In the framework of nonperturbative quantum field theory, the critical phenomena of one-dimensionalextended Hubbard model (EHM) at half-filling are discussed from weak to intermediate interactions. After the EHMbeing ...In the framework of nonperturbative quantum field theory, the critical phenomena of one-dimensionalextended Hubbard model (EHM) at half-filling are discussed from weak to intermediate interactions. After the EHMbeing mapped into two decoupled sine-Gordon models, the ground state phase diagram of the system is derived in anexplicit way. It is confirmed that the coexisting phases appear in different interaction regimes which cannot be foundby conventional theoretical methods. The diagram shows that there are seven different phase regions in the groundstate, which seems not to be the same as previous discussions, especially the boundary between the phase separationand condensed phase regions. The phase transition properties of the model between various phase regions are studied indetail.展开更多
Perturbation theory is an important tool in quantum mechanics. In this paper, we extend the traditional perturbation theory to open nonlinear two-level systems, treating decoherence parameter γ as a perturbation. By ...Perturbation theory is an important tool in quantum mechanics. In this paper, we extend the traditional perturbation theory to open nonlinear two-level systems, treating decoherence parameter γ as a perturbation. By this virtue, we give a perturbative solution to the master equation, which describes a nonlinear open quantum system. The results show that for small decoherence rate γ the ratio of the nonlinear rate C to the tunneling coefficient V （i.e., r = O/V） determines the validity of the perturbation theory. For small ratio r, the perturbation theory is valid, otherwise it yields wrong results.展开更多
Assisted by the bead pull technique,nonresonant perturbation theory is applied for measuring and tuning the field of the linac accelerating structure.The method is capable of making non-touching amplitude and phase me...Assisted by the bead pull technique,nonresonant perturbation theory is applied for measuring and tuning the field of the linac accelerating structure.The method is capable of making non-touching amplitude and phase measurements,real time mismatch feedback and field tuning.Some key considerations of the measurement system and of a C-band traveling-wave structure are discussed,and the bead pull measurement and the tuning of the C-band traveling-wave linac accelerating structure are presented at last.展开更多
Cosmological perturbation theory is a key tool to study the universe.The linear or first order theory is well understood,however,developing and applying the theory beyond linear order is at the cutting edge of current...Cosmological perturbation theory is a key tool to study the universe.The linear or first order theory is well understood,however,developing and applying the theory beyond linear order is at the cutting edge of current research in theoretical cosmology.In this article,I will describe some signatures of non-linear perturbation theory that do not exist at linear order,focusing on vorticity generation at second order.In doing so,we discuss why this,among other features such as induced gravitational waves and non-Gaussianities,shows that cosmological perturbation theory is crucial for testing models of the universe.展开更多
文摘In the framework of nonperturbative quantum field theory, the critical phenomena of one-dimensionalextended Hubbard model (EHM) at half-filling are discussed from weak to intermediate interactions. After the EHMbeing mapped into two decoupled sine-Gordon models, the ground state phase diagram of the system is derived in anexplicit way. It is confirmed that the coexisting phases appear in different interaction regimes which cannot be foundby conventional theoretical methods. The diagram shows that there are seven different phase regions in the groundstate, which seems not to be the same as previous discussions, especially the boundary between the phase separationand condensed phase regions. The phase transition properties of the model between various phase regions are studied indetail.
基金Supported by National Natural Science Foundation of China under Grant No. 61078011
文摘Perturbation theory is an important tool in quantum mechanics. In this paper, we extend the traditional perturbation theory to open nonlinear two-level systems, treating decoherence parameter γ as a perturbation. By this virtue, we give a perturbative solution to the master equation, which describes a nonlinear open quantum system. The results show that for small decoherence rate γ the ratio of the nonlinear rate C to the tunneling coefficient V （i.e., r = O/V） determines the validity of the perturbation theory. For small ratio r, the perturbation theory is valid, otherwise it yields wrong results.
基金supported by Program of Shanghai Subject Chief Scientist and Natural Science Foundation of China (key program) (Grant No. 08XD1405400)
文摘Assisted by the bead pull technique,nonresonant perturbation theory is applied for measuring and tuning the field of the linac accelerating structure.The method is capable of making non-touching amplitude and phase measurements,real time mismatch feedback and field tuning.Some key considerations of the measurement system and of a C-band traveling-wave structure are discussed,and the bead pull measurement and the tuning of the C-band traveling-wave linac accelerating structure are presented at last.
文摘Cosmological perturbation theory is a key tool to study the universe.The linear or first order theory is well understood,however,developing and applying the theory beyond linear order is at the cutting edge of current research in theoretical cosmology.In this article,I will describe some signatures of non-linear perturbation theory that do not exist at linear order,focusing on vorticity generation at second order.In doing so,we discuss why this,among other features such as induced gravitational waves and non-Gaussianities,shows that cosmological perturbation theory is crucial for testing models of the universe.
