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1.
WANG Chun-liang 《中国光学》2010,3(1):11-26
Spontaneously Generated Coherence(SGC) refers to a kind of quantum coherence induced by the process of spontaneous emission. It can greatly affect the dynamics of a quantum system, and accounts for a variety of important phenomena. Many efforts have been devoted to this topic, aiming to investigate the essence of quantum coherence and advanced technologies. However, the existence of SGC needs rigorous requirements which can hardly been fulfilled in atoms placed in a free space. Therefore we must give particular considerations to investigate this coherence experimentally. In this paper, a few interesting phenomena related to SGC are summarized, such as gain without inversion, coherent population trapping, phase sensitive spec- tra, and modifications of absorption, emission, and refraction. We also review the investigations on the reali- zation of SGC, such as modifying the vacuum, coupling levels with static fields, simulating SGC with coherence induced by coherent fields, and studying SGC in special materials. 相似文献
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This paper deals with the absorption spectra of a weak probe in a four-level Doppler-broadened system driven by three coherent fields. The main aim is to extend earlier studies of the spontaneous emission spectrum and to present a comprehensive survey of the spectral features of this system. In addition to a derivation of exact formulae for the spectra, we give an explanation with the help of an appropriate set of dressed atomic states. We also get a deeper insight into the physical origin of gain in view of the existence of a population inversion between the levels of the lasing transition. Finally, we explore the effect of Doppler broadening on the absorption profile of the weak probe. 相似文献
4.
The spontaneous emission spectra of a five-level double tripod-type atom embedded in photonic crystals (PCs) are investigated by means of two external fields driving different atomic transitions. We find that due to the quantum interference effects caused by two driving fields, the spontaneous emission spectra exhibit different features from the case of only one driving field. The influences of the parameters of two external driving fields, photonic band-gap (PBG), as well as the atomic initial states on the spectra are analyzed in detail. It is shown that some interesting phenomena such as spectral-line enhancement, spectral-line suppression, spectral-line narrowing, the appearance of dark lines, and multi-peak structures can be observed in the spectra by appropriately modulating the available system parameters. These investigations may find applications in high-precision spectroscopy. 相似文献
5.
Spontaneous emission from a microwave-driven four-level atom in an anisotropic photonic crystal
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The spontaneous emission from a microwave-driven four-level atom embedded in an anisotropic photonic crystal is studied. Due to the modified density of state(DOS) in the anisotropic photonic band gap(PBG) and the coherent control induced by the coupling fields, spontaneous emission can be significantly enhanced when the position of the spontaneous emission peak gets close to the band gap edge. As a result of the closed-loop interaction between the fields and the atom,the spontaneous emission depends on the dynamically induced Autler–Townes splitting and its position relative to the PBG.Interesting phenomena, such as spectral-line suppression, enhancement and narrowing, and fluorescence quenching, appear in the spontaneous emission spectra, which are modulated by amplitudes and phases of the coherently driven fields and the effect of PBG. This theoretical study can provide us with more efficient methods to manipulate the atomic spontaneous emission. 相似文献
6.
Electromagnetically induced phase grating controlled by spontaneous emission is studied. The results show that the diffraction efficiency of phase grating is strikingly enhanced due to the existence of spontaneously generated coherence (SGC), and the diffraction efficiency of 35% can be obtained in optimal SGC parameter case. Furthermore, at large SGC parameter, the high efficiency of phase grating can be maintained by the application of weak coupled and relatively strong probe fields, and choosing the proper length of atomic sample. At the same time, in such an atomic system, the SGC effect depends on incoherent pump. 相似文献
7.
Effect of spontaneously generated coherence on inversionless lasing gain in an atomic system with Doppler broadening 总被引:1,自引:0,他引:1
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We have studied the effect of the spontaneously generated coherence
(SGC) on gain of lasing without inversion (LWI) in a closed
three-level $\Lambda $-type atomic system with Doppler broadening. It
is shown that, regardless of the driving and probe fields being co-
or counter-propagating, at a suitable value of the Doppler width, we
can obtain a much larger LWI gain with SGC than that without SGC; and
the region of the LWI gain spectrum with SGC is obviously larger than
that without SGC. When the Doppler width takes a constant value, the
gain does not monotonically decrease or increase with increasing
strength of SGC, the largest LWI gain can be obtained by adjusting
strength of SGC. Generally speaking, the co-propagating probe and
driving fields is favourable to obtain a larger LWI gain. 相似文献
8.
We display the phenomenon of the hole burning which appearing without saturation field under the effect of different parameters. Theoretically the effect of spontaneously generating coherence (SGC) on the probe polarization spectrum in a Doppler broadened four-level N-type atomic system are investigated when the two driven and probe fields are arranged in copropagating and counterpropagating configurations which play an important role in appearing the coherent hole-burning (CHB) phenomenon. The condition of appearing the hole burning in the polarization spectrum at the presence of spontaneously generating coherence (SGC) and the nonradiative decay rates is that the wave number fields are different. 相似文献
9.
We theoretically investigated transient response of open and closed three-level ladder-type atomic system with or without the spontaneously generated coherence (SGC) which could be satisfied with the help of an incoherent pumping. The existence of the SGC effect makes the open and closed system to be distinguished. We compared transient response of weak probe between open and closed system and found that transient properties exhibit different features by adjusting some related parameters, such as the relative phase between probe and coupling fields, the angle between two dipole moments. 相似文献
10.
