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Giant dipole resonance with exact treatment of thermal fluctuations  [PDF]
P. Arumugam,G. Shanmugam,S . K. Patra
Physics , 2004, DOI: 10.1103/PhysRevC.69.054313
Abstract: The shape fluctuations due to thermal effects in the giant dipole resonance (GDR) observables are calculated using the exact free energies evaluated at fixed spin and temperature. The results obtained are compared with Landau theory calculations done by parameterizing the free energy. The Landau theory is found to be insufficient when the shell effects are dominating.
Resonance fluorescence of a trapped three-level atom  [PDF]
Marc Bienert,Wolfgang Merkel,Giovanna Morigi
Physics , 2003, DOI: 10.1103/PhysRevA.69.013405
Abstract: We investigate theoretically the spectrum of resonance fluorescence of a harmonically trapped atom, whose internal transitions are $\Lambda$--shaped and driven at two-photon resonance by a pair of lasers, which cool the center--of--mass motion. For this configuration, photons are scattered only due to the mechanical effects of the quantum interaction between light and atom. We study the spectrum of emission in the final stage of laser--cooling, when the atomic center-of-mass dynamics is quantum mechanical and the size of the wave packet is much smaller than the laser wavelength (Lamb--Dicke limit). We use the spectral decomposition of the Liouville operator of the master equation for the atomic density matrix and apply second order perturbation theory. We find that the spectrum of resonance fluorescence is composed by two narrow sidebands -- the Stokes and anti-Stokes components of the scattered light -- while all other signals are in general orders of magnitude smaller. For very low temperatures, however, the Mollow--type inelastic component of the spectrum becomes visible. This exhibits novel features which allow further insight into the quantum dynamics of the system. We provide a physical model that interprets our results and discuss how one can recover temperature and cooling rate of the atom from the spectrum. The behaviour of the considered system is compared with the resonance fluorescence of a trapped atom whose internal transition consists of two-levels.
Effects of thermal shape fluctuations and pairing fluctuations on the giant dipole resonance in warm nuclei  [PDF]
A. K. Rhine Kumar,P. Arumugam,N. Dinh Dang
Physics , 2015, DOI: 10.1103/PhysRevC.91.044305
Abstract: Apart from the higher limits of isospin and temperature, the properties of atomic nuclei are intriguing and less explored at the limits of lowest but finite temperatures. At very low temperatures there is a strong interplay between the shell (quantal fluctuations), statistical (thermal fluctuations), and residual pairing effects as evidenced from the studies on giant dipole resonance (GDR). In our recent work [Phys. Rev. C \textbf{90}, 044308 (2014)], we have outlined some of our results from a theoretical approach for such warm nuclei where all these effects are incorporated along within the thermal shape fluctuation model (TSFM) extended to include the fluctuations in the pairing field. In this article, we present the complete formalism based on the microscopic-macroscopic approach for determining the deformation energies and a macroscopic approach which links the deformation to GDR observables. We discuss our results for the nuclei $^{97}$Tc, $^{120}$Sn, $^{179}$Au, and $^{208}$Pb, and corroborate with the experimental data available. The TSFM could explain the data successfully at low temperature only with a proper treatment of pairing and its fluctuations. More measurements with better precision could yield rich information about several phase transitions that can happen in warm nuclei.
Interference of Resonance Fluorescence from two four-level atoms  [PDF]
T. Wong,S. M. Tan,M. J. Collett,D. F. Walls
Physics , 1996, DOI: 10.1103/PhysRevA.55.1288
Abstract: In a recent experiment by Eichmann et al., polarization-sensitive measurements of the fluorescence from two four-level ions driven by a linearly polarized laser were made. Depending on the polarization chosen, different degrees of interference were observed. We carry out a theoretical and numerical study of this system, showing that the results can largely be understood by treating the atoms as independent radiators which are synchronized by the phase of the incident laser field. The interference and its loss may be described in terms of the difference between coherent and incoherent driving of the various atomic transitions in the steady-state. In the numerical simulations, which are carried out using the Monte Carlo wave function method, we remove the assumption that the atoms radiate independently and consider the photodetection process in detail. This allows us to see the total interference pattern build up from individual photodetections and also to see the effects of superfluorescence, which become important when the atomic separation is comparable to an optical wavelength. The results of the calculations are compared with the experiment. We also carry out simulations in the non steady-state regime and discuss the relationship between the visibility of the interference pattern and which-path considerations.
Resonance Fluorescence of Fused Silica by the Depopulation of the Ground State  [PDF]
Fuat Bayrakceken,Korkut Yegin
International Journal of Photoenergy , 2012, DOI: 10.1155/2012/359384
Abstract: Spectroscopically pure fused silica has been used in many applications ranging from optoelectronics and optical fibers to laser flash spectroscopy. Although ultraviolet light irradiated optical absorption spectra and coherence fluorescence of silicon dioxide have been studied in the past, we present discrete absorption and resonance coherent fluorescence line of silicon dioxide which were recorded photographically at 288.2?nm. This discrete fluorescence is observed at room temperature using high photon flux (1024 photon/pulse) excitation spectroscopy. 1. Introduction Resonance fluorescence occurs when atoms/molecules absorb and reemit radiation at the same wavelength. Resonance fluorescence line corresponds to the transition between an electronic excited state and the ground state. The wavelengths of the absorption ( ) and fluorescence ( ) are the same for resonance transitions. Resonance fluorescence process of silicon dioxide is shown in Figure 1. Figure 1: Resonance fluorescence of SiO 2. Coherent resonance fluorescence and ultraviolet (UV) light induced optical absorption spectra were reported in [1] and resonance fluorescence was observed in the 250–255?nm band at room temperature by high photon flux excitation spectroscopy. As discussed in previous works [1–7], fused silica exhibits coherent fluorescence in the ultraviolet C region (UV-C). UV grade fused silica is an amorphous form of silicon dioxide made from flame hydrolysis of silicon tetrachloride. On top of high UV transmission, it has the properties of low thermal expansion coefficient and high laser damage threshold. Amorphous fused silica form bonds in definite vectorial positions in space such that ring structures that connect molecules can exist [8, 9]. A random network of atoms in fused silica was shown in [10] and reproduced in Figure 2. Ring structures consist of tetrahedral atomic arrangements and most ring structures contain five or six ring members simply because the bond angle between O–Si–O permits formation of almost perfect tetrahedrons with less strain energy. Figure 2: Ball and stick model of fused silica in random network (encircled are three-fold and four-fold ring structures) (reproduced from [ 10]). The vibrational level patterns for silicon dioxide are not complex for six- or eight rings, which, in turn, enables one to observe transitions in 250–255?nm band as discrete narrow bands [1]. The bandwidths of these coherent emissions were reported approximately 1/25?nm in [1]. These narrow absorption and emission lines are reproduced from [1] with the permission Bayrak?eken
Cavity-Induced Enhancement of Squeezing in Resonance Fluorescence of a V-Type Three-Level Atom
ZHOU Lu,LI Gao-Xiang,ZHAN Ming-Sheng,
周鲁
,李高翔,詹明生

