Quantum-trajectory approach to cavity quantum electrodynamics with up to three-atom collective effects

We present a quantum-trajectory treatment of the dynamics of a high-Q cavity mode interacting with a low-density atomic beam in the strong coupling regime. We consider up to three-atom collective effects, and evaluate their contribution to the destabilization of cavity field trapping states for mean number of atoms in the cavity both much smaller than one (micromaser or microlaser), and on the order of one (approaching a mesoscopic regime).     

Traveling-wave atom cavity interaction in the single-atom microlaser

We demonstrated traveling-wave atom-cavity interaction in the single-atom microlaser by tilting the atomic beam from its usual orientation of normal incidence with respect to the cavity mode. Laser-tuning curves, measured for various excitation pulse areas, are in good agreement with one-atom microlaser-maser theory.     

The magnesium ramsey interferometer: Applications and prospects

In this paper it will be shown that an atom interferometer, based on the coherent splitting of the atomic wavefunction by four travelling waves (Ramsey interferometer), may be explained by a purely mechanical interpretation. As our first application of this Ramsey interferometer we have measured the phase shifts respectively optical length changes in a magnesium atomic beam caused by the acceleration of the partial atomic wave in one arm of the interferometer. This acceleration was achieved by the dipole force exerted by an off-resonant crossing laser beam which interacted with the ground state part of the wavefunction only. Further applications of this interferometer and improvements due to laser cooling will be discussed.     

Cavity phase-shift error evaluation in a magnesium atomic beam frequency standard

In high resolution atomic or molecular beam spectroscopy, where the Ramsey interrogation method is used, one of uncertainty sources in determining the resonance frequency accurately is the phase-shift of the electromagnetic radiation in the cavity. This phenomenon, which depends on losses and asymmetries, is analyzed in a general way for a transverse atomic beam dimension much larger than the transition wavelength, a case which occurs in Mg or Ca beam frequency standards and the effects of different misalignments in collimated or divergent beams are examined. Numerical evaluations have been performed in the special case of an experimental Mg beam frequency standard. Divergence plays an important role in determining the cavity phase shift frequency error which is reduced about 100 times with respect to the case of a collimated beam.     

激光减速原子束频标的建议

本文提出一个激光减速的碱金属原子束频标的方案。用共振激光束对原子束同时进行减速和选态,使原子速率降到10m/s以下,而光抽运作用使原子自动集中到基态超精细结构中具有最大磁量子数的塞曼子能级上。为避免重力场中束轨迹下垂,用偏转磁铁或多束激光使束由水平转成垂直向上,然后用级联磁共振使原子过渡到频标所需的m_F=0能级。利用原子上升和重力场中自由下落两次通过单个微波谐振腔而取得Ramsey共振信号,线宽约为¹Hz。信号用另一束激光检测。予期这种频标的稳定度和准确度可比现有束型频标提高一个数量级以上。文中详细讨论了激光减速和选态的方法,克服横向加热效应的措施,实现级联磁共振的办法,以及获得垂直束装置的设计等。     

A proposal for testing complementarity with cavity QED techniques

We propose a method to test Bohr complemetarity with cavity QED techniques. It involves an atomic beam passing through two Ramsey zones and a nonresonant cavity initially filled with a strong coherent field. In the absence of the cavity field the probability of finding the atom in a definite state exhibits interference. Due to the dispersive atom-field interaction the paths by which the atom reach the definite state are remarked and thus the interference is destroyed. The associated quantum eraser is also presented.     

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.     

拉曼喷泉原子钟

利用托曼光场代替喷泉原子钟的微波腔实现拉曼喷泉原子钟.将分离托曼光场技术与冷原子喷泉技术相结合.避免了存真空腔内放置微波腔,简化了真空系统.同时还保持了很高的准确度.采用半经典理论研究了冷原子喷泉与托曼光场的相互作用过程.得到了冉赛(Ramsey)条纹.比较了托曼喷泉原子钟与热铯束拉曼原子钟,前者有更小的体积和功耗,其精度可能达到或超过商用小铯钟.还比较了拉曼喷泉原子钟与微波喷泉原子钟的差别,分析了光子反冲的影响,提出利用同向传播和相向传播的两台拉曼原子钟测最精细结构常数.     

