Quantum chaos and fractals with atoms in cavities

We study the coupled translational, electronic, and field dynamics of the combined system “a two-level atom + a single-mode quantized field + a standing-wave ideal cavity”. In the semiclassical approximation with a point-like atom, interacting with the classical field, the dynamics is described by the Heisenberg equations for the atomic and field expectation values which are known to produce semiclassical chaos under appropriate conditions. We derive Hamilton–Schrödinger equations for probability amplitudes and averaged position and momentum of a point-like atom interacting with the quantized field in a standing-wave cavity. They constitute, in general, an infinite-dimensional set of equations with an infinite number of integrals of motion which may be reduced to a dynamical system with four degrees of freedom if the quantized field is supposed to be initially prepared in a Fock state. This system is found to produce semiquantum chaos with positive values of the maximal Lyapunov exponent. At exact resonance, the semiquantum dynamics is regular. At large values of detuning |δ|1, the Rabi atomic oscillations are usually shallow, and the dynamics is found to be almost regular. The Doppler–Rabi resonance, deep Rabi oscillations that may occur at any large value of |δ| to be equal to |αp₀|, is found numerically and described analytically (with α to be the normalized recoil frequency and p₀ the initial atomic momentum). Two gedanken experiments are proposed to detect manifestations of semiquantum chaos in real experiments. It is shown that in the chaotic regime values of the population inversion z_out, measured with atoms after transversing a cavity, are so sensitive to small changes in the initial inversion z_in that the probability of detecting any value of z_out in the admissible interval [−1,1] becomes almost unity in a short time. Chaotic wandering of a two-level atom in a quantized Fock field is shown to be fractal. Fractal-like structures, typical with chaotic scattering, are numerically found in the dependence of the time of exit of atoms from the cavity on their initial momenta.     

Measurement of the Distribution of Magnetic Field in Gyrotron of ECRH System on HL-2A Tokamak

In ECRH system of HL-2A tokamak, we chose a new type of gyrotron imported from Russia. We finished the installation and testing last year with the help of Russian experts. We got a lot of useful data and satisfying results after our experiments with the operating of gyrotron.     

Enhancement of the Kerr effect for a quantum dot in a cavity

Nonlinear susceptibility of a quantum dot (QD) embedded in a two-sided cavity, is studied theoretically from a weak-coupling to a strong-coupling regime. In the relevance of a quantum logic gate, the corresponding nonlinear phase shifts (Kerr effect) are estimated for coherent wavepackets including one photon on average. In the weak-coupling regime, the phase shift enhances strongly as a function of a coupling constant between the cavity photon and QD, and eventually saturates in the strong-coupling regime. We also show transmission spectra to evaluate the efficiency of the phase shift. Although the efficiency decreases monotonically in the weak-coupling regime, it rises in the strong-coupling regime.     

回旋管输出窗热性质的研究

一、引 言 输出窗是回旋管的能量输出端口,它的特性直接影响到回旋管的性能和寿命。输出窗的设计包括电特性和热特性的研究。当输出功率增加时,热特性的研究变得非常重要以便寻求合理有效的冷却措施。 输出窗由波导和介质片(块)两部分组成。回旋管的输出波导是圆波导,介质一般做成     

THE FIRST EXPERIMENT OF A THz GYROTRON WITH A PULSE MAGNET

A THz gyrotron with a pulse magnet has been designed, constructed and operated in FIR FU. It is developed as one of high frequency gyrotrons included in Gyrotron FU Series. The gyrotron has already achieved the first experimental result for high frequency operations whose radiation frequency exceeds 1 THz. In this paper, the design detail and the operation test results for sub-terahertz to terahertz range are described. The second harmonic operation is confirmed experimentally at the expected frequency of 1.005 THz due to TE_6,11 cavity mode at the magnetic field intensity of 19.0 T.     

