Doppler-Rabi oscillations of a two-level atom moving in a cavity

The interaction with a quantum mode of a high-Q cavity is considered for a two-level atom uniformly moving along the classical trajectory. The method of dressed states is employed to deduce the recursion relation for the probability of atomic transition with photon emission. It is shown that the dependence of the transition probability on the position of a moving atom in the cavity and the magnitude of this probability are qualitatively influenced by the ratio between the Doppler shift of transition frequency and the Rabi frequency of atom-field system.     

Collapse and revival of the Doppler-Rabi oscillations of a moving atom in a cavity

Collapse and revival of the Doppler-Rabi oscillations of a two-level atom moving in a cavity electromagnetic field are analyzed. The coupled atom-field dynamics are predicted accurately by numerical calculation and approximately by using the stationary phase approximation combined with the Poisson summation formula. The collapse and revival patterns are shown to be qualitatively different in the cases of moving atom and atom at rest. In particular, quantum revivals of Doppler-Rabi oscillations occur with a period determined by the Doppler shift of the atomic transition frequency. This regime of Doppler-Rabi oscillations requires that the Rabi frequency and the Doppler shift satisfy the condition Ω_R ? Ω_D. Under the inverse relation, the collapse- revival phenomenon generally does not occur. It is shown that even a small amount of atom-cavity detuning eliminates collapse-revival behavior. The analysis is performed for both coherent and thermal cavity fields.     

Thermal Entanglement Between a Jaynes-Cummings Atom and an Isolated Atom

We studied the entanglement of a quantum system consisting of a Jaynes-Cummings atom, thermal lossless cavity and an isolated atom. The analytical expressions of the atom-atom negativity for separable and entangled initial atomic states were obtained. The influence of a detuning between the atomic transition frequency and the field frequency and direct dipole-dipole interaction on an atom-atom entanglement is examined. We showed that for a separable initial atomic states a detuning might cause high atom-atom entanglement in the presence of the dipole-dipole interaction. We also obtained that for an entangled initial atomic state a detuning causes a stabilization of an entanglement oscillations both for model with dipole-dipole interaction and model without such interaction.     

含Kerr介质的Λ型三能级原子系统中光场的相位性质

研究了充满Kerr介质的高Q腔中与Λ型三能级原子非共振喇曼作用的单模腔场的相位演化特性,分析了光场频率与原子本征频率的单光子失谐量和Kerr介质对光场相位概率分布、相位扩散和相位频率漂移的影响.     

Doppler-Rabi oscillations of a moving atom due to the roentgen interaction in a cavity

The dynamics of energy exchange between an atom moving in a high-Q cavity and the cavity field is analyzed by taking into account the Roentgen interaction. A two-level atom coupled to a Fock or coherent state of an optical or microwave cavity is considered. The mean cavity photon number required for high-frequency Doppler-Rabi oscillations to occur is relatively high for both Fock-and coherent-state cavity fields and increases with the atomic transition frequency. Conditions are found when the Roentgen interaction plays a key role in the Doppler-Rabi oscillations and must be taken into account, in addition to the conventional electric field-dipole interaction.     

动态各向同性光子晶体中二能级原子的自发辐射

研究了动态各向同性光子晶体中二能级原子自发辐射的性质,主要讨论了光子晶体能带带边频率随时间作阶跃调制和三角函数周期调制两种情况下,原子上能级占据数随时间的演化特性.当光子晶体能带带边频率随时间作阶跃调制时,原子上能级占据数随时间的演化不仅和上能级与能带带边的相对位置δ有关,更依赖于阶跃调制发生的时刻.调制发生时刻不同,调制后原子上能级占据数随时间的演化也不同.当光子晶体能带带边频率随时间作三角函数周期调制时,二能级原子上能级占据数随时间作总体衰减的准周期振荡.通过选择调制频率和调制初相位可调控准周期振荡的频率、峰值与谷值的大小以及占据数的总体衰减速度等.     

