Coherent effects in a three-photon CPT process of Ca+

Linewidth narrowing and other quantum coherent effects based on three-photon coherent population trapping (CPT) in Ca⁺ ions are investigated. If the propagation directions of the three lasers obey the phase matching condition, the dark linewidth resulting from the CPT can be very narrow, and it can be controlled by adjusting the parameters of the lasers.     

Frequency Stability of Atomic Clocks Based on Coherent Population Trapping Resonance in ^85Rb

An atomic clock system based on coherent population trapping （CPT） resonance in 85Rb is reported, while most past works about the CPT clock are in ST Rb. A new modulation method （full-hyperfine-frequency-splitting modulation） is presented to reduce the effect of light shift to improve the frequency stability of the CPT clock in SSRb. The experimental results show that the short-term frequency stability of the CPT clock in SSRb is in the order of 10^-10/s and the long-term frequency stability can achieve 1.5 × 10^-11/80000s, which performs as well as 87 Rb in CPT resonance. This very good frequency stability performance associated with the low-cost and low-power properties of SSRb indicates that an atomic clock based on CPT in SSRb should be a promising candidate for making the chip scale atomic clock.     

Light-Induced shifts in the frequency of a multiphoton radiooptical SHF resonance in alkali atoms

A computation is carried out for light-induced shifts in the frequency of a multiphoton radiooptical SHF resonance in alkali atoms on the basis of the quantum formalism of spherical tensors. The components of a light-induced shift in frequency at magneto-independent 0–0– and 1,–1-transitions in⁸⁷Rb atoms under the conditions of isotopic filtration of the resonance light of pumping are calculated. The difference between the temperatures of a filter cell is discovered at which the point of zero shift in the frequency of radiooptical resonance is attained. The components of the light-induced shift of frequency in optically oriented⁸⁷Rb and¹³³Cs atoms are compared in the absence of collisional reorientation in excited state. The prevailing role of the tensor component of light-induced shift in pumping by the D₁-line of a head doublet and the effect of the orientational dependence of the frequency of a multiphoton resonance on change in the sign of the pumping source radiation polarization are noted. St. Petersburg State Polytechnical University, 29 Politekhnicheskaya Str., St. Petersburg, 195251, Russia. Translated from Zburnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 832–838, November–December, 1998.     

基于磁共振的水下非接触式电能传输系统建模与损耗分析

文章对基于磁共振的水下非接触式电能传输系统在海水中的传输机理以及电涡流损耗进行了分析. 首先基于互感模型, 建立了空气中磁共振非接触式电能传输系统的数学模型, 分析了系统的频率特性, 从理论上对频率分裂现象进行了解释. 然后针对海水环境, 通过麦克斯韦方程组建立系统的数学模型, 通过级数展开, 略去高阶项, 得到计算电涡流损耗的近似公式, 分析了电涡流损耗与线圈半径、谐振频率、传输距离、磁感应强度的关系, 为水下非接触式电能传输系统的总体设计提供了理论依据. 最后通过实验验证了在空气中和海水中进行非接触式电能传输的异同, 以及电涡流损耗与各项参数的关系. 实验表明: 在空气中当传输距离为50 mm、传输功率为100 W时, 效率在80%以上; 在海水中当传输距离为50 mm、传输功率为100 W时, 效率约为67%, 说明基于磁共振的水下非接触式电能传输系统在海水中也有很好的应用前景.     

Development of the quantum discriminator for compact atomic clock

In the Laboratory of Frequency Standards, Quantum Radiophysics Division, Lebedev Physical Institute, a compact atomic standard of frequency and time is being developed. The results of this study make it possible to achieve a narrower metrological resonance of coherent population trapping (CPT) than in developed foreign analogues of compact atomic clocks, which will have a direct effect on the standard stability. The effect of the combination of buffer gas and antirelaxation coating on the CPT amplitude and resonance width are studied; parameters of short-cavity diode lasers (SCDLs) specially developed in collaboration with the Polyus Research and Development Institute are studied. A prototype of the compact physical discriminator for the atomic clock is developed and assembled. The dark width of the metrological resonance in the discriminator is less than 1 kHz, which theoretically implies the development of a compact atomic clock with a stability (Allan parameter) no worse than 3 · 10⁻¹² per hour.     