Circuit analysis of the compound quasi-optical power combiner

In 1991, we developed a new type of quasi-optical power combiner, called a compound quasi-optical power combiner, at Ka-band. In this paper, the circuit of such a compound quasi-optical power combiner is analysed. Its equivalent circuit model is proposed. The circuit equations, the balance condition, the injection locking and the stabilized condition of the compound quasi-optical power combiner are studed by the equivalent circuit model. As an example, a compound quasi-optical power combiner which consists of two single—cavity, two—device power combiners is analysed     

High sensitivity CW-cavity ring down spectroscopy of water in the region of the 1.5 μm atmospheric window

The absorption spectrum of natural water vapour around 1.5 μm has been recorded with a typical sensitivity of 5 × 10⁻¹⁰ cm⁻¹ by using a CW-cavity ring down spectroscopy set up based on fibred DFB lasers. A series of 31 DFB lasers has allowed a full coverage of the 6130.8-6748.5 cm⁻¹ (1.63-1.48 μm) region corresponding to the H transparency band of the atmosphere. The line parameters (wavenumber and intensity) of a total of 5190 lines, including 4247 lines of water vapor, were derived by a one by one fit of the lines to a Voigt profile. Different isotopologues of water (H₂¹⁶O, H₂¹⁸O, H₂¹⁷O, and HD¹⁶O) present in natural abundance in the sample contribute to the spectrum. For the main isotopologue, H₂¹⁶O, 2130 lines were measured with line intensities as weak as 10⁻²⁹ cm/molecule while only 926 lines (including a proportion of 30% inaccurate calculated lines) with a minimum intensity of 3 × 10⁻²⁷ cm/molecule are provided by the HITRAN and GEISA databases. Our comparison in the whole 5750-7965 cm⁻¹ region, has also evidenced that an error in the process of conversion of the intensity units from cm⁻²/atm to cm⁻¹/(molecule × cm⁻²) at 296 K, has led to H₂¹⁶O line intensities values listed in the HITRAN-2000 database, systematically 8 % below the original FTS values. The rovibrational assignment was performed on the basis of the ab initio calculations by Schwenke and Partridge with a subsequent refinement and validation using the Ritz combination principle together with all previously measured water transitions relevant to this study. This procedure allowed determining 172, 139, 71, and 115 new energy levels for the H₂¹⁶O, H₂¹⁸O, H₂¹⁷O, and HD¹⁶O isotopologues, respectively. The results are compared with the available databases and discussed in regard of previous investigations by Fourier transform spectroscopy. The spectrum analysis has showed that most of the transitions which cannot be assigned to water are very weak and are due to impurities such as carbon dioxide and ammonia, leaving only about 3% of the observed transitions unassigned. The interest of a detailed knowledge of water absorption for trace detectors developed in the 1.5 μm range is underlined: for instance HDO contributes significantly to the considered spectrum while no HDO line parameters are provided by the HITRAN database.     

Bending loss measurement using a fiber cavity ringdown scheme

A novel sensitive technique for the determination of losses in fiber cavities is presented. The method is based on the cavity ringdown scheme implemented in silica-based single-mode fibers. Bending losses of fiber cavities of different lengths have been measured showing all an oscillating behavior with respect to the curvature radius of the fiber as predicted by a theoretical model. The best minimum detectable absorbance per cavity pass achieved by this new method is 1.72×10⁻³ dB within a 10 m-long cavity. This limit suffices well for an accurate determination of optical bending losses even in bend-insensitive fibers. Furthermore, the comparison of the measured bending losses with a theoretical model allows the extraction of different fiber parameters. Good agreement has been found between the experimentally derived parameters and literature data.     

大耦合孔同轴输出腔的3维解析分析

 在高功率微波器件中，通常采用大耦合孔的同轴微波输出腔，该腔为3维结构。采用场等效原理将腔体、耦合孔及其输出负载(行波边界)进行分区,每个区域中的场由界面上的磁流密度决定。采用格林函数积分法可得每个区域中的3维场,再由各个区域的场匹配方程求得腔体的谐振频率、特性阻抗、有载品质因数、模式分布等参数。为腔体的计算和设计提供一种计算模型。     

耦合双原子Jaynes-Cummings模型的腔场谱H

研究了处于激发态的两原子与高Q腔场相互作用单光子过程的腔场谱,给出了初始光场为光子数态、相干态、压缩真空态时的腔场谱数值计算结果,分析了原子间偶极-偶极相互作用强度gα对腔场谱结构的影响.发现真空场Rabi峰,当gα较弱时为4峰,gα较强时为3峰结构;弱场数态(n＞0)时为5峰,强场时为3峰结构.相干态和压缩真空态时,谱结构与光子数分布有关,一般为复杂的多峰结构.结果表明,gα对峰位峰高都有影响,破坏了谱结构的对称性,但这种影响只在真空场和弱场时才较明显.