Impurity absorption of light involving resonant states of shallow donors in quantum wells

The energy spectrum of localized and resonant states of shallow donors in heterostructures GaAs/Al_xGa_1?xAs with quantum wells is calculated. The widths of the resonant states belonging to the second size quantization subband are determined. It is shown that the width of a resonance level is mainly determined by the interaction with optical phonons. The spectrum of impurity absorption of light due to electron transitions from the ground state of the donor to the resonant states belonging to the second size quantization subband is calculated.     

Realization of a singlet state via adiabatic evolution of dark eigenstates

A scheme is proposed for the generation of a singlet state |S₃〉 of three ions by appropriate adiabatic evolutions. In the scheme, losses due to the spontaneous transitions of atoms and the excitation of phonons are efficiently suppressed by employing adiabatic passage and appropriately choosing the additional detuning, and the interaction time does not need to be accurately adjusted.     

Conformation and dipole moment of tetrahydropyran-4-one by microwave spectroscopy

The microwave spectrum of tetrahydropyran-4-one has been studied in the frequency region 18 to 40 GHz. The rotational constants for the ground state and nine vibrationally excited states have been derived by fitting a-type R-branch transitions. The rotational constants for the ground state are (in MHz) A = 4566.882 ± 0.033, B = 2538.316 ± 0.003, C = 1805.878 ± 0.004. From information obtained from the gas-phase far-infrared spectrum and relative intensity measurements, these excited states are estimated to be ～ 100 cm^?1 above the ground state for the first excited state of the ring-bending and ～ 185 cm^?1 for the first excited state of the ring-twisting mode. Stark displacement measurements were made for several transitions and the dipole moment components determined by least-squares fitting of the displacements: (in Debye) |μ_a| = 1.693 (0.001), |μ_b| = 0.0, |μ_c| = 0.300 (0.013) yielding a total dipole moment μ_tot = 1.720 (0.003). A model calculation to reproduce the rotational parameters indicates that the data are consistent with the chair conformation.     

两格点两电子Hubbard-Holstein模型极化子的量子纠缠特性

本文利用相干态正交化展开方法, 对两格点两电子Hubbard-Holstein极化子模型的能谱以及动力学特性进行了精确求解. 讨论了耦合强度g、平均声子数n以及电子 初态对纠缠演化特性及系统冯诺依曼熵的影响. 数值计算结果表明: 1)纠缠度随时间的演化呈现出良好的周期性, 当其他的参数固定时, 演化周期随耦合强度g增大逐渐减小, 与平均声子数n无关; 2)系统冯诺依曼熵同电子状态占有率表现出严格的同步演化特性; (3) 在弱耦合强度和低平均声子数下, 初始电子态c_2↑⁺ c_2↓⁺|O>_e或c_1↑⁺ c_1↓⁺ |O>_e较c_1↑⁺c_2↓⁺—c_1↓⁺ c_2↑⁺具有更大的最大冯诺依曼熵, 并随耦合强度增大、平均声子数的增加而逐渐接近.     

Two-phonon bound states in imperfect crystals

The question of the occurrence of two-phonon bound states in imperfect crystals is investigated. It is shown that the anharmonicity mediated two-phonon bound state which is present in perfect crystals gets modified due to the presence of impurities. Moreover, the possibility of the occurrence of a purely impurity mediated two-phonon bound state is demonstrated. The bound state frequencies are calculated using the simple Einstein oscillator model for the host phonons. The two-phonon density of states for the imperfect crystal thus obtained has peaks at the combination and difference frequencies of two host phonons besides the peaks at the bound state frequencies. For a perfect crystal the theory predicts a single peak at the two-phonon bound state frequency in conformity with experimental observations and other theoretical calculations. Experimental data on the two-phonon infrared absorption and Raman scattering from mixed crystals of GA_1−c Al _c P and Ge_1−c Si _c are analysed to provide evidence in support of impurity-mediated two-phonon bound states. The relevance of the zero frequency (difference spectrum) peak to the central peak observed in structural phase transitions, is conjectured; This work is a part of the thesis to be submitted by one of the authors (SS) in partial fulfilment of the degree of Doctor of Philosophy to Utkal University, Bhubaneswar, India.     

