Sharif Digital Repository

Optical metasurfaces are 2D structures of a repetitive arrangement of a number of nanoparticles that are artificially constructed and do not exist in nature. Important applications of optical metasurfaces are meta lenses, flexible solar cells and extremely small antennas. Fabricating surfaces with nanoparticles of proper geometry under light radiation along with elastic deformation, we can have optical metasurfaces with selective reflection or transparency in the visible spectrum. The aim of this project is modeling of an optical metasurface with elastic deformation leading to change of color and transparency. For this purpose, assuming vertical light radiation and linear polarization, we... 

In this thesis, we study optomechanics of subwavelength nanoparticles based on the Green's function formulation. First, we investigate the optical force exerted upon Rayleigh particles in the free space using the dipole approximation method. Then, we present a new method based on the Taylor expansion of the polarization field to calculate the optical forces beyond the Rayleigh regime. Subsequently, we study the optical force exerted upon Rayleigh particles in non-free spaces, and model the backaction effect using the scattering Green's function. We show that the backaction effect can modify the polarizability of the particle and thereby can affect the gradient force, radiation pressure, and... 

The electromagnetic (EM) force is the pivot on which this thesis revolves. We inspect different formulations of the distribution of the EM force (and momentum) inside matter, and show that the Einstein-Laub force density is incompatible with special relativity. We study the exerted EM force on small particles in depth, and explain when the conventional dipole approximation fails to yield accurate results. We propose an all-dielectric structure which is able to trap very small dielectric particles (of diameters as small as 10 nm). One of the achievements of this thesis is an explanation for an adverse phenomenon observed in many experiments on the optomechanical systems employing... 

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... 

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... 

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... 

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... 

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, 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... 

The coupling of optical and mechanical degrees of feedom via radiation pressure has been a subject of early research in the context of gravitational wave detection. Recent experimental advances have allowed studying the modifications of mechanical dynamics provided by radiation pressure. First, this thesis reviews the consequences of dynamic back-action in optical microcavities with mechanical degree of feedom, and presents a unified treatment of its two manifestations: the parametric instability (mechanical amplification or oscillation) and radiation pressure back-action cooling. Then, by considering the Fabry-Perot cavity with two movable mirrors, and using Multi-Reflection Method, we... 

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... 

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...