Lineshape asymmetry for joint coherent population trapping and three-photon N resonances

We show that a characteristic two-photon lineshape asymmetry arises in coherent population trapping (CPT) and three-photon (N) resonances, because both resonances are simultaneously induced by modulation sidebands in the interrogating laser light. The N resonance is a three-photon resonance in which a two-photon Raman excitation is combined with a resonant optical pumping field. This joint CPT and N resonance can be the dominant source of lineshape distortion, with direct relevance for the operation of miniaturized atomic frequency standards. We present the results of both an experimental study and theoretical treatment of the asymmetry of the joint CPT and N resonance under conditions typical to the operation of an N resonance clock.     

VIPA-based two-component detection for a coherent population trapping experiment

We demonstrate a two-component detection of a coherent population trapping(CPT) resonance based on virtually imaged phased array(VIPA). After passing through a VIPA, the two coupling lights with different frequencies in the CPT experiment are separated in space and detected individually. The asymmetric lineshape is observed experimentally in the CPT signal for each component, and the comparison with the conventional detection is presented. The shift of the CPT resonant frequency is studied with both the two-component and one-component detections. Our scheme provides a convenient way to further study the CPT phenomenon for each frequency component.     

平行线偏光激发CPT共振方案实验研究

目前的相干布居囚禁(CPT)原子钟和CPT磁场计中普遍采用圆偏振光方案 (σ⁺-σ⁺)实现CPT共振, 该方案对原子的利用率较低. 为了提高原子的利用率, 本文实验研究了通过平行线偏振相干双色光与⁸⁷Rb原子作用实现CPT共振的方案(lin//lin). 与σ⁺-σ⁺方案相比较, lin//lin方案消除了极化暗态, 获得更多工作原子. 在相同的实验条件下, 开展对比实验研究获得了信噪比为σ⁺-σ⁺方案2倍, 微分线型信号的中心斜率为σ⁺-σ⁺方案1.65倍的CPT共振信号. 研究结果表明该方案是实现低功耗原子钟、磁场计等设备的理想候选.     

Dependence of the ^85Rb coherent population trapping resonance characteristic on the pressure of N2 buffer gas

In order to exploit its potential applications, we experimentally study the dependence of ^85 Rb-based coherent population trapping （CPTi resonance on N2 buffer gas with 6 vapor cells filled with natural rubidium and N2. The experiments are carried out at different pressures and temperatures, and the results reveal that higher cell temperature makes the resonance more sensitive to N2 pressure. Thus, it is importmlt to choose a proper buffer gas pressure at a given cell temperature. This work provides valuable data for the application of 85Rb CPT resonance with a buffer gas of N2.     

Metastability of amorphous silicon from silicon network rebonding

We propose a network rebonding model for light-induced metastability in amorphous silicon, involving bonding rearrangements of silicon and hydrogen atoms. Nonradiative recombination breaks weak silicon bonds and generates dangling bond-floating bond pairs, with very low activation energies. The transient floating bonds annihilate, generating local hydrogen motion. Charged defects are also found. Support for these processes is found with tight-binding molecular dynamics simulations. The model accounts for major experimental features of the Staebler-Wronski effect including electron-spin resonance data, the t(1/3) kinetics of defect formation, two types of metastable dangling bonds, and hysteretic annealing.     

Diffusion-induced Ramsey narrowing

Diffusion-induced Ramsey narrowing is characterized and identified as a general phenomenon, in which diffusion of coherence in and out of an interaction region such as a laser beam induces spectral narrowing of the associated resonance line shape. Illustrative experiments and an intuitive analytical model are presented for this spectral narrowing effect, which occurs commonly in optically interrogated atomic systems and may also be relevant to quantum dots and other solid-state spin systems.     