Design and test of the microwave cavity in an optically-pumped Rubidium beam frequency standard

We are developing a compact rubidium atomic beam frequency standard with optical pumping and detection.The cavity for microwave interrogation is an important part of the clock.The cavity in our design is a Ramsey-type,E-bend one,which is the same as the conventional method in most cesium beam clocks.Requirements for the design are proposed based on the frequency shift associated with the cavity.The basic structure of the cavity is given by theoretical analysis and detailed dimensions are determined by means of electromagnetic field simulation with the help of commercial software.The cavity is manufactured and fabricated successfully.The preliminary test result of the cavity is given,which is in good agreement with the simulation.The resonant frequency is 6.835 GHz,equal to the clock transition frequency of87Rb,and the loaded quality factor is 500.These values are adjustable with posts outside the cavity.Estimations on the Ramsey line width and several frequency shifts are made.     

Atomic clocks based on coherent population trapping: a review

The paper gives an overview of the use of the coherent population trapping phenomenon (CPT) in alkali-metal atoms in the implementation of atomic frequency standards. Several avenues are examined. These include: the approach using a combination of the CPT phenomenon and the Ramsey separated interaction field technique on an atomic beam; the passive approach in a cell in which the microwave hyperfine resonance excited by the CPT phenomenon is detected directly on the transmitted radiation; the maser approach in which the same resonance is observed by means of stimulated emission in a microwave cavity-cell arrangement; and, finally, the proposed approach using pulses in a time sequence that implements the combined CPT–Ramsey separated interaction field technique in time rather than in space. A review of field and laboratory implementations using these approaches is made.     

Cold atom space clock with counter-propagating atoms

<正>We discuss the feasibility of realizing a cold atom space clock with counter-propagating cold atoms in microgravity.The design of the space clock is based on an atomic beam clock with Ramsey cavity,except that magneto-optical trap(MOT) is placed at each side.Cold atoms are launched simultaneously from the MOTs at both sides of the clock and they move at the counter-direction towards each other.The velocity of the launched atoms is precisely controlled to Ramsauer-Townsend resonance so that no additional collision frequency shift takes place.Such configuration can efficiently cancel the frequency shift resulting from cavity phase shift and increase the signal-to-noise ratio(SNR).     

Atomic Spectrum in Ramsey Separated Oscillating Fields with Three Interaction Regions

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Atomic Spectrum in Ramsey Separated Oscillating Fields with Three Interaction Regions

Comparing with the situation of Ramsey separated oscillating fields used in Cesium atomic beam frequency standard, the transition probability spectrum of two-level atoms in the Ramsey separated oscillating fields with three interaction regions has been derived under the condition of near resonance. The new characteristic of atomic spectrum with excessive microwave power was analyzed in detail. Meantime, the predicted new characteristic of atomic spectrum was confirmed by numerical method in this paper.     

Creation of atomic W state in a cavity by adiabatic passage

We propose two relatively robust schemes to generate controllable (deterministic) atomic W states of three Λ-like atoms interacting with an optical cavity and a laser beam. Losses due to atomic spontaneous emissions and to cavity decay are efficiently suppressed by employing adiabatic passage technique and appropriately designed atom-field couplings. In these schemes the three atoms traverse the cavity-mode and the laser beam and become entangled in the free space outside the cavity.     

在时域实验研究扩散诱导的Ramsey压窄

基于Duan-Lukin-Cirac-Zoller(DLCZ)方案,在时域上研究了扩散诱导的Ramsey压窄.以87Rb热原子系综为研究对象,观测到缓冲气体,激光束尺寸和镀石蜡Rb池均可以导致Ramsey压窄现象.实验结果和文献中重复相互作用模型预期的一致.     

