逻辑门操控腔内多光子过程中原子最大相干性恢复
Logic gate Control of Maximum Coherence Restore of Atom in Multiphoton Process

考虑初始处于最大纠缠态的两全同二能级原子，将其中一个注入单模真空态腔场中发生多光子共振相互作用，将腔外原子及腔场视为腔内原子的环境，研究通过操作腔外原控制腔内原子最大相干性恢复。考察对腔外原子作Haddmard(H)逻辑门操作及基态测量前后，腔内原子约化密度矩阵非对角元时间演化曲线。结果表明：对腔外原子操作前，腔内任意 光子过程原子密度矩阵非对角元任意时刻都为零，总是处于混合态或经典态，相干性不能恢复。对腔外原子操作后，在光子数 过程中，腔内原子密度矩阵非对角元呈现周期为 的时间演化，在 时刻最大相干性恢复及态被制备。对于多光子（ ）的过程，腔内原子密度矩阵非对角元时间演化呈高频振荡，振幅呈非线性变化，最大相干性恢复周期变小、恢复次数增多。通过利用腔场与原子之间的共振相互作用和原子之间的纠缠，可实现腔内原子相干性恢复远程控制。与单光之过程相比，多光子过程更有利于原子相干性的恢复。
Considering two identical two-level atoms initially in maximally entangled state, we inject one atom into a single mode vacuum cavity to produce multiphoton resonance while the other is outside the cavity. The cavity field and atom outside the cavity are seen as the environment, and we investigate the control of atomic maximum coherence restore in the cavity. We investigate the time evolution curve of the off-diagonal elements of the reduced density matrix for the atom inside the cavity before and after performing logic gate operation and the ground state measurement on the atom outside the cavity. The results show that (1) No operations on the atom outside the cavity, the off-diagonal elements of the reduced density matrix for the atom inside the cavity in arbitrary k photon process are zero at any moment, that is the atom inside the cavity is always in a mixed state or classical state, and its coherence is always suppressed. (2) In the case of photon number , after Hadamard gate gate operations and ground state measurements, the off-diagonal elements in the reduced density matrix of the atom inside the cavity show time evolution with period 2π/ , at nπ/ , the maximal coherence is restored and coherent superposition state are prepared. (3) if two atoms are in the coherent superposition state initially, the maximum coherence severe decay for the atom inside the cavity before manipulating atom qubit outside the cavity. However performing any logic gate (besides of H-gate) operations on the atom outside the cavity, the maximum coherence of the atom inside the cavity will restore periodically. For the photon number , the off-diagonal elements in the reduced density matrix of the atom inside the cavity will evolute in high frequency oscillation as time ,its amplitude will vary nonlinearly, recreased recovery period and increase recovery times of the maximum coherence of the atom inside the cavity. So that, it is realizable to control the coherence restoration for the atom inside the cavity by means of the resonance between the atoms and the cavity, the entanglement associated the atoms. Comparing with a single photon process, multiphoton process may be more