Sharif Digital Repository

Optomechanical systems have attracted considerable attention in the last decade. Such a raising prominence is mainly due to its capability in providing new insight into the quantum behavior of macroscopic objects and exploring the interface between quantum and classical mechanics. Alongside this fundamental quest, cavity optomechanics has many other benefits, ranging from very precise measurements on forces and positions to quantum information processing. In this thesis, we investigate quantum properties of such systems. Particularly, we study cooling of the mechanical resonator toward its ground state and the entanglement between this mechanical resonator and the cavity field. Cooling the... 

Optomechanical systems have attracted much attention over the last decades, especially as a macroscopic lab for observing quantum mechanical effects . In this thesis , optomechanical quantum memories are studied . In p articularl , we study cooling of the mechanical resonator down to its ground state, which is the necessary condition to obtain a good quantum memory and also explore the limitations of cooling and storing protocols . Quantum state of light can be stored in the mechanical mode of the system by optomchanically induced transparency effect (OMIT) . This effect is formally equivalent to electromagnetically induced transparency effect (EIT) which is seen in an ensemble of... 

A cavity optomechanical system is created when the resonance frequency of an optical cavity is influenced by the position of a mechanical oscillator. To observe quantum effects and quantum applications of these systems, cooling of mechanical mode(s) participating in these interactions is very important. At first, the dissertation focus on the trend that people were trying to study radiation pressure theoretically and experimentally and then present classical and the quantum picture of radiation pressure. Next, the diverse geometries are based on the optomechanical interaction are described concisely. Fabry-Perot cavity with one degree of freedom has considered and then the Stokes and The... 

Circuit model quantum computing, provides a powerful tool that allows humans to process information faster. Excessive noise and its impact on quantum systems which can lead to data loss are major obstacls in accessing quantum computers, since the systems proposed to make quantum computers are indeed open systems, noise can cause data loss. Therefore, the achievement of quantum computing, has been delayd. One of the most effective ways to neutralize this noise is to use a geometric phase to make evolutions. Holonomic quantum gates utilize the geometric phase to implement the noise resilience gate. In this thesis, we intend to use a composite optomechanical system, consisting of two optical... 

Continuous-variable quantum key distribution (CV-QKD) protocols, that share an unconditionally secure key between at least two legitimate parties, are based on the modulation of information on the continuous characteristics of light. CV-QKD is low-cost, has a high rate, and is compatible with conventional technology. However, one of the major drawbacks of CV-QKD is its poor performance at long distances. Such a limitation can be overcome with the assistance of noiseless linear amplifiers (NLAs). In this thesis, we aim to use Quantum scissor (QS), as a realistic NLA, to overcome this limitation. To this end, we suggested a three-photon QS that truncates all multiphoton number states with... 

Optical bistability is one of the most important results of nonlinear optics. The term optical bistability refers to the situation in which two different output intensities are possible for a given input intensity. Interest in optical bistability stems from its potential usefulness as a switch for use in optical communication and in optical computing. Optical bistability is resulted by nonlinear phenomena such as kerr effect, two photon absorption and saturable absorber. In this thesis, we study the optical bistability in a double-coupler ring resonator, in which the right half of ring is made of an erbium doped fiber amplifier for compensating the loss by the gain of EDFA, and the left half... 

In this thesis, chaotic behavior of a photonic micro-resonator is investigated. First, a Lagrangian formulation is introduced for the system. Then, by applying a multi-reflection method, a closed formula is obtained for the radiation pressure. Use of this equation in the coupled differential equations describing dynamics of the problem gives us a suitable model for exploring the behavior of the micro-resonator. In this stage, we compare our results with experimental data too. On the other hand, using above mentioned formulation, chaotic behavior of the micro-resonator is investigated using numerical method. Finally, a period-doubling route to chaos appears in our results as is observed in... 

Photonic quasi-crystals fibers as well as photonic crystal fibers have very interesting features, such as endlessly single mode, ultraflattened dispersion and high birefringence. Due to the wavelength dependence of their cladding and the ability to manipulate the air holes in the cladding can improve physical properties of fibers. Recently photonic quasi-crystal fibers have been studied due to interesting structure and observation of improved physical properties in them than the photonic crystal fibers and their applications in communication systems. In this thesis and in the first section, we have studied and reviewed the various optical properties of photonic quasi-crystal fiber with fold... 

In this dissertation, we propose and analytically investigate a scheme for effective three-dimensional cooling of a nanoparticle optically trapped in a Fabry-Perot cavity using multiple cavity modes. By employing active feedback cooling using amplitude modulation of cavity modes, our approach allows to access the UHV regime without the need for any additional means like an external tweezer or a radio-frequency trapping approach. For a set of feasible experimental parameters, we demonstrate that the cooling rates achievable are sufficient to overcompensate recoil heating. Therefore the approach is suited to trap a particle for indefinite times at UHV pressures, where air damping cannot... 

