Sharif Digital Repository

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... 

Considering the widespread applications of amides, synthesis of these compounds is of great importance. The one pot oxidative addition of amines to aldehydes is one of the most simple and appealing approaches to synthesis amides. With the aim of developing a mild and convenient approach towards preparation of amides, numerous methods have been reported for this important process over the past few decades. These improvements have been mostly related to the optimization of reaction conditions and the use of more challenging substrates including diverse derivatives of aldehydes, and also design a novel and effective catalytic systems. Due to the various advantages of supported heterogeneous... 

Research on the characteristics of the near field earthquakes has been very popular in recent years due to the considerable damages they have caused to the structures located within the vicinity of seismic sources. The incapability of response spectra for structural damage assessment has been revealed through recent investigations. The recorded data show that the near field earthquakes are often accompanied by a large energy pulse in the beginning of the records caused by the so-called directivity phenomenon. That has encouraged many researchers to study the possibility of using the velocity pulse of these records to evaluate the imposed seismic demands on structures. Thus, investigating the... 

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... 

In this project, nonocrystalline zinc coatings with grain sizes within the range of 22-63 nanometers were produced on yellow-brass plates by electroplating in an acidic chloride bath in the presence and absence of additive has been investigated.current densities and bath stirring speeds change from 2 to 6 A/dm2 and 0 to 400 rpm respectively.To determine crystallite size, X-ray diffraction technique (XRD) was utilized;it was found that the use of additive has effectively refined the grain size and optimum current density is 3 A/dm2 to reach this objective.. it was observed that grain size increased continuously with increase in bath stirring speed. The results coming from XRD tests were... 

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.... 

Considering the widespread applications of α-aminonitriles, their synthesis is of great importance. The Strecker reaction represents a direct and appealing approach for the preparation of α-aminonitriles. With the aim of developing a mild and convenient approach towards the construction of α-aminonitriles, numerous methods have been reported for this important process over the past few decades. These have been mostly related to the optimization of reaction conditions and the use of more challenging substrates including ketimines and ketiminium salts and design of novel and effective catalytic systems. Due to the various advantages of supported heterogeneous catalysts and in our aim to... 

Financial and monetary markets are appropriate areas of applying Chaos Theory. Firstly, current theories of financial and monetary economics state that economic and financial variables such as exchange rates and stock prices are stochastic, so forecasting them is almost impossible. Secondly, if we find the hidden ordered and deterministic trends, we can achieve considerable profits. In this piece of research, we evaluate different methods and tests of detecting chaos in financial time series, and choose the most applicable methods to test financial markets’ indices. The main three indices of Tehran Stock Exchange, including Price, Finance and Industry indices, are examined. A sample of the...