二维光量子阱共振隧穿光谱特性的改善

用时域有限差分法研究了光子晶体量子阱中的量子化能态.研究发现,开腔与闭腔光量子阱结构共振透射峰的数目相同,位置几乎不变,但闭腔光量子阱出射光强更强,透射率更大,频率选择性更好,品质因子Q值更高.同时计算了开腔和闭腔光量子阱光场分布,结果表明,开腔光量子阱为行波阱,闭腔光量子阱为驻波阱,充分证实了闭腔光量子阱更能束缚光场的设想,对其作用机理进行了探讨.     

光子的自旋与光波的偏振

从宏观以及微观两个方面对光子的自旋与光波的偏振态作了简要的说明,并从原子角动量的变化规律说明了角动量与光子自旋之间的关系,也为进一步研究光的本性提供了一些观点。     

非线性光子晶体中原子辐射光场的非经典性质

讨论了非线性光子晶体微腔中二能级原子在相干场驱动下腔场的频谱特性及光子的统计性质.研究结果表明,当光子晶体的态密度很大时,如果腔场模与原子共振荧光Mollow峰的中心峰共振,则腔场的涨落压缩到量子散弹噪声之下,且与线性光子晶体微腔的情况相比其谱线峰值变大.当驱动场频率较大时光子服从亚Poisson分布,且非常接近Poisson分布.     

非线性光子晶体中原子辐射光场的非经典性质

讨论了非线性光子晶体微腔中二能级原子在相干场驱动下腔场的频谱特性及光子的统计性质.研究结果表明,当光子晶体的态密度很大时,如果腔场模与原子共振荧光Mollow峰的中心峰共振,则腔场的涨落压缩到量子散弹噪声之下,且与线性光子晶体微腔的情况相比其谱线峰值变大.当驱动场频率较大时光子服从亚Poisson分布,且非常接近Poisson分布. 关键词： 光子晶体 参量振荡 非弹性谱 二阶相关函数     

耗散环境下二比特体系的量子关联性质研究

利用Quantum Discord(QD)判据,研究了与热库相互作用的二比特体系的量子关联性质.讨论了在不同初态下体系量子关联随时间的变化,以及热库的平均光子数m,n和原子的自发辐射率γ对体系量子关联性质的影响.结果表明,在不同的初态下,体系可以得到不同性质的量子关联;而且当原子自发辐射率γ取固定值时,QD的衰减会随m,n取值的减小而减慢,热库平均光子数都为零的情况下能够得到最大范围的量子关联;此外,当热库平均光子数m,n取确定值时,随着γ取值的减小,QD的衰减也会随之减慢,此时同样会得到较大范围的量子关联.说明较小的热库平均光子数以及原子自发辐射率γ能够减弱QD的衰减,从而获得生命力较强的体系量子关联.     

Quantum Teleportation and Resonance Information Transfer from One Atom to Another at Arbitrary Interatomic Distances

The feasibility of resonance transfer of quantum information from one double-level atom to another that is at an arbitrary distance from the former one has been proved. Symmetric and antisymmetric combinations of the wave functions of individual atoms are considered. When taking into account the interatomic dipole–dipole interaction, a certain energy corresponds to each wave function. A solution has been found to a system of equations for the amplitudes of the probability that a resonance photon will be absorbed by one of the system atoms, and it has been shown that the interaction of the system with actual photons has the result that the wave function of the final state of the system can be represented as a linear combination of the functions < 00|, < 0n|, and < n0| corresponding to the ground and excited states of individual atoms. The amplitude of the probability of each of these states depends on the interatomic distance and on the parameters of the action of actual photons on atoms. Three types of solution to the system of equations have been investigated for the resonance and nonresonance absorption of photons and different interatomic distances. It has been shown that when atoms are at an infinite distance from one another, so that there is no dipole–dipole interaction of atoms, quantum information can be transferred from one atom to another with a characteristic time considerably shorter than the time it takes for a photon to cover the interatomic distance. This effect is referred to as the effect of quantum teleportation in a system of resonance atoms.     

共线和非共线模式下单光子探测器定标比对实验研究

采用相关光子法定标单光子探测器的量子效率对提高光学载荷的辐射定标准确度具有重要意义.利用355nm连续激光泵浦BBO晶体产生Ⅰ类自发参量下转换,在共线和非共线两种相位匹配模式下分别测量了单光子探测器雪崩光电二极管在736nm波段的量子效率.结果表明,共线和非共线两种模式测量结果的合成不确定度分别为0.71%和0.39%,相对偏差均优于0.4%,这两种模式都可以定标探测器量子效率,且具有很好的一致性.最后比较了两种模式定标探测器量子效率的优缺点,该研究为以后利用相关光子法对遥感器进行辐射定标提供了晶体相位匹配模式选择的依据.     

