Sharif Digital Repository

One of the most elusive problems in quantum mechanics is the transition between classical and quantum physics. This problem can be traced back to the Schrodinger's cat. A key element that lies at the center of this problem is the lack of a clear understanding and characterization of macroscopic quantum states. Our understanding of Macroscopic Quantumness relies on states such as the Greenberger-Horne-Zeilinger(GHZ) or the NOON state. Here we take a first principle approach to this problem. We start from coherence as the key quantity that captures the notion of quantumness and demand the quantumness to be collective and macroscopic. To this end, we introduce macroscopic coherence which is the... 

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... 

Quantum Information Processing (QIP) is one of the active areas of research in both theoretical and experimental physics. Any experimental technique that is used for a scalable implementation of QIP must satisfy DiVincenzo’s criteria [17]. Nuclear Magnetic Resonance (NMR) satisfies many of these conditions, but it is not scalable and cannot initialize the qubits to pure state [28]. NMR can be a great platform for studying the fundamentals of QIP. In this project, for a two­qubit system, we prepare pseudo pure states from the initial mixed states by using unitary operations and implement CNOT gates. According to the results of our experiments, we can apply all the gates with high fidelity.... 

In this thesis, we attempt to construct a model that can predict whether someone will retweet a tweet. For this purpose, we construct a machine learning model and we use Twitter’s network features as our model’s input. We collect about 1300 random tweets and their retweets to make retweet cascades. By collecting or calculating users’ features in each retweet cascade, we construct our desired input data for our model. We test both random forest and neural networks as our machine learning section of the model. Random forest is the most accurate of the two models, predicting retweet actions with an accuracy of 0.89. Additionally, we find out that two features of the network have the greatest... 

The importance of using a fast and automatic method to classify variable stars for large amounts of data is undeniable. There have been many attempts for classifying variable stars by traditional algorithms, which require long pre-processing time. In recent years, neural networks as classifiers have come to notice. This thesis proposes the Hierarchical Classification technique, which contains several models with the same network structure. Our pre-processing method produces input data by using light curves and the period. We use OGLE-IV variable stars database to train and test the performance of Convolutional Neural Networks based on the Hierarchical Classification technique. We see that... 

There are different approaches for implementing quantum gates as the main elements of quantum computers. In this thesis, we use the quantum optimal control approach to implement quantum gates. For this purpose, we use the two common methods of optimization, Krotov and second-order GRAPE of L-BFGS-B type to implement gates. First, we implement three gates X, CNOT and TOffoli, using both methods, and then, in order to compare and benchmark these methods, we also investigate a number of one, two, and three-qubit random gates. It is essential to implement and simulate high-quality gates in the shortest possible time. Therefore, in this thesis, we compare and benchmark the optimization execution... 

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... 

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... 

Physics underlies computer science because computation is a physical process. The fundamental question about computers is: What computations can be performed efficiently, and what computations are intractable? This is a question about the laws of physics and the consequences of those laws.Though we don’t know how to prove it from first principles,we have good reasons to believe that there are computational problems which are too hard to solve using digital computers based on classical physics, yet can be solved by computers which exploit quantum phenomena such as interference and entanglement. This is one of deepest distinctions ever made between classical and quantum physics, and it poses... 

Many quantum protocols that utilize entanglement are implemented between two distant bases. For various reasons, these two bases may not have a shared reference frame. In such cases, the mentioned protocols need to operate independently of the coordinate system. Therefore, identifying the entanglement of shared states between these two bases is not feasible with conventional methods, and alternative approaches must be found. The main focus of this thesis is to develop methods for identifying entangled states between two bases without the existence of a shared reference frame. In this thesis, we begin with a comprehensive review of the history of entanglement witnesses. Next, we investigate... 

The fuel consumption of displacement ships is one of the vital and sensitive issues in the marine transportation industry, which affects all economic and environmental aspects. There are few important parameters for displacement ships that can be changed and optimized to reduce fuel consumption and the resulting pollutants. In this study, extreme trim has been selected as one of these important parameters and it has been studied numerically using Star CCM+ software. It should be noted that the extreme trim approach is used when returning from a trip (when there is no load). The results obtained in the extreme trim mode showed a decrease of 26.76% in the resistance of the KVLCC2 tanker-ship... 

There are several methods for measuring thin film thickness, however, for the analysis of liquid film motors [1] we need a method which is capable of measuring the thickness using a single image of the film. In this work, we use the colors that appear on thin films, such as soup bubbles, which is a result of light interference to calculate the thickness of the layer  

With confidence in the recorded observations, the RLS method no longer estimates the recorded measurements by sensors, i.e. the displacement and speed of the floors, and only estimates the parameters. In contrast, in the EKF method, in addition to estimating the structure's parameters, a more precise estimation of the observations recorded by the sensors has been done by accepting the noise in the recorded observations. These methods, which are based on the Bayesian updating, investigate the two primary sources of uncertainty in a problem: a) measurement noise or observation noise, and b) process noise, which includes modeling errors. In these methodologies, the unknown system parameters,... 

In this thesis the sequent calculi for intuitionistic logic have been studied and compared with these calculi in classical logic, moreover soundness and completeness theorems for these calculi have been proved. Also an algorithmic method is presented to construct the proof-search with this feature that proof-search terminates and the subformula property preserved. In particular the analysis and comparison of two calculi IG and SIC provided by Tassi and Corsi have been done. Finally, we consider the calculus SJC, stack-based Jankov calculus which is similar to SIC and describes proof-search procedure for weak excluded middle logic. If the proof-search is successful in each calculus SIC or... 

In this study, different metal oxides were impregnated on the surface of ZSM-5 employed as photocatalysis for degradation of methylene blue dye used in the presence of ultraviolet light. The final products were characterized by powder X-ray diffraction (XRD) and fourier transform infrared (FT-IR) method. According to the proposed mechanism for the photocatalytic degradation of methylene blue based on these results, it was found that the reaction followed from the first-order mechanism. The results indicated that rate constant for pure ZSM-5 was 9.3〖 ₓ10〗^(-3) (min-1). Furthermore the impregnated ZSM-5 having 12% zinc oxide demonstrated the highest photocatalytic activity with rate constant... 

The vortex tube is a simple device that injects compressed gas (air) tangentially into the vortex chamber through one or more injection nozzles. After entering, the flow becomes rotational and an axial cold flow goes towards the cold outlet and a peripheral hot flow goes towards the hot outlet. Besides all the different applications of the vortex tube, the main application of this device is cooling. Here, the goal is to optimize the geometry and physical conditions to improve the performance, which is done by using a commercial software and numerical analysis of a vortex tube to understand the flow physics and optimization. In this research, we use experimental and numerical data for...