Analysis of a teleportation scheme involving cavity field states in a linear superposition of Fock states

We analyse a teleportation scheme of cavity field states. The experimental sketch discussed makes use of cavity quantum electrodynamics involving the interaction of Rydberg atoms with superconducting (micromaser) cavities as well as with classical microwave (Ramsey) cavities. In our scheme the Ramsey cavities and the atoms play the role of auxiliary systems used to teleport a field state, which is formed by a linear superposition of vacuum |∅〉 and the one-photon state |1〉, from a micromaser cavity to another.     

Proposed search for an electric-dipole moment using laser-cooled 171Yb atoms

We propose an experiment to search for a permanent atomic electric-dipole moment (EDM) using laser-cooled 171Yb atoms launched in an atomic fountain. A uniform B field sets the quantization axis, and the Ramsey separated-oscillatory-fields method is used to measure the Zeeman precession frequency of the atoms. Laser beams of appropriate polarization are used for preparation and detection in a given magnetic sublevel. The signature of an EDM is a shift in the Ramsey resonance correlated with application of a large E field. The precision is expected to be at least 20 times better than current limits because the use of a cold atomic beam allows application of E field 10 times larger than in a vapor cell, and the interaction time with the E field is 200 times larger compared to a thermal beam. The leading source of systematic error in beam experiments, the ×/c motional magnetic field, is reduced considerably because of the near-perfect reversal of velocity between up and down trajectories through the E-field region.     

Entangled Radiation through an Atomic Reservoir Controlled by Coherent Population Trapping

We show that it is possible to generate Einstein-Podolsky-Rosen （EPR） entangled radiation using an atomic reservoir controlled by coherent population trapping. A beam of three-level atoms is initially prepared in nearcoherent population trapping （CPT） state and acts as a long-lived coherence-controlled reservoir. Four-wave mixing leads to amplification of cavity modes resonant with RabJ sidebands of the atomic dipole transitions. The cavity modes evolve Jnto an EPR state, whose degree of entanglement is controlled by the intensities and the frequencies of the driving fields. This scheme uses the long-lived CPT coherence and is robust against spontaneous emission of the atomic beam. At the same time, this scheme is implemented in a one-step procedure, not in a two-step procedure as was required in Phys. Rev. Lett. 98 （2007） 240401.     

脉冲光抽运铷原子钟的Ramsey信号特性研究

基于以小型化磁控管微波腔实现的脉冲光抽运铷原子钟,研究了自由演化时间对Ramsey信号特性的影响,讨论了横向弛豫时间对钟信号对比度的影响.该原子钟的自由演化时间为3ms时,Ramsey信号中心条纹的对比度为52%,散弹噪声极限优于1.7×10-14(τ=1s).利用Ramsey信号的对比度和吸收泡内的光密度,计算得到了原子钟内铷吸收泡的纵向和横向弛豫时间分别为1.95ms和2.45ms.本文研究为进一步提高脉冲光抽运铷原子钟的性能提供了重要依据.     

Quantum trajectory studies of many-atom and finite transit-time effects in a cavity QED microlaser or micromaser

Studies of microlasers and micromasers generally assume that at most one atom is present in the resonator and transit times are much shorter than cavity lifetimes. We use quantum trajectory simulations to investigate the behavior of a microlaser/micromaser in which multiple atoms may be present and atom transit times can be comparable to the cavity decay time. Many-atom events are shown to destroy trap state resonances even for a mean intracavity atom number as small as 0.1. Away from trap states, results for mean photon number agree with a single-atom, weak-decay theory. However the variance of the photon number distribution increases relative to micromaser theory by an amount proportional to the product of the interaction time and cavity decay rate. This excess variance is interpreted as resulting from cavity decay during the atomic transit time.