Sharif Digital Repository

Studying the puzzling aspects of quantum phenomenon is quite important subject from different points of view. It must be specially regarded through some major aspects such as: wave-particle dualty, Bell’s theorem no-go theorems, complementarity, entanglement and measurement problem. In this project, we survey subsequently the above topics with a careful attention regarding the measurement problem. One of the most relevant ways claiming to solve measurement problem is the decoherence theory. Scrutinizing the details of formalism and description basis of decoherence, we critically explain and asses the different aspects of this theory  

The measurement problem is one of the issues that is still under debate about the Quantum theory. A significant part of literature during the recent years includes the standard point of view about this problem (including the separation of microscopic and macroscopic domains) and the criticisms of some major physicists in this context. Among these, alternative theories and interpretations have been getting more attention. Experimental tests of Quantum Mechanics in the macroscopic domain and their comparison with alternative theories have always encountered various difficulties (in particular the decoherence phenomenon). Anyway, towards the end of the last century, with the advances in... 

Although quantum mechanics has thrilled a multitude of successes since its birth, it has also generated puzzles that persist to this day. These puzzles are largely connected with the role of measurement in quantum mechanics. Therefore, we are dealing with individual phenomena and that our possibilities of handling the measuring instruments allow us only to make a choice between the different complementary types of phenomena. Within the framework of delayed-choice experiments, the choice between complementary types of phenomena is postponed to the moments after the preparation of system is a superposition state. Regarding the probability theory, we have concluded that the delayed-choice... 

The origin of life is one of the fundamental problems of the science, which is not yet answered appositely. The building blocks of life’s molecules, including nucleic acids (DNA and RNA) and proteins, are composed of carbohydrates and amino acids. At the chemical level, these building blocks have definite chirality. This phenomenon is known as biological homochirality. Due to the fact that this phenomenon has taken place in the early stages of life, it is believed that the life’s origin is to a great extent connected to the origin of biological homochirality. Like every other system, at the microscopic level, life’s molecules are composed of atoms which are governed by the lows of quantum... 

Considering the consistency between the predictions of a theory with what is observed in experience, Quantum Mechanics is the most accurate theory in the history of physics. However, is does not present us an unmbigiuos and realistic description about the nature of the microscopic phenomena. At the heart of these issues is the so-called measurement problem. The formalism of the quantum mechanics is unitary and deterministic. Nevertheles, when one does measurements, the unitary process of the evolution of wave-function breaks due to a stochastic abruption. The results of the measurements are in correspondence with the everyday experience of the observer. Yet, the theory itself does not... 

Decoherence is one of the candidates for solving the measurement problem, and is among the group of theories which are trying to solve the measurement problem within the quantum theory, by removing the wave function reduction axiom. The main idea is to consider the environment of the system which was ignored in the classical physics. The openness of a quantum systems makes the system and its environment entangled, and that leads to the transmission of system information to the environment, and finally, the system loses its individuality. This approach claims that since the observer can’t control and consider all the degrees of freedom of the environment and has only access to the system,... 

Quantum Theory leads to results that are consistent with the very high accuracy with experience and also includes a wide range of empirical phenomena. Hence, quantum mechanics is accepted as the best and most acclaimed physical theory. However, there is still no consensus between physicists on the interpretation of parts of this theory. One of the unresolved issues in quantum mechanics is the measurement problem. The basis of the measurement problem is a kind of transition from the quantum world to the classical world. The fundamental question that arises here is, where is the boundary between quantum mechanics and classical mechanics? and how can be described the transition from quantum... 

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... 

In the early days of quantum mechanics it seemed that, this theory is presented to describe atoms and molecules. As the time went on, by distinguishing different applications of quantum mechanics a question raised in scientists minds. Is it possible to see strange quantum effects in every day life. In this regard several attempt have been made to see such properties. One of these phenomena is observing interference effects for Fulleren molecules. In this thesis we investigate different properties of a macroscopic quantum system in different situations. We showed that an asymmetric double well potential, which is a macroscopic quantum system in interaction with environment violates... 

It has been about a century since the introduction of the theory of quantum mechanics. This theory is a branch of physics that describes the behavior of nature in very small scales and microscopic systems . Since no quantum system is entirely isolated from its surroundings , it is necessary to study their interactions with the environment to understand them accurately. The theory of open quantum systems provides the theoretical and conceptual framework needed to consider these interactions. Then using the appropriate quantum operations , the evolution of the combined system can be investigated. Moreover , considering the environmental effects, some quantum features such as dissipation... 

In quantum mechanics different states of a system can only be found after a measurement is performed and before the measurement the system may not be in any particular state unless it was prepared in a certain manner. Even so there is no telling the state of system. This behavior raised questions such as: why results of a measurements happen to be in certain states and not in others? And also why an apparatus picks one result over the others? The Decoherence and Transition from quantum to classical behavior may hold the answer to this questions. An example of such transition, one can name the wave-particle duality in double slit experiment. Another example is the formation of straight tracks...