Several Physical Problems Based On Cavity And Cavity Optomechanical Systems

Since 1980s,quantum computing and quantum information processing,the inter-disciplines which combine physical science and information science,based on quantum mechanics have attracted much attention from theories to experiments to practical appli-cations.Our thesis will study quantum entanglement,quantum illumination and quantum-phase-transition phenomena based on cavity and cavity optomechanical systems which are familiar in the fields of quantum optics and quantum information.First,we propose to realize quantum entanglement between distant matter qubits in the coupling system between cavity and single atom.Our scheme doesn't involve any interference inculding single-photon interference and double-photon interference.Our proposal could be used to realize free-loophole bell test and secure quantum communi-cation.We apply quantum trajectory method to analyze the state's time evolution of the two-atom and one-photon system.When a right circular photon is detected,the state of the whole system reduced to an entangled state of two matter qubits.We choose 87Rb as the atom to realize our entangled state.In some specific parameter settings,we get a high fidelity entangled state in finite time.Second,we study the quantum illumination based on multi-mode optomechanical system in microwave regime.In the weak coupling regime of optomechanical system,our method can get a better error probability than classical system of the same transmitted energy.Moreover,we optimize the time delay of the microwave signal.The result signal-to-noise ratio still have a significant advantage over classical system.Finally,based on circuit QED system,we study the quantum-phase-transition phe-nomena of the coupling system involves a few qubits and a single-mode resonator.In the single-qubit case,in the ?q/?r?? limit where ?q is the frequency of qubit and?r is the single-mode resonator's frequency,and ultrastrong-coupling regime,the system undergoes quantum phase transition.When two-coupling terms induced by capacitor and inductor respectively are beyond critical points,there will be the occurrence of three different superradiant phases.Moreover,when the two-coupling terms are equivalent,the Goldstone mode emerges.In addition,we study the few-qubit variation model of Dicke model and find the presence and absence of superradiant phases with the qubit-number parity.