两原子双光子Jaynes-Cummings模型的腔场谱

研究了两个偶极相互作用二能级原子与高Q腔场双光子相互作用的腔场谱.给出了初始光场为Fock态、相干态和压缩真空态时的计算结果并解释了谱结构的形成,分析了原子间的偶极相互作用和初态的交换对称性对腔场谱的影响.发现当两原子均处于激发态时,腔场谱只在初始光场为真空态时出现4峰结构,而在其它初始场时,都呈现出奇数峰,这与相应的辐射谱偶数峰的结构明显不同.而两原子只有一个处于激发态时,腔场谱结构主要由原子初态是否具有交换对称性决定. 关键词：     

耦合双原子Jaynes-Cummings模型的腔场谱H

研究了处于激发态的两原子与高Q腔场相互作用单光子过程的腔场谱,给出了初始光场为光子数态、相干态、压缩真空态时的腔场谱数值计算结果,分析了原子间偶极-偶极相互作用强度gα对腔场谱结构的影响.发现真空场Rabi峰,当gα较弱时为4峰,gα较强时为3峰结构;弱场数态(n＞0)时为5峰,强场时为3峰结构.相干态和压缩真空态时,谱结构与光子数分布有关,一般为复杂的多峰结构.结果表明,gα对峰位峰高都有影响,破坏了谱结构的对称性,但这种影响只在真空场和弱场时才较明显.     

耦合双原子与非线性相干态相互作用模型的腔场谱

研究了两个偶极 偶极相互作用的全同二能级原子与高Q腔内非线性相干态光场相互作用过程的腔场谱 .讨论了原子间耦合强度、初始场光子数分布和初始场强度的改变对光谱结构的影响.     

耦合双原子与单模场喇曼相互作用模型的腔场谱

研究了存在偶极-偶极相互作用的两个等同二能级原子与单模光场喇曼耦合过程的腔场谱.结果表明,当两原子处于同一能级时,腔场谱在弱场和强场条件下相应地为五峰和三峰结构.当两原子初态处于不同能级时,交换对称性对谱结构有明显的影响. 原子间的相互作用只在初始场很弱时才会影响谱结构.     

原子与弱相干腔场相互作用系统中的量子特性

考虑腔场处于弱相干态的情况,研究了两个全同的二能级原子与耦合腔相互作用系统中原子的偶极压缩和原子间的纠缠特性。研究结果表明,随耦合腔耦合系数增大,原子的偶极压缩减弱。另一方面,随耦合腔耦合系数增大,原子间的纠缠也减弱,这一结果与耦合腔处于真空态的情况相反。     

双模相干态和压缩真空态光场-非等同两原子体系的腔场谱

研究了两个非等同二能级原子与双模腔场相互作用过程的腔场谱.导出了双模初始光场处于任意量子态时腔场谱的计算公式,给出了光场处于相干态和压缩真空态时的数值结果,讨论了相对耦合常数R=g2/g1和初始场强对腔场谱的影响.发现相干态光场的腔场谱在R很小时为双峰,在R接近于1时为3峰.压缩真空态的腔场谱在弱场条件下表现为复杂的多峰结构,在强场条件下则只有单一经典共振峰或裂距很小的双峰.     

非等同两原子与双模叠加态腔场的拉曼相互作用

研究了处于双模腔中的两个非等同二能级原子与叠加态光场的拉曼相互作用,推导出了两模光场均处于光子数态和任意叠加态时腔场谱的计算公式,给出了两模初始场为相干态和压缩真空态时谱结构的数值结果,讨论了相对耦合常数R=g2/g1和初始场强对腔场谱的影响.发现腔场谱结构不仅与初始场强有关,还随初始场光子数分布的变化而改变.     