The time-resolved ADMR in the photolysis of the polymethylene-linked system of xanthone and xanthene: Power dependence

The time-resolved ADMR (absorption-detected magnetic resonance) spectrum of the polymethylene linked biradical generated in the photolysis of α-(xanthene-2-carbonyloxy)-ω-(xanthene-2-carbonyloxy) dodecane is observed at various microwave power. When the lower microwave power is low, the ADMR spectrum is totally negative (the absorbance of xanthyl radical decreases by the microwave irradiation) and is interpreted in terms of the hyperfine structure of the terminal radicals. In contrast with this, the ADMR spectrum obtained at high microwave field consists of two components: central component and wing component. The central component is positive and is interpreted in terms of the deceleration of the intersystem crossing by microwave, which is known as the spin locking. The wing component is negative and the linewidth is much larger than that of the central one. It is ascribed to the transitions from |T₊₁> and |T_?1> states to singlet state having a slight |T₀> character. It is proposed that the width of the time resolved spectrum is due to the fluctuation of the exchange integral (modulated exchange integral) by the motion of the polymethylene chain. The time dependence of the central and wing components and the conditions for observation of them are discussed.     

ESR study of exchange coupled pairs in copper diethyldithiocarbamate—explanation of the low temperature hyperfine anomaly

A study of the hyperfine interaction in the ESR of Cu-Cu pairs in single crystals of copper diethyldithiocarbamate as a function of temperature has shown distinct differences in the hyperfine structure in the two fine structure transitions at 20 K, the spectrum not having the same hyperfine intensity pattern in the low field fine structure transition in contrast to that of the high field transition. The details of the structure of both the fine structure transitions in the 20 K spectrum have now been explained by recognizing the fact that the mixing of the nuclear spin states caused by the anisotropic hyperfine interaction affects the electron spin states | + 1 > and | −> differently. This has incidentally led to a determination of the sign ofD confirming the earlier model. The anomalous hyperfine structure is found to become symmetric at 77 K and 300 K. It is proposed that the reason for this lies in the dynamics of spin-lattice interaction which limits the lifetime of the spin states in each of the electronic levels | − 1 >, | 0 > and | + 1 > The estimate of spin-lattice relaxation time agrees with those indicated from other studies. The model proposed here for the hyperfine interaction of pairs in the electronic triplet state is of general validity.     

Intervalley electron scattering by phonons in (AlAs)1(GaAs)3(001) superlattices

Intervalley electron scattering by phonons in (AlAs)₁(GaAs)₃(001) superlattices is studied using the pseudopotential method and a phenomenological model of the bonding forces. The deformation potentials between the conduction band extrema of the superlattice involving short-and long-wavelength phonons are calculated. It is shown that the mixing of states from the zinc-blende L valleys plays a greater role in intervalley scattering in a superlattice than the Γ-X mixing. In particular, due to L-L mixing, the Γ-X ₃ transitions, analogous to Γ-L transitions in zinc blende, have higher intensities than the analogues of Γ-X transitions (Γ₁-M ₅ and (Γ₁-Γ₃ transitions). The deformation potentials averaged over the scattering channels in the superlattice agree with the corresponding potentials in a solid solution, but all transitions in the superlattice have higher intensities for the lower states.     

Microwave spectrum,dipole moment,and structure of 3-aminopropanol

The microwave spectra of 3-aminopropanol and three of its deuterium substituted isotopic species have been investigated in the 26.5 to 40 GHz frequency region. The rotational spectrum of only one conformer has been assigned in which presumably a hydrogen bond of the OH---N type exists. The rotational spectra of a number of excited vibrational states have been observed and assignments made for some of these excited states. The average intensity ratio for the rotational transitions between the ground and excited vibrational states indicates that the first excited state is about 120 cm^?1 above the ground state.and the next higher state is roughly 200 cm^?1 above the ground vibrational state. The dipole moment was determined from the Stark effect measurements to be 3.13 ± 0.04 D with its principal axes components as |μ_a| = 2.88 ± 0.03 D, |μ_b| = 1.23 ± 0.04 D and |μ_c| = 0.06 ± 0.01 D. The possibility of another conformer where the hydrogen bond could be of NH---O type was explored, but the spectra of such a conformer could not be identified.     