采用时间演化算符方法,研究∧-型=三能级原子与纠缠相干态光场共振相互作用的辐射谱.给出了辐射谱一般公式,并讨论在纠缠相干态光场驱动下的辐射频谱结构.结果表明,无论下能级简并与否纠缠相干态光场平均光子数很小时均出现拉比分裂,且强度随双模光场纠缠程度的增加而增加.当两下能级简并时,若两模场的平均光子数较小,辐射谱呈现对称多峰结构,若两模场的平均光子数较大,辐射谱呈现对称五峰结构.当两下能级非简并时,若两模场的平均光子数较小,辐射谱呈现对称多峰结构.若两模场的平均光子数较大,辐射谱呈现对称十峰结构.纠缠相干光与非纠缠相干光辐射谱的本质差别有两点:一是双模光场强量子关联导致纠缠度越强拉比峰强度越高;二是存在纠缠时由于两模场相干性导致辐射谱呈现对称多峰结构. 相似文献
11.
G. H. Yang L. Zhou 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,47(2):277-282
We investigate two identical Λ-type atoms in free space, and focus
on the entanglement between the two atoms. We derive a master equation for
the atomic subspace and solve it analytically to show how the spontaneous
emission from the two atoms system induces entanglement. The magnitude of
the entanglement and the steady state entanglement are found to be strongly
dependent on the initial states and the orientation of the dipoles of the
two atoms. 相似文献
12.
We study the effects of quantum interference in the spontaneous emission spectrum of a four-level driven atomic system. We use three strong laser fields to drive the atom and a weak laser field to prepare the initial state of the atom. The atomic system exhibits Autler-Townes triplet in the spectrum. The single Lorentzian peak splits into triplet and their widths are controlled by the relative strengths of the laser fields. 相似文献
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We present a scheme for the quantum storage of single photons using electromagnetically induced transparency (EIT) in a low-finesse optical cavity, assisted by state-selected spontaneous atomic emission. Mediated by the dark mode of cavity EIT, the destructive quantum interference between the cavity input-output channel and state-selected atomic spontaneous emission leads to strong absorption of single photons with unknown arrival time and pulse shapes. We discuss the application of this phenomenon to photon counting using stored light. 相似文献
14.
D.G. Angelakis P.L. Knight 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):247-250
We show how entangled atomic pairs can be prepared in order to test the Bell inequalities. The scheme is based on the interaction
of the atoms with a highly localized field mode within a photonic crystal. The potential of using optically separated transitions
and the stability of the entangled state to spontaneous emission could lead to the closure of the communication and the detection
loopholes appearing in experiments so far. The robustness of the scheme against detector inefficiencies, the spread in the
atomic velocities and the fact that the entangled pairs are not generated simultaneously is also studied.
Received 31 July 2001 and Received in final form 30 November 2001 相似文献
15.
We propose a scheme to generate a Greenberger-Horn-Zeilinger (GHZ) state of four atoms trapped in a two-mode optical cavity via an adiabatic passage. The scheme is robust against moderate fluctuations of the experimental parameters. Numerical calculations show that the excited probabilities of both the cavity modes and the atoms are tiny and depend on the pulse peaks of the classical laser fields. For certain decoherence due to the atomic spontaneous emission and the cavity decay, there exits a range of pulse peaks to get a high fidelity. 相似文献
16.
We study the control of spontaneous emission in a five-level atomic system driven by four fields. We show that with the variation
of dynamical variables, namely, Rabi frequencies and carrier phases of driven fields, a wide variety of the spectral behavior
can be obtained, including extreme spectral narrowing. Our system can be found easily in real atoms. 相似文献
17.
We have studied the probe gain via a double-Λ atomic system with a pair of closely lying lower levels in the presence of two probe and two coherent pump fields. The inversionless gain can be realized by using nondegenerate four-wave mixing under the condition of spontaneously generated coherence(SGC) owing to near-degenerate lower levels. Note that by using SGC, two probe fields can be amplified with more remarkable amplitudes, and the gain spectra of an extremely narrow linewidth can be obtained. Last but not least, our results show that the probe gain is quite sensitive to relative phases due to the SGC presence which allows one to modulate the gain spectra periodically by phase modulation, and can also be influenced by all laser field intensities and frequencies, and the angles between dipole elements. 相似文献
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19.
C.-Q. Cao C.-G. Yu H. Cao 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):279-284
The spontaneous emission of an excited atom is analyzed by quantum stochastic trajectory approach without both rotating-wave
approximation and Markovian approximation. The atom finite size effect is also taken into account. We show by an example that
the correction due to the counter-rotating wave term is rather small, even for the largest atomic number of real nuclei.
Received 10 July 2002 / Received in final form 12 November 2002 Published online 4 February 2003 相似文献
20.
Possible Realization of Cluster States and Quantum Information Transfer in Cavity QED via Raman Transition
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We present a scheme to generate cluster states with many scheme, no transfer of quantum information between the atoms in cavity QED via Raman transition. In this atoms and cavities is required, the cavity fields are only virtually excited and thus the cavity decay is suppressed during the generation of cluster states. The atoms are always populated in the two ground states. Therefore, the scheme is insensitive to the atomic spontaneous emission and cavity decay. We also show how to transfer quantum information from one atom to another. 相似文献