利用单光子微激射器产生强压缩腔场的理论研究

本文研究了初时占据上能级的二能级原子在相等的时间间隔中依次与初始处于相干态的单模腔场的相互作用,发现若初始场较强时,在这一过程中可以始终使场处于压缩态,并使之不断得到压缩,同时还简要地讨论了原子与压缩态腔场的相互作用。 关键词：     

单模辐射场与耦合双原子相互作用系统中场熵的压缩特性

研究了单模辐射场与耦合双原子相互作用系统中场熵的压缩特性,讨论了系统初始状态及原子间偶极相互作用对场熵压缩特性的影响.数值计算结果表明,当系统初始时刻处于合适的相干叠加态时,场熵呈现出周期性压缩现象,其压缩深度和压缩时间与原子间偶极相互作用强度有关. 关键词： 单模辐射场 耦合双原子 光场熵压缩     

在腔场与可移动镜子系统中对镜子位置的测量

描述利用腔场与镜的相互作用,对镜的位置坐标进行测量选域以使腔场变为Fock态的叠加态.并进一步讨论其压缩特性及相干性,通过数值计算,发现该腔场有非经典效应,即有一定的压缩效应和反聚束效应.     

Quantum Dynamics of Atomic Spatial Decoherence in a Squeezed Vacuum Field

We study the localization dynamics for a two level atom coupling with a single-mode cavity field initially in a squeezed vacuum state. The reduced density matrix for the atomic spatial degrees of freedom is given analytically where its decay behavior is described by a decoherence factor. It is found that the atomic spatial decoherence is induced by the back-action of the photon emitted from the atom and depends strongly on the field’s squeezed constant. For sufficiently large squeezed constant, the decoherence can occur in finite time. Our results also show that the maximal decay is related with the atomic position.     

Entangling Two Multi-atomic Clusters Through a Cavity Field

Two atomic clusters, which have NA and Ns two-level atoms, respectively, are placed in a cavity but separated spatially. There is no direct interaction between the atoms. All the atoms interact with a single-mode of the cavity field. Quantum entanglement between the two atomic clusters is investigated for various initial states of the two atomic clusters and the field. When the cavity field is initially in a Fock state, we find that the time evolution of entanglement quasi-periodically oscillates regardless of the initial states of atoms. The oscillation period increases as the initial photon number increases. When all the atoms in both of the atomic clusters are initially in the excited state, we show that there is no entanglement between the atomic clusters with NA = NB = 1 regardless the initial state of the cavity field. However, when either NA or NB is larger than one, we find that the entanglement always exists even for a strong thermal field. In cases with different initial states of the atomic clusters, we notice that the entanglement becomes stronger as number of the atoms increases. When all the atoms in both of the clusters in the ground state, we also find that the entanglement can be enhanced even by a thermal field. We also notice that a single qubit can be entangled with multi-atoms which are initially in the ground state by the cavity field initially being in vacuum, thermal, coherent, and squeezed states.     

Entanglement Dynamics of Two Atoms in the Squeezed Vacuum and the Coherent Fields

We investigate the entanglement dynamics of two atoms in a double damping Jaynes-Cummings model. The two atoms are initially in the Bell states and each is in a squeezed vacuum cavity field or coherent cavity field. Compared with the case in coherent field, the atomic entanglement in the squeezed vacuum field is stronger under the same conditions. The results show that we can adopt appropriate parameters such as mean photon number, detuning, the atomic spontaneous decay and the cavity decay, to realize better control of atomic entanglement in quantum information processing. What’s worth mentioning is that proper choosing of the last two parameters enables us to decrease disentanglement period and postpone the moment when the entanglement disappears. Finally, the atomic entanglement in double damping and non-identical Jaynes-Cummings model is obtained

     

Exact results on decoherence and entanglement in a system of N driven atoms and a dissipative cavity mode

We solve the dynamics of an open quantum system where N strongly driven two-level atoms are equally coupled on resonance to a dissipative cavity mode. Analytical results are derived on decoherence, entanglement, purity, atomic correlations and cavity field mean photon number. We predict decoherencefree subspaces for the whole system and the N-qubit subsystem, the monitoring of quantum coherence and purity decay by atomic populations measurements, the conditional generation of atomic multi-partite entangled states and of cavity cat-like states. We show that the dynamics of atoms prepared in states invariant under permutation of any two components remains restricted within the subspace spanned by the completely symmetric Dicke states. We discuss examples and applications in the cases N = 3, 4. An erratum to this article can be found at     

