Tunable Phase-Coherent Source of the Bichromatic Light Field for the Spectroscopy of Resonances of the Coherent Population Trapping in Rare-Earth Atoms

A technique for creating the source of a bichromatic laser field with a stable mean value of the difference frequency is realized. The spectral characteristics of a femtosecond passive mode-locked laser are used in this technique. Such a source operating in the region of 780 nm is created. The possibility of using the phenomenon of coherent population trapping (CPT) in three-level systems of the rare-earth atoms for the development of secondary frequency standards in the optical range is considered. The contributions of the processes affecting the width and contrast of the CPT resonances and defining their attainable Q factors are studied. The prospects of using the experimental technique developed for the spectroscopy of the CPT resonances in samarium and thulium vapors are discussed.     

Characteristics of coherent population trapping in multilevel systems for magnetometry in plasma research

An analysis is presented of the feasibility of measurements of local poloidal magnetic fields in toroidal magnetic fusion devices using coherent population trapping (CPT) in hydrogen-like probing atoms. A measurement scheme is examined in which CPT suppresses the resonance fluorescence from a probing beam of light neutrals with Zeeman-split levels. Feasibility requirements for CPT in three- and five-level systems are discussed. As a result, a theory of CPT-based magnetometry is developed for a system significantly more complex than the conventional three-level Λ system. A theoretical analysis shows that this technique can be used to measure a local safety factor in a toroidal device to an accuracy of a few percent.     

Electromagnetic interaction in theory with Lorentz invariant CPT violation

An attempt is made to incorporate the electromagnetic interaction in a Lorentz invariant but CPT violating non-local model with particle–antiparticle mass splitting, which is regarded as a modified QED. The gauge invariance is maintained by the Schwinger non-integrable phase factor but the electromagnetic interaction breaks C, CP and CPT symmetries. Implications of the present CPT breaking scheme on the electromagnetic transitions and particle–antiparticle pair creation are discussed. The CPT violation such as the one suggested in this Letter may open a new path to the analysis of baryon asymmetry since some of the Sakharov constraints are expected to be modified.     

Production of (4)(double Lambda)H hypernuclei

An experiment demonstrating the production of double-Lambda hypernuclei in (K(-),K(+)) reactions on (9)Be was carried out at the D6 line in the BNL alternating-gradient synchrotron. The technique was the observation of pions produced in sequential mesonic weak decay, each pion associated with one unit of strangeness change. The results indicate the production of a significant number of the double hypernucleus (4)(double Lambda)H and the twin hypernuclei (4)(Lambda)H and (3)(Lambda)H. The relevant decay chains are discussed and a simple model of the production mechanism is presented. An implication of this experiment is that the existence of an S = -2 dibaryon more than a few MeV below the double Lambda mass is unlikely.     

Triplon modes of puddles

Free fluctuations of the contact line of large drops ("puddles") of wavelength lambda > kappa(-1), the capillary length, cannot be seen on a solid substrate because even a small but finite hysteresis is enough to block these slow modes. We show here that vertical vibrations of the substrate (at frequency omegaE, acceleration Lambda) above a threshold amplitude Lambda(c) release the line and excite contour oscillations (triplons). We observe harmonic modes and parametric excitations at omegaE/2. We construct the phase diagram (Lambda, omegaE) of these subharmonic modes and we study their growth dynamics: they slow down near the threshold of the contour instability.     

Coherent lambda-sigma coupling in s-shell hypernuclei

It is found that the suppression due to two-body LambdaN-SigmaN coupling solves the overbinding problem in (5)(Lambda)He but it, in turn, causes a severe underbinding in the four-body systems. The shortage of this binding is overcome by introducing explicitly the Lambda-Sigma coupling which is equivalent to the LambdaNN three-body force. This three-body force becomes strong in the 0(+) states of (4)(Lambda)H and (4)(Lambda)He according to the coherently added enhancement. The 0(+)-1(+) splitting in (4)(Lambda)H and (4)(Lambda)He is found partly due to the LambdaN spin-spin interaction and partly due to the Lambda-Sigma coupling in the recent Nijmegen soft-core potential.     