非共振耗散腔耦合系统的发射光谱

研究了非共振耗散二能级双原子与双单模腔耦合系统发射光谱的性质。探讨了原子和腔场之间的失谐、腔场衰减率及原子失相对该系统发射光谱的影响。结果表明,体系的腔场谱呈现出三重峰结构,原子发射谱呈现出二重峰结构。非共振情况时,腔场谱和原子发射谱的图像皆为非对称图像。在原子与腔场失谐时,与共振情况相比,峰位发生了明显的漂移,且中峰明显增大。增大腔场与原子的失谐,会引起边峰向低频段漂移,并改变其光谱强度;增大原子与腔场的失谐,可以使光谱整体向低频段漂移,并改变其所有峰的光谱强度。随着腔场衰减率的增大,共振情况下,会导致边峰的强度减小;失谐情况下,会导致所有峰的强度均减小。随着原子失相的增大,共振或失谐情况下,会使光谱所有峰的强度均减小。     

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.     

Control and Transfer of Entanglement between Two Atoms Driven by Classical Fields under Dressed-State Representation

We have studied the dynamics and transfer of the entanglement of the two identical atoms simultaneously interacting with vacuum field by employing the dressed-state representation. The two atoms are driven by classical fields. The influence of the initial entanglement degree of two atoms, the coupling strength between the atom and the classical field and the detuning between the atomic transition frequency and the frequency of classical field on the entanglement and atomic linear entropy is discussed. The initial entanglement of the two atoms can be transferred into the entanglement between the atom and cavity field when the dissipation is neglected. The maximally entangled state between the atoms and cavity field can be obtained under some certain conditions. The time of disentanglement of two atoms can be controlled and manipulated by adjusting the detuning and classical driving fields. Moreover, the larger the cavity decay rate is, the more quickly the entanglement of the two atoms decays.     

运动的二能级原子与双模量子化腔场的相互作用

研究了一个微波激射器, 其腔内是单个运动的二能级原子与一双模量子化腔场的相互作用. 用修饰态来描述系统态矢量, 分析了在热原子状态下, 双模光场配制成不同的状态, 失谐量 对微波激射器的原子辐射率的影响. 关键词： 二能级原子 双模量子化腔场 原子辐射率     

Momentum Transfer and Effect of Motion of Atomic Mass Centre on an Atom-Cavity System

For a special ∧-type atom with dark state, the problem of momentum transfer is discussed in detail. Effect of moving mass centre on atomic dynamics for various initial conditions is also studied. The numerical results show that the Doppler effect exercised by the motion of atomic mass centre can lead to the modified phenomenon of oscillation collapse and revival in the transition probability and the atomic population inversion.     

含克尔介质微波激射器的原子辐射率

建立了含克尔介质微波激射器(micromaser with Kerr medium)的基本量子原理,分析计算了处于不同方式(热原子和超冷原子状态)下的二能级原子沿z轴穿过处于相干态的含克尔介质微腔的原子辐射率,并着重讨论了克尔介质与单模辐射场作用的耦合强度χ、失谐量Δ和原子注入速率r对原子辐射概率的影响. 关键词： 含克尔介质微波激射器 热原子和超冷原子 原子辐射率     

Transmission of ultracold atoms through a micromaser: detuning effects

The transmission probability of ultracold atoms through a micromaser is studied in the general case where a detuning between the cavity mode and the atomic transition frequencies is present. We generalize previous results established in the resonant case (zero detuning) for the mesa mode function. In particular, it is shown that the velocity selection of cold atoms passing through the micromaser can be very easily tuned and enhanced using a non-resonant field inside the cavity. Also, the transmission probability exhibits with respect to the detuning very sharp resonances that could define single cavity devices for high accuracy metrology purposes (atomic clocks).Received: 25 March 2003, Published online: 17 February 2004PACS: 42.50.-p Quantum optics - 32.80.-t Photon interactions with atoms - 32.80.Lg Mechanical effects of light on atoms, molecules, and ions     

Entanglement of a two-level atom and its spontaneous emission near the edge of a photonic band gap

The entanglement of a two-level atom and its radiation field near the edge of a photonic band gap is studied by using the quantum entropy. Unlike the free space case, there is a steady-state entanglement between the atom and its spontaneous emission field even when the atomic transition frequency lies outside the band gap. Moreover, the degree of entanglement, which is due to the formation of atom–photon bound dressed state, depends on the detuning of the atomic transition frequency from the photonic band edge and can be controlled by a controllable photonic band gap crystal.     

