Sharif Digital Repository

One of the problems facing quantum computation is errors due to interaction with the environment which destroy coherence of quantum states. Most schemes to design a quantum computer therefore focus on finding ways to minimize the interactions of the qubits with the environment. Constructing such systems with large numbers of qubits which are infallible is a hard task and far from being achieved in the near future. There is another quantum computational model which is called topological quantum computation, proposing a different solution. Qubits of this model are quasiparticles of a 2-dimensional topologically ordered system that are called Anyons. In this model gates are nonabelian... 

Quantum states are highly susceptible to noise and can lose their coherence easily. Thus, for the large-scale quantum algorithms results to be valid, it is necessary to use an error correction process to eliminate the errors. The theory of quantum error correction provides a comprehensive methodology for protecting quantum states against noise. In this theory, by adding ancilla qubits and carefully encoding, quantum states are prepared such that they can be robust to a great extent against errors. To perform a scalable quantum computation, we face an even more daunting task. If our quantum gates are imperfect, everything we do will add to the error. So the quantum error correction could be... 

Single molecule magnets due to their magnetic tunneling effect and the interaction they have with an external magnetic field are used widely in quantum computing and also the storage of data with high capacities. Polyoxometalates that are used as counter ions for cationic single molecule magnets, are able to affect their spin-couple nature via a magnetic exchange and also have an influence on the crystal accumulation in order to change the magnetic property of the molecule. In this research the probability of sedimenting a cationic single molecule magnet, [Mn4O2(CH3COO)7(bipy)2]+, with the use of anionic polyoxometalates with Keggin structures has been investigated. Thus, the single... 

In this report, we have formulated a new technique for characterizing quantum optical processes based on probing unknown processes only with coherent states and simply by measuring normally-ordered moments of output states. Our method has two substantial advantages in comparison with previous methods.First, for practical purposes of uantum-optical communications and information, predicting of the classicality or nonclassicality of output states from an unknown quantum process is generally important. Because of truncation of the Hilbert space in the Fock basis and/or exploiting Klauder theorem, antecedent methods failed to carry out foretelling the [non]classicality features of the process’... 

Quantum computation is an unconventional way to compute employing quantum Physics. In this way of computation, quantum superposition and quantum entanglement have crucial roles to surpass common ways of computation. There is a special method for quantum computing which is known as “measurementbased quantum computation” (MBQC). In this method, sequential single-site measuring a highly-entangled state is used to perform computation. All of the existing MBQC models can be described in the “correlation space,” a virtual space corresponding to the physical space, of tensor network states. In this thesis, we introduce a recipe for designing such MBQC models. We elaborate our designing for... 

The silicon vacancy in silicon carbide is a strong emergent candidate for applications in quantum information processing. 4H, 6H and 3C polytypes of SiC all host coherent and optically addressable defect spin states. Electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR) investigations suggest that silicon vacancy point defects in SiC possess properties similar to those of the NV center in diamond. We provide a new theoretical frame to explain a wider range of experimental results. Employing a proposed generalized Hubbard model, with the help of electronic structure programs, DFT, second quantization, and various computational approaches, we obtain new... 

one of the important challenges for implementation of Quantum Computation is fabrication of Quantum Wires that transport the Quantum Information from one part of the Quantum Hardware to the other parts. Heisenberg Spin Chains are promising candidate for this. In article [28] Gaussian wave packets on the spin chains are used to encode the logical qubits. In this model, to implement unitary operation on these qubits, extra interaction are designed in some parts of the spin chains. As Gaussian wave packets move along this interactions, the desired unitary operators act on them. In fact, this is an static model without external control to perform Quantum Computation. In spite of many interesting... 

antum computers are necessary to simulate quantum systems. e fragility of qubits in presence of decoherence and external noise is the biggest obstacle in realizing a quantum computer. To overcome su problems, topological quantum computation has been introduced by Kitaev that combines the main quantum feature of the quantum world, namely, superposition of states, with the robustness of classical bits whi is the result of a macroscopic number of very small entities, comprising ea bit. In this way, topological features whi are robust against local perturbations are used for storing information. Kitaev’s model is a famous many-body model, whi has topologically degenerate ground states,... 