Detection of the power spectrum of cosmic microwave background lensing by the Atacama Cosmology Telescope

We report the first detection of the gravitational lensing of the cosmic microwave background through a measurement of the four-point correlation function in the temperature maps made by the Atacama Cosmology Telescope. We verify our detection by calculating the levels of potential contaminants and performing a number of null tests. The resulting convergence power spectrum at 2° angular scales measures the amplitude of matter density fluctuations on comoving length scales of around 100 Mpc at redshifts around 0.5 to 3. The measured amplitude of the signal agrees with Lambda cold dark matter cosmology predictions. Since the amplitude of the convergence power spectrum scales as the square of the amplitude of the density fluctuations, the 4σ detection of the lensing signal measures the amplitude of density fluctuations to 12%.     

Experimental umbilic diabolos in random optical fields

The intensity of a random optical field consists of bright speckle spots (maxima) separated from dark areas (minima and optical vortices) by saddle points. We show that hidden in this complicated landscape are umbilic points--singular points at which the eigenvalues Lambda (+/-) of the Hessian matrix that measure the curvature of the landscape become degenerate. Although not observed previously in random optical fields, umbilic points are the most numerous of all special points, outnumbering maxima, minima, saddle points, and vortices. We show experimentally that the directions of principal curvature, the eigenvectors Psi (+/-), rotate about intensity umbilic points with positive or negative half-integer winding number, in accord with theory, and that Lambda (+) and Lambda (-) generate a double cone known as a diabolo. At optical vortices the curvature of the amplitude is singular, and we show from both theory and experiment that for this landscape Psi (+/-) rotate about vortex centers with a positive integer winding number. Diabolos can be classified as elliptic or hyperbolic, and we present initial results for the measured fractions of these two different types of umbilic diabolos.     

Regularization,renormalization and “peratization” in effective field theory for two nucleons

We discuss conceptual aspects of renormalization in the context of effective field theories for the two-nucleon system. It is shown that, contrary to widespread belief, the renormalization scheme dependence of the scattering amplitude can only be eliminated up to the order the calculations are performed. We further consider an effective theory for an exactly solvable quantum mechanical model which possesses a long- and short-range interaction to simulate pionful effective field theory. We discuss the meaning of low-energy theorems in this model and demonstrate their validity in calculations with a finite cutoff \( \Lambda\) as long as it is chosen of the order of the hard scale in the problem. Removing the cutoff by taking the limit \( \Lambda\) \( \rightarrow\) ∞ yields a finite result for the scattering amplitude but violates the low-energy theorems and is, therefore, not compatible with the effective field theory framework.     

A high statistics measurement of the Lambda(+)(c) lifetime

A high statistics measurement of the Lambda(+)(c) lifetime from the Fermilab fixed-target FOCUS photoproduction experiment is presented. We describe the analysis technique with particular attention to the determination of the systematic uncertainty. The measured value of 204.6 +/- 3.4 (stat) +/- 2.5 (syst) fs from 8034 +/- 122 Lambda(+)(c)-->pK(-)pi(+) decays represents a significant improvement over the present world average.     

Emergence of U(1) symmetry in the 3D XY model with Zq anisotropy

We study the three-dimensional XY model with a Zq anisotropic term. At temperatures T相似文献   

小型环形激光器中He-Ne气体放电辉光压制的光学方法

为解决小型环形激光器输出信号信噪比随腔长减小而下降的问题,研制了一种压制He-Ne气体放电辉光的滤光片。该滤光片的中心波长为632.8nm,入射角为45°,其基片是截止波长为550nm的短波截止红色玻璃,基片前表面镀有19层瞙系结构为{HL2HLHLHLH2LHLHLHLH2LH}的窄带滤光片,后表面镀有4层非规整减反膜。使用离子溅射法和石英晶振膜厚监控方式制备了该滤光片,并对其进行了反向工程拟合,拟合的理论曲线与用Lambda950分光光度计正入射实测的透过率曲线较为吻合。将该滤光片胶合在环形激光器的输出镜后表面,其有用的激光信号幅值基本不变,而噪声幅值下降了约80%,表明该滤光片从光学上使输出信号的信噪比提高了5倍,降低了后续电路处理的负担及复杂度,为小型环形激光器的研制起到了一定的作用。     