中国物理快报 , 2008,
Abstract: The quadrature squeezing spectra in the resonance fluorescence of a V-type three-level atom driven by a coherent field and coupled to a single-mode cavity is investigated. For weak excitation, the fluorescence field exhibit squeezing in the out-of-phase quadrature. The coupling between the atom and the cavity mode can greatly enhance the squeezing centred at the laser frequency. More importantly, for strong excitation, under the effect of the cavity-atom coupling, the in-phase quadrature of fluorescence can exhibit two-mode squeezing at the two inner sideband frequencies. By working in the dressed-state representation and hiring secular approximation, we give an analytical explanation for the effect. The result shows, under appropriate conditions, the squeezing can be greatly enhanced by appropriately tuning the cavity resonant frequency.
Probing quantum-mechanical level repulsion in disordered systems by means of time-resolved selectively-excited resonance fluorescence  [PDF]
A. V. Malyshev,V. A. Malyshev,J. Knoester
Physics , 2007, DOI: 10.1103/PhysRevLett.98.087401
Abstract: We argue that the time-resolved spectrum of selectively-excited resonance fluorescence at low temperature provides a tool for probing the quantum-mechanical level repulsion in the Lifshits tail of the electronic density of states in a wide variety of disordered materials. The technique, based on detecting the fast growth of a fluorescence peak that is red-shifted relative to the excitation frequency, is demonstrated explicitly by simulations on linear Frenkel exciton chains.
腔场耦合的二能级原子荧光谱
Resonance Fluorescence Spectrum of Two-level Atom in Cavity
 [PDF]

张雪华,戚辉,李林,葛向红,李梦
- , 2018,
Abstract: 过光与物质相互作用的主方程计算了强场激励的二能级原子与单模腔耦合的稳态荧光谱。在腔场的强耦合作用下,三峰Mollow谱的每个成分都分裂为多重的,这种现象由腔场使原子修饰态能级漂移而导致的,荧光谱的具体结构则依赖于驱动场的拉比频率和原子-腔的耦合系数。
We calculate the spectrum of resonance fluorescence from a two-level atom coupled to a single cavity mode and driven by a strong field from master equation . In the strong-coupling limit, each Mollow triplet component is split into a multiplet which can be explained by shifts of the dressed statethe of atom caused by the strong cavity field. The structure of the resonance fluorescence spectrum depends on the coupling coefficient of atom-cavity and Rabi frequency of driven field.
Fluorescence from doubly driven four-level atoms - A density matrix approach  [PDF]
Andal Narayanan,R. Srinivasan,Ashok Vudayagiri,Uday Kumar Khan,Hema Ramachandran
Physics , 2004,
Abstract: The unusually narrow features in the fluorescence from Rubidium-85 driven by cooling and repumper laser fields, reported in an earlier experiment [1] are explained on the basis of a four-level density matrix calculation. Quantum effects alter the efficiency of atom transfer by the probe (repumper) laser to the levels connected by the pump (cooling) laser. This combined with the double resonance condition [1], results in velocity selection from co-propagating and counter propagating probe and pump beams resulting in narrow fluorescence peaks from a thermal gas at room temperature.
Quantum fluctuations of mesoscopic damped double resonance RLC circuit with mutual capacitance--inductance coupling in thermal excitation state
Quantum fluctuations of mesoscopic damped double resonance RLC circuit with mutual capacitance-inductance coupling

Xu Xing-Lei,Li Hong-Qi,Wang Ji-Suo,
徐兴磊
,李洪奇,王继锁

中国物理 B , 2007,
Abstract: Based on the scheme of damped harmonic oscillator quantization and thermo-field dynamics (TFD), the quantization of mesoscopic damped double resonance RLC circuit with mutual capacitance--inductance coupling is proposed. The quantum fluctuations of charge and current of each loop in a squeezed vacuum state are studied in the thermal excitation case. It is shown that the fluctuations not only depend on circuit inherent parameters, but also rely on excitation quantum number and squeezing parameter. Moreover, due to the finite environmental temperature and damped resistance, the fluctuations increase with the temperature rising, and decay with time.
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