Kerr介质中三能级原子与双模场相互作用的电子跃迁转移

本文研究了充满Kerr介质腔中的V型三能级原子与双模腔场的非共振相互作用,讨论了Kerr效应和失谐量对原子占有态几率的影响.结果表明:Kerr效应和场模失谐都将使原子中发生电子跃迁转移现象.     

Effect of Moving Mass Center on Atomic Transition Probability in a Single-Mode Cavity

By considering a two-level atom coupling with a single-mode cavity field which is prepared in three different initial states respectively, the influence of spatial motion of the atomic centre of mass on the atomic transition probability is studied. It is shown that the oscillation with collapse and revival in atomic transition probability may be suppressed due to Doppler effect.     

Effects of atomic motion in a standing-wave laser field on the Rabi oscillations

We study the effects of the two-level-atom motion in a standing-wave laser field on the Rabi oscillations. In the presence of the resonance optical Stern–Gerlach effect, the atomic wave packet, centered initially at a node of the standing wave, is shown to evolve in such a way that the atomic population inversion remains zero when the initially de-excited atom moves between the nodes, then collapses to the ground level upon crossing the nodes, and practically returns to zero after that. This coherent population trapping is explained in the dressed-state picture. The Doppler–Rabi resonance, i.e., maximum Rabi oscillations at large values of the atom–field detuning, becomes possible if the detuning is equal to the Doppler shift. A simple formula for the population inversion is derived in the Raman–Nath approximation.     

Proliferation of atomic wave packets at the nodes of a standing light wave

A quantum analysis is presented of the motion and internal state of a two-level atom in a strong standing-wave light field. Coherent evolution of the atomic wave-packet, atomic dipole moment, and population inversion strongly depends on the ratio between the detuning from atom-field resonance and a characteristic atomic frequency. In the basis of dressed states, atomic motion is represented as wave-packet motion in two effective optical potentials. At exact resonance, coherent population trapping is observed when an atom with zero momentum is centered at a standing-wave node. When the detuning is comparable to the characteristic atomic frequency, the atom crossing a node may or may not undergo a transition between the potentials with probabilities that are similar in order of magnitude. In this detuning range, atomic wave packets proliferate at the nodes of the standing wave. This phenomenon is interpreted as a quantum manifestation of chaotic transport of classical atoms observed in earlier studies. For a certain detuning range, there exists an interval of initial momentum values such that the atom simultaneously oscillates in an optical potential well and moves as a ballistic particle. This behavior of a wave packet is a quantum analog of a classical random walk of an atom, when it enters and leaves optical potential wells in a seemingly irregular manner and freely moves both ways in a periodic standing light wave. In a far-detuned field, the transition probability between the potentials is low, and adiabatic wave-packet evolution corresponding to regular classical motion of an atom is observed.     

Influences of Detuning on Geometrical Quantum Discord Dynamics in Double Jaynes-Cummings System

We consider the case that the two-level atom off-resonantly interacts with cavity field via a one-photon hopping in double Jaynes-Cummings system. Geometrical quantum discord (GQD) is adopted to quantify the degree of correlation between two subsystems. GQD dynamics between two atoms, between cavity fields, as well as between atom and cavity fields are studied. The influences of detuning on GQD are discussed. The results obtained using the numerical method show that GQD between two atoms, between cavity fields, and between atom and cavity fields all display periodic oscillations. Furthermore, their periodic oscillations frequencies increase with the increase of detuning. On the other hand, GQD between two cavity fields and that between atom and cavity are weakened with increase of detuning.

     

Atomic self-trapping induced by single-atom lasing

We study atomic center of mass motion and field dynamics of a single-atom laser consisting of a single incoherently pumped free atom moving in an optical high-Q resonator. For sufficient pumping, the system starts lasing whenever the atom is close to a field antinode. If the field mode eigenfrequency is larger than the atomic transition frequency, the generated laser light attracts the atom to the field antinode and cools its motion. Using quantum Monte Carlo wave function simulations, we investigate this coupled atom-field dynamics including photon recoil and cavity decay. In the regime of strong coupling, the generated field shows strong nonclassical features such as photon antibunching, and the atom is spatially confined and cooled to sub-Doppler temperatures.