Preparation Of Spin Squeezing In Hybrid Quantum Systems

With the development of quantum optics and quantum information,we have gradually developed from the classical world to the quantum field.As all experiments need sufficient theoretical support,the theoretical research will largely determine the direction of future research.Quantum optics,a new subject in the quantum field,plays a significant role in scientific research.Spin squeezing is one of the typical pure quantum effects in quantum optics.Spin squeezing has been widely used in quantum measurement,quantum computing,quantum networks,and other fields.Significantly,spin squeezing can effectively improve the measurement accuracy in quantum measurement.In addition,spin squeezing is also related to quantum entanglement and quantum chaos,so it is essential to study spin squeezing.At present,scientists have proposed many new schemes for preparing spin squeezing in the current research.For example,spin squeezing was prepared by optical microcavities,carbon nanotube materials,diamond waveguides,nanomechanical oscillators,etc.Diamond,as a semiconductor material,has excellent quantum properties.Therefore,we can use diamond vacancy centers to prepare spin squeezing.In previous studies,nitrogen-vacancy centers have attracted extensive attention due to their excellent performance at room temperature.The main disadvantage of nitrogen-vacancy centers is the short phonon lines limiting the quantum properties,compared to silicon-vacancy centers with zero phonon lines as well as high emissivity.Therefore,we propose two new schemes to prepare spin squeezing states using hybrid systems by coupling silicon-vacancy centers to rectangular diamond waveguides and nanomechanical resonators’ magnetic tips,respectively.Since any system inevitably interacts with the environment and leads to decoherence,we consider the open quantum systems.Preparing spin squeezing with a higher degree and more prolonged duration is also an essential target.This thesis is divided into four parts.Firstly,in the introduction,we introduce the current development of quantum information and quantum optics,as well as spin squeezing.Then we briefly introduce two different hybrid quantum systems used to prepare spin squeezing.The second part,as the theoretical foundation,mainly gives the theoretical basics of the whole thesis,including the definition of spin squeezing,the quantum master equation,and three kinds of pictures in quantum mechanics.The third part and the fourth part are the focus of this thesis.In the third part,we study the theoretical model of spin squeezing by coupling silicon-vacancy centers to rectangular diamond waveguide cavities.By calculating and writing out the Hamiltonian of the hybrid system,we deduce the evolution of the correlation operator with time by means of the master equation,and use MATLAB programming for numerical simulation analysis.By setting reasonable experimental parameters,we find that the spin squeezing can be prepared greatly in the current model,and the external field is more conducive to the generation of spin squeezing.In the fourth part,we consider the scheme of spin squeezing using magnetic coupling between silicon-vacancy centers and nanomechanical resonators’ magnetic tips and apply an external gradient magnetic field to it.Similarly,we analyze the dynamic evolution of the system and write out the Hamiltonian.Under the condition of adiabatic approximation,we use the master equation to analyze it numerically and get the ideal spin squeezed state finally.In the last part,we give the summary and prospects of current research.