Evolution of microwave quantum states in terms of measurable ordered moments of creation and annihilation operators

The detection of microwave states is complicated by strong thermal noise, which is inevitably introduced by linear amplifiers. We show how to extract from measured data normally or anti-normally ordered moments of photon creation and annihilation operators, the set of which contains complete information on the quantum state of an electromagnetic field. Equations for the evolution of the quantum state are derived in terms of moments. Using this approach, we consider in detail issues of decoherence and thermalization of microwave quantum states. Results are illustrated using the examples of Fock, coherent, squeezed, thermal, and even and odd coherent states (Schrödinger cat states).     

Solvable dynamics of N driven two-level atoms coupled to a dissipative cavity mode

We solve exactly the dynamics of N strongly driven two-level atoms equally coupled on resonance to a dissipative cavity mode. Analytical results are derived on decoherence, entanglement, purity, atomic correlations and cavity field mean photon number. Decoherence-free subspaces are predicted for the whole system and the N-qubit subsystem. Multi-partite entangled states and cavity cat-like states can be conditionally generated. The decay of quantum coherence and purity can be monitored by joint measurements on atomic populations. Atoms prepared in states invariant under permutation of any two components evolve within the subspace spanned by the completely symmetric Dicke states. Applications to N = 3, 4 are discussed.     

Quantum coherence dynamics of a three-level atom in a two-mode field

The correlated dynamics of a three-level atom resonantly coupled to an electromagnetic cavity field is calculated (Λ, V, and L models). A diagrammatic representation of quantum dynamics is proposed for these models. As an example, Λ-atom dynamics is examined to demonstrate how the use of conventional von Neumann’s reduction leads to internal decoherence (disentanglement-induced decoherence) and to the absence of atomic coherence under multiphoton excitation. The predicted absence of atomic coherence is inconsistent with characteristics of an experimentally observed atom-photon entangled state. It is shown that the correlated reduction of a composite quantum system proposed in [18] qualitatively predicts the occurrence and evolution of atomic coherence under multiphoton excitation if a seed coherence is introduced into any subsystem (the atom or a cavity mode).     

Dynamics of dispersive photon-number QND measurements in a micromaser

A numerical analysis of dispersive quantum nondemolition measurement of the photon number of a microwave cavity field is presented. Simulations show that a key property of the dispersive atom-field interaction used in Ramsey interferometry is the extremely high sensitivity of the dynamics of atomic and field states to basic parameters of the system. When a monokinetic atomic beam is sent through a microwave cavity, a qualitative change in the field state can be caused by an uncontrollably small deviation of parameters (such as atom path length through the cavity, atom velocity, cavity mode frequency detuning, or atom-field coupling constants). The resulting cavity field can be either in a Fock state or in a super-Poissonian state (characterized by a large photon-number variance). When the atoms have a random velocity spread, the field is squeezed to a Fock state for arbitrary values of the system’s parameters. However, this makes detection of Ramsey fringes impossible, because the probability of detecting an atom in the upper or lower electronic state becomes a random quantity almost uniformly distributed over the interval between zero and unity, irrespective of the cavity photon number.     

Experimental progress in optical manipulation of single atoms for cavity QED

Cavity QED, as a fundamental system and research field, not only illuminates the primary aspects of decoherence and coherence in quantum dynamics, but also advances quantum information science. Manipulation of single atoms, in the context of cavity QED, is the essential element and has been becoming a hot issue for the past two decades. In this review paper, we will concentrate on the experimental aspects for manipulating the neutral atoms strongly coupled to a high-finesse cavity in the optical regime, including atomic cooling and trapping, different configurations of atom transportation and the wide variety of quantum outgrowths based on cavity QED, such as one atom laser, single photon source, etc. The cavity QED system at Shanxi University is briefly introduced.