态|Ψ(3)>q中广义电场分量的偶数次N次方Y压缩

构造了由多模复共轭虚相干态、多模复共轭虚相干态的相反态和多模复共轭相干态的线性叠加所组成的一种新型的三态叠加多模叠加态光场|Ψ⁽³⁾>_q.利用多模压缩态理论,研究了态|Ψ⁽³⁾>_q中广义电场分量的偶数次等幂次N次方Y压缩特性.结果发现:态|Ψ⁽³⁾>_q是一种典型的三态叠加多模非经典光场;当压缩次数N等于2P且P为2m’+1(m’=0,1,2,…,…)时,如果各模的初始相位φ_j(j=1,2,3,…,…,q)、态间的初始相位差(θ₁-θ₂)、(θ₁-θ₃)和(θ₂-θ₃),以及各单模相干态光场的总的平均光子数等分别满足各自的取值条件,则在这种情况下态|Ψ⁽³⁾>_q的广义电场分量可呈现出偶数次的广义非线性等幂次2(2m’+1)次方Y压缩效应.     

Phonons in mixed valence systems

The effect of valence changes due to f?d electronic transitions on phonons is studied. A large electronic density of states at the Fermi-energy in the intermediate valence state causes significant softening of the longitudinal acoustic and optic phonons and large phonon line-widths. These phonon renormalizations due to strong electron-lattice coupling are largest for phonon wavevectors q along the (111)-direction and maximal at the zone-boundary for LO modes and nearly half-way towards the zone-boundary in the case of LA mode. The results agree well with recent neutron scattering data on Sm_0.75Y_0.25S.     

Rotational selection rules for doublet-quartet transitions in asymmetric top molecules

Selection rules on the rotational structure of doublet-quartet transitions in asymmetric top molecules are discussed on the basis of the spin-orbit coupling mechanism, rather than by symmetry arguments, and some additional rules are found with respect to a previous work. In the case that the combining doublet and quartet states are appreciably mixed only with levels directly connected to them by the spin-orbit operator, it turns out that, except for the very low values of the rotational quantum numbers, branches with |ΔN ? ΔJ| > 1 are essentially forbidden. Thus, branches with ΔN = ± 3 (T and N branches) are not expected to be observable. In this case, it is found also that in a high magnetic field transitions with ΔM_s = ±2 are forbidden, and only ΔM_s = 0, ±1 bands are expected to occur. All these restrictions are removed if the combining states are also appreciably contaminated by states indirectly connected to them by the spin-orbit operator, through intermediate levels.     

Strain effects on the polarized optical properties of InGaN with different In compositions

Strain effects on the polarized optical properties of c-plane and m-plane In_x1-xN were discussed for different In compositions (x=0, 0.05, 0.10, 0.15) by analyzing the relative oscillator strength (ROS) and energy level splitting of the three transitions related to the top three valence bands (VBs). The ROS was calculated by applying the effective-mass Hamiltonian based on k. p perturbation theory. For c-plane In_xGa_1-xN, it was found that the ROS of | X > and | Y >-like states were superposed with each other. Especially, under compressive strain, they dominated in the top VB whose energy level also went up with strain, while the ROS of the | Z >-like state decreased in the second band. For m-plane In_xGa_1-xN under compressive strain, the top three VBs were dominated by | X >, | Z >, and | Y >-like states, respectively, which led to nearly linearly-polarized light emissions. For the top VB, ROS difference between | X > and | Z >-like states became larger with compressive strain. It was also found that such tendencies were more evident in layers with higher In compositions. As a result, there would be more TE modes in total emissions from both c-plane and m-plane InGaN with compressive strain and In content, leading to a larger polarization degree. Experimental results of luminescence from InGaN/GaN quantum wells (QWs) showed good coincidence with our calculations.     