Many have claimed that quantum mechanics is playing a non-trivial, i.e. further from merely governing atomic and molecular realm, in living. If so, clearly quantum mechanics should have played a key role in the origin of life especially in the transition from chemical evolution to biological (Darwinian) evolution. Long before quantum aspects of living systems came to focus, It was known that all the amino acids are right handed and all the sugars are left handed in living systems. Bio-molecules having the same sense of chirality, i.e. optical activity, are called biohomochirality. Detailed studies on the structure and functioning of biomolecules buttressed the idea that the selection of... 

In this thesis the structure and potential energy surfaces of Lidocaine and bupivacaine were studied by DFT method at B3LYD level calculation using 6-311++G basis set. Both compounds were calculated in water, dimetylsulfoxide, and carbontetracholoride as the solvent using the PCM model.Since the molecules meant to be studied were polar, level of energy in polar solvent is higher than non-polar solvent . The most considerable increase was observed in the amount of energy at 0.01 hartree for water compared with carbon tetracholoride. By changeing in solvent environment the most considerable difference in bond length was observed as 0.01 Ǻ.The spin spin coupling constants 1JCH, 2JCH, 2JHH,... 

The study of energy and structure of fentanyl was performed by using quantum mechanical calculations method of Density Functional Theory(DFT) at the computational level B3 L YP and the basis set 6-311++G^(**). Proton-proton and proton-carbon coupling constants were computed around dihedral angles  and . All Karplas equation indicating the relation between coupling constants (namely 〖(_^"1" )"J" 〗_"CH" ^ ، 〖(_^"2" )"J" 〗_"HH" ^ ، 〖(_^"2" )"J" 〗_"CH" ^ ، 〖(_^"2" )"J" 〗_"CH" ^ ، 〖(_^"3" )"J" 〗_"CH" ^ ، 〖(_^"3" )"J" 〗_"HH" ^ and appropriate dihedral angles were extracted. The impact of three water solvents, dimethyl sulfoxide, and carbon tetrachloride with different polarity on the values of... 

Signal transmission of information on noiseless and lossy channels is an important issue in data transmission. Using the amplifier in the transmission channels is a good solution to help send information on longer channels. In classical communication, information can be coded in the amplitude or phase of the field and an amplifier is responsible for amplifying these parameters. If we consider the conditions ideal and ignore electrical noises, Classical mechanics does not impose any restrictions on the amplification of arbitrary classical signals. Instead, in quantum telecommunications the information encoded on the quadrature of the electromagnetic field are mounted on quantum states, such... 

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... 

Two qubit density matrices which are of X-shape, are a natural generalization of Bell Diagonal States recently simulated on the IBM quantum device. We propose a quantum circuit for simulation of a general X-state on the same quantum device and study its properties for several values of the extended parameter space. We also show by specific measurements, that their X-shape is robust against noisy quantum gates. To further physically motivate this study, we invoke the two-spin Heisenberg XYZ system and show that for a wide class of initial states, it leads to dynamical density matrices which are X-states. Due to the symmetries of this Hamiltonian, we show that by only two qubits, one can... 

In recent years, there were many studies on developing quantum computers, and due to the progress of these developments, the investigation of finding problems that might show quantum supremacy become interesting. In order to capture the quantum advantages over classical computing, the many-body problems are reliable choices to study. For example, the simulation of many-body problems in high-energy physics is attractive because of the challenges and difficulties that we found during classical simulations. In the many-particle problems, we have large systems with many degrees of freedom and we should use our resources to simulate them. Also, the limitations we have for using perturbative... 

The relation between BQP and PH has been one of the most fundamental open questions since the beginning of the field of quantum computational complexity. Despite the common belief that BQP contains problems outside the polynomial hierarchy, no real progress had been made in solving the problem even in relativized world. In 2009, Aaronson took the first serious step by proposing an oracle problem to separate the relation version of these two complexity classes. Finally, based on Aaronson’s works, in 2018 Raz and Tal separated BQP and PH relative to an oracle in a breakthrough work. This thesis studies the tools and techniques used to solve this challenging problem