腔损耗对规则注入单原子微激光的影响

用解密度矩阵主方程的方法研究了在原子与场相互作用期间考虑腔损耗情况下规则注入的单原子微激光。通过数值模拟给出了有损耗情形注入率r与腔损耗系数c之间应满足的阈值条件，并讨论了不同腔损耗对稳态光子数分布和平均光子数的影响。     

Photon statistics of the micromaser with a Kerr medium

We have established the master equation for the micromaser with a Kerr medium,we have studied the photon statics of the micromaser with a Kerr medium field and analysed the influence of the Kerr effect on the photon statistics,The influence of the Kerr effect on the photon statistics is different in two regimes,In the thermal-atom regime,the Kerr effect produces quantum noise,and decreases the mean photon number.In the ultracold-atom regime,with the increase of the nonlinear parameter of the Kerr medium,the stability of the mean photon number and the normalized variance enhances the mean photon number,and the normalized variance exhibits collapse-revival phenomena periodically,their resonance peaks become lower,and the photon statistics of more and more regions are sub-Poissonian.     

How to measure the phase diffusion dynamics in the micromaser

We propose a realistic scheme for measuring the micromaser linewidth by monitoring the phase diffusion dynamics of the cavity field. Our strategy consists of exciting an initial coherent state with the same photon number distribution as the micromaser steady-state field, singling out a purely diffusive process in the system dynamics. After the injection of a counterfield, measurements of the population statistics of a probe atom allow us to derive the micromaser linewidth in all ranges of the relevant parameters, establishing experimentally the distinctive features of the micromaser spectrum due to the discreteness of the electromagnetic field.     

How to measure the decoherence of a micromaser field under well controlled conditions

We discuss a possible realization of a quantum register with controllable decoherence in terms of /0> and /1> photon number states of a micromaser field. It is shown how to create in the Jaynes-Cummings model a superposition state of /0> and /1> photon number states inside a closed micromaser cavity. The loss of phase coherence between these two states can subsequently be measured by a second probe atom monitoring the decoherence of the field. A technique is proposed for forming the superposition of number states /0> and /1> using the time structure of the Rabi oscillation. The proposed method avoids problems with stray fields at the cavity holes, which disturb the coherence of the atomic superposition, and offers a way to study how the coupling strength to the environment influences the decoherence rate, displaying the robustness of physical qubits and the fidelity of quantum computations.     

Detuning effects in the vertical cold-atom micromaser

The quantum theory of the cold atom micromaser including the effects of gravity is established in the general case where the cavity mode and the atomic transition frequencies are detuned. We show that atoms which classically would not reach the interaction region are able to emit a photon inside the cavity. The system turns out to be extremely sensitive to the detuning and in particular to its sign. A method to solve the equations of motion for non resonant atom-field interaction and arbitrary cavity modes is presented.     

Generating and probing a two-photon fock state with a single atom in a cavity

A two-photon Fock state is prepared in a cavity sustaining a "source mode" and a "target mode," with a single circular Rydberg atom. In a third-order Raman process, the atom emits a photon in the target while scattering one photon from the source into the target. The final two-photon state is probed by measuring by Ramsey interferometry the cavity light shifts induced by the target field on the same atom. Extensions to other multiphoton processes and to a new type of micromaser are briefly discussed.     

Photon emission from a two-level atom moving in a cavity

The interaction of a two-level atom uniformly moving along a classical trajectory with a high-Q cavity quantum mode is analyzed. The dressed-state method is used to derive a recurrence formula for the transition probability of the atom with photon emission; the temporal dynamics of this probability qualitatively depends on the Doppler shift of the atomic transition frequency, on the Rabi frequency of the atom-field system, and on the detuning of the atomic transition frequency from the field mode frequency. The emission dynamics of a moving atom is very sensitive to the detuning. Rabi-type oscillations with a frequency equal to the Doppler shift can arise under certain conditions. At resonance, the emission probability of a moving atom can considerably exceed the emission probability of an atom at rest. A plane-parallel-mirror cavity and a confocal spherical-mirror cavity are considered. It is shown that the peculiarities of Doppler-Rabi oscillations must be taken into account in micromaser theory.     

PHOTON STATISTICS OF THE MICROMASER WITH ULTRA COLD Λ-TYPE THREE-LEVEL ATOMS

We have established the master equation for the micromaser with the ultra-cold Λ-type three-level atoms and studied the photon statistics of the micromaser field. We find that as the atoms become colder,the change of the mean photon-number and the normalized standerd deviation become more regular, and their resonance peaks become sharper. For zero-temperature cavity,there are some regins in which the photon statistics are sub-Poissonian.With the increase of the cavity temperature,both the mean photon-number and the normalized standard deviation increase. When the cavity temperature is high enough, the sub-Poissonian property may disappear.     