Precision spectroscopy of metastable hydrogen and antihydrogen with a Lamb-shift polarimeter

A spinfilter, the most important component of a Lamb-shift polarimeter, can be used to produce a beam of metastable hydrogen (deuterium) atoms in one hyperfine state (α1, α2 and together with the Sona transition β3). As function of a magnetic field separated transitions between the 2S _1/2 metastable hyperfine states seem to be observable as well as single transitions into the short-lived 2P _1/2 and 2P _3/2 states. The Breit-Rabi diagrams for these states can be measured with good precision. Furthermore, the hyperfine splittings and the Lamb shift can be observed as well. Application of this method to anti-hydrogen atoms are suggested.     

Wigner function for the generalized excited pair coherent state

This paper introduces the generalized excited pair coherent state （GEPCS）. Using the entangled state 〈η〉 representation of Wigner operator, it obtains the Wigner function for the GEPCS. In the ρ-γ phase space, the variations of the Wigner function distributions with the parameters q, α, k and l are discussed. The tomogram of the GEPCS is calculated with the help of the Radon transform between the Wigner operator and the projection operator of the entangled state ｜η1, η2, τ1, τ2｜. The entangled states ｜η〉 and ｜η1, η2, τ1, τ2〉 provide two good representative space for studying the Wigner functions and tomograms of various two-mode correlated quantum states.     

Phase separation and vortex states in the binary mixture of Bose-Einstein condensates

The phase separation and vortex states in a two-component Bose-Einstein condensate consisting of |F = 1, m _f = 1〉 and |2, 1〉 internal spin states of ⁸⁷Rb atoms are considered in the framework of the Thomas-Fermi approximation. It is shown that in the nonrotating system, the atoms in the state |1, ?1〉 form a shell around the atoms in the state |2, 1〉. The critical angular velocity for each state is calculated. These velocities depend drastically on the relative concentrations of the components, the critical angular velocity of the outer component being less than the angular velocity of the inner one. It is shown that the atoms in the |1, ?1〉 state can form a rotating ring around the resting core of the atoms in the |2, 1〉 state.     

Experimental investigation of evaporative cooling mixture of bosonic 87Rb and fermionic 40K atoms with microwave and radio frequency radiation

We investigate sympathetic cooling fermions ⁴⁰K by evaporatively cooling bosonic ⁸⁷Rb atoms in a magnetic trap with microwave and radio frequency induced evaporations in detail. The mixture of bosonic and fermionic atoms is prepared in their polarized spin states |F=9/2, m_F=9/2> for ⁴⁰K and |F=2, m_F=2> for ⁸⁷Rb, which is trapped in Quadrupole--Ioffe--Configuration trap. Comparing microwave with radio frequency evaporatively cooling bosonic ⁸⁷Rb atoms with sympathetically cooling Fermi gas ⁴⁰K, we find that the presence of rubidium atoms in the |2,1> Zeeman states, which are generated in the evaporative process, gives rise to a significant loss of ⁴⁰K due to inelastic collisions. Thus, the rubidium atoms populated in the |2, 1> Zeeman states should be removed in order to effectively perform sympathetically cooling ⁴⁰K with the evaporatively cooled ⁸⁷Rb atoms.     

Resonant states of shallow acceptors in uniaxially deformed germanium

The states of shallow acceptors in uniaxially deformed germanium are studied theoretically. A non-variational numerical computational method is developed for determining the energy and wave functions of localized states of holes in the acceptor field as well as the states of the continuous spectrum (including resonant impurity states). The dependence of the energy of the lower resonant state on strain is studied. It is found that this state is formed from the excited 4Γ ₈ ⁺ state with a binding energy of 1.3 meV (in the absence of deformation) and not from the ground state. The results presented in this work may be useful in the study of the conditions for the generation of far IR radiation in deformed p-Ge, which involves optical transitions between resonant and localized acceptor states.     

Quantum states transfer between coupled fields

We study the exchange of states in coupled fields along their time evolution. The coupling is described by a quadratic form in terms of annihilation and creation operator in the field Hamiltonian. An analytical approach is employed to describe the time evolution of the field state in Fock's space and the conditions for an arbitrary initial states to be transferred with 100% fidelity is determined. We show that only for initial states C₀|0>+C_N|N>, this situation can occurs. The important |1〉↔|0〉 qubits transfer is a particular case of this transference of number state. The relation between the coupling constant and characteristic field frequencies for complete state transference is also determined.