Review of chip-scale atomic clocks based on coherent population trapping

Research on chip-scale atomic clocks （CSACs） based on coherent population trapping （CPT） is reviewed. The back- ground and the inspiration for the research are described, including the important schemes proposed to improve the CPT signal quality, the selection of atoms and buffer gases, and the development of micro-cell fabrication. With regard to the re- liability, stability, and service life of the CSACs, the research regarding the sensitivity of the CPT resonance to temperature and laser power changes is also reviewed, as well as the CPT resonance＇s collision and light of frequency shifts. The first generation CSACs have already been developed but its characters are still far from our expectations. Our conclusion is that miniaturization and power reduction are the most important aspects calling for further research.     

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.     

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.     

Triple quantum nutation in the two-level NMR system in the rotating frame

The authors present the detailed theory and the new results associated with the triple quantum (TQ) nutation and the line narrowing effect of the TQ resonance in the two-level NMR system which we reported previously. The TQ resonance is induced in the spin-locked system by the oscillating field produced by the sinusoidal phase modulation (PM) of the RF field. The theory predicts that the TQ nutation is accompanied by several higher frequency oscillations and we detected them experimentally by improving the detection system. These higher frequency oscillations are due to the fluctuation of the angle between the transverse or effective field causing the TQ nutation and the RF field. We obtain the result that the modulation index 2phim of the PM is the key parameter that essentially controls the conditions of the TQ resonance and the narrowing effect. Under the exact TQ resonance, the ratio of the TQ resonance frequency to the Larmor frequency of the RF field depends only on phim, and the secular part of the magnetic dipole Hamiltonian of a like spin system in the triply rotating frame disappears at a particular value of phim. The condition is different from that of the well-known magic angle condition.     

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     

Compact phase delay technique for increasing the amplitude of coherent population trapping resonances in open Lambda systems

We propose and demonstrate a novel technique for increasing the amplitude of coherent population trapping (CPT) resonances in open Lambda systems. The technique requires no complex modifications to the conventional CPT setup and is compatible with standard microfabrication processes. The improvement in the CPT resonance amplitude as a function of intensity of the excitation light agrees well with the theory based on ideal open and closed Lambda systems.     

High-contrast coherent population trapping resonances using four-wave mixing in 87Rb

We demonstrate very high-contrast coherent population trapping(1) (CPT) resonances by using four-wave mixing in (87)Rb atoms. In the experiment, we take advantage of the spectral overlap between F=2-->F(?) and F=3-->F(?) optical resonances on the D1 line of (87)Rb and (85)Rb atoms, respectively, to eliminate the DC-light background from the CPT resonance signal. We observe a CPT resonance with a contrast in the range of 90%, compared with a few percent achieved by alternative methods.     

Line-shape of dark line and maser emission profile in CPT

The paper is concerned with the line shapes of resonance phenomena observed in Coherent Population Trapping (CPT) applied to alkali atoms in a cell containing a buffer gas. Significant asymmetries and departures from a Lorentzian shape have been observed in connection with the measurement of dark lines and CPT maser emission profiles. Measurements are reported as a function of the power and frequency tuning of the laser used to create the CPT phenomenon. The paper reports on different experimental conditions and a comparison between theory and experiments is made for the cases of cesium and rubidium in a buffer gas. Received 3 March 2000 and Received in final form 10 April 2000     

About the Zeeman Light-Induced Frequency Shift of the Radio-Optical Resonance in Optically Oriented Isotopes of Alkali Metals

Results of calculations of tensor and vector components of the light-induced frequency shift of the radio-optical resonance in optically oriented potassium, rubidium, and cesium vapors are presented. The feasibility of cancellation of the tensor and vector components by the proper choice of the sign of pump light polarization is demonstrated. The influence of buffer inert argon and helium gases on the Zeeman light-induced shift of the resonant frequency in the unresolved radio-frequency absorption spectrum of rubidium-87 vapors is studied.