超冷V型三能级原子注入的微波激射:原子相干性对腔场光子统计的影响

建立了超冷V型三能级原子注入的微波激射的腔场光子统计的量子理论,研究了原子相干性对光子统计性质的影响.发现腔内原子的发射概率随腔长变化的曲线中存在着共振峰和非共振平台,原子相干性对这些共振峰和非共振平台的绝对大小和相对比例具有灵活的可调性.原子发射概率的这些特点对腔场光子统计产生了直接的影响.平均光子数随腔长变化的曲线中也存在着共振峰和非共振平台;给定腔长,适当调节原子相干参量,可以使光子数分布向大、小光子数两个方向灵活地移动,平均光子数也相应地增加和减少.研究中还发现,适当选取原子相干参量,光子统计在大 关键词： 微波激射 超冷V型三能级原子 原子相干性 光子统计     

Two-Photon Micromaser with Initial Atomic Coherence

We investigate the quantum dynamics of a two-photon micromaser pumped by atoms injected in the superposition state of the upper and intermediate levels. We simulate a master equation governing the system by the Monte Carlo wavefunction approach and analyse the steady-state behaviour as a function of the atomic transit time. The atomic coherence can effectively enhance the intensity and sub-Poissonian of the cavity field as compared with the atomic mixture. It is also discovered that the phase of the cavity field can be shifted by adjusting the detuning between the atom and field. This result shows that it is possible to manipulate the phase of the cavity field by detuning, due to atomic coherence.     

频率变化场与原子相互作用系统中原子的信息熵压缩

利用J-C模型,考虑场频率随时间以正弦函数形式作小量变化,在旋波近似下,研究了二能级原子与单模辐射场相互作用系统中原子的信息熵压缩特性.利用数值计算方法给出原子的信息熵压缩因子随时间的演化曲线.研究结果表明:原子的信息熵仅在演化的初期呈现压缩效应,初始的原子分布角、光场强度和场频率随时间的变化对原子的信息熵压缩有明显影响.场频率随时间的变化对原子的信息熵压缩因子的演化具有调制作用,随场频率变化的幅值增大,调制作用增强,压缩效应减弱.     

内腔多原子直接俘获的强耦合腔量子力学系统的构建

腔内中性原子的长时间控制与俘获一直是腔量子电动力学(QED)中的一个难题,极大地制约了人们相干操控单原子及其与光相互作用的研究.基于传统Fabry-Perot光学腔,设计了一套易于内腔原子操控的强耦合腔QED系统,其典型参数为:腔长3.5 mm精细度约为57000,(g0,κ,γ)=2π×(1.48,0.375,2.61)MHz,临界光子数和原子数分别为1.54和0.89.该系统的特点是:能够在腔内直接实现冷原子磁光阱,并建立腔内光学晶格,实现腔内可控数目的中性原子的长时间俘获.通过合理选择构建光学偶极阱和原子成像系统,可实现对腔内单个原子或原子阵列的操控、探测、成像等.该系统可以克服传统腔QED系统中转移原子的困难,大幅增加腔内原子的寿命,为构建以腔QED系统为基础的量子信息演示平台提供了一种可能.     

Generation of sub-Poissonian light by a four-level microlaser with a high-Q cavity

We develop a kinetic theory that describes the behavior of a monatomic four-level laser when the atom is fixed inside a high-Q optical cavity. Such a statement of the problem is similar to that used in the experiment of G. M. Meyer, H.-J. Briegel, and H. Walther [Europhys. Lett. 37, 317 (1997)]. The condition that the number of photons is large and the photon fluctuations are small is employed. We show that by selecting the parameters of the periodic electromagnetic pulses exciting the atom one can achieve regular pumping of the upper laser level and generate sub-Poissonian laser light. We also discuss the reasons why the statistical pattern of the radiation differs from the micromaser pattern with regular injection of atoms. Zh. éksp. Teor. Fiz. 116, 485–502 (August 1999)     

微波激射器注入原子的反转特性

建立了含克尔介质微波激射器腔场稳态光子数分布的表达式.研究了在热原子、临界和超 冷原子的方式下微波激射器中原子在稳态时的反转特性. 结果表明：注入的二能级原子在不 同方式下，原子的反转特性不一样. 在热原子方式下，原子在一部分腔长L的区域无反转， 且随原子注入速率的增大，反转区域和反转概率增大. 在临界方式下，原子的反转呈现周期 性的坍塌和复苏现象. 而在冷原子方式下，原子在腔长L的全部区域无反转. 克尔效应和失 谐量使原子的反转概率减小. 关键词： 微波激射器 原子反转 光子统计 克尔效应     

Teleportation via decay

We present a rare example of a decay mechanism playing a constructive role in quantum information processing. We show how the state of an atom trapped in a cavity can be teleported to a second atom trapped in a distant cavity by the joint detection of photon leakage from the cavities. The scheme, which is probabilistic, requires only a single three level atom in a cavity. We also show how this scheme can be modified to a teleportation with insurance.     