Formulation and picture of quantum phase

Based on the concept of classical phase, we formulate a new explanation for the quantum phase from the quantum mechanical point of view. The quantum phase is the canonically conjugate variable of an angular momentum operator, which corresponds to the angular position φ in an actual physical space with a classical reference frame, but it takes a complex exponential form e ^iφ≡cosφ+i sinφ in the abstract Hilbert space of a quantum reference frame. This formulation is simply the famous Euler formula in a complex number field. In particular, when φ = π/2, the correlative quantum phase is a unitary pure imaginary number e ^iπ/2≡cos(π/2)+i sin(π/2) ≡ i. By using a photon state-vector function that is the general solution of photon Schr?dinger equation and can completely describe a photon’s behavior, we discuss the relationship between the angular momentum of a photon and the phase of the photon; we also analyze the intrinsic relationship between the macroscopic light wave phase and the microscopic photon phase.     

Theoretical investigation of an acoustic wave in molecular magnets via electromagnetically induced transparency

Using the Schrödinger-Maxwell equations, we theoretically investigate the propagation properties of a transverse acoustic wave in a crystal of molecular magnets in the presence of two strong ac resonant magnetic fields and a weak acoustic wave. The acoustic wave can freely propagate in the magnetic molecule medium (under appropriate conditions) due to quantum interference. Furthermore, using the slowly varying envelope approximation, we discuss the propagation equation of the acoustic wave, which includes the high order nonlinear term. The results show that a crystal of molecular magnets can support the propagation of acoustic wave solitons via electromagnetically induced transparency. We also obtain the analytical expressions for the phase shift and absorption coefficient of the acoustic wave within certain parameters.     

利用光子回声技术产生光的三体纠缠态的研究

量子纠缠是实现量子通信和量子计算的重要资源,其中多体纠缠更是构建量子网络实现全局量子计算的基础。本文主要研究如何利用经典的光子回声技术实现光量子态的三体纠缠。在自由空间中向掺杂稀土离子的固态离子系综中射入经典光场,当离子体系达到相位重构条件时即可获得三束存在纠缠的量子光场。基于本方案纠缠产生的技术特点,发现其在提高量子中继器的工作效率上有着潜在的应用价值。     

脉冲激发三能级体系半导体量子点的单光子发射效率

研究了脉冲激发下单个半导体量子点中单光子发射的统计特性.在旋转波近似条件下，由系统粒子数演化主方程并结合量子回归理论推导了二阶相关函数的运动方程，利用此方程讨论了二阶相关函数随输入脉冲面积的关系.在窄脉冲宽度的脉冲激发下，单光子的发射概率p和效率η都随着强度的增强而产生振荡.研究表明，采用窄脉冲宽度，当输入脉冲面积在π附近时可以得到较高的单光子发射效率. 关键词： 半导体量子点 单光子发射 三能级系统     

High‐resolution spectral characterization of two photon states via classical measurements

Quantum optics plays a central role in the study of fundamental concepts in quantum mechanics, and in the development of new technological applications. Typical experiments employ sources of photon pairs generated by parametric processes such as spontaneous parametric down‐conversion and spontaneous four‐wave‐mixing. The standard characterization of these sources relies on detecting the pairs themselves and thus requires single photon detectors, which limit both measurement speed and accuracy. Here it is shown that the two‐photon quantum state that would be generated by parametric fluorescence can be characterised with unprecedented spectral resolution by performing a classical experiment. This streamlined technique gives access to hitherto unexplored features of two‐photon states and has the potential to speed up design and testing of massively parallel integrated nonlinear sources by providing a fast and reliable quality control procedure. Additionally, it allows for the engineering of quantum light states at a significantly higher level of spectral detail, powering future quantum optical applications based on time‐energy photon correlations.     

广义量子干涉原理及对偶量子计算机

我们综述最近提出的广义量子干涉原理及其在量子计算中的应用。广义量子干涉原理是对狄拉克单光子干涉原理的具体化和多光子推广,不但对像原子这样的紧致的量子力学体系适用,而且适用于几个独立的光子这样的松散量子体系。利用广义量子干涉原理,许多引起争议的问题都可以得到合理的解释,例如两个以上的单光子的干涉等问题。从广义量子干涉原理来看双光子或者多光子的干涉就是双光子和双光子自身的干涉,多光子和多光子自身的干涉。广义量子干涉原理可以利用多组分量子力学体系的广义Feynman积分表示,可以定量地计算。基于这个原理我们提出了一种新的计算机,波粒二象计算机,又称为对偶计算机。在原理上对偶计算机超越了经典的计算机和现有的量子计算机。在对偶计算机中,计算机的波函数被分成若干个子波并使其通过不同的路径,在这些路径上进行不同的量子计算门操作,而后这些子波重新合并产生干涉从而给出计算结果。除了量子计算机具有的量子平行性外,对偶计算机还具有对偶平行性。形象地说,对偶计算机是一台通过多狭缝的运动着的量子计算机,在不同的狭缝进行不同的量子操作,实现对偶平行性。目前已经建立起严格的对偶量子计算机的数学理论,为今后的进一步发展打下了基础。本文着重从物理的角度去综述广义量子干涉原理和对偶计算机。现在的研究已经证明,一台d狭缝的n比特的对偶计算机等同与一个n比特+一个d比特(qudit)的普通量子计算机,证明了对偶计算机具有比量子计算机更强大的能力。这样,我们可以使用一台具有n+log2d个比特的普通量子计算机去模拟一个d狭缝的n比特对偶计算机,省去了研制运动量子计算机的巨大的技术上的障碍。我们把这种量子计算机的运行模式称为对偶计算模式,或简称为对偶模式。利用这一联系反过来可以帮助我们理解广义量子干涉原理,因为在量子计算机中一切计算都是普通的量子力学所允许的量子操作,因此广义量子干涉原理就是普通的量子力学体系所允许的原理,而这个原理只是是在多体量子力学体系中才会表现出来。对偶计算机是一种新式的计算机,里面有许多问题期待研究和发展,同时也充满了机会。在对偶计算机中,除了幺正操作外,还可以允许非幺正操作,几乎包括我们可以想到的任何操作,我们称之为对偶门操作或者广义量子门操作。目前这已经引起了数学家的注意,并给出了广义量子门操作的一些数学性质。此外,利用量子计算机和对偶计算机的联系,可以将许多经典计算机的算法移植到量子计算机中,经过改造成为量子算法。由于对偶计算机中的演化是非幺正的,对偶量子计算机将可能在开放量子力学的体系的研究中起到重要的作用。     

