum technology. Transferring the output state of a quantum processor to the next processor, which can be at an arbitrary distance from the first processor, is one of the direct applications of quantum state transfer. On the other hand, entanglement transmission is a necessary prerequisite for quantum protocols. For example, preparing the entangled pair in a laboratory and transferring one share of an entangled pair to another place in order to create entanglement between different points is essential for building quantum networks. Also,... 

Entanglement is one of the quantum resources that has crucial applications in many quantum tasks such as quantum teleportation, quantum key distribution, and quantum computations. Therefore, identifying entangled states is of great importance to us. There are various methods for distinguishing entangled states from separable states; however, each method is applicable under specific conditions or for special quantum states. One of these methods is measuring an observable, which, if its expectation value is negative, indicates the entanglement of the state; otherwise, it shows its separability. These observables are called entanglement witnesses, and for every entangled state, there exists at... 

We are interested in the relation between entanglement and quantum phase transitions. We have presented a formulation on how the entanglement of a very large the system is related to the entanglement of a small part of system. The renormalization of entanglement is an indicator of the critical behavior of the models. The framework of our approach is introduced about the Ising model. In particular, we show that derivative of entanglement developes a minimum close to the critical point. We further clarify that this minimum point approaches to the exact critical point of the system as the system becomes thermodynamic. This phenomenon is governed by an exponent that is closely related to the... 

In recent studies, it has been shown that entanglement is not the only kind of genuinely quantum correlation. There exist models of quantum computation that provide exponential speed up over the best known classical algorithms and don’t have any quantum entanglement. These models show that in some cases separable state can be very useful in quantum computing models. Look for a property that causes the performance of these scenarios, quantum correlation being one of the most important concepts, including but not limited to entanglement. Local noise can produce quantum correlations on an initially classically correlated state, provided that it is not represented by a unital or semiclassical... 

Coupling of optical and mechanical degrees of freedom through radiation pressure was, first, observed in the experiments for detection of gravitational waves. Recent experimental advances have granted reality to the long-hankered-after coupling between microscopic and macroscopic systems. In the first step, this thesis will review different aspects of cavity Optomechanics, such as: cooling, side-band formation and dynamics of an Optomechanical cavity. Then we will go further and study the Optomechanical dynamics of a cavity in the presence of an atom. To do so, we will analyze the entanglement, created between the center of mass motion of the atom and the mirror and will probe into its... 

In this thesis, we have implemented the quantum renormalization group method to study quantum spin systems. We reviewed the recent progress to calculate the quantum information properties of these models. The recent investigations show that concurrence and entanglement are two quantities which can show quantum critical properties of the quantum systems. More specifically, the derivative of entanglement and the second derivative of ground state energy show divergent behavior at the quantum critical point. Moreover, the ground state fidelity for two different parameters close to quantum critical point shows a drop which leads to a divergent behavior in its corresponding susceptibility. We have... 

In this M.Sc. thesis the behavior patterns of the cavity quantum electrodynamics of complex systems are analyzed, such systems are quantum optic multi-partite systems and consist of an arbitrary number of quantum dots in interaction with arbitrary number of cavity modes.
First, the coefficients matrix of the ket sate of the system was measured, in order to achieve it; the general time-dependent state of the most general possible system was specified. Its related Hamiltonian was written, and finally the Schrodinger equation was measured in different coupling regimes. It was done in Schrodinger picture without any approximation.Second, the presence probabilities of the quantum dots of any... 

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  

Entanglement is the most important quantity in quantum information processing tasks. However the provision of the required entanglement between various quantum parts is one of the most challenging breakthroughs in realization of quantum processors. One of the scenarios for entangling various parts is use of naturally interacting qubits, called “spin chains”. The low level of required control and the ability of entangling mesoscopicaly separated parts cause such systems to be attractive for using in future low dimensional silicone compatible technology quantum processors. Accordingly in this thesis by considering a ferromagnetic spin system in which is conserved and by initializing the...