半导体中电子-空穴对的相干态、复合辐射和噪声压缩

本文讨论了在光的相干激发下,半导体中电子-空穴对的玻色近似和SU(2)相干态的产生,讨论了两种情形下电子-空穴对噪声特性和复合辐射特性,给出了电子-空穴对的二阶相干函数和分布函数,说明了玻色近似相当于SU(2)群到谐振子群的收缩。 关键词：     

半导体中激子的叠加态及其复合辐射

本文在玻色近似和“非玻色近似”两种情形下,讨论单激子和双激子Dicke和Fock叠加态及处在这些态的激子的压缩特性、反聚束特性和亚泊松统计特性。文中指出了处在这些态的激子的复合辐射光也可具有这些非经典特性,并对各种情形所得结果作了比较和解释。 关键词：     

半导体中激子的叠加态及其复合辐射

本文在玻色近似和“ 非玻色近似” 两种情形下, 讨论单激子和双激子Dicke和Fock 叠加态及处在这些态的激子的压缩特性、反聚束特性和亚泊松统计特性.文中指出了处在这些态的激子的复合辐射光也可具有这些非经典特性, 并对各种情形s所得结果作了比较和解释. 关键词：     

非平衡玻色凝结的相干态处理

基于平均场和Bogoliubov近似,将由外界相干抽运场产生并与库耦合的非平衡玻色凝结体系的哈氏量线性化。发现若忽略体系与库的耦合,则线性化后的哈氏量的动力学代数为Heisenberg和SU(1,1)李代数,利用相干态方法计算了它的本征值和本征函数——平移压缩粒子数态与一般SU(1,1)相干态的直积。尔后引进元激发的推迟格林函数计算耦合情形下元激发的能谱,进而给出弱耦合情形下激子体系的态函数。 关键词：     

双模SU(1,1)相干态光场与V-型三能级原子玻色-爱因斯坦凝聚体相互作用系统中光场的压缩特性

在双模SU(1,1)相干态光场和V-型三能级原子玻色-爱因斯坦凝聚体相互作用系统中,应用全量子理论,在旋波近似下,研究了双模光场的压缩特性,分别讨论了光场与原子之间的耦合常数、原子之间的相互作用和光场参数对光场压缩特性的影响.研究表明,光场的两个正交分量均被周期性压缩,光场与原子的耦合系数和原子间的相互作用强度增大时均使得光场正交分量涨落的周期缩短;光场参数的变化不影响光场压缩的周期,对压缩深度有一定的影响.     

超导体中库珀对的SU(2)与Glauber相干态——库珀对与约瑟夫森超流性的量子特性研究

本文利用类自旋算符证明BCS超导基态波函数是单个库珀对SU(2)相干态波函数的直积、且在一定条件下为库珀对体系的SU(2)相干态波函数。若两块处在BCS超导基态的超导体耦合在一起,则体系仍处在SU(2)相干态,且在一定条件下为定态超辐射态。在SU(2)群到谐振子群的收缩下,库珀对的SU(2)相干态变为Glauber相干态。讨论了两种情形下库珀对与约瑟夫森超流性的量子噪声、分布及二阶相关特性。     

自旋体系的一般SU(2)相干态

本文引进自旋体系的一般SU(2)相干态,讨论它的压缩特性、反聚束特性及其产生。证明当SU(2)群收缩到谐振子群时,一般SU(2)相干态转变成一般Glauber相干态,并给出有关的收缩结果。 关键词：     

SU(1,1)群的非齐次逆微分实现

利用玻色振子的逆算符构造了SU(1,1)群的生成元和不可约表示的相干态,导出了SU(1,1)群的非齐次逆微分实现.     

双参数变形多模玻色算符的代数结构及其应用(Ⅰ)

构造了两个满足量子Heisenberg-Weyl代数的双参数变形多模玻色算符,研究了它们的代数结构,作为应用,给出了双参数变形多模量子群SU(2)_q,s和SU/(1,1)_q,s的Holstein-Primakoff实现,并分别构造了这两个玻色算符二次幂的本征态,证明了它们的完备性.     

SU(2)群的非齐次逆微分实现

利用玻色振子的逆算符构造了SU(2)群的生成元和不可约表示的相干态,进而导出了SU(2)群的非齐次逆微分实现.     

Cascade Two-photon Correlated-emission Optical Bistability

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New method for detection of exciton Bose condensation using stimulated two-photon emission

An investigation is reported of stimulated two-photon emission by Bose-condensed excitons accompanied by a coherent two-exciton recombination, i.e., by simultaneous recombination of two excitons with opposite momenta leaving unchanged the occupation numbers of exciton states with momenta p≠0. Raman light scattering (RLS) accompanied by a similar two-exciton recombination (or production of two excitons) is also analyzed. The processes under consideration can occur only if a system contains Bose condensate, so their detection can be used as a new method to reveal Bose condensation of excitons. The recoil momentum, which corresponds to a change in the momentum of the electromagnetic field in the processes, is transferred to phonons or impurities. If the recoil momentum is transmitted to optical phonons with frequency ω ₀ ^s , whose occupation numbers are negligible, and the incident light frequency satisfies ω<2Ω, where Ω_=Ω−ω ₀ ^s is the difference frequency and Ω is the light frequency corresponding to the recombination of an exciton with zero momentum, stimulated two-photon emission and RLS with coherent two-exciton recombination give rise to a line at 2Ω_ −ω and an anti-Stokes component at ω+2Ω_, respectively. For ω2Ω_ the RLS spectrum contains Stokes and anti-Stokes components at frequencies ω±2Ω_, whereas stimulated two-photon emission is impossible. Formulas for the cross sections at finite temperatures are obtained for the processes under consideration. Our estimates indicate that a spectral line at 2Ω_−ω, corresponding to the stimulated two-photon emission accompanied by coherent optical phonon-assisted two-exciton recombination can be experimentally detected in Cu₂O. Zh. éksp. Teor. Fiz. 115, 1353–1376 (April 1999)     

A New Bosonization Method for Photoexcited Electronic States and Its Application to Nonlinear Optical Responses

We derive a bosonized Hamiltonian for a semiconductor quantum well with a light field by a new bosonization method taking exactly into account the composite-particle effects of excitons. Then we apply the bosonized Hamiltonian to the four-wave-mixing (FWM) processes. The obtained Hamiltonian describes two-boson states corresponding to bound and unbound two-exciton states and guarantees exclusion of unphysical states, which cannot exist in the fermionic space due to the Pauli exclusion principle. Calculated results of the FWM signals are in good agreement with the experimental ones, and therefore, the bosonized Hamiltonian turns out to be able to describe two-exciton correlations effectively.     

Exciton-exciton interaction in coupled quantum wells

The exciton-exciton interaction is investigated for spatially indirect excitons in coupled quantum wells. The Hartree-Fock and Heitler-London approaches are improved by a full two-exciton calculation including the van der Waals effect. Using these potentials for the singlet and triplet channel, the two-body scattering matrix is calculated and employed to derive a modified relation between exciton density and blue shift. Such a relation is of central importance for gauging exciton densities on the way toward Bose condensation.