级联差频产生太赫兹辐射的理论研究

针对差频产生太赫兹(THz)辐射转换效率低的缺点,提出了级联差频的新机理以提高转换效率,并以ZnTe晶体为例,对级联差频产生THz辐射的原理和过程进行了理论研究.通过对级联差频耦合波方程组的求解,得出了ZnTe晶体中级联差频的最佳抽运条件和ZnTe晶体的最佳长度,并且分析了晶体吸收、波矢失配及抽运强度对级联差频的影响.计算结果表明,通过级联差频可以大大提高THz波的转换效率,其光子转换效率甚至可以超过Manley-Rowe关系的限制. 关键词： 太赫兹辐射 差频 级联 ZnTe晶体     

Coincidence Imaging and interference with coherent Gaussian beams

we present a theoretical study of coincidence imaging and interference with coherent Gaussian beams. The equations for the coincidence image formation and interference fringes are derived, from which it is clear that the imaging is due to the corresponding focusing in the two paths. The quality and visibility of the images and fringes can be high simultaneously. The nature of the coincidence imaging and interference between quantum entangled photon pairs and coherent Gaussian beams are different. The coincidence image with coherent Gaussian beams is due to intensity-intensity correspondence, a classical nature, while that with entangled photon pairs is due to the amplitude correlation a quantum nature. Selected from Acta Sinica Quantum Optica, 2005, 11(4)(in Chinese)     

Generation of pair coherent state using weak cross-Kerr media

We firstly give a nonlocal method for generating pair coherent state with two traveling wave fields in distinct districts. The experimental scheme proposed is based on a two-mode photon number matching process, which employs weak cross-Kerr media and on/off detection. Then we discuss the details for implementing this scheme, showing that it is robust against the low quantum efficiency of photon detectors and offers nearly perfect pair coherent states. Finally, we show how a two-mode Schrödinger cat state and a generalized two-mode correlated photon number state can be prepared via this matching process.     

Photon wave function formalism for analysis of Mach–Zehnder interferometer and sum-frequency generation

Biakynicki-Birula introduced a photon wave function similar to the matter wave function that satisfies the Schrödinger equation. Its second quantization form can be applied to investigate nonlinear optics at nearly full quantum level. In this paper, we applied the photon wave function formalism to analyze both linear optical processes in the well-known Mach–Zehnder interferometer and nonlinear optical processes for sum-frequency generation in dispersive and lossless medium. Results by photon wave function formalism agree with the well-established Maxwell treatments and existing experimental verifications.     

Bose condensation of exciton polaritons in an optical microcavity

Two methods are considered for producing traps for exciton polaritons in an optical microcavity with an embedded quantum well. The first method for controlling polaritons consists in producing a polariton trap governed by the longitudinal confinement of photons. Traps of this type can be created using an optical microcavity with a variable width. In traps of the second type, the exciton confinement is ensured by a weak potential that is applied to a quantum well with excitons or when this well is subjected to an inhomogeneous deformation. The behavior of a two-component Bose condensate of photons and excitons is analyzed theoretically. The Bose condensate is described by the coupled system of equations of the Gross-Pitaevskii type. The approximate wave functions and the spatial profiles of coupled photon and exciton condensates are obtained.     

光纤中单光子传输方程的求解及分析

量子信息在光纤中传输时,会受到光纤损耗、色散、非线性效应等多因素的影响,将产生传输态的演化与能量转移.本文以单模光纤传输方程以及电磁场量子化理论为基础,对单模光纤中基模模场进行量子化处理,推导并建立了考虑损耗、色散、非线性效应后的单光子传输方程.基于微扰法对单光子非线性传输方程进行了求解,给出了稳定解存在的必要条件及其所满足的色散方程.深入讨论了广域光功率随微扰频率的变化关系,并且分析了光纤色散、非线性效应对解的影响.为量子光纤传输系统性能的深入研究奠定了理论基础.