Quantum - Based Deterministic Transmission Of Quantum Micro - Cavity System Based On Quantum Control

This thesis firstly reviews the recent progress of studies on quantum state transfer (QST) and introduces the quantum control theory developed in recent years based on Lyapunov method. Secondly,this thesis focuses on discussing the QST schemes in four sections:the deterministic QST for single atom unknown state, unknown entangled state transfer for two atoms. Control led-Not gate for two atoms and deterministic QST for single atom unknown state based on Lyapunov control, and putting forward the theoretical strategy for implementing the above tasks.Study results of the first section show that, in an effective Ising model of three distant atoms, the unknown atomic state can be transferred from one atom to another deterministically through the implementation of replicating the only required operation of turning on/off the local laser fields applied on two atoms synchronously. For example, to implement the QST between atoms 1 and 2, the only required operation is implementing the operation of turning on/off the local laser fields applied on the starting atom 1 and the auxiliary atom 3, and replicating a similar operation on the auxiliary atom 3 and the target atom 2. Study results of the second section of the thesis show that, in the same quantum system, the unknown two-atom entangled state can be transferred from one pair of atoms to another through replicating the only required operation of turning on/off the local laser field applied on the target atom. For example, to transfer the unknown entangled state from atoms 1 and 2 to atoms 2 and 3, the only required operation is turning on/off the local laser field applied on atom 1 and consequently turning on/off the local laser field applied on atom 3. Study results of the third section show that, two-atom Controlled-Not gate can be deterministically implemented through the operation of turning on/off the local laser field applied on the controlled atom and consequently leave the controlling atom alone in its cavity for a certain time.In these studies, the affect of atomic spontaneous emission on the fidelity of QST is discussed. It is shown that, the fidelity of QST is decreased by the atomic spontaneous emission. However, the combination of spontaneous emission and operating time error can reduce the time cost of the operation of single atom QST at maximum fidelity, which can speed up the implementation of QST. It is also shown that, for small value of atomic spontaneous emission, the fidelity of two-atom entangled state transfer is still close to 100%. One advantage of the schemes is that the only required condition to keep the validity of the derivalion of secular Hamiltonian is the coupling strength Γ0 between the local laser field and the atom and the Ising coupling strength J0 satisfy the condition Γ0<<J0. While in the case of weak coupling between the laser field and the atom, the affect of the photon leakage along short fiber (in order of meter) on the condition can be neglected. Another advantage of the schemes is that they are insensitive to the variation of cavity leakage since they work under the condition of Δ≈k>>g.Study results of the fourth section show that, the QST based on two-step Lyapunov control for unknown atomic state can be implemented through the single atom Stark shift induced by the large detuning between cavity field frequency and the atomic internal transition.Compared with those of the first section, the study results in this section are more meaningful for practical quantum information processings since the fidelity of the QST for unknown atomic state in this scheme can converge to 100% monotonically.