Systems with permutation symmetry are prevalent in physics. In practical applications of quantum information, we frequently deal with multipartite quantum states that are invariant under permutations. These states may have complex structures that are hard to deal with due to quantum correlations between the parties. Luckily, symmetry can lead to independence. An important aspect of our research is to study the useful tools to harness symmetry in quantum information, to efficiently tackle the complexity.A representative example of such tools, is the quantum de Finetti theorem, which tells us that one part of a symmetric state can be treated as a mixture of identically prepared quantum states... 

Quantum key distribution (QKD), as one of the applications in quantum information processing, allows two distant legitimate parties to establish a set of secure keys even in the presence of an untrusted environment controlled by an eavesdropper. In general, QKD mainly includes two families, namely, discrete variable quantum key distribution (DV-QKD) and continuous variable quantum key distribution (CV-QKD). In CV-QKD system, the sender Alice, encodes information on the quadratures of the optical field with Gaussian modulation, and the receiver Bob, decodes the secret information with homodyne or heterodyne detection so that this system promises a higher secret key rate than its DV-QKD... 

In quantum communication,polarization degree of freedom is of particular importance, as polarization is used in many quantum key sharing protocols. During the transmission of photons, the polarization may be affected by environmental factors and change, for exam- ple, changes in tension and temperature disturb the polarization. In this thesis, methods of compensation for polarization change is investigated like by applying electric field, mag- netic field, strain,also a review of methods of measuring polarization disturbance and its compensation in quantum transmission lines, especially fiber optics, design and construction of compensators (electrical polarization controllers), based on... 

Quantum key distribution is one of the practical quantum information technologies in labo- ratories with existing equipments.In quantum key distribution protocols, the main challenge is the secrecy of key distribution. One of the new methods of quantum channel error esti- mation is the use of weak measurement. In this thesis, after introducing the main quantum key distribution protocols, we introduce weak measurement and sequential weak measure- ment concepts: the weak measurement methods are exployed to obtain the phase difference between two polarizations with high accuratly. It is also used for in line monitoring and error estimation parameters in some quantum key distribution protocols.... 

Optical memories are key elements in integrated photonics circuits. Semiconductor micro-ring lasers are good candidates in designing and constructing optical memories. Designing of these memories are usually inactive and are based on nonlinear optics such as Kerr effect or saturation absorption. Bifurcation analyses show that semiconductor micro-ring lasers coupled with waveguide, in the presence of external feedback, have two stable modes. At the coupling point, clockwise and counter clockwise states for one mode have zero and for another mode have π phase differences. In this project, by using boundary conditions, we obtain resonance frequency of a system of two semiconductor lasers in the... 

Communication is nothing but making correlation between sent and received data via mediating particles and in quantum communications these are the quantum carriers that create these correlations. Since quantum carriers can be correlated in ways inaccessible to classical carriers, quantum communication protocols can perform tasks that are classically impossible or less efficient. Therefore, it is expected that in a suitable model, the quantum advantage of any quantum communication protocol can be expressed in terms of the quantum correlations of its carriers. Here we consider two quantum communication protocols, namely remote state preparation (RSP) and quantum locking of classical... 

The primary objective of this thesis is to provide solutions addressing some security loopholes in continuous variables quantum key distribution protocols. The coherent detection method is utilized in this particular quantum key distribution scheme, which is a phase-sensitive detection. To measure in the quantum noise limit in the detection part, we need a local optical oscillator, which must possess a high intensity and a consistent phase correlation with the quantum signal. Therefore, reconstructing the emitter’s reference phase in the receiver’s detection system is considered as one of the most critical challenges in these protocols. In order to attain this goal, in the early versions of... 

The concept of entanglement exists in the common area of the quantum optics and quantum information. Quantum optics is the best tools for investigating of this quantum informational phenomenon experimentally. One of the instruments that let us observes experimentally macroscopy entangeled state is Fabry-Perot Cavity. Striking of photons with the mirror of cavity transfer effective mommentom to it, and oscilating of mirror creates new modes: stocks and anti-stocks modes. Studing quantum state of these modes shows the entangling between photon and phonon (oscilating of mirror) modes. We assume that light beam enters the cavity from a semi-transparent mirror. So cavity is the system with... 

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... 

Nowadays, fiber sensors have lots of usage in complicated structure and oil industries. There is some ways for leak detection in pipelines to low the cost of damage. One of the best is using the distributed fiber sensors for monitoring and detection of leakage in pipelines because of their ability to accuracy measurment. The leakage produces some kind of acostic wave that affect on fiber optic as a stress. There is lot of methodes to measure the location of stress in fiber. One of them is measuring the polarization mode coupling. A polarization diversity detection system for location of polarization mode coupling has been studied both theoretically and experimentally for use with... 

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...