Asymmetries in the nonmesonic weak decay of polarized lambda hypernuclei

The nonmesonic weak decay of polarized Lambda hypernuclei is studied for the first time by taking into account, with a Monte Carlo intranuclear cascade code, the nucleon final state interactions. A one-meson-exchange model is employed to describe the Lambda-->N-->nN processes in a finite nucleus framework. The relationship between the intrinsic Lambda asymmetry parameter a(Lambda) and the asymmetry a(M)(Lambda) accessible in experiments is discussed. A strong dependence of a(M)(Lambda) on nucleon final state interactions and detection threshold is obtained. Our results for a(M)(Lambda) are consistent with (11)(Lambda)B--> and (12)(Lambda)C--> data but disagree with observations in (5)(Lambda)H-->e.     

Tracking interacting dark states through higher order absorption resonances

A three photon resonance arising due to coherent population trapped (CPT) states in multi-level systems, is experimentally shown to be a powerful spectral marker to detect interacting CPT states. In systems showing N type or double Λ type level configurations, these absorption resonances can be used to identify spectral positions of maximal interactions between competing CPT ground states. The contrast of the absorption resonance serves to identify even partially destructive interactions between the CPT states, eliminating the need for strong resonant changes of ground state coherence for identification. We demonstrate this effect in a room temperature, gaseous collection of ⁸⁷Rb. atoms. Three laser fields interact with a double Λ configuration in the Zeeman degenerate levels of the ground state 5S_1/2S_{1/2}, F = 1 and those of the excited states 5P_3/2P_{3/2}, F = 0,1, around the D2 line. The three-photon resonance is studied in the counter-propagating third field when the other two co-propagating fields satisfy the two-photon resonance condition necessary for creation of CPT states. We envisage that this absorption feature in the third field, can become a veritable tool to quantify degradation of CPT induced effects in engineered quantum states using multi-level systems.     

Temperature dependence of coherent population trapping resonances

We measure the properties of coherent population trapping (CPT) resonances in Cs vapor cells as a function of temperature. We expected the CPT signal to increase with higher vapor density, but instead the signal fades away above a certain density. Two possible density-dependent explanations are discussed: spin-exchange collisions, which are found to give no relevant contribution at the temperatures considered here, and increased absorption due to the optical thickness of the vapor. The dependence of the dark-line resonance amplitude as a function of cell temperature can be well represented by a simple model based on the optical thickness of the vapor as a function of temperature. Received: 30 November 2001 / Published online: 7 February 2002     

芯片原子钟相干布居囚禁谱线特性研究

通过微型原子蒸汽室产生质量满足要求的相干布居囚禁(CPT)信号是实现芯片原子钟的关键之一.本实验通过对光源实施频率调制和对光场与⁸⁷Rb原子作用产生的信号作相敏解调获得高信噪比的CPT微分谱线, 利用CPT微分谱线研究了CPT信号随工作参数变化的规律以及信号质量对原子钟频率稳定度的影响, 所获研究结果与理论模型预期相符合, 实验结果为芯片原子钟推荐了最佳工作参数.实验所采用的方法利用芯片原子钟自身的资源就可以实施, 因此为芯片原子钟开展性能研究和实施工作参数优化提供了实用的手段.     

Subkilohertz linewidths measured by heterodyne-detected coherent population trapping in sodium vapor

Subkilohertz spectroscopy by coherent population trapping (CPT) has been performed in Na atomic vapor. The system employs a frequency-swept acousto-optic modulator for bichromatic excitation as well as a heterodyne-lock-in detection technique that permits the direct measurement of the CPT dispersion curves at a good signal-to-noise ratio. A CPT linewidth of -400 Hz was measured as well as a steep refractive-index dispersion of as much as 3.3 x 10(-10) Hz(-1), corresponding to a group velocity of 1800 m/s.     

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.