Cavity-enhanced light scattering in optical lattices to probe atomic quantum statistics

Different quantum states of atoms in optical lattices can be nondestructively monitored by off-resonant collective light scattering into a cavity. Angle resolved measurements of photon number and variance give information about atom-number fluctuations and pair correlations without single-site access. Observation at angles of diffraction minima provides information on quantum fluctuations insensitive to classical noise. For transverse probing, no photon is scattered into a cavity from a Mott insulator phase, while the photon number is proportional to the atom number for a superfluid.     

Conditional measurements in micromasers: Role of counter-rotating processes

We study dynamics of a micromaser field when atoms are conditionally measured at the exit from the micromaser resonator. We assume the micromaser field to be initially prepared in the vacuum state and all atoms entering the cavity are considered to be in their lower states. We consider a conditional measurement when only those realizations of the experiment are taken into account when all atoms after the interaction with the cavity field are detected in their lower states. This kind of experimental configuration allows us to study in detail the role of the counter-rotating processes in the atom field interaction. In particular, we show that as a consequence of the interplay between the rotating-wave and counter-rotating processes a quasi steady state of the micromaser field is created in the cavity. We analyse quantum-statistical properties of the micromaser field as a function of the atom-field coupling constant (given in units of the field frequency) and the interaction time.We thank Dr. Gabriel Drobný for discussions and we acknowledge the support by the Grant Agency of the Slovak Acad. Sci. (Grant No. GA SAV 2/1152/94) and by the East-West Program of the Austrian Acad. Sci. under the contract No. 45.367/1-IV/6a/94 of the Österreichisches Bundesministerium für Wissenschaft und Forschung.     

Anomalous Effects of Driving Field Linewidth on a One-Atom Dressed-State Laser

We examine the effects of driving field linewidth on a one-atom dressed state laser. Unexpectedly, the linewidth leads to anomalous effects on the cavity field. The mean photon number of the cavity field is raised or the normalized variance is reduced to a certain degree as the linewidth increases for an appropriate range of parameters. The responsible mechanism is attributed to the fluctuation-induced modification of the electromagnetic reservoir where the atom stays.     

位相损耗腔中简并双光子拉曼耦合系统中的熵特性

研究了简并双光子拉曼耦合过程中存在位相损耗时,光场原子系统线性熵、光场线性熵和原子线性熵的特性,讨论了原子相干性和光场平均光子数对各线性熵的影响.结果表明:由于位相损耗的存在使系统的线性熵除初始时刻为零外,其他时刻均大于零,且与原子初始状态无关,即原子相干性对系统线性熵没有影响.当原子初始处于激发态或基态时,原子线性熵呈现出较完美的周期性;而在原子初始处于激发态和基态的叠加态时,原子的线性熵始终为零.随光场平均光子数的增加,各线性熵均会增大. 关键词： 位相损耗 简并双光子拉曼耦合过程 线性熵     

Effect of the spatial inhomogeneity of a field in a micromaser experiment with the selective measurement of atomic states

It is shown that the theoretical analysis of a micromaser experiment with the selective measurement of atomic states is impossible without consideration of the spatial structure of the field and of the statistical spread of the atomic velocities in the cavity. An approximate theory, ignoring the dynamic effects associated with the mentioned factors, yields not only quantitatively, but also qualitatively different theoretical predictions. The dynamics of the field and the mean number of photons in the trapping states realized in this case differ significantly from the predictions of the idealized standard theory used at present. Along with the process of establishment of the stationary Fock state of the field, under certain conditions, it appears possible to form the quasistationary quantum state of the field with large fluctuations of the number of photons, accompanied by the exit of the field from the cavity (“quasi-dissipation”), and the following stepwise transition into the state of the electromagnetic vacuum. It is shown that, under the conditions of the micromaser experiment, the information about the states of atoms, passed through the cavity, in the case considered, does not allow one to draw an unambiguous conclusion